- Email: [email protected]
Experimental investigation of flat plate solar collector using CeO2-water nanofluid
Energy Conversion and Management 155 (2018) 32–41
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Experimental investigation of flat plate solar collector using CeO2-water nanofluid
MARK
⁎
M.A. Sharafeldina,b, , Gyula Grófa a b
Department of Energy Engineering, Budapest University of Technology and Economics, Budapest, Hungary Mechanical Engineering Department, Faculty of Engineering Shoubra, Benha University, Benha, Egypt
A R T I C L E I N F O
A B S T R A C T
Keywords: Flat-plate collector Collector efficiency CeO2 nanoparticles CeO2-water nanofluid
Using nanofluids in thermal energy devices, such as flat-plate solar collectors, is gradually making progress, and getting awareness in the scientific community. Experiments were performed to study the effect of using CeO2water on the efficiency of flat-plate solar collector by three different volume fractions of CeO2 nanoparticles of 0.0167%, 0.0333% and 0.0666%, while the mean particle dimension was kept constant at 25 nm. An ultrasonic process was used for maintaining the stability of the CO2-water nanofluid. The working fluid mass flux rates were 0.015, 0.018 and 0.019 kg/s m2. The experiments were carried out in Budapest, Hungary on the latitude of 47°28′N and longitude of 19°03′E. Higher collector efficiency was achieved when using CeO2-water nanofluid compared to results achieved with water application. Based on present data, the efficiency of the collector is directly proportional with the mass flux rate and with the volume fraction in the ranges of the present study. Experiments indicate that the highest rise in efficiency of the collector at zero value of [(Ti – Ta)/GT] is 10.74%, for volume fraction (φ ) 0.066%, and for mass flux rate of 0.019 kg/s m2 compared to water.
1. Introduction In the past few years, scientists raised general attention to nanoparticles with less than 100 nm in size. It was found out that the tiny particles hold by fluids and make a remarkable change or even the properties of fluids. Based on this fact, it was observed that a lot of nano-scale materials added to fluids changed their thermal properties, as well as the performance of thermal devices. Solar collectors are one of these devices which take advantage of the observed properties of nanofluid. In this part, when getting a focus view on using nanofluid as the working fluid in flat-plate types of solar collectors, will be presented. Table 1 shows different experimental investigation of performance of flat plate solar collector when using nanofluid as a working fluid. Although all above studies didn’t modify the conventional solar collector design, other researchers made some modification in the design of solar collector such as Faizal et al. [24] who used numerical methods to design a smaller solar collector that can produce the same desired output temperature as the bigger one. From his study, it was found that by applying nanofluid the cost of solar collector, embodied energy and CO2 emissions were reduced. Colangelo et al. [25] modified the design of the flat-plate collector by rearranging bottom and top headers to reduce the sedimentation of the clusters of nanoparticles,
⁎
and, in this way, they were able to apply high nanoparticle concentration for the first time ever. Sekhar et al. [26] investigated convective heat transfer analysis for a horizontal circular pipe with Al2O3 nanofluids at different volume concentrations in mixed laminar flow range. Based on Latest review studies [28–35] no research had been done to detect the effect of CeO2-water nanofluid on the efficiency of a flatplate collector although it had good thermal properties as Tiwari et al. [27] found. Also, CeO2 nanoparticles has several benefits like:
• It has good availability and easy to prepare • it’s price isn’t high so it has a good economic potential • the stability of it with water is high comparing to other nanoparticles • No toxicity or flammability was observed when it was using so it environmental friendly.
This paper is focusing on studying the performance of a flat-plate collector using CeO2-water nanofluid as working fluid instead of using distilled water. Also, making a stable CeO2-water nanofluid using ultrasonic technique is an aim for this work. On other side, examine to what extent the thermal performance is affected by adding CeO2 nanoparticles and using different mass flux rate is deeply studied in this
Corresponding author at: Budapest University of Technology and Economics, Budapest, Hungary. E-mail address: [email protected] (M.A. Sharafeldin).
http://dx.doi.org/10.1016/j.enconman.2017.10.070 Received 22 August 2017; Received in revised form 13 October 2017; Accepted 24 October 2017 0196-8904/ © 2017 Published by Elsevier Ltd.
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Nomenclature
Ac Cp Cpbf Cpnp Cpnf FR GT knf kbf knp ṁ R2 Ta Ti To Qu
overall coefficient of heat loss (W/m2 K) volume flow rate (L/h)
UL V·
surface area of the solar collector (m2) heat capacity of (J/kg K) heat capacity of base fluid (water) (J/kg K) heat capacity of nanoparticles (J/kg K) heat capacity of nanofluid (J/kg K) heat removal factor solar radiation normal to collector (W/m2) thermal conductivity of nanofluid (W/m K) thermal conductivity of base fluid (W/m K) thermal conductivity of nanoparticles (W/m K) mass flow rate of nanofluid (kg/s) root Mean Square Error ambient temperature (K) collector inlet temperature (K) collector outlet temperature (K) useful heat energy rate (W)
Greek symbols
τα ηi ρnf ρnp ρ bf φ
absorption-transmittance product instantaneous efficiency density of nanofluid (kg/m3) density of nanoparticles (kg/m3) density of base fluid (kg/m3) volume fraction of nanoparticles
Subscripts base fluid nanofluid nanoparticles
bf nf np
purpose of this standard is to introduce test methods to detect thermal performance of solar collectors that use single-phase fluids without significant internal energy storage. According to ASHRAE Standard 932003 [36] solar collector should examine at 0.02 kg/s m2 or at recommended flow rate as manufacturer. Therefore, we use these mass flux rate of 0.015, 0.018, and 0.019 kg/s m2 as it in the range of recommended by manufacturer and also it just below the standard mass flux of 0.02 kg/s m2. The thermal performance of the solar collector is calculated by determining the values of instantaneous efficiency of different combinations of incident radiation, ambient temperature, and inlet fluid temperature. In addition, experiments must be done under steady-state conditions. The instantaneous efficiency is defined as the ratio of useful energy, Qu, and the solar energy received by absorber plate of collector, AcGT and it is calculated by Eq. (1) below.
paper. A detailed discussion about the effect of environmental parameters like ambient temperature and solar radiation is held in presented work by using the reduced temperature parameter, [(Ti–Ta)/GT], as independent variable in several figures. 2. Methodology This section is presented in two parts. The first part deals with nanofluid preparation and the second part describes the set-up that has been used for experiments on the flat plate solar collector. 2.1. Preparation method and characterization In this study, deionized water and water-based CeO2 nanofluids were utilized as working fluids. Commercial spherical shape CeO2 nanopowder (supplier: M K Impex, Canada) of 99.9% purity and 25 nm average diameter was used for the experimental investigation. Distilled water served as reference fluid. The CeO2 nanoparticles, insoluble in water, had a density of 7.123 g/cm3. The nanofluids were prepared by a two-step method where CeO2 nanoparticles were dispersed into the base fluid directly first; later they were oscillated continuously for about 90 min, and 50% amplitude in an ultrasonic homogenizer (Bandelin, SONOPULS HD 2200, output power maximum 200 W).
ηi =
Qu A cGT
(1)
The useful heat energy rate is calculated by using Eq. (2), and can also be determined in terms of the energy absorbed by the absorber, and the energy lost from the absorber as given by Eq. (3). · Qu = ṁ Cp (To−T) i = ρV C p (To−T) i
(2)
The useful heat energy rate can be also described as the difference between energy absorbed by the absorber plate and the energy loss from the absorber as:
2.2. Experimental procedure
Qu = A c FR [GT (τα)−UL (Ti−Ta)] Experimental apparatus diagram and picture is shown in Figs. 1 and 2, respectively. The experiments were performed in Budapest (latitude 47°28′N longitude 19°03′E). The specifications of the collector are given in Table 2. The collector type is TS 300 from Naplopó Kft. in Hungary and the inclination was 45 degree. An electrical pump was used to circulate the working fluid, while a heat exchanger transferred heat from the solar collector to the tank. The tank capacity was nearly 500 l. A flow meter was used to measure fluid flow rate. To control flow rate, a simple valve was also installed after the electric pump. Also, a series of Pt-100 resistance thermometers were fitted to the collector in order to measure the temperature of the working fluid in the collector both in- and outbound. The ambient temperature was measured by a thermometer, while the total solar radiation was measured by a LP PYRA 03 solar meter.
(3)
So the instantaneous efficiency can be expressed by Eqs. (4) or (5)
ηi = ηi =
ρV·Cp (To−T) i (4)
A cGT A c FR [GT (τα)−UL (Ti−Ta)] A cGT
T −T ηi = FR (τα)−FR UL ⎛ i a ⎞ ⎝ GT ⎠ ⎜
(5)
⎟
(6)
Eq. (6) which defines the instantaneous efficiency is known as the Hottel-Whillier equation. FR is known as the collector heat removal factor and is expressed by Eq. (7),
FR =
ṁ Cp (To−T) i A c [G T (τα)−UL (Ti−Ta)]
(7)
where, ṁ is the mass flow rate of the working fluid, Ti is the collector inlet temperature, To is the collector outlet temperature, Ta is the ambient temperature, G T is the global solar radiation normal to the collector, A c is the surface area of the solar collector, τα is the absorption-
3. Testing method In the current study, ASHRAE Standard 93-2003 [36] was the basis to investigate the thermal performance of the solar collector. The 33
34
Graphene Copper Oxide Aluminum Oxide Titanium oxide and Silicon Oxide Multiwall carbon nanotubes SiO2 Grapheme nanoplatelets graphene oxide Al2O3 nanofluid
MgO/water
Fe nanoparticle
Noghrehabadi et al. [18] Vakili et al. [19] Vincely et al. [20] Kim et al. [21]
Verma et al. [22]
Owolabi et al. [23]
Jeon et al. [16]
Verma et al. [17]
Cu-water
Jamal-Abad et al. [9]
Graphene Alumina, Copper Oxide and Zirconium Oxide gold Nano-rods
SiO2- mixture of EG and water (50:50 vol%)
Meibodi et al. [8]
Ahmadi et al. [14] Devarajan et al. [15]
CuO-water SiO2-nanofluid Cu-H2O nanofluids
Moghadam et al. [5] Faizal et al. [6] He et al. [7]
(CuO/H2O) silver nanofluid Al2O3 and CuO nanofluid
CuO-H2O
Goudarzi et al. [4]
Michael et al. [11] Polvongsri et al. [12] Munuswamy et al. [13]
MWCNT
Yousefi et al. [3]
TiO2-water
Al2O3-nanofluid with and without Triton X-100
Yousefi et al. [2]
Said et al. [10]
0.1% and 0.3% volume fraction
Al2O3-water
Said et al. [1]
0.25, 0.5, 0.75, 1.0, 1.25 and 1.5% volume fraction 0.5% weight fraction
1%weight fraction 0.0005, 0.001 and 0.005 wt fraction 0.005, 0.01 and 0.02 wt fraction 0.5%,1%,1.5% volume fraction
gold Nano-rods dispersed in three plasmonic nanofluids are 1.85, 2.65 and 5.17 From 0.25 % to 2% volume fraction
0.01 % and 0.02 % weight fraction 0.2% and 0.4% weight fraction
0.05% volume fraction 1000 and 10,000 ppm 0.2% and 0.4% volume fraction
0.1–0.3% volume fraction
0.05% and 0.1% weight fraction
0.4% volume fraction 0.2% and 0.4% volume fraction 0.01%, 0.02 %, 0.04 %, 0.1 %, 0.2 % weight fraction 0.5%,0.75%1% volume fraction
0.1%, 0.2% and 0.4% weight fraction
0.2% and 0.4%. weight fraction
0.2% and 0.4% weight fraction
Volume or Weight fraction
Nanofluid
Research
Table 1 Experimental studies for nanofluids with flat-plate solar collectors.
40-nm
40 nm
12 nm Particle diameter 2 μm 300 nm 20,50and 100 nm
From 7 nm to 45 nm differ from material to another
16 nm
less than 100 nm 40 nm
75 m 20 nm 40 nm
21 nm
35 nm
40 m
40 nm 15 nm 25 nm and 50 nm
40 nm
10–30 nm
15 nm
13 nm
Nano-size
2
3
3
2
3
2
3
efficiency was enhanced when using SiO2/water nanofluid • thermal collector enhanced with using Grapheme nanoplatelets • solar collector efficiency increased by 7.3% • the highest efficiency increased by 24.1% for the solar collector with 1.0 vol% Al O • The nanofluid of 20 nm-nanoparticles and a mass flow rate of 0.047 kg/s efficiency enhancement was 9.34% for 0.75% particle volume • Collector concentration at flow rate 1.5 lpm • The thermal efficiency was 59.5% and 50.5% for with and without nanofluid
oxide/water, Titanium oxide /water, and Silicon oxide/water comparing to water as the base fluid.
• • • efficiency increased by 23.47% 16.97%, 12.64%, 8.28%, 5.09% and 4.08%, • The respectively for Multiwall carbon, graphene/water, Copper oxide/water, Aluminum
for CuO Thermal efficiency increased by 18.87%. The solar collector efficiency for Al2O3, CuO, ZrO2, and water was 55, 51.3,47, and 38%, respectively. Solar thermal collectors performance was enhanced using plasmonic nanofluids.
2
results showed that the efficiency of the collector at 0.05 wt% was approximately • The 24% more than that of the pure-base fluids energy efficiency increased by 76.6% whereas the highest exergy efficiency • The achieved is 16.9% for 0.1 vol% and 0.5 kg/min thermal performance of the solar water heater enhanced by 6.3% • the nano-fluid improved the solar collector performance • the experimentation, the best collector efficiency obtained in a 25-LPD solar • From collector is Al O 0.4% volume frac-tion, which increased to 12% for Al O and 7%
approximately between 4 and 8%.
energy efficiency increased by 83.5% when 0.3% volume fraction • The exergy efficiency was enhanced by up to 20.3% • the using the 0.2 wt% Al O - nanofluid increased the efficiency of the solar collector by • 28.3% using the surfactant, the maximum enhanced efficiency was 15.63% • ByResults show that by increasing the weight fraction from 0.2% to 0.4%, there is a • substantial increase in the efficiency. the surfactant causes an increase in the efficiency. • Using 0.1 wt% nanofluid in 0.0083 kg/s mass flow rate of fluid the maximum thermal • For efficiency was increased by 25.6% the use of nanofluid with SDS as surfactant the maximum collector efficiency is • With increased by 24.2% solar collector efficiency increased by 16.7% • the found that the efficiency of the solar collector increased by 23.5% • Itthewasefficiency of the solar collector was enhanced by 23.83% • showed that when the heat loss parameter limits to zero, an increase in • Findings nanofluid concentration from 0 to 1% results in an efficiency enhancement
Remarks
M.A. Sharafeldin, G. Gróf
Energy Conversion and Management 155 (2018) 32–41
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 1. Layout of a test rig.
ρnf = ρnp (φ) + ρ bf (1−φ)
(9)
Thermal conductivity of nanofluid can be estimated as following equation [39].
knf = kbf
[knp + (n−1) kbf + φ (kbf −knp)]
(10)
Where φ indicates the volume fraction of nanoparticles, n is equal to 3 as the shape of particles are spherical as [39]. Thermal conductivity of nanoparticles plays an important role to increase thermal conductivity of nanofluid and consequently the thermal performance of collector. The thermal properties of nanofluids are presented in Table 3. The values of τand α depend on the design of collector and the value of FR depends on flow rate, hence, for normal incidence conditions and at given quantities of mass flux rate and volume fraction the values of FR, τandα do not change significantly in the range of tested temperatures. So, according to Eq. (6), the collector efficiency is expressed as a straight line. This line intersects the vertical axis (efficiency) at FR (τα ). At this point, the collector efficiency reaches its maximum value, and the inlet temperature to the collector is equal to ambient temperature. The parameter FR (τα ) is called “absorbed 42 energy parameter” or “optical efficiency”. The slop of straight line is equal to FR UL and expresses how energy has removed from the solar collector; it is also called “removed energy parameter”.
Fig. 2. Pictures of a test rig.
Table 2 Specifications of the flat-plate solar collector. Specification
Dimension
Width: Height: Depth: Width module size: Full solar surface: Free glass surface: Absorber surface: Liquid space capacity: Cover glass thickness: Thermal insulation thickness and material: Absorber absorption coefficient Absorber emission factor
1009 mm 2009 mm 75 mm 1040 mm 2.03 m2 1.78 m2 1.78 m2 1.57 l 4 mm 40 mm rock wool 0.95 0.13
4. Uncertainty analysis Uncertainty analysis is an important task in experimental studies since it shows the accuracy of measurements. In this part, the aim is to determine the value of uncertainty in efficiency of solar collector. Based on Eq. (4), the uncertainty in efficiency depends on mass flow rate, heat capacity, inlet and outlet temperature of working fluid, surface area of the solar collector, and solar radiation. The uncertainty of temperature data is determined by the precision Table 3 Values of FR UL and FR (τα ) for water of different mass flux rates.
transmittance product, and UL is defined as the overall coefficient of heat loss, while Cp is the heat capacity of working fluid. The heat capacity of the nanofluid is calculated as follows [37].
(ρCp)nf = (ρCp)np (φ) + (ρCbf ) bf (1−φ)
[knp + (n−1) kbf −(n−1) φ (kbf −knp)
CeO2 Nano powder Water CeO2-water (0.0167%) CeO2-water (0.033%) CeO2-water (0.066%)
(8)
Density of the mixture can be evaluated according to the following equation [39]. 35
Cp (J/kg K)
ρ (kg/m3)
k(W/K.m)
460 [47] 4180 4175 4171 4162
7220 [47] 998 999 1000 1002
12 [47] 0.598 0.624 0.651 0.707
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
of Pt-100 sensors (in our experiments, the precision of sensor is ± 0.1 °C). In Eq. (4), the instantaneous collector efficiency can be calculated with mass flow rate, heat capacity, temperatures, surface area of the solar collector, and solar radiation. The precision of LP PYRA 03 solar meter is ± 2%. 0.5
2
2 2 2 δηi ⎡ δṁ ⎞2 ⎛ δCp ⎞ ⎛ δ (To−Ti ) ⎞ + ⎛ δAc ⎞ + ⎛ δGT ⎞ ⎤ = ⎢⎛ +⎜ ⎟ + ⎥ ηi ṁ ⎠ ⎝ GT ⎠ ⎦ ⎝ Ac ⎠ ⎝ (To−Ti ) ⎠ ⎝ Cp ⎠ ⎣⎝ ⎜
⎟
⎜
⎟
⎜
⎟
(11)
δṁ / ṁ ⩽ 1.5%,δCp/ Cp ⩽ 0.1%, δ (To−Ti )/(To−Ti ) ⩽ [(δ (To−Ti )/(To−T ))2 + (δ (To−Ti )/(To−Ti ))2]0.5 = [(0.1/(40))2 + (0.1/(31))2]0.5 = 0.4%
δAc / Ac ⩽ 0.12%,δGT / GT ⩽ 2%,δηi / ηi ⩽ 2.53% Therefore, after calculation process the maximum uncertainty in the efficiency becomes 2.53%. 5. Stability of nanofluid Ultrasonic is used to break up agglomeration and to promote the dispersion of nanoparticles into base fluids to get more stable nanofluid as Mahbubul et al. [40] reported. Ultrasonic techniques have a significant effect on the surface and the structure of nanoparticles, and grant long-term, stable and well-dispersed nanofluids, and better particle breakdown. After several experiments for CeO2-water Nanofluid, we found that higher concentration gave less stability so we choose these concentrations. On other hand low concentration didn’t give good result so we choose for particles concentrations was between 0.0167% −0.066%. Fig. 3, shows the visual appearance of the different nanofluid with no sign of aggregation for a period of 7 days. According to earlier studies, Said et al. [1], in nanofluid with higher concentration (higher volume fraction) of particles, nanoparticles tended to agglomerate; therefore, the stability of the nanofluid weakened. It was also noted that the stability of the prepared nanofluid with a lower volume fraction of nanoparticles, mixed with the base fluid, was stable for a longer period of time compared to the nanofluids with higher volume fraction. In the present study, the stability of nanofluid was measured by zeta potential machine. (PALS Zeta potential analyzer Ver. 3.37 from Brookhven Instruments). The mean value of zeta potential for 0.0666% volume fraction was -36.91 mV which was considered as a sign of physical stability according to Mahbubul et al. [40].
Fig. 3. Stability of CeO2 after 7 days of preparation.
conditions. A test period was 15 min long as in [2]. The experimental results were shown in graphs that indicate the collector efficiency against a reduced temperature parameter [(Ti–Ta)/GT]. All the presented data were collected in several days, and the best result was finally chosen. The maximum variations in ambient and inlet temperature in each test period is ± 0.8 °C and ± 0.5 °C, respectively; while in global radiation, it is ± 30 W/m2. Hence, our data follow the instructions presented in the ASHRAE Standard 93-2003. All experimental results are shown in graphs and equations, both describing the collector efficiency against a reduced temperature parameter. The efficiency of solar collector was tested for various mass flux rates of 0.015, 0.018 and 0.019 kg/s m2. Each test was made in several days and the best experimental data was finally chosen. The experimental data were fitted linear equations to show the characteristic parameters of the flat-plate solar collector in order to make a comparison of the effect of various volume flow rates as [38]. The efficiency parameters, the removed energy parameters, FR UL and the absorbed energy parameters, FR (τα ), at each volume flow rate, are shown in Table 4. All mass flux rates indicated that all measured data were the base of the fitted linear equation. The R2 which is known as Root Mean Square Error used to show how the data points close to linear fitted curve. These value seemed less in this case than in the individual flow rate cases. Table 4. displays the values of FR (τα ) and FR UL for 0.019 kg/s m2 as highest. Based on Fig. 4, the solar collector efficiency increases as the mass flux rates rises [28].
6. Thermal performance The enhancement in thermal properties of fluids when using nanoparticles was examined and confirmed in several papers like [37,39,41–45]. Among these paper and also the presented paper a deeply discussion was made to show the reason of thermal effect of adding nanoparticles to water. The results presented in this paper are focused in studying the effect of adding CeO2 Nanoparticles on water. The dissociation is divided to two main parts, firstly study the pure water, and secondly study nanofluid. A comparison between the results of both pure water and nanofluid is shown below at different mass flux. Also, for nanofluid, volume fraction of nanoparticles has a remarkable effect on thermal properties of nanofluid so three different volume fraction (0.0167, 0.033 and 0.066) are studied.
6.2. Nanofluid as a working fluid The observed values of the absorbed energy parameter, FR (τα ) and the removed energy parameter, FRUL, for CeO2 nanofluid at same mass Table 4 Values of FR UL and FR (τα ) for water of different mass flux rates.
6.1. Water as working fluid The experiments were carried out at the time interval of 10 am to 4 pm local time. This experiment time was divided into 6 sections, called test runs (e.g. each test run was designated 60 min). Also, each test run was divided into several test periods in quasi-steady state 36
Mass flux (kg/s m2)
FR UL
FR (τα )
R2
0.015 0.018 0.019
3.6257 3.8961 3.7574
0.621 0.6333 0.6301
0.9734 0.968 0.9896
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 4. Efficiency of solar collector using only water.
flux rate are summarized in Table 5. The result are arranged in Table 5 based on same mass flux rate. The efficiency of the collector for nanofluid is drawn against reduced temperature parameters (Ti − Ta)/GT. As shown in Fig. 6 and Table 5, the volume fraction of CeO2 nanofluid had a noticeable effect on the efficiency of the flat-plate solar collector. The collector heat removal factor FR values is shown in Fig. 5. It was calculated using equation (7). The results showed that heat removable factor for nanofluid is more than water. Also, it rises with the increasing of mass flux rate. As the volume fraction of nanofluid increases the value of heat removable factor gets up. Based on these results, the convective heat transfer coefficient was higher than that of water and both absorbed energy parameter, FR (τα ) and the removed energy parameter, FRUL, for CeO2 nanofluid is increased [12]. As a result of that the performance of solar collector is enhanced when using CeO2nanofluid. Results showed that the absorbed energy parameters, FR (τα ) values for CeO2 nanofluid, were higher than using only water for all applied mass flux rates and volume fractions. As visualized in Fig. 6(a) and Table 5, for mass flux rate of 0.015 kg/s m2, the absorbed energy
Table 5 Values of FR UL and FR (τα ) for CeO2/water nanofluid and water based on same mass flux rates. Mass flux (kg/s m2)
Volume fraction φ%
FR UL
FR (τα )
R2
0.015
0.0167 0.033 0.066 Pure water
−4.7354 −7.4975 −10.555 −3.6257
0.6428 0.6782 0.687 0.621
0.9684 0.9937 0.9884 0.9734
0.018
0.0167 0.033 0.066 Pure water
−5.1247 −7.9044 −10.964 −3.7574
0.6512 0.6837 0.6919 0.6301
0.9558 0.9804 0.9543 0.9896
0.019
0.0167 0.033 0.066 Pure water
−5.9593 −7.8871 −11.029 −3.8961
0.6675 0.696 0.7013 0.6333
0.9795 0.975 0.9886 0.968
Fig. 5. Heat removable factor at different flow rate and different volume fraction of nanofluid.
37
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 6. Linear characteristics for efficiency at different mass flux rate: (a) 0.015 kg/s m2 (b) 0.018 kg/s m2 (c) 0.019 kg/s m2.
parameter, FR (τα ) values for CeO2 nanofluid were higher than that of water by 3.51%, 9.21%, and 10.63%, for volume fraction (φ) 0.0167%, 0.0333% and 0.0666%, respectively. Although, the removed energy parameter, FRUL values for CeO2 nanofluid increased by 30.61%, 106.79%, and 191.12% compared to water, while the volume fraction
(φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As visualized in Fig. 6 (b) and Table 5, for mass flux rate of 0.018 kg/s m2, the absorbed energy parameter, FR (τα ) values for CeO2 nanofluid were higher than that of water by 3.35%, 8.03%, and 9.81%, for volume fraction (φ) 0.0167%, 0.0333% and 0.0666%, respectively. Raising the values of 38
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Table 6 Values of FR UL and FR (τα ) for CeO2/water nanofluid and water based on same volume fractions. Volume fraction φ%
Mass flux (kg/s m2)
FR UL
FR (τα )
R2
0.0167
0.015 0.018 0.019
−4.7534 −5.1247 −5.7656
0.6428 0.6512 0.6675
0.9684 0.9558 0.9795
0.033
0.015 0.018 0.019
−7.4975 −7.6154 −7.8871
0.6782 0.6807 0.696
0.9937 0.9833 0.975
0.066
0.015 0.018 0.019
−10.555 −10.964 −11.092
0.687 0.6919 0.7013
0.9884 0.9543 0.9886
Pure water
0.015 0.018 0.019
−3.6257 −3.8961 −3.7574
0.621 0.6333 0.6301
0.9734 0.968 0.9896
Table 7 Intersections of nanofluids characteristics of water. Mass flux (kg/s m2)
Volume φ% fraction
Intersection (Ti – Ta)/GT
0.015
0.0167 0.033 0.066
0.02 0.015 0.01
0.018
0.0167 0.033 0.066
0.016 0.014 0.009
0.019
0.0167 0.033 0.066
0.019 0.016 0.01
0.0666% volume fraction had the highest absorbed energy and heat loss but the 0.0333% volume fraction showed the best-performed characteristics when comparing the results in Table 5. It can be concluded from the present work that up to a certain volume fraction of nanoparticles the performance of the flat-plate collectors might be increased. Although there were higher efficiencies in case of 0.066% volume fraction but it was valid only for a short range; generally the 0.033% volume fraction performances were higher. When the volume fraction was too low, the effect on the heat transfer increase was small, while the increased volume fraction caused higher heat transfer. However, the efficiency of solar collector did not depend only on values of FR (τα ), and FRUL but also depended on reduced temperature parameters [(Ti – Ta)/GT]. For lower values of [(Ti – Ta)/GT] – high irradiation – the efficiency of the collector with volume fraction of nanoparticles (φ) 0.066% was higher than others. Therefore, as the value of [(Ti – Ta)/GT] increased the efficiency of the volume fraction of nanoparticles (φ) 0.0333%, it became higher than others, and finally, the volume fraction of nanoparticles (φ) 0.0167%, efficiency reached the maximum values at the highest values of [(Ti – Ta)/GT]. These cases were accepted for all studied mass flux rate, 0.015 kg/s m2, 0.018 kg/s m2, and 0.019 kg/s m2 as shown in Fig. 6(a), (b) and (c), respectively. The explanation of this behavior of nanoparticles is as follows. Lower values of [(Ti – Ta)/GT] meant low temperature difference or high solar radiation. Hence, higher volume fraction of nanofluid is preferred as it absorbed more heat than others and less particles tend to agglomerate compering to lower volume fraction nanofluid. Based on that, the micro heat transfer resulted because of the collision of particles is higher so the efficiency directly proportional to the volume fraction of nanoparticles (φ) . Although, as the values of [(Ti – Ta)/GT] increased the mean fluid temperature rises lead to rise the viscosity of nanofluids which rose the thickness of the boundary layer. Hence, the heat transfer rate reduced [7] causing reduced performance. Also, as the temperature increases the thermal conductivity of nanofluid rises and consequently the overall heat transfer coefficient goes up and removed heat transfer (FR UL ) becomes lager. Form other hand, the solar radiation decreases which reduced absorbed energy and increases heat loss. The higher heat loss coefficient (FR UL ) means greater slope for the efficiency line. Hence, by rising the reduced temperature parameter the outlet temperature of nanofluids declined more rapidly than the outlet temperature of water [31] so the efficiency of collector reduces accordingly to Eq. (4).
FRUL compared to water are 36.39%, 102.68%, and 191.8%, while the volume fraction (φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As it can be seen in Fig. 6(c) and Table 5, for mass flux rate of 0.019 kg/ s m2, values of FR (τα ) were raised by 5.4 %, 9.9% and 10.74%, and for volume fraction (φ ) 0.0167%, 0.0333%, 0.0666%, respectively. The values of FRUL for CeO2 nanofluid were increased by 47.98%, 102.44%, and 183.08%, compared to water, while volume fraction (φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As we can find in Table 3 the value of thermal conductivity for nanofluids is more than pure water. Several reasons was mentioned in previous work to find reasons for that as [37,39,41–45]. In presented work we believed that Brownian motion played the main role of this enhancement as we used forced circulation pump. The pump increased the random motion of the particles which increased the collision between liquid molecules and solid particles, so this was what caused the increase in the convective heat transfer coefficient and the efficiency in Eq. (4). Also, it is worth to note that Reynolds number in presented cases isn’t less than 2100 which is mean that turbulent flow is achieved. Turbulence in fluid increases the fluctuations and mixing of nanoparticles so more heat transfer by diffusion. Also, turbulence helps to prevent the presence of particles free regions which increase the thermal resistance of the liquid. On the other hand, we can’t neglect the effect of liquid layering at liquid particle interface as we use particles with diameter less than 30 nm. However, a certain value of the reduced temperature parameter, [(Ti – Ta)/GT], limited this fact, and it could be detected by finding the intersection between the line representing water and that of nanofluid efficiency with the same mass flux rate - but different volume fractions as shown in Fig. 6(a),(b),(c). The values of the reduced temperature parameter, [(Ti – Ta)/GT], of intersections are in Table 7. Before the intersections, the efficiency values of the solar collector using nanofluid were higher than with applied water. Consequently, after the intersection there was a reverse trend there. This reverse trend could be explained as follows. When the reduced temperature parameter, [(Ti – Ta)/GT], increased, the solar radiation value declined; but the increased heat transfer caused higher mean temperature and higher heat loss compared to pure water [2]. The higher heat loss coefficient, (FR UL ), meant a steeper slope for the efficiency line. Hence, by increasing the reduced temperature parameter, the outlet temperature of nanofluids reduced more rapidly than the outlet temperature of water [24], so the efficiency of collector decreased accordingly to Eq. (4).
6.2.2. Effect of mass flux rate of nanofluid on efficiency Fig. 7 shows the efficiency of the solar collector using volume fraction (φ) of 0.0167%, 0.0333%, and 0.0666%, and applying CeO2 with different-mass flux rate of 0.015, 0.018 and 0.019 kg/s m2. The values of FR UL and FR (τα ) were indicated in Table 6, for same volume fraction to make it more clear and easy to detect. The changes of the FR (τα ) and FRUL values for different volume fraction (φ ) and mass fluxes were listed previously, they are not repeated here again. Generally, the FR (τα ) energy absorbance factors gradually increases as the mass flux rate increased in the case of each volume fraction. The FR UL heat loss factor values shows the same tendencies for all the
6.2.1. Effect of volume fraction of nanofluid on efficiency The effect of volume fraction of nanofluid on the efficiency of a flatplate collector was interlaced. Based on several previous work such as [43–45] and [46] Nusselt number and heat transfer rise with the increasing in volume fraction of nanoparticles as large number of particles increase the micro convection effect between particles and base fluid. The 39
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 7. Efficiency of solar collector at different volume fractions of CeO2/water nanofluid: (a) φ% = 0.0167% (b) φ% = 0.033% (c) φ% = 0.066% .
applied volume fractions, increasing flow rate caused more heat loss factors. This is because increasing the mass flux rate caused enhancement in Brownian motion, turbulence of the particles in the nanofluid, and the Reynolds and Nusselt numbers [2,32,5].
7. Conclusions A study was performed experimentally to determine the efficiency curves of a flat-plate solar collector with using nanofluid of CeO2-water as working fluid. The stability of CeO2-water nanofluid was weak. 40
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
flat-plate solar water heater. Energy Fuels 2016;30:9908–13. [16] Jeon Jongwook, Park Sunho, Lee Bong Jae. Analysis on the performance of a flatplate volumetric solar collector using blended plasmonic nanofluid. Sol Energy 2016;132:247–56. [17] Verma Sujit Kumar, Tiwari Arun Kumar, Chauhan Durg Singh. Experimental evaluation of flat plate solar collector using nanofluids. Energy Convers Manage 2017;134:103–15. [18] Noghrehabadi Aminreza, Hajidavaloo Ebrhim, Moravej Mojtaba. Experimental investigation of efficiency of square flat-plate solar collector using SiO2/water nanofluid. Case Stud Therm Eng 2016;8:378–86. [19] Vakili M, Hosseinalipour SM, Delfani S, Khosrojerdi S, Karami M. Experimental investigation of graphene nanoplatelets nanofluid-based volumetric solar collector for domestic hot water systems. Sol Energy 2016;131:119–30. [20] Anin Vincely D, Natarajan E. Experimental investigation of the solar FPC performance using graphene oxide nanofluid under forced circulation. Energy Convers Manage 2016;117:1–11. [21] Kim Hyeongmin, Kim Jinhyun, Cho Honghyun. Experimental study on performance improvement of U-tube solar collector depending on nanoparticle size and concentration of Al2O3 nanofluid. Energy 2017;118:1304–12. [22] Verma Sujit Kumar, Tiwari Arun Kumar, Chauhan Durg Singh. Performance augmentation in flat plate solar collector using MgO/water nanofluid. Energy Convers Manage 2016;124:607–17. [23] Owolabi Afolabi L, Al-Kayiem Hussain H, Baheta Aklilu T. Performance investigation on a thermal energy storage integrated solar collector system using nanofluid. Int J Energy Res 2017;41:650–7. [24] Faizal M, Saidur R, Mekhilef S, Alim MA. Energy, economic and environmental analysis of metal oxides nanofluid for flat-plate solar collector. Energy Convers Manage 2013;76:162–8. [25] Colangelo Gianpiero, Favale Ernani, Miglietta Paola, de Risi Arturo, Milanese Marco, Laforgia Domenico. Experimental test of an innovative high concentration nanofluid solar collector. Appl Energy 2015;154:874–81. [26] Raja Sekhara Y, Sharmab KV, Thundil Karupparaj R, Chiranjeevi C. Heat transfer enhancement with Al2O3 nanofluids and twisted tapes in a pipe for solar thermal applications. Proc Eng 2013;64:1474–84. [27] Tiwari Arun Kumar, Ghosh Pradyumna, Sarkar Jahar. Heat transfer and pressure drop characteristics of CeO2/water nanofluid in plate heat exchanger. Appl Therm Eng 2013;57:24–32. [28] Leong KY, Ong Hwai Chyuan, Amer NH, Norazrina MJ, Risby MS, Ku Ahmad KZ. An overview on current application of nanofluids in solar thermal collector and its challenges. Renew Sustain Energy Rev 2016;53:1092–105. [29] Kasaeian Alibakhsh, Eshghi Amin Toghi, Sameti Mohammad. A review on the applications of nanofluids in solar energy systems. Renew Sustain Energy Rev 2015;43:584–98. [30] Verma Sujit Kumar, Tiwari Arun Kumar. Progress of nanofluid application in solar collectors: A review. Energy Convers Manage 2015;100:324–46. [31] Javadi FS, Saidur R, Kamalisarvestani M. Investigating performance improvement of solar collectors by using nanofluids. Renew Sustain Energy Rev 2013;28:232–45. [32] Hussein Ahmed Kadhim. Applications of nanotechnology to improve the performance of solar collectors – recent advances and overview. Renew Sustain Energy Rev 2016;62:767–92. [33] Reddy KS, Kamnapure Nikhilesh R, Srivastava Shreekant. Nanofluid and nanocomposite applications in solar energy conversion systems for performance enhancement: a review. Int J Low-Carbon Technol 2017;12:1–23. [34] Eggers Jan Rudolf, Kabelac Stephan. Nanofluids revisited. Appl Therm Eng 2016;106:1114–26. [35] Muhammad Mahmud Jamil, Muhammad Isa Adamu, Sidik Nor Azwadi Che, Yazid Muhammad Noor Afiq Witri Muhammad, Mamat Rizalman, Najafic G. The use of nanofluids for enhancing the thermal performance of stationary solar collectors: a review. Renew Sustain Energy Rev 2016;63:226–36. [36] ASHRAE Standard 93–2003, Methods of testing to determine the thermal performance of solar collectors, Atlanta, GA, USA, 2003. [37] Zhou SQ, Ni R. Measurement of the specific heat capacity of water-based Al2O3 nanofluid. Appl Phys Lett 2008;92:1–3. [38] Beghi G. Performance of solar energy converters. Italy: Lectures of a course held at the Joint Research Centre, ISPRA; 1981. Nov. 11-18. [39] Zhang X, Gu H, Fujii M. Effective thermal conductivity and thermal diffusivity of nanofluids containing spherical and cylindrical nanoparticles. Exp Therm Fluid Sci 2007;31:593–9. [40] Mahbubul IM, Saidur R, Amalina MA, Elcioglu EB, Okutucu-Ozyurt T. Effective ultrasonication process for better colloidal dispersion of nanofluid. Ultrason Sonochem 2015;26:361–9. [41] Chon CH, Kihm KD. Thermal conductivity enhancement of nanofluids by Browian motion. J Heat Transf 2005;127(8):810. [42] Iacobazzi Fabrizio, Milanese Marco, Colangelo Gianpiero, Lomascolo Mauro, Risi Arturo de. An explanation of the Al2O3 nanofluid thermal conductivity based on the phonon theory of liquid. Energy 2016;116:786–94. [43] Sheikholeslami M, Ganji DD. Heat transfer of Cu-water nanofluid flow between parallel plates. Powder Technol 2013;235:873–9. [44] Sheikholeslami Mohsen, Ganji Davood Domiri. Nanofluid flow and heat transfer between parallel plates considering Brownian motion using DTM. Comput Methods Appl Mech Eng 2015;283:651–63. [45] Sheikholeslami M, Rashidi MM, Ganji DD. Numerical investigation of magnetic nanofluid forced convective heat transfer in existence of variable magnetic field using two phase model. J Mol Liq 2015;212:117–26. [46] Calvin Li H, Peterson GP. Experimental investigation of temperature and volume fraction variations on the effective thermal conductivity of nanoparticle suspensions (nanofluids). J Appl Phys 2006;99:084314. [47] Mogensen Mogens, Sammes Nigel M, Tompsett Geoff A. Physical, chemical and electrochemical properties of pure and doped ceria. Solid State Ionics 2000;129:63–94.
Three different volume fractions of 0.0167%, 0.0333%, and 0.0666% were tested at three mass flux rates, including 0.015, 0.018, and 0.019 kg/s m2. The experiments and results elucidated that using CeO2water nanofluid increased the efficiency of the solar collector more efficiently than using only water. Findings dedicated that the maximum efficiency when reduced temperature parameter, [(Ti – Ta)/GT], equals to zero was 10.74%, volume fraction (φ ) was 0.066% and mass flux rate was 0.019 kg/s m2. However, for a wide range of reduced temperature parameters, [(Ti – Ta)/GT], the best performance was found with the application of 0.0333% volume fraction for all mass flux rates, as it can be followed in Fig. 6. The changes in absorbed energy parameter, FR (τα ) vary from 3.51% to 10.74%, and in removed energy parameter, FR UL vary from 30.61% to 191.8%, compared to the water with the same mass flux rates. The efficiency of the collector was directly proportional with the mass flux rate, and it seemed that an optimal volume fraction might be the 0.0333% for the present study’s ranges. To the best of our knowledge, this has been the first study ever focusing on the efficiency analysis of a flat-plate solar collector using CeO2-water nanofluid. Accordingly, using different values of volume fraction (φ ) and several mass flux rates must be done, in order to find out the effect of these variables on the efficiency of flat-plate solar collectors. Acknowledgment The authors would like to thank Professor István Csontos and Dr. Enikő Krisch for their help and support. The authors would like to thank the “Egyptian Ministry of Higher Education” (MOHE) for the invaluable professional promotion of the Stipendium Hungaricum scholarship provided for the PhD studies carried out in Hungary. References [1] Said Z, Saidur R, Sabiha MA, Hepbasli A, Rahim NA. Energy and exergy efficiency of a flof-plate solar collector using pH treated Al2O3 nanofluid. J Clean Prod 2016;112:3915–26. [2] Yousefi Tooraj, Veysia Farzad, Shojaeizadeha Ehsan, Zinadinib Sirus. An experimental investigation on the effect of Al2O3-H2O nanofluid on the efficiency of flatplate solar collectors. Renew Energy 2012;39:293–8. [3] Yousefi Tooraj, Veisy Farzad, Shojaeizadeh Ehsan, Zinadini Sirus. An experimental investigation on the effect of MWCNT-H2O nanofluid on the efficiency of flat-plate solar collectors. Exp Therm Fluid Sci 2012;39:207–12. [4] Goudarzi K, Shojaeizadeh E, Nejati F. An experimental investigation on the simultaneous effect of CuO-H2O nanofluid and receiver helical pipe on the thermal efficiency of a cylindrical solar collector. Appl Therm Eng 2014;73:1234–41. [5] Moghadam Ali Jabari, Farzane-Gord Mahmood, Sajadi Mahmood, Hoseyn-Zadeh Monireh. Effects of CuO/water nanofluid on the efficiency of a flat-plate solar collector. Exp Therm Fluid Sci 2014;58:9–14. [6] Faizal M, Saidur R, Mekhilef S, Hepbasli A, Mahbubul IM. Energy, economic, and environmental analysis of a flat-plate solarcollector operated with SiO2 nanofluid. Clean Techn Environ Policy 2015;17:1457–73. [7] He Qinbo, Zeng Shequan, Wang Shuangfeng. Experimental investigation on the efficiency of flat-plate solar collectors with nanofluids. Appl Therm Eng 2015;88:165–71. [8] Meibodi Saleh Salavati, Kianifar Ali, Niazmand Hamid, Mahian Omid, Wongwises Somchai. Experimental investigation on the thermal efficiency and performance characteristics of a flat plate solar collector using SiO2/EG–water nanofluids. Int Commun Heat Mass Transf 2015;65:71–5. [9] Jamal-Abad Milad Tajik, Zamzamian A, Imani E, Mansouri M. Experimental study of the performance of a flat-platecollector using Cu-Water nanofluid. J Thermophys Heat Transf 2013;27(4):756–60. [10] Said Z, Sabiha MA, Saidur R, Hepbasli A, Rahim NA, Mekhilefand S, et al. Performance enhancement of a Flat Plate Solar collector using Titanium dioxide nanofluid and Polyethylene Glycol dispersant. J Clean Prod 2015;92:343–53. [11] Michael Jee Joe, Iniyan S. Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations. Energy Convers Manage 2015;95:160–9. [12] Polvongsri Sarawut, Kiatsiriroat Tanongkiat. Performance analysis of flat-plate solar collector having silver nano-fluid as a working fluid. Heat Transf Eng 2014;35:1183–91. [13] Munuswamy Dinesh Babu, Madhavan Venkata Ramanan, Mohan Mukunthan. Comparison of the effects of Al2O3 and CuO nanoparticles on the performance of a solar flat-plate collector. J Non-Equilib Thermodyn 2015;40(4):265–73. [14] Ahmadi Alireza, Ganji Davood Domiri, Jafarkazemi Farzad. Analysis of utilizing Graphene nanoplatelets to enhance thermal performance of flat plate solar collectors. Energy Convers Manage 2016;126:1–11. [15] Devarajan Yuvarajan, Babu Munuswamy Dinesh. Analysis on the influence of nanoparticles of alumina, copper oxide, and zirconium oxide on the performance of a
41
Contents lists available at ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Experimental investigation of flat plate solar collector using CeO2-water nanofluid
MARK
⁎
M.A. Sharafeldina,b, , Gyula Grófa a b
Department of Energy Engineering, Budapest University of Technology and Economics, Budapest, Hungary Mechanical Engineering Department, Faculty of Engineering Shoubra, Benha University, Benha, Egypt
A R T I C L E I N F O
A B S T R A C T
Keywords: Flat-plate collector Collector efficiency CeO2 nanoparticles CeO2-water nanofluid
Using nanofluids in thermal energy devices, such as flat-plate solar collectors, is gradually making progress, and getting awareness in the scientific community. Experiments were performed to study the effect of using CeO2water on the efficiency of flat-plate solar collector by three different volume fractions of CeO2 nanoparticles of 0.0167%, 0.0333% and 0.0666%, while the mean particle dimension was kept constant at 25 nm. An ultrasonic process was used for maintaining the stability of the CO2-water nanofluid. The working fluid mass flux rates were 0.015, 0.018 and 0.019 kg/s m2. The experiments were carried out in Budapest, Hungary on the latitude of 47°28′N and longitude of 19°03′E. Higher collector efficiency was achieved when using CeO2-water nanofluid compared to results achieved with water application. Based on present data, the efficiency of the collector is directly proportional with the mass flux rate and with the volume fraction in the ranges of the present study. Experiments indicate that the highest rise in efficiency of the collector at zero value of [(Ti – Ta)/GT] is 10.74%, for volume fraction (φ ) 0.066%, and for mass flux rate of 0.019 kg/s m2 compared to water.
1. Introduction In the past few years, scientists raised general attention to nanoparticles with less than 100 nm in size. It was found out that the tiny particles hold by fluids and make a remarkable change or even the properties of fluids. Based on this fact, it was observed that a lot of nano-scale materials added to fluids changed their thermal properties, as well as the performance of thermal devices. Solar collectors are one of these devices which take advantage of the observed properties of nanofluid. In this part, when getting a focus view on using nanofluid as the working fluid in flat-plate types of solar collectors, will be presented. Table 1 shows different experimental investigation of performance of flat plate solar collector when using nanofluid as a working fluid. Although all above studies didn’t modify the conventional solar collector design, other researchers made some modification in the design of solar collector such as Faizal et al. [24] who used numerical methods to design a smaller solar collector that can produce the same desired output temperature as the bigger one. From his study, it was found that by applying nanofluid the cost of solar collector, embodied energy and CO2 emissions were reduced. Colangelo et al. [25] modified the design of the flat-plate collector by rearranging bottom and top headers to reduce the sedimentation of the clusters of nanoparticles,
⁎
and, in this way, they were able to apply high nanoparticle concentration for the first time ever. Sekhar et al. [26] investigated convective heat transfer analysis for a horizontal circular pipe with Al2O3 nanofluids at different volume concentrations in mixed laminar flow range. Based on Latest review studies [28–35] no research had been done to detect the effect of CeO2-water nanofluid on the efficiency of a flatplate collector although it had good thermal properties as Tiwari et al. [27] found. Also, CeO2 nanoparticles has several benefits like:
• It has good availability and easy to prepare • it’s price isn’t high so it has a good economic potential • the stability of it with water is high comparing to other nanoparticles • No toxicity or flammability was observed when it was using so it environmental friendly.
This paper is focusing on studying the performance of a flat-plate collector using CeO2-water nanofluid as working fluid instead of using distilled water. Also, making a stable CeO2-water nanofluid using ultrasonic technique is an aim for this work. On other side, examine to what extent the thermal performance is affected by adding CeO2 nanoparticles and using different mass flux rate is deeply studied in this
Corresponding author at: Budapest University of Technology and Economics, Budapest, Hungary. E-mail address: [email protected] (M.A. Sharafeldin).
http://dx.doi.org/10.1016/j.enconman.2017.10.070 Received 22 August 2017; Received in revised form 13 October 2017; Accepted 24 October 2017 0196-8904/ © 2017 Published by Elsevier Ltd.
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Nomenclature
Ac Cp Cpbf Cpnp Cpnf FR GT knf kbf knp ṁ R2 Ta Ti To Qu
overall coefficient of heat loss (W/m2 K) volume flow rate (L/h)
UL V·
surface area of the solar collector (m2) heat capacity of (J/kg K) heat capacity of base fluid (water) (J/kg K) heat capacity of nanoparticles (J/kg K) heat capacity of nanofluid (J/kg K) heat removal factor solar radiation normal to collector (W/m2) thermal conductivity of nanofluid (W/m K) thermal conductivity of base fluid (W/m K) thermal conductivity of nanoparticles (W/m K) mass flow rate of nanofluid (kg/s) root Mean Square Error ambient temperature (K) collector inlet temperature (K) collector outlet temperature (K) useful heat energy rate (W)
Greek symbols
τα ηi ρnf ρnp ρ bf φ
absorption-transmittance product instantaneous efficiency density of nanofluid (kg/m3) density of nanoparticles (kg/m3) density of base fluid (kg/m3) volume fraction of nanoparticles
Subscripts base fluid nanofluid nanoparticles
bf nf np
purpose of this standard is to introduce test methods to detect thermal performance of solar collectors that use single-phase fluids without significant internal energy storage. According to ASHRAE Standard 932003 [36] solar collector should examine at 0.02 kg/s m2 or at recommended flow rate as manufacturer. Therefore, we use these mass flux rate of 0.015, 0.018, and 0.019 kg/s m2 as it in the range of recommended by manufacturer and also it just below the standard mass flux of 0.02 kg/s m2. The thermal performance of the solar collector is calculated by determining the values of instantaneous efficiency of different combinations of incident radiation, ambient temperature, and inlet fluid temperature. In addition, experiments must be done under steady-state conditions. The instantaneous efficiency is defined as the ratio of useful energy, Qu, and the solar energy received by absorber plate of collector, AcGT and it is calculated by Eq. (1) below.
paper. A detailed discussion about the effect of environmental parameters like ambient temperature and solar radiation is held in presented work by using the reduced temperature parameter, [(Ti–Ta)/GT], as independent variable in several figures. 2. Methodology This section is presented in two parts. The first part deals with nanofluid preparation and the second part describes the set-up that has been used for experiments on the flat plate solar collector. 2.1. Preparation method and characterization In this study, deionized water and water-based CeO2 nanofluids were utilized as working fluids. Commercial spherical shape CeO2 nanopowder (supplier: M K Impex, Canada) of 99.9% purity and 25 nm average diameter was used for the experimental investigation. Distilled water served as reference fluid. The CeO2 nanoparticles, insoluble in water, had a density of 7.123 g/cm3. The nanofluids were prepared by a two-step method where CeO2 nanoparticles were dispersed into the base fluid directly first; later they were oscillated continuously for about 90 min, and 50% amplitude in an ultrasonic homogenizer (Bandelin, SONOPULS HD 2200, output power maximum 200 W).
ηi =
Qu A cGT
(1)
The useful heat energy rate is calculated by using Eq. (2), and can also be determined in terms of the energy absorbed by the absorber, and the energy lost from the absorber as given by Eq. (3). · Qu = ṁ Cp (To−T) i = ρV C p (To−T) i
(2)
The useful heat energy rate can be also described as the difference between energy absorbed by the absorber plate and the energy loss from the absorber as:
2.2. Experimental procedure
Qu = A c FR [GT (τα)−UL (Ti−Ta)] Experimental apparatus diagram and picture is shown in Figs. 1 and 2, respectively. The experiments were performed in Budapest (latitude 47°28′N longitude 19°03′E). The specifications of the collector are given in Table 2. The collector type is TS 300 from Naplopó Kft. in Hungary and the inclination was 45 degree. An electrical pump was used to circulate the working fluid, while a heat exchanger transferred heat from the solar collector to the tank. The tank capacity was nearly 500 l. A flow meter was used to measure fluid flow rate. To control flow rate, a simple valve was also installed after the electric pump. Also, a series of Pt-100 resistance thermometers were fitted to the collector in order to measure the temperature of the working fluid in the collector both in- and outbound. The ambient temperature was measured by a thermometer, while the total solar radiation was measured by a LP PYRA 03 solar meter.
(3)
So the instantaneous efficiency can be expressed by Eqs. (4) or (5)
ηi = ηi =
ρV·Cp (To−T) i (4)
A cGT A c FR [GT (τα)−UL (Ti−Ta)] A cGT
T −T ηi = FR (τα)−FR UL ⎛ i a ⎞ ⎝ GT ⎠ ⎜
(5)
⎟
(6)
Eq. (6) which defines the instantaneous efficiency is known as the Hottel-Whillier equation. FR is known as the collector heat removal factor and is expressed by Eq. (7),
FR =
ṁ Cp (To−T) i A c [G T (τα)−UL (Ti−Ta)]
(7)
where, ṁ is the mass flow rate of the working fluid, Ti is the collector inlet temperature, To is the collector outlet temperature, Ta is the ambient temperature, G T is the global solar radiation normal to the collector, A c is the surface area of the solar collector, τα is the absorption-
3. Testing method In the current study, ASHRAE Standard 93-2003 [36] was the basis to investigate the thermal performance of the solar collector. The 33
34
Graphene Copper Oxide Aluminum Oxide Titanium oxide and Silicon Oxide Multiwall carbon nanotubes SiO2 Grapheme nanoplatelets graphene oxide Al2O3 nanofluid
MgO/water
Fe nanoparticle
Noghrehabadi et al. [18] Vakili et al. [19] Vincely et al. [20] Kim et al. [21]
Verma et al. [22]
Owolabi et al. [23]
Jeon et al. [16]
Verma et al. [17]
Cu-water
Jamal-Abad et al. [9]
Graphene Alumina, Copper Oxide and Zirconium Oxide gold Nano-rods
SiO2- mixture of EG and water (50:50 vol%)
Meibodi et al. [8]
Ahmadi et al. [14] Devarajan et al. [15]
CuO-water SiO2-nanofluid Cu-H2O nanofluids
Moghadam et al. [5] Faizal et al. [6] He et al. [7]
(CuO/H2O) silver nanofluid Al2O3 and CuO nanofluid
CuO-H2O
Goudarzi et al. [4]
Michael et al. [11] Polvongsri et al. [12] Munuswamy et al. [13]
MWCNT
Yousefi et al. [3]
TiO2-water
Al2O3-nanofluid with and without Triton X-100
Yousefi et al. [2]
Said et al. [10]
0.1% and 0.3% volume fraction
Al2O3-water
Said et al. [1]
0.25, 0.5, 0.75, 1.0, 1.25 and 1.5% volume fraction 0.5% weight fraction
1%weight fraction 0.0005, 0.001 and 0.005 wt fraction 0.005, 0.01 and 0.02 wt fraction 0.5%,1%,1.5% volume fraction
gold Nano-rods dispersed in three plasmonic nanofluids are 1.85, 2.65 and 5.17 From 0.25 % to 2% volume fraction
0.01 % and 0.02 % weight fraction 0.2% and 0.4% weight fraction
0.05% volume fraction 1000 and 10,000 ppm 0.2% and 0.4% volume fraction
0.1–0.3% volume fraction
0.05% and 0.1% weight fraction
0.4% volume fraction 0.2% and 0.4% volume fraction 0.01%, 0.02 %, 0.04 %, 0.1 %, 0.2 % weight fraction 0.5%,0.75%1% volume fraction
0.1%, 0.2% and 0.4% weight fraction
0.2% and 0.4%. weight fraction
0.2% and 0.4% weight fraction
Volume or Weight fraction
Nanofluid
Research
Table 1 Experimental studies for nanofluids with flat-plate solar collectors.
40-nm
40 nm
12 nm Particle diameter 2 μm 300 nm 20,50and 100 nm
From 7 nm to 45 nm differ from material to another
16 nm
less than 100 nm 40 nm
75 m 20 nm 40 nm
21 nm
35 nm
40 m
40 nm 15 nm 25 nm and 50 nm
40 nm
10–30 nm
15 nm
13 nm
Nano-size
2
3
3
2
3
2
3
efficiency was enhanced when using SiO2/water nanofluid • thermal collector enhanced with using Grapheme nanoplatelets • solar collector efficiency increased by 7.3% • the highest efficiency increased by 24.1% for the solar collector with 1.0 vol% Al O • The nanofluid of 20 nm-nanoparticles and a mass flow rate of 0.047 kg/s efficiency enhancement was 9.34% for 0.75% particle volume • Collector concentration at flow rate 1.5 lpm • The thermal efficiency was 59.5% and 50.5% for with and without nanofluid
oxide/water, Titanium oxide /water, and Silicon oxide/water comparing to water as the base fluid.
• • • efficiency increased by 23.47% 16.97%, 12.64%, 8.28%, 5.09% and 4.08%, • The respectively for Multiwall carbon, graphene/water, Copper oxide/water, Aluminum
for CuO Thermal efficiency increased by 18.87%. The solar collector efficiency for Al2O3, CuO, ZrO2, and water was 55, 51.3,47, and 38%, respectively. Solar thermal collectors performance was enhanced using plasmonic nanofluids.
2
results showed that the efficiency of the collector at 0.05 wt% was approximately • The 24% more than that of the pure-base fluids energy efficiency increased by 76.6% whereas the highest exergy efficiency • The achieved is 16.9% for 0.1 vol% and 0.5 kg/min thermal performance of the solar water heater enhanced by 6.3% • the nano-fluid improved the solar collector performance • the experimentation, the best collector efficiency obtained in a 25-LPD solar • From collector is Al O 0.4% volume frac-tion, which increased to 12% for Al O and 7%
approximately between 4 and 8%.
energy efficiency increased by 83.5% when 0.3% volume fraction • The exergy efficiency was enhanced by up to 20.3% • the using the 0.2 wt% Al O - nanofluid increased the efficiency of the solar collector by • 28.3% using the surfactant, the maximum enhanced efficiency was 15.63% • ByResults show that by increasing the weight fraction from 0.2% to 0.4%, there is a • substantial increase in the efficiency. the surfactant causes an increase in the efficiency. • Using 0.1 wt% nanofluid in 0.0083 kg/s mass flow rate of fluid the maximum thermal • For efficiency was increased by 25.6% the use of nanofluid with SDS as surfactant the maximum collector efficiency is • With increased by 24.2% solar collector efficiency increased by 16.7% • the found that the efficiency of the solar collector increased by 23.5% • Itthewasefficiency of the solar collector was enhanced by 23.83% • showed that when the heat loss parameter limits to zero, an increase in • Findings nanofluid concentration from 0 to 1% results in an efficiency enhancement
Remarks
M.A. Sharafeldin, G. Gróf
Energy Conversion and Management 155 (2018) 32–41
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 1. Layout of a test rig.
ρnf = ρnp (φ) + ρ bf (1−φ)
(9)
Thermal conductivity of nanofluid can be estimated as following equation [39].
knf = kbf
[knp + (n−1) kbf + φ (kbf −knp)]
(10)
Where φ indicates the volume fraction of nanoparticles, n is equal to 3 as the shape of particles are spherical as [39]. Thermal conductivity of nanoparticles plays an important role to increase thermal conductivity of nanofluid and consequently the thermal performance of collector. The thermal properties of nanofluids are presented in Table 3. The values of τand α depend on the design of collector and the value of FR depends on flow rate, hence, for normal incidence conditions and at given quantities of mass flux rate and volume fraction the values of FR, τandα do not change significantly in the range of tested temperatures. So, according to Eq. (6), the collector efficiency is expressed as a straight line. This line intersects the vertical axis (efficiency) at FR (τα ). At this point, the collector efficiency reaches its maximum value, and the inlet temperature to the collector is equal to ambient temperature. The parameter FR (τα ) is called “absorbed 42 energy parameter” or “optical efficiency”. The slop of straight line is equal to FR UL and expresses how energy has removed from the solar collector; it is also called “removed energy parameter”.
Fig. 2. Pictures of a test rig.
Table 2 Specifications of the flat-plate solar collector. Specification
Dimension
Width: Height: Depth: Width module size: Full solar surface: Free glass surface: Absorber surface: Liquid space capacity: Cover glass thickness: Thermal insulation thickness and material: Absorber absorption coefficient Absorber emission factor
1009 mm 2009 mm 75 mm 1040 mm 2.03 m2 1.78 m2 1.78 m2 1.57 l 4 mm 40 mm rock wool 0.95 0.13
4. Uncertainty analysis Uncertainty analysis is an important task in experimental studies since it shows the accuracy of measurements. In this part, the aim is to determine the value of uncertainty in efficiency of solar collector. Based on Eq. (4), the uncertainty in efficiency depends on mass flow rate, heat capacity, inlet and outlet temperature of working fluid, surface area of the solar collector, and solar radiation. The uncertainty of temperature data is determined by the precision Table 3 Values of FR UL and FR (τα ) for water of different mass flux rates.
transmittance product, and UL is defined as the overall coefficient of heat loss, while Cp is the heat capacity of working fluid. The heat capacity of the nanofluid is calculated as follows [37].
(ρCp)nf = (ρCp)np (φ) + (ρCbf ) bf (1−φ)
[knp + (n−1) kbf −(n−1) φ (kbf −knp)
CeO2 Nano powder Water CeO2-water (0.0167%) CeO2-water (0.033%) CeO2-water (0.066%)
(8)
Density of the mixture can be evaluated according to the following equation [39]. 35
Cp (J/kg K)
ρ (kg/m3)
k(W/K.m)
460 [47] 4180 4175 4171 4162
7220 [47] 998 999 1000 1002
12 [47] 0.598 0.624 0.651 0.707
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
of Pt-100 sensors (in our experiments, the precision of sensor is ± 0.1 °C). In Eq. (4), the instantaneous collector efficiency can be calculated with mass flow rate, heat capacity, temperatures, surface area of the solar collector, and solar radiation. The precision of LP PYRA 03 solar meter is ± 2%. 0.5
2
2 2 2 δηi ⎡ δṁ ⎞2 ⎛ δCp ⎞ ⎛ δ (To−Ti ) ⎞ + ⎛ δAc ⎞ + ⎛ δGT ⎞ ⎤ = ⎢⎛ +⎜ ⎟ + ⎥ ηi ṁ ⎠ ⎝ GT ⎠ ⎦ ⎝ Ac ⎠ ⎝ (To−Ti ) ⎠ ⎝ Cp ⎠ ⎣⎝ ⎜
⎟
⎜
⎟
⎜
⎟
(11)
δṁ / ṁ ⩽ 1.5%,δCp/ Cp ⩽ 0.1%, δ (To−Ti )/(To−Ti ) ⩽ [(δ (To−Ti )/(To−T ))2 + (δ (To−Ti )/(To−Ti ))2]0.5 = [(0.1/(40))2 + (0.1/(31))2]0.5 = 0.4%
δAc / Ac ⩽ 0.12%,δGT / GT ⩽ 2%,δηi / ηi ⩽ 2.53% Therefore, after calculation process the maximum uncertainty in the efficiency becomes 2.53%. 5. Stability of nanofluid Ultrasonic is used to break up agglomeration and to promote the dispersion of nanoparticles into base fluids to get more stable nanofluid as Mahbubul et al. [40] reported. Ultrasonic techniques have a significant effect on the surface and the structure of nanoparticles, and grant long-term, stable and well-dispersed nanofluids, and better particle breakdown. After several experiments for CeO2-water Nanofluid, we found that higher concentration gave less stability so we choose these concentrations. On other hand low concentration didn’t give good result so we choose for particles concentrations was between 0.0167% −0.066%. Fig. 3, shows the visual appearance of the different nanofluid with no sign of aggregation for a period of 7 days. According to earlier studies, Said et al. [1], in nanofluid with higher concentration (higher volume fraction) of particles, nanoparticles tended to agglomerate; therefore, the stability of the nanofluid weakened. It was also noted that the stability of the prepared nanofluid with a lower volume fraction of nanoparticles, mixed with the base fluid, was stable for a longer period of time compared to the nanofluids with higher volume fraction. In the present study, the stability of nanofluid was measured by zeta potential machine. (PALS Zeta potential analyzer Ver. 3.37 from Brookhven Instruments). The mean value of zeta potential for 0.0666% volume fraction was -36.91 mV which was considered as a sign of physical stability according to Mahbubul et al. [40].
Fig. 3. Stability of CeO2 after 7 days of preparation.
conditions. A test period was 15 min long as in [2]. The experimental results were shown in graphs that indicate the collector efficiency against a reduced temperature parameter [(Ti–Ta)/GT]. All the presented data were collected in several days, and the best result was finally chosen. The maximum variations in ambient and inlet temperature in each test period is ± 0.8 °C and ± 0.5 °C, respectively; while in global radiation, it is ± 30 W/m2. Hence, our data follow the instructions presented in the ASHRAE Standard 93-2003. All experimental results are shown in graphs and equations, both describing the collector efficiency against a reduced temperature parameter. The efficiency of solar collector was tested for various mass flux rates of 0.015, 0.018 and 0.019 kg/s m2. Each test was made in several days and the best experimental data was finally chosen. The experimental data were fitted linear equations to show the characteristic parameters of the flat-plate solar collector in order to make a comparison of the effect of various volume flow rates as [38]. The efficiency parameters, the removed energy parameters, FR UL and the absorbed energy parameters, FR (τα ), at each volume flow rate, are shown in Table 4. All mass flux rates indicated that all measured data were the base of the fitted linear equation. The R2 which is known as Root Mean Square Error used to show how the data points close to linear fitted curve. These value seemed less in this case than in the individual flow rate cases. Table 4. displays the values of FR (τα ) and FR UL for 0.019 kg/s m2 as highest. Based on Fig. 4, the solar collector efficiency increases as the mass flux rates rises [28].
6. Thermal performance The enhancement in thermal properties of fluids when using nanoparticles was examined and confirmed in several papers like [37,39,41–45]. Among these paper and also the presented paper a deeply discussion was made to show the reason of thermal effect of adding nanoparticles to water. The results presented in this paper are focused in studying the effect of adding CeO2 Nanoparticles on water. The dissociation is divided to two main parts, firstly study the pure water, and secondly study nanofluid. A comparison between the results of both pure water and nanofluid is shown below at different mass flux. Also, for nanofluid, volume fraction of nanoparticles has a remarkable effect on thermal properties of nanofluid so three different volume fraction (0.0167, 0.033 and 0.066) are studied.
6.2. Nanofluid as a working fluid The observed values of the absorbed energy parameter, FR (τα ) and the removed energy parameter, FRUL, for CeO2 nanofluid at same mass Table 4 Values of FR UL and FR (τα ) for water of different mass flux rates.
6.1. Water as working fluid The experiments were carried out at the time interval of 10 am to 4 pm local time. This experiment time was divided into 6 sections, called test runs (e.g. each test run was designated 60 min). Also, each test run was divided into several test periods in quasi-steady state 36
Mass flux (kg/s m2)
FR UL
FR (τα )
R2
0.015 0.018 0.019
3.6257 3.8961 3.7574
0.621 0.6333 0.6301
0.9734 0.968 0.9896
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 4. Efficiency of solar collector using only water.
flux rate are summarized in Table 5. The result are arranged in Table 5 based on same mass flux rate. The efficiency of the collector for nanofluid is drawn against reduced temperature parameters (Ti − Ta)/GT. As shown in Fig. 6 and Table 5, the volume fraction of CeO2 nanofluid had a noticeable effect on the efficiency of the flat-plate solar collector. The collector heat removal factor FR values is shown in Fig. 5. It was calculated using equation (7). The results showed that heat removable factor for nanofluid is more than water. Also, it rises with the increasing of mass flux rate. As the volume fraction of nanofluid increases the value of heat removable factor gets up. Based on these results, the convective heat transfer coefficient was higher than that of water and both absorbed energy parameter, FR (τα ) and the removed energy parameter, FRUL, for CeO2 nanofluid is increased [12]. As a result of that the performance of solar collector is enhanced when using CeO2nanofluid. Results showed that the absorbed energy parameters, FR (τα ) values for CeO2 nanofluid, were higher than using only water for all applied mass flux rates and volume fractions. As visualized in Fig. 6(a) and Table 5, for mass flux rate of 0.015 kg/s m2, the absorbed energy
Table 5 Values of FR UL and FR (τα ) for CeO2/water nanofluid and water based on same mass flux rates. Mass flux (kg/s m2)
Volume fraction φ%
FR UL
FR (τα )
R2
0.015
0.0167 0.033 0.066 Pure water
−4.7354 −7.4975 −10.555 −3.6257
0.6428 0.6782 0.687 0.621
0.9684 0.9937 0.9884 0.9734
0.018
0.0167 0.033 0.066 Pure water
−5.1247 −7.9044 −10.964 −3.7574
0.6512 0.6837 0.6919 0.6301
0.9558 0.9804 0.9543 0.9896
0.019
0.0167 0.033 0.066 Pure water
−5.9593 −7.8871 −11.029 −3.8961
0.6675 0.696 0.7013 0.6333
0.9795 0.975 0.9886 0.968
Fig. 5. Heat removable factor at different flow rate and different volume fraction of nanofluid.
37
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 6. Linear characteristics for efficiency at different mass flux rate: (a) 0.015 kg/s m2 (b) 0.018 kg/s m2 (c) 0.019 kg/s m2.
parameter, FR (τα ) values for CeO2 nanofluid were higher than that of water by 3.51%, 9.21%, and 10.63%, for volume fraction (φ) 0.0167%, 0.0333% and 0.0666%, respectively. Although, the removed energy parameter, FRUL values for CeO2 nanofluid increased by 30.61%, 106.79%, and 191.12% compared to water, while the volume fraction
(φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As visualized in Fig. 6 (b) and Table 5, for mass flux rate of 0.018 kg/s m2, the absorbed energy parameter, FR (τα ) values for CeO2 nanofluid were higher than that of water by 3.35%, 8.03%, and 9.81%, for volume fraction (φ) 0.0167%, 0.0333% and 0.0666%, respectively. Raising the values of 38
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Table 6 Values of FR UL and FR (τα ) for CeO2/water nanofluid and water based on same volume fractions. Volume fraction φ%
Mass flux (kg/s m2)
FR UL
FR (τα )
R2
0.0167
0.015 0.018 0.019
−4.7534 −5.1247 −5.7656
0.6428 0.6512 0.6675
0.9684 0.9558 0.9795
0.033
0.015 0.018 0.019
−7.4975 −7.6154 −7.8871
0.6782 0.6807 0.696
0.9937 0.9833 0.975
0.066
0.015 0.018 0.019
−10.555 −10.964 −11.092
0.687 0.6919 0.7013
0.9884 0.9543 0.9886
Pure water
0.015 0.018 0.019
−3.6257 −3.8961 −3.7574
0.621 0.6333 0.6301
0.9734 0.968 0.9896
Table 7 Intersections of nanofluids characteristics of water. Mass flux (kg/s m2)
Volume φ% fraction
Intersection (Ti – Ta)/GT
0.015
0.0167 0.033 0.066
0.02 0.015 0.01
0.018
0.0167 0.033 0.066
0.016 0.014 0.009
0.019
0.0167 0.033 0.066
0.019 0.016 0.01
0.0666% volume fraction had the highest absorbed energy and heat loss but the 0.0333% volume fraction showed the best-performed characteristics when comparing the results in Table 5. It can be concluded from the present work that up to a certain volume fraction of nanoparticles the performance of the flat-plate collectors might be increased. Although there were higher efficiencies in case of 0.066% volume fraction but it was valid only for a short range; generally the 0.033% volume fraction performances were higher. When the volume fraction was too low, the effect on the heat transfer increase was small, while the increased volume fraction caused higher heat transfer. However, the efficiency of solar collector did not depend only on values of FR (τα ), and FRUL but also depended on reduced temperature parameters [(Ti – Ta)/GT]. For lower values of [(Ti – Ta)/GT] – high irradiation – the efficiency of the collector with volume fraction of nanoparticles (φ) 0.066% was higher than others. Therefore, as the value of [(Ti – Ta)/GT] increased the efficiency of the volume fraction of nanoparticles (φ) 0.0333%, it became higher than others, and finally, the volume fraction of nanoparticles (φ) 0.0167%, efficiency reached the maximum values at the highest values of [(Ti – Ta)/GT]. These cases were accepted for all studied mass flux rate, 0.015 kg/s m2, 0.018 kg/s m2, and 0.019 kg/s m2 as shown in Fig. 6(a), (b) and (c), respectively. The explanation of this behavior of nanoparticles is as follows. Lower values of [(Ti – Ta)/GT] meant low temperature difference or high solar radiation. Hence, higher volume fraction of nanofluid is preferred as it absorbed more heat than others and less particles tend to agglomerate compering to lower volume fraction nanofluid. Based on that, the micro heat transfer resulted because of the collision of particles is higher so the efficiency directly proportional to the volume fraction of nanoparticles (φ) . Although, as the values of [(Ti – Ta)/GT] increased the mean fluid temperature rises lead to rise the viscosity of nanofluids which rose the thickness of the boundary layer. Hence, the heat transfer rate reduced [7] causing reduced performance. Also, as the temperature increases the thermal conductivity of nanofluid rises and consequently the overall heat transfer coefficient goes up and removed heat transfer (FR UL ) becomes lager. Form other hand, the solar radiation decreases which reduced absorbed energy and increases heat loss. The higher heat loss coefficient (FR UL ) means greater slope for the efficiency line. Hence, by rising the reduced temperature parameter the outlet temperature of nanofluids declined more rapidly than the outlet temperature of water [31] so the efficiency of collector reduces accordingly to Eq. (4).
FRUL compared to water are 36.39%, 102.68%, and 191.8%, while the volume fraction (φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As it can be seen in Fig. 6(c) and Table 5, for mass flux rate of 0.019 kg/ s m2, values of FR (τα ) were raised by 5.4 %, 9.9% and 10.74%, and for volume fraction (φ ) 0.0167%, 0.0333%, 0.0666%, respectively. The values of FRUL for CeO2 nanofluid were increased by 47.98%, 102.44%, and 183.08%, compared to water, while volume fraction (φ) was 0.0167%, 0.0333%, and 0.0666%, respectively. As we can find in Table 3 the value of thermal conductivity for nanofluids is more than pure water. Several reasons was mentioned in previous work to find reasons for that as [37,39,41–45]. In presented work we believed that Brownian motion played the main role of this enhancement as we used forced circulation pump. The pump increased the random motion of the particles which increased the collision between liquid molecules and solid particles, so this was what caused the increase in the convective heat transfer coefficient and the efficiency in Eq. (4). Also, it is worth to note that Reynolds number in presented cases isn’t less than 2100 which is mean that turbulent flow is achieved. Turbulence in fluid increases the fluctuations and mixing of nanoparticles so more heat transfer by diffusion. Also, turbulence helps to prevent the presence of particles free regions which increase the thermal resistance of the liquid. On the other hand, we can’t neglect the effect of liquid layering at liquid particle interface as we use particles with diameter less than 30 nm. However, a certain value of the reduced temperature parameter, [(Ti – Ta)/GT], limited this fact, and it could be detected by finding the intersection between the line representing water and that of nanofluid efficiency with the same mass flux rate - but different volume fractions as shown in Fig. 6(a),(b),(c). The values of the reduced temperature parameter, [(Ti – Ta)/GT], of intersections are in Table 7. Before the intersections, the efficiency values of the solar collector using nanofluid were higher than with applied water. Consequently, after the intersection there was a reverse trend there. This reverse trend could be explained as follows. When the reduced temperature parameter, [(Ti – Ta)/GT], increased, the solar radiation value declined; but the increased heat transfer caused higher mean temperature and higher heat loss compared to pure water [2]. The higher heat loss coefficient, (FR UL ), meant a steeper slope for the efficiency line. Hence, by increasing the reduced temperature parameter, the outlet temperature of nanofluids reduced more rapidly than the outlet temperature of water [24], so the efficiency of collector decreased accordingly to Eq. (4).
6.2.2. Effect of mass flux rate of nanofluid on efficiency Fig. 7 shows the efficiency of the solar collector using volume fraction (φ) of 0.0167%, 0.0333%, and 0.0666%, and applying CeO2 with different-mass flux rate of 0.015, 0.018 and 0.019 kg/s m2. The values of FR UL and FR (τα ) were indicated in Table 6, for same volume fraction to make it more clear and easy to detect. The changes of the FR (τα ) and FRUL values for different volume fraction (φ ) and mass fluxes were listed previously, they are not repeated here again. Generally, the FR (τα ) energy absorbance factors gradually increases as the mass flux rate increased in the case of each volume fraction. The FR UL heat loss factor values shows the same tendencies for all the
6.2.1. Effect of volume fraction of nanofluid on efficiency The effect of volume fraction of nanofluid on the efficiency of a flatplate collector was interlaced. Based on several previous work such as [43–45] and [46] Nusselt number and heat transfer rise with the increasing in volume fraction of nanoparticles as large number of particles increase the micro convection effect between particles and base fluid. The 39
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
Fig. 7. Efficiency of solar collector at different volume fractions of CeO2/water nanofluid: (a) φ% = 0.0167% (b) φ% = 0.033% (c) φ% = 0.066% .
applied volume fractions, increasing flow rate caused more heat loss factors. This is because increasing the mass flux rate caused enhancement in Brownian motion, turbulence of the particles in the nanofluid, and the Reynolds and Nusselt numbers [2,32,5].
7. Conclusions A study was performed experimentally to determine the efficiency curves of a flat-plate solar collector with using nanofluid of CeO2-water as working fluid. The stability of CeO2-water nanofluid was weak. 40
Energy Conversion and Management 155 (2018) 32–41
M.A. Sharafeldin, G. Gróf
flat-plate solar water heater. Energy Fuels 2016;30:9908–13. [16] Jeon Jongwook, Park Sunho, Lee Bong Jae. Analysis on the performance of a flatplate volumetric solar collector using blended plasmonic nanofluid. Sol Energy 2016;132:247–56. [17] Verma Sujit Kumar, Tiwari Arun Kumar, Chauhan Durg Singh. Experimental evaluation of flat plate solar collector using nanofluids. Energy Convers Manage 2017;134:103–15. [18] Noghrehabadi Aminreza, Hajidavaloo Ebrhim, Moravej Mojtaba. Experimental investigation of efficiency of square flat-plate solar collector using SiO2/water nanofluid. Case Stud Therm Eng 2016;8:378–86. [19] Vakili M, Hosseinalipour SM, Delfani S, Khosrojerdi S, Karami M. Experimental investigation of graphene nanoplatelets nanofluid-based volumetric solar collector for domestic hot water systems. Sol Energy 2016;131:119–30. [20] Anin Vincely D, Natarajan E. Experimental investigation of the solar FPC performance using graphene oxide nanofluid under forced circulation. Energy Convers Manage 2016;117:1–11. [21] Kim Hyeongmin, Kim Jinhyun, Cho Honghyun. Experimental study on performance improvement of U-tube solar collector depending on nanoparticle size and concentration of Al2O3 nanofluid. Energy 2017;118:1304–12. [22] Verma Sujit Kumar, Tiwari Arun Kumar, Chauhan Durg Singh. Performance augmentation in flat plate solar collector using MgO/water nanofluid. Energy Convers Manage 2016;124:607–17. [23] Owolabi Afolabi L, Al-Kayiem Hussain H, Baheta Aklilu T. Performance investigation on a thermal energy storage integrated solar collector system using nanofluid. Int J Energy Res 2017;41:650–7. [24] Faizal M, Saidur R, Mekhilef S, Alim MA. Energy, economic and environmental analysis of metal oxides nanofluid for flat-plate solar collector. Energy Convers Manage 2013;76:162–8. [25] Colangelo Gianpiero, Favale Ernani, Miglietta Paola, de Risi Arturo, Milanese Marco, Laforgia Domenico. Experimental test of an innovative high concentration nanofluid solar collector. Appl Energy 2015;154:874–81. [26] Raja Sekhara Y, Sharmab KV, Thundil Karupparaj R, Chiranjeevi C. Heat transfer enhancement with Al2O3 nanofluids and twisted tapes in a pipe for solar thermal applications. Proc Eng 2013;64:1474–84. [27] Tiwari Arun Kumar, Ghosh Pradyumna, Sarkar Jahar. Heat transfer and pressure drop characteristics of CeO2/water nanofluid in plate heat exchanger. Appl Therm Eng 2013;57:24–32. [28] Leong KY, Ong Hwai Chyuan, Amer NH, Norazrina MJ, Risby MS, Ku Ahmad KZ. An overview on current application of nanofluids in solar thermal collector and its challenges. Renew Sustain Energy Rev 2016;53:1092–105. [29] Kasaeian Alibakhsh, Eshghi Amin Toghi, Sameti Mohammad. A review on the applications of nanofluids in solar energy systems. Renew Sustain Energy Rev 2015;43:584–98. [30] Verma Sujit Kumar, Tiwari Arun Kumar. Progress of nanofluid application in solar collectors: A review. Energy Convers Manage 2015;100:324–46. [31] Javadi FS, Saidur R, Kamalisarvestani M. Investigating performance improvement of solar collectors by using nanofluids. Renew Sustain Energy Rev 2013;28:232–45. [32] Hussein Ahmed Kadhim. Applications of nanotechnology to improve the performance of solar collectors – recent advances and overview. Renew Sustain Energy Rev 2016;62:767–92. [33] Reddy KS, Kamnapure Nikhilesh R, Srivastava Shreekant. Nanofluid and nanocomposite applications in solar energy conversion systems for performance enhancement: a review. Int J Low-Carbon Technol 2017;12:1–23. [34] Eggers Jan Rudolf, Kabelac Stephan. Nanofluids revisited. Appl Therm Eng 2016;106:1114–26. [35] Muhammad Mahmud Jamil, Muhammad Isa Adamu, Sidik Nor Azwadi Che, Yazid Muhammad Noor Afiq Witri Muhammad, Mamat Rizalman, Najafic G. The use of nanofluids for enhancing the thermal performance of stationary solar collectors: a review. Renew Sustain Energy Rev 2016;63:226–36. [36] ASHRAE Standard 93–2003, Methods of testing to determine the thermal performance of solar collectors, Atlanta, GA, USA, 2003. [37] Zhou SQ, Ni R. Measurement of the specific heat capacity of water-based Al2O3 nanofluid. Appl Phys Lett 2008;92:1–3. [38] Beghi G. Performance of solar energy converters. Italy: Lectures of a course held at the Joint Research Centre, ISPRA; 1981. Nov. 11-18. [39] Zhang X, Gu H, Fujii M. Effective thermal conductivity and thermal diffusivity of nanofluids containing spherical and cylindrical nanoparticles. Exp Therm Fluid Sci 2007;31:593–9. [40] Mahbubul IM, Saidur R, Amalina MA, Elcioglu EB, Okutucu-Ozyurt T. Effective ultrasonication process for better colloidal dispersion of nanofluid. Ultrason Sonochem 2015;26:361–9. [41] Chon CH, Kihm KD. Thermal conductivity enhancement of nanofluids by Browian motion. J Heat Transf 2005;127(8):810. [42] Iacobazzi Fabrizio, Milanese Marco, Colangelo Gianpiero, Lomascolo Mauro, Risi Arturo de. An explanation of the Al2O3 nanofluid thermal conductivity based on the phonon theory of liquid. Energy 2016;116:786–94. [43] Sheikholeslami M, Ganji DD. Heat transfer of Cu-water nanofluid flow between parallel plates. Powder Technol 2013;235:873–9. [44] Sheikholeslami Mohsen, Ganji Davood Domiri. Nanofluid flow and heat transfer between parallel plates considering Brownian motion using DTM. Comput Methods Appl Mech Eng 2015;283:651–63. [45] Sheikholeslami M, Rashidi MM, Ganji DD. Numerical investigation of magnetic nanofluid forced convective heat transfer in existence of variable magnetic field using two phase model. J Mol Liq 2015;212:117–26. [46] Calvin Li H, Peterson GP. Experimental investigation of temperature and volume fraction variations on the effective thermal conductivity of nanoparticle suspensions (nanofluids). J Appl Phys 2006;99:084314. [47] Mogensen Mogens, Sammes Nigel M, Tompsett Geoff A. Physical, chemical and electrochemical properties of pure and doped ceria. Solid State Ionics 2000;129:63–94.
Three different volume fractions of 0.0167%, 0.0333%, and 0.0666% were tested at three mass flux rates, including 0.015, 0.018, and 0.019 kg/s m2. The experiments and results elucidated that using CeO2water nanofluid increased the efficiency of the solar collector more efficiently than using only water. Findings dedicated that the maximum efficiency when reduced temperature parameter, [(Ti – Ta)/GT], equals to zero was 10.74%, volume fraction (φ ) was 0.066% and mass flux rate was 0.019 kg/s m2. However, for a wide range of reduced temperature parameters, [(Ti – Ta)/GT], the best performance was found with the application of 0.0333% volume fraction for all mass flux rates, as it can be followed in Fig. 6. The changes in absorbed energy parameter, FR (τα ) vary from 3.51% to 10.74%, and in removed energy parameter, FR UL vary from 30.61% to 191.8%, compared to the water with the same mass flux rates. The efficiency of the collector was directly proportional with the mass flux rate, and it seemed that an optimal volume fraction might be the 0.0333% for the present study’s ranges. To the best of our knowledge, this has been the first study ever focusing on the efficiency analysis of a flat-plate solar collector using CeO2-water nanofluid. Accordingly, using different values of volume fraction (φ ) and several mass flux rates must be done, in order to find out the effect of these variables on the efficiency of flat-plate solar collectors. Acknowledgment The authors would like to thank Professor István Csontos and Dr. Enikő Krisch for their help and support. The authors would like to thank the “Egyptian Ministry of Higher Education” (MOHE) for the invaluable professional promotion of the Stipendium Hungaricum scholarship provided for the PhD studies carried out in Hungary. References [1] Said Z, Saidur R, Sabiha MA, Hepbasli A, Rahim NA. Energy and exergy efficiency of a flof-plate solar collector using pH treated Al2O3 nanofluid. J Clean Prod 2016;112:3915–26. [2] Yousefi Tooraj, Veysia Farzad, Shojaeizadeha Ehsan, Zinadinib Sirus. An experimental investigation on the effect of Al2O3-H2O nanofluid on the efficiency of flatplate solar collectors. Renew Energy 2012;39:293–8. [3] Yousefi Tooraj, Veisy Farzad, Shojaeizadeh Ehsan, Zinadini Sirus. An experimental investigation on the effect of MWCNT-H2O nanofluid on the efficiency of flat-plate solar collectors. Exp Therm Fluid Sci 2012;39:207–12. [4] Goudarzi K, Shojaeizadeh E, Nejati F. An experimental investigation on the simultaneous effect of CuO-H2O nanofluid and receiver helical pipe on the thermal efficiency of a cylindrical solar collector. Appl Therm Eng 2014;73:1234–41. [5] Moghadam Ali Jabari, Farzane-Gord Mahmood, Sajadi Mahmood, Hoseyn-Zadeh Monireh. Effects of CuO/water nanofluid on the efficiency of a flat-plate solar collector. Exp Therm Fluid Sci 2014;58:9–14. [6] Faizal M, Saidur R, Mekhilef S, Hepbasli A, Mahbubul IM. Energy, economic, and environmental analysis of a flat-plate solarcollector operated with SiO2 nanofluid. Clean Techn Environ Policy 2015;17:1457–73. [7] He Qinbo, Zeng Shequan, Wang Shuangfeng. Experimental investigation on the efficiency of flat-plate solar collectors with nanofluids. Appl Therm Eng 2015;88:165–71. [8] Meibodi Saleh Salavati, Kianifar Ali, Niazmand Hamid, Mahian Omid, Wongwises Somchai. Experimental investigation on the thermal efficiency and performance characteristics of a flat plate solar collector using SiO2/EG–water nanofluids. Int Commun Heat Mass Transf 2015;65:71–5. [9] Jamal-Abad Milad Tajik, Zamzamian A, Imani E, Mansouri M. Experimental study of the performance of a flat-platecollector using Cu-Water nanofluid. J Thermophys Heat Transf 2013;27(4):756–60. [10] Said Z, Sabiha MA, Saidur R, Hepbasli A, Rahim NA, Mekhilefand S, et al. Performance enhancement of a Flat Plate Solar collector using Titanium dioxide nanofluid and Polyethylene Glycol dispersant. J Clean Prod 2015;92:343–53. [11] Michael Jee Joe, Iniyan S. Performance of copper oxide/water nanofluid in a flat plate solar water heater under natural and forced circulations. Energy Convers Manage 2015;95:160–9. [12] Polvongsri Sarawut, Kiatsiriroat Tanongkiat. Performance analysis of flat-plate solar collector having silver nano-fluid as a working fluid. Heat Transf Eng 2014;35:1183–91. [13] Munuswamy Dinesh Babu, Madhavan Venkata Ramanan, Mohan Mukunthan. Comparison of the effects of Al2O3 and CuO nanoparticles on the performance of a solar flat-plate collector. J Non-Equilib Thermodyn 2015;40(4):265–73. [14] Ahmadi Alireza, Ganji Davood Domiri, Jafarkazemi Farzad. Analysis of utilizing Graphene nanoplatelets to enhance thermal performance of flat plate solar collectors. Energy Convers Manage 2016;126:1–11. [15] Devarajan Yuvarajan, Babu Munuswamy Dinesh. Analysis on the influence of nanoparticles of alumina, copper oxide, and zirconium oxide on the performance of a
41