Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids

ICHMT-02980; No of Pages 7 International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt

F

a

7

a r t i c l e

Department of Materials and Nano Physics, KTH Royal Institute of Technology, SE-16440 Kista, Stockholm, Sweden Department of Energy Technology, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden

i n f o

a b s t r a c t

Nanostructured solid particles dispersed in a base liquid are a new class of nano-engineered colloidal solutions, defined with a coined name of nanofluids (NFs). These fluids have shown potential to enhance heat transfer characteristics of conventional base liquids utilized in heat transfer application. We recently reported on the fabrication and thermo-physical property evaluation of SiC NF systems, containing SiC particles with different crystal structure. In this study, our aim is to investigate the heat transfer characteristics of a particular α-SiC NF with respect to the effect of α-SiC particle concentration and different base liquids on the thermo-physical properties of NFs. For this purpose, a series of NFs with various α-SiC NPs concentration of 3, 6 and 9 wt.% were prepared in different base liquids of distilled water (DW) and distilled water/ethylene glycol mixture (DW/EG). Their thermal conductivity (TC) and viscosity were evaluated at 20 °C. NF with DW/EG base liquid and 9 wt.% SiC NP loading exhibited the best combination of thermo-physical properties, which was therefore selected for heat transfer coefficient (HTC) evaluation. Finally, HTC tests were performed and compared in different criteria, including equal Reynolds number, equal mass flow rate and equal pumping power for a laminar flow regime. The results showed HTC enhancement of NF over the base liquid for all evaluation criteria; 13% at equal Reynolds number, 8.5% at equal volume flow and 5.5% at equal pumping power. Our findings are among the few studies in the literature where the heat transfer enhancement for the NFs over its base liquid is noticeable and based on a realistic situation. © 2014 Published by Elsevier Ltd.

Available online xxxx Keywords: Nanofluids SiC nanoparticles Thermal conductivity Viscosity Heat transfer coefficient Pumping power

R

E

C

T

8 9 17 18 10 19 11 12 13 14 15 16

b

O

5 6

R O

4

Nader Nikkam a, Ehsan B. Haghighi b, Mohsin Saleemi a, Mohammadreza Behi b, Rahmatollah Khodabandeh b, Mamoun Muhammed a, Björn Palm b, Muhammet S. Toprak a,⁎

P

3Q1

D

2

Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids☆

E

1

37

R

36

1. Introduction

39 40

New advanced suspensions containing solid nanoparticles (NPs) in traditional heat transfer fluids such as distilled water (DW), ethylene glycol (EG) or their mixture (DW/EG) are called nanofluids (NFs) [1]. These dispersions have become attractive due to their potential benefits and applications in cooling industry, such as cooling of electronics, transport vehicles, data centers, and power generation devices [2–4]. For more than hundred years since Maxwell [5], scientists and engineers have made great investigations to improve the thermal conductivity (TC) of traditional heat-exchange fluids by dispersing millimeter- or micrometer-sized particles in base liquids. Nevertheless, the major

43 44 45 46 47 48

U

41 42

N C O

38

☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author at: Isafjordsgatan 22, SE-16440 Kista, Stockholm, Sweden. E-mail addresses: [email protected] (N. Nikkam), [email protected] (E.B. Haghighi), [email protected] (M. Saleemi), [email protected] (M. Behi), [email protected] (R. Khodabandeh), [email protected] (M. Muhammed), [email protected] (B. Palm), [email protected] (M.S. Toprak).

20 21 22 23 24 25 26 27 28 29 30 31 32 33 35 34

problems with the use of such large particles are the rapid settling of these particles, clogging the miniature channels, increased abrasion, and much increase in the pumping power. Due to small sizes and very large specific surface areas of the NPs, NFs may have novel properties such as higher TC, minimal clogging during flow and improved HTC. These features of NFs have motivated many scientists to study the heat transfer performance and flow characteristics of various NFs with different NPs and base liquids. There are several studies in the literature using different NF formulations and comparing their HTC with that of the corresponding base liquid. So far different types of NPs such as metallic and ceramic NPs have been used to prepare NFs and their heat transfer characteristics have been studies. Detailed literature reviews of the heat transfer behavior of NFs have been provided by Yu et al. [8] and Murshed et al. [9]. Ceramic NPs are more favorable than metallic NPs, as they incorporate much easier into the base liquid. They also exhibit better chemical stability over long period of times compared to metal NPs [10]. However, ceramics generally have low TCs with few exceptions such as SiC NPs which have one of the highest TC (TC value for α-type SiC is 490 W/m K) [11]. Additionally, these materials are commercially available for the fabrication of NFs via two-step method, wherein NPs are acquired and then dispersed

http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011 0735-1933/© 2014 Published by Elsevier Ltd.

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122

126 127 128 129 130 131

C

92 93

E

90 91

R

88 89

R

86 87

O

2.2. Characterization techniques

144

F

84 85

C

82 83

N

80 81

U

78 79

Silicon carbide (SiC) particles with an alpha type crystal structure (α-SiC) were purchased from Superior Graphite (USA) and were utilized to fabricate a series of NFs with 3 wt.%, 6 wt.% and 9 wt.% NP loading. For this purpose, α-SiC NPs were dispersed in distilled water (DW) as the base liquid (two-step method preparation) to obtain 9 wt.% SiC NF. Then the suspension was mixed by ultrasonic mixing and the pH

134 135 136 137 138 139 140 141 142 143

Powder X-ray diffraction (XRD) was performed to identify the crystal structure of the material, using a Philips X'pert pro super Diffractometer with Cu Kα source (λ = 1.5418 Å). Scanning electron microscopy (SEM) analysis of α-SiC particles was performed by using FEG-HR SEM (Zeiss-Ultra 55). Average solvodynamic particle size distribution was evaluated by Beckmann-Coulter Delsa Nano C system. TC of NFs was measured by using TPS 2500 instrument (HotDisk model 2500), which works based on the transient plane source (TPS) method. The validity of the TPS instrument was checked by comparing with a standard source for the thermodynamic properties of water (IAPWS reference) and compared to the reference the accuracy of measurement for distilled water was within 2%—as described earlier [20]. Finally, the viscosity of NFs was evaluated using a DV-II+ Pro-Brookfield viscometer. A closed-loop system was used to perform HTC tests, using the setup presented in detail in [21].

145 146

3. Results and discussion

160

3.1. Structure and morphology analysis

161

SiC material exists in various crystalline forms; two major crystal structures are cubic and hexagonal [22]. It is important to identify the crystal phase of SiC; therefore, X-ray diffraction (XRD) analysis was carried out on as-received NPs. Fig. 1(a) displays the powder XRD pattern of SiC NPs, which is indexed for the hexagonal crystal structure of SiC (JCPDS # 01-073-1663), namely α-SiC. The morphology of the particles was analyzed by scanning electron microscopy (SEM) and a micrograph is shown in Fig. 1(b). There is a wide size dispersion, which makes it quite difficult to estimate the size of α-SiC NPs from the micrographs; nevertheless, a rough estimation was performed by counting more than 200 particles resulting in an average particle size of 115 ± 35 nm.

162 163

3.2. Dynamic light scattering (DLS) analysis

173

DLS analysis was performed to estimate the dispersed size of SiC NPs in base fluid, in order to understand the influence of the effective size of dispersed NPs in the base liquid. DLS analysis results are shown in Fig. 2 for NFs in distilled water and DW/EG media. A wide range of particle size distribution (150–4500 nm) with an average peak value of ~1290 nm

174

O

2.1. Materials and methods

76 77

R O

125

75

P

2. Experimental

73 74

132 133

D

124

71 72

of NFs was adjusted to ~ 9.5 in order to obtain stable NFs—where SiC NPs have a highly negative surface charge as detailed in Ref. [16]. NFs with 6 wt.% and 3 wt.% α-SiC NPs were prepared by diluting the 9 wt.% NF with a proper amount of DW. This is done to assure that the processing history of the samples is identical. In order to fabricate DW/EG (50/50% by wt.%) based α-SiC NFs, the same fabrication procedure was followed, using DW/EG as the base liquid, so that three NFs with varying α-SiC NPs were prepared. All NFs (Table 1) were stable for more than two weeks without any visual precipitation. Since one of our aims was to study the real effect of α-SiC NPs on the thermophysical properties of NFs, the use of surfactant/surface modifiers was strictly avoided.

T

123

in the base liquids [6]. Therefore, α-SiC NPs can be a promising candidate for fabrication of efficient NF for heat transfer applications. Although there are limited studies on TC and/or viscosity of SiC NFs with different base liquids [10,12–15], few studies have reported on heat transfer characteristics of α-SiC NFs. Timofeeva et al. [14,15] investigated α-SiC NFs with water and DW/EG base liquids, where they showed the effect of different factors on the thermo-physical properties of α-SiC NFs—including TC and viscosity of NFs, and also the HTC of DW/EG and water based suspensions with α-SiC NPs. Their investigation on water-based α-SiC NFs showed that the increases in TC were high but the increase in the viscosity with the introduction of 4.1 vol.% (~13 wt.%) α-SiC NPs led to a reduction in HTC, being up to 15% worse than that of water as the base liquid (at equal velocity) [14]. Although using larger particle sizes and pH adjustment significantly decreased the viscosity of suspensions, still for water based α-SiC NFs the HTC was just slightly higher than that of base liquid [14]. When they changed the base liquid of NF to the DW/ EG mixture with a 50/50 volume ratio (at the same 13 wt.% SiC NP loading), 14.2% enhancement on the HTC of NFs was obtained for a turbulent flow regime at 71 °C [15] while water based NFs were scarcely comparable with that of base liquid. We recently studied on the fabrication and thermo-physical property evaluation of four different DW/EG based (50/50 weight ratio) SiC NF systems fabricated by dispersing SiC NPs with different crystal structures of α- and β-types (9 wt.% α- and β-SiC NFs) [16]. The results revealed that among all suspensions, NF with particular α-type SiC particles exhibited better combination of thermophysical properties by TC enhancement of ~20% with only 14% increased viscosity as compared to the respective base liquid. This indicated the capability of this particular NF for further heat transport characteristic investigations including HTC tests. The effect of base liquid on the thermo-physical properties including TC and viscosity of NFs is not well investigated and understood in the literature yet. There are few reports in the literature indicating some general trends about the effect of the base liquid; Xie et al. [17,18] fabricated suspensions with the same Al2O3 NPs in EG, water, glycerol and pump oil and showed an increase in the relative TC value of NFs with a decrease in the TC of the base liquid. Tsai et al. [19] reported that the alteration of the base liquid viscosity (from 4.2 to 5500 cP, by mixing two base liquids with approximately the same TC) resulted in a decrease in the TC of the Fe2O3 NFs as the viscosity of the base liquid increased. Timofeeva et al. [15] investigated comparatively SiC NFs in water and DW/EG mixture with controlled concentration, particle sizes and pH. Their investigations showed that the relative change in TC due to the addition of 4.1 vol.% (13 wt.%) α-SiC NPs is around 5% higher in DW/EG compared to their achieved result in water [14]. In this work, our aim is to fabricate α-SiC NFs and investigate the effect of the base liquid and α-SiC NP concentration on the thermo-physical and transport characteristics of these NFs including HTC test. For this purpose, stable α-SiC NFs with various NP loading and two different base liquids (distilled water and DW/EG) were fabricated. The base liquid was a mixture of DW/EG (50:44.5 by vol.%; 50:50 weight ratio). The thermo-physical properties of NF including TC and viscosity were measured at 20 °C. Finally, HTC tests were performed and compared in different criteria such as equal Reynolds number, mass flow rate and pumping power for the α-SiC NF with optimum properties in a laminar flow regime.

69 70

E

2

α-SiC NF-DW/EG-3 wt.% α-SiC NF-DW/EG-6 wt.% α-SiC NF-DW/EG-9 wt.% α-SiC NF-DW-3 wt.% α-SiC NF-DW-6 wt.% α-SiC NF-DW-9 wt.%

NP ID

α-SiC NP α-SiC NP α-SiC NP α-SiC NP α-SiC NP α-SiC NP

149 150 151 152 153 154 155 156 157 158 159

164 165 166 167 168 169 170 171 172

175 176 177 178 t1:1 t1:2

Table 1 Details of fabricated α-SiC NFs. Sample ID

147 148

Base liquid

DW/EG (50:44.5) by vol.% DW/EG (50:44.5) by vol.% DW/EG (50:44.5) by vol.% Distilled water Distilled water Distilled water

NP loading

t1:3

(vol.%)

(wt.%)

t1:4

0.95 1.9 2.85 0.95 1.9 2.85

3 6 9 3 6 9

t1:5 t1:6 t1:7 t1:8 t1:9 t1:10

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

30

40

50

60

(116)

(203) (204) (205)

(109)

(107)

(101) (103) (104) (105)

Intensity (a.u.) 20

(108)

JCPDS # 01-073-1663

(006)

(a)

3

70

80

186 187 188 189 190 191

3.3. TC and viscosity measurements on NFs containing α-SiC NPs

193 194

There are two major thermo-physical properties that are influenced by the addition of NPs in the base liquid; namely TC and viscosity of NFs. TC is the most significant property that can be studied to predict the heat transfer enhancement of prepared NFs. Secondly, viscosity is also an essential factor in designing efficient NF for heat transfer applications since the Prandtl and Reynolds numbers, pressure drop and the resulting pumping power depend on it [23,24]. Particularly in the laminar flow regime, the pressure drop is directly proportional to the viscosity of NFs. Therefore, efficient NFs for heat transfer applications not only should demonstrate effective thermal transport properties such as higher TC, but also its viscosity increase, due to the addition of NPs into the base liquid, should be as little as possible. Hence, formulation

204

E

R

R

202 203

5.0 4.5 4.0 3.5 3.0

N C O

200 201

α-SiC-W/EG α-SiC-Water

U

199

Intensity

197 198

C

192

195 196

2.5 2.0 1.5 1.0 0.5 0.0 100

1000

Diameter (nm) Fig. 2. Particle size distribution of α-SiC NPs in DW and DW/EG base liquids.

R O

P

184 185

of NFs with a greater relative TC value with a minimal impact of NPs on NF viscosity is highly desired. Base liquid is one of the essential factors which influence the thermo-physical properties of NFs. In this work we also studied the effect of two different base liquids on the TC and viscosity of α-SiC NFs. The two base liquid systems of distilled water and DW/EG with the ratio of 50/50 by wt.% (50/44.5 by vol.%) were selected. A series of stable NFs, containing 3 wt.%, 6 wt.% and 9 wt.% α-SiC NPs, were fabricated by dispersing the as received α-SiC NPs in water and DW/EG, which is followed by preparation of NFs with 6 wt.% and 3 wt.% by diluting NF containing 9 wt.% α-SiC NPs (Table 1). NFs with various NP concentrations were evaluated to study the effect of NP concentration on their TC and viscosity. Fig. 3(a)–(d) displays the absolute TC (Knf) and relative TC (Knf/Kbl) of water based α-SiC NFs at various SiC particle loadings of 3 wt.%, 6 wt.% and 9 wt.% at 20 °C. Higher TC values of α-SiC NF than that of the water as base liquid and higher TC with increasing particle loadings are obtained, as displayed in Fig. 3(a). Fig. 3(b) shows the relative TC of α-SiC NFs at 20 °C for different particle concentrations, showing minimum and maximum TC enhancements of 1% and ~15.2% for NFs with 3 wt.% and 9 wt.% particle loadings at 20 °C, respectively. Fig. 3(c) displays the results of viscosity tests for the same water based NFs, indicating an increase in viscosity with increasing particle loading. Fig. 3(d) presents the relative viscosity of α-SiC NFs at 20 °C: a maximum increase of ~ 22.7% in viscosity was obtained for 9 wt.% α-SiC NF. Comparison between the results of this study and that reported by Singh et al. [10] revealed that at around the same (6 wt.%) particle loading of α-SiC, although nearly the same TC enhancement value was obtained for water based NFs, about ~20% lower viscosity increase was obtained in the present study. Although the reason is not clear, using commercial NF samples which may contain different dispersant(s) or having smaller hydrodynamic size (via DLS; 170 nm) [10] may influence the viscosity of NF negatively, while in our work the use of dispersant was strictly avoided and as described, DLS analysis showed 1290 nm for α-NPs in water media. The same NP loadings, preparation method, dilution process and pH adjustment (pH: 9.5) were used to fabricate new series of NFs (Table 1) in DW/EG base fluid—as it is a widely used heat transfer fluid. TC and viscosity tests on these NFs were performed at 20 °C and the results are presented in Fig. 4(a)–(d). Based on Fig. 4(a), TC evaluation results reveal higher TC values for α-SiC NF, as well as higher TC values with increasing concentration of α-SiC particles in DW/EG base NFs. Fig. 4(b) shows the relative TC at 20 °C, indicating minimum and maximum TC enhancements of ~ 9.2% and 20% for NFs with 3 wt.% and 9 wt.% particle loadings, respectively. A comparison between the TC enhancements of α-SiC NF-DW/EG (with 9 wt.% particle loading) at 20 °C and that reported by Timofeeva et al. [15], where they investigated a commercial DW/EG based NFs, revealed that our NFs exhibit higher TC enhancement even at ~4 wt.% lower NP concentration. It shows the better effective thermal

D

182 183

was obtained for α-SiC NPs in water. When it comes to DW/EG media, a smaller average size (520 nm) with a narrower size distribution was observed as compared to the DW dispersed sample, indicating the significant effect of DW/EG on the particle clustering and the dispersion property of SiC particles. On the other hand, EG may play an important role as dispersant, which assists to stabilize smaller agglomerates/aggregates as compared to distilled water media. Therefore, its presence may reduce the agglomeration size in the suspensions. A comparison between SEM and DLS results for α-SiC NPs displays that the predicted sizes from DLS method are larger than the primary particle size estimated from SEM micrographs. This difference clearly indicates the presence of aggregated α-SiC NPs in the base liquids, originating from as-received α-SiC NPs, which is inherently due to the production method/process of SiC NPs.

E

180 181

T

179

O

Fig. 1. (a) Powder XRD pattern, and (b) SEM micrograph of as-received α-SiC NPs.

F

2θ(degree)

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253

4

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

1.24

0.80

0.70

1.20

(a)

1.16

Knf / Kbl

Knf (W/mK)

0.75

Water Base Liquid α-SiC NF-W-3wt% α-SiC NF-W-6wt% α-SiC NF-W-9wt%

0.65 0.60

α-SiC NF-W-3wt% α-SiC NF-W-6wt% α-SiC NF-W-9wt%

(b)

1.12 1.08 1.04 1.00 0.96

0.55

0.92 0.50 18

22

20

1.28

1.32

(c)

1.24

α-SiC NF-W-3wt% α-SiC NF-W-6wt% α-SiC NF-W-9wt%

1.20

1.20

μnf /bl

1.16 1.12 1.08

1.16 1.12 1.08

1.04

1.04

1.00 1.00 20

22

D

18

Temperature(oC)

(d)

P

μnf (Cp)

1.24

Water Base Liquid α-SiC NF-W-3wt% α-SiC NF-W-6wt% α-SiC NF-W-9wt%

R O

1.28

22

Temperature(oC)

F

20

Temperature(oC)

O

18

18

20

22

Temperature(oC)

therefore the interaction between the NPs and the base liquid is 257 increased by increasing particle concentration. Fig. 4(d) shows the rela- 258 tive viscosity of α-SiC NFs at 20 °C, which clearly shows that the viscosity 259

T

C

0.48

0.44

0.40

C

0.38 0.36

4.8

1.15 1.10

20

1.05

22

17

Temperature(oC)

18

19

20

21

22

23

Temperature(oC)

W/EG Base Liquid α-SiC NF-W/EG-3wt% α-SiC NF-W/EG-6wt% α-SiC NF-W/EG-9wt%

(c)

1.20 1.18 1.16

α-SiC NF-W/EG-3wt% α-SiC NF-W/EG-6wt% α-SiC NF-W/EG-9wt%

(d)

μnf /μbl

U

5.2

N

18

(b)

1.20

O

0.42

α-SiC NF-W/EG-3wt% α-SiC NF-W/EG-6wt% α-SiC NF-W/EG-9wt%

1.25

R

0.46

1.30

Knf / Kbl

0.50

(a)

R

W/EG Base Liquid α-SiC NF-W/EG-3wt% α-SiC NF-W/EG-6wt% α-SiC NF-W/EG-9wt%

0.52

E

0.54

Knf (W/mK)

256

performance of NFs presented in this work. Fig. 4(c) displays the results of viscosity evaluation, revealing that the viscosity increased as the particle concentration is increased. This is expected as the interfacial area;

μnf (Cp)

254 255

E

Fig. 3. Thermo-physical characterizations of water based α-SiC NFs: (a) absolute TC, (b) relative TC, (c) absolute viscosity, and (d) relative viscosity (all results are recorded at 20 °C).

1.14

4.4

1.12 1.10

4.0

1.08 1.06

3.6 18

20

22 o

Temperature ( C)

1.04 18

20 Temperature (oC)

22

Fig. 4. Thermo-physical characterizations of DW/EG based α-SiC NFs: (a) absolute TC, (b) relative TC, (c) absolute viscosity, and (d) relative viscosity (all results are recorded at 20 °C).

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

277 278 279 280 281 282 283 284 285 286

3.4. HTC investigations

288 289

A closed-loop system was utilized to perform forced convective experiments, in order to perform the HTC test in the laminar flowregime and evaluate its validity. A detailed description of the setup and the experiments to demonstrate its validity can be found in our recent publication [21] where the test results indicated that the classical correlation, such as Shah Equation [26], could predict the HTC of NF in the laminar flow regime successfully. Comparing the results at equal Reynolds number may be misleading [27,28]. HTCs can be compared using different criteria such as equal Reynolds number as shown in Fig. 6(a), mass flow rate in Fig. 6(b) and pumping power in Fig. 6(c). NFs have higher viscosity than the base liquids; therefore, a higher flow rate (higher velocity) is desired to have the same Reynolds number for NFs as the base liquid. A more realistic comparison of HTC performance is at constant pumping power, velocity, or flow rate [15,29,30]. Comparing on this basis, only few NFs previously investigated showed higher HTC than those of their base liquids [15,28,30,31]. Most of the NFs reported in the earlier literature had viscosity increases that

302 303 304

600

1200

1500

1800

2100

Re (-)

1200 1100 1000 900 800

(b)

W/EG Base Liquid α-SiC NF-W/EG-9wt%

1300

700 600

500 200

400

600

800

1000

1200

1400

Volume Flow Rate (mL/min) 1400

W/EG Base Liquid α-SiC NF-W/EG-9wt%

1300 1200

(c)

C

1100

E

1000 900 800 700 600 500 400

300 0

100

200

300

400

500

600

700

Pumping Power (mV) Fig. 6. Experimental evaluation of HTC for α-SiC NF-DW/EG-9 wt.% vs (a) Reynolds number, (b) volume flow rate, and (c) pumping power.

30

25

(a)

W/EG Water

25

20 15 10 5 0

900

1400

μnf /μbl

300 301

500

R

298 299

600

R

296 297

N C O

294 295

U

292 293

Knf /Kbl

290 291

700

T

287

800

F

275 276

900

O

273 274

1000

R O

271 272

1100

P

269 270

h (w/m2K)

267 268

h (w/m2K)

266

1200

D

264 265

(a)

W/EG Base Liquid α-SiC NF-W/EG-9wt%

1300

h (w/m2K)

262 263

1400

changes in parallel to the NP concentration. The minimum and maximum increases of ~6.8% and 14% in viscosity were observed for NFs containing 3 wt.% and 9 wt.% α-SiC NP loading, respectively. The TC and viscosity values of SiC NFs with different base liquids, as water and DW/EG mixture, at different α-SiC particle concentration are summarized in Fig. 5(a) and (b). SiC NFs with DW/EG base liquid result in ~ 5%–8% higher TC enhancements than water at the same particle loading. The base liquid effect cannot be explained only by considering the lower TC of the DW/EG base liquid because the difference in TC enhancement values expected from relevant theory is less than 0.1% [25]. This base liquid effect obtained in different NF systems is most likely related to better wettability (lower value of the interfacial thermal resistance) of SiC NPs in DW/EG than in water based NFs [14]. NFs with DW/EG base liquid show much lower increase in viscosity except for NF at particle loading of 3 wt.%, as displayed in Fig. 5(b). Moreover, at the same NP concentration, SiC–water NFs show ~ 2%–7% higher increase in viscosity values compared to NFs in DW/EG base liquid at 6 wt.% and 9 wt.% particle loading. This suggests that if water is selected as the base liquid, a higher pumping power is required for heat transfer applications. DW/EG based NFs exhibited higher efficiencies compared to the similar distilled water based NF, as heat transfer fluid, due to the effect of the base liquid. As a result, among all NFs, DW/EG base NF containing 9 wt.% α-SiC particles (α-SiC NF-DW/EG-9 wt.%) is a promising candidate, which may be utilized as efficient coolant in heat transfer applications. Therefore, HTC tests were designed and performed for this selected sample, in order to evaluate the capacity of this NF for practical convective heat-transfer applications.

E

260 261

5

W/EG Water

(b)

20 15 10 5

3 wt%

6 wt%

9 wt%

α_ SiC Concentration

0

3 wt%

6 wt%

9 wt%

α_ SiC Concentration

Fig. 5. Comparison of the change in (a) TC, and (b) viscosity of SiC NFs with DW and DW/EG as base liquids and various particle loadings of α-SiC NPs at 20 °C.

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

332 333 334 335 336 337 338 339 340 341 342 343 344

348 349 350

C

330 331

E

328 329

R

326 327

R

324 325

O

322 323

C

320 321

20

15

N

318 319

U

316 317

Enhancement of HTC (%)

314 315

5. Uncited references

367 Q2

F

We presented on the fabrication and evaluation of highly stable water and DW/EG based α-SiC NFs, containing various concentrations of α-SiC NPs, for heat transfer application. The thermo-physical properties of NFs including TC and viscosity in different base liquids and with

312 313

[7,32]

O

347

311

R O

4. Conclusion

309 310

351 352

Acknowledgments

10

5

0

Pumping Power Reynolds Volume Flow Rate (mW) (-) (ml/min)

Comparison Criteria Fig. 7. Comparative analysis of experimental results (HTC vs. Reynolds number, volume flow rate and pumping power) for α-SiC NF-DW/EG-9 wt.%.

353 354 355 356 357 358 359 360 361 362 363 364 365 366

368 369

P

346

307 308

various concentration of α-SiC NPs were measured at 20 °C. TC enhancement for both NFs systems with different base liquids were observed, due to the presence of α-SiC NPs. TC of NFs increased with the increase of α-SiC NP concentration. The DW/EG based NFs exhibited higher efficiencies as heat transfer fluids than the similar distilled water based NFs. Among all suspensions, NFs with 9 wt.% α-SiC NPs and DW/EG base liquid (α-SiC NF-DW/EG-9 wt.%) exhibited the most promising performance: highest TC enhancement of 20% with only 14% increase in viscosity. Therefore, this NF was selected for performing HTC tests in a laminar flow regime. The results obviously point out that DW/EG based α-SiC NF is an appropriate candidate in the laminar flow regime, with an improvement of 5.5% at the equal pumping power as an accurate and realistic basis of comparison was achieved for HTC tests in the laminar regime. It indicates the capability of this kind of NFs to be used in practical heat transfer applications and the feasibility of commercialization.

The financial support of the EU (Project Reference: 228882) and 370 Swedish Research Council—VR NanoHex (Enhanced Nano-fluid Heat 371 Q3 Exchange) project for this study is highly appreciated. 372 References

[1] X. Wang, X. Xu, S.U.S. Choi, Thermal conductivity of nanoparticle–fluid mixture, J. Thermophys. Heat Transf. 13 (4) (1999) 474–480. [2] X.Q. Wang, A.S. Mujumdar, Review on nanofluids. Part II: experiments and applications, Braz. J. Chem. Eng. 25 (4) (2008) 631–648. [3] K.D. Sarit, Nanofluids—the cooling medium of the future, Heat Transf. Eng. 27 (10) (2006) 1–2. [4] S. Lee, S.U.S. Choi, Application of metallic nanoparticle suspensions, ANL, 1997. [5] J.C. Maxwell, A Treatise on Electricity and Magnetism, 1Clarendon Press, Oxford, UK, 1873. 365. [6] S.U.S. Choi, Nanofluids: From Vision to Reality through Research, J. Heat Transf. Trans. ASME 131 (3) (2009) 033106–033109. [7] H. Zhu, Y. Lin, Y. Yin, A novel one-step chemical method for preparation of copper nanofluids, J. Colloid Interface Sci. 277 (1) (2004) 100–103. [8] W. Yu, D.M. France, J.L. Routbort, S.U.S. Choi, Review and comparison of nanofluid thermal conductivity and heat transfer enhancements, Heat Transf. Eng. 29 (5) (2008) 432–460. [9] S.M.S. Murshed, C.A. Nieto de Castro, M.J.V. Lourenco, M.L.M. Lopes, F.J.V. Santos, A review of boiling and convective heat transfer with nanofluids, Renew. Sust. Energ. Rev. 15 (5) (2011) 2342–2354. [10] D. Singh, E. Timofeeva, W. Yu, J. Routbort, D. France, D. Smith, J.M. Lopez-Cepero, An investigation of silicon carbide-water nanofluid for heat transfer applications, J. Appl. Phys. 105 (6) (2009) 064306. [11] R.A. Andrievski, Synthesis, structure and properties of nanosized silicon carbide, Rev. Adv. Mater. Sci. 22 (2009) 1–20. [12] H. Xie, J. Wang, T. Xi, Y. Liu, Thermal conductivity of suspensions containing nanosized SiC particles, Int. J. Thermophys. 23 (2) (2002) 571–580. [13] S.W. Lee, S.D. Park, S. Kang, I.C. Bang, J.H. Kim, Investigation of viscosity and thermal conductivity of SiC nanofluids for heat transfer applications, Int. J. Heat Mass Transfer 54 (1–3) (2011) 433–438. [14] E.V. Timofeeva, D.S. Smith, W. Yu, D.M. France, D. Singh, J.L. Routbort, Particle size and interfacial effects on thermo-physical and heat transfer characteristics of water-based α-SiC nanofluids, Nanotechnology 21 (21) (2010) 215703–215710. [15] E.V. Timofeeva, W. Yu, D.M. France, D. Singh, J.L. Routbort, Base fluid and temperature effects on the heat transfer characteristics of SiC in ethylene glycol/H2O and H2O nanofluids, J. Appl. Phys. 109 (1) (2011) 014914. [16] N. Nikkam, M. Saleemi, E.B. Haghighi, M. Ghanbarpour, R. Khodabandeh, M. Muhammed, B. Palm, M.S. Toprak, Fabrication, characterization and thermophysical property evaluation of water/ethylene glycol based SiC nanofluids for heat transfer applications, Nano-Micro Lett. 6 (2) (2014) 178–189. [17] H.Q. Xie, J.C. Wang, T.G. Xi, Y. Liu, F. Ai, Q.R. Wu, Thermal conductivity enhancement of suspensions containing nanosized alumina particles, J. Appl. Phys. 91 (7) (2002) 4568–4572. [18] H.Q. Xie, J.C. Wang, T.G. Xi, Y. Liu, F. Ai, Dependence of the thermal conductivity of nanoparticle–fluid mixture on the base fluid, J. Mater. Sci. Lett. 21 (19) (2002) 1469–1471. [19] T.H. Tsai, L.S. Kuo, P.H. Chen, C.T. Yang, Effect of viscosity of base fluid on thermal conductivity of nanofluids, Appl. Phys. Lett. 93 (23) (2008) 233121–233123.

T

345

canceled out and sometimes obscured the TC enhancement obtained in NFs [14,30,33–35]. Fig. 6(a) shows the HTC of α-SiC NF and base liquid versus Reynolds number (range of 500 to 1800). The value of HTC for NF increases both for the base liquid and the NF with increasing Reynolds number. NFs show a slightly higher increase of HTC than the base liquid in higher Reynolds numbers in the laminar flow regime, resulting in about ~13% (average value) increase in HTC over the base liquid. Fig. 6(b) illustrates variation of the HTC with respect to the volume flow rate for the NF and base liquid (range of 300 to 1200 ml/min). It should be noted that there is a major increase of HTC for NF in the measured flow rates. Similar to the analysis of HTC versus Reynolds number, a slightly higher HTC value of NF over the base liquid is observed for the volume flow rate. The increase of NF's HTC according to this criterion is roughly 8.5% in the measured range. In contrast to the conventional heat transfer performance consideration, pumping power applied to run the flow through cooling systems is a crucial focus area. Pumping power can be introduced as a measure of friction force over the tube wall. It is also seen from Fig. 6(c) that the similar incremental trend exists for HTC versus pumping power. However, the relative increase with respect to two former criteria (Reynolds number and volume flow rate) is lower. The HTC for α-SiC NF is approximately 5.5% higher in the measured range. Our result is higher than previous study on water based α-SiC NFs by Timofeeva et al. [14]. Their investigation revealed that although the increase in TC was significant, the high increase in the viscosity resulted in the HTC being up to 15% worse than that of the base liquid. In a turbulent flow regime, at 71 °C, about 14.2% improvement of HTC (based on constant velocity or pumping power) for a NF with DW/EG base liquid containing 13 wt.% SiC NPs loading is reported [15]. Since the result is based on the turbulent flow regime and obtained at a higher temperature, a direct comparison between our achievement and their observation is not possible, as the difference may be due to the different flow regime, higher test temperature (higher T, leading to lower viscosity) or higher concentration of α-SiC NPs in their NF. A comparative graph for HTC evaluation of the NF for the three criteria is presented in Fig. 7. In all evaluation criteria NF performed significantly better than the base liquid in the HTC tests. Specifically the achieved enhancements are: 13% at equal Reynolds number, 8.5% at equal volume flow and 5.5% at equal pumping power. This reveals promising characteristics for this NF for use in convective heat transfer applications, such as electronics cooling.

D

305 306

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

E

6

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420

N. Nikkam et al. / International Communications in Heat and Mass Transfer xxx (2014) xxx–xxx

[29] W. Yu, D.M. France, E.V. Timofeeva, D. Singh, J.L. Routbort, Thermophysical propertyrelated comparison criteria for nanofluid heat transfer enhancement in turbulent flow, Appl. Phys. Lett. 96 (21) (2010) (213109 - 213109-3). [30] K.S. Hwang, S.P. Jang, S.U.S. Choi, Flow and convective heat transfer characteristics of water-based Al2O3 nanofluids in fully developed laminar flow regime, Int. J. Heat Mass Transfer 52 (1–2) (2009) 193–199. [31] S. Torii, Y. Wen-Jei, Heat transfer augmentation of aqueous suspensions of nanodiamonds in turbulent pipe flow, J. Heat Transf. 131 (4) (2009) 043203–043205. [32] Y. Gao, R. Wahi, A.T. Kan, J.C. Falkner, V.L. Colvin, A.B. Tomson, Adsorption of cadmium on anatase nanoparticles effect of crystal size and pH, Langmuir 20 (2004) 9585–9593. [33] D.P. Kulkarni, P.K. Namburu, H.E. Bargar, D.K. Das, Convective heat transfer and fluid dynamic characteristics of SiO2 ethylene glycol/water nanofluid, Heat Transf. Eng. 29 (12) (2008) 1027–1035. [34] B.C. Pak, Y.I. Cho, Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles, Exp. Heat Transf. 11 (2) (1998) 151–170. [35] W. Williams, L.W. Hu, J. Buongiorno, Experimental investigation of turbulent convective heat transfer and pressure loss of alumina/water and zirconia/water nanoparticle colloids (nanofluids) in horizontal tubes, J. Heat Transf. 130 (4) (2008) 042412–042417.

N C O

R

R

E

C

T

E

D

P

R O

O

F

[20] E.B. Haghighi, Z. Anwar, I. Lumbreras, S.A. Mirmohammadi, M. Behi, R. Khodabandeh, B. Palm, Screening single phase laminar convective heat transfer of nanofluids in a micro-tube, J. Phys. Conf. Ser. 395 (1) (2012) (012036-012036-11). [21] E.B. Haghighi, M. Saleemi, N. Nikkam, R. Khodabandeh, M.S. Toprak, M. Muhammed, B. Palm, Accurate basis of comparison for convective heat transfer in nanofluids, Int. Commun. Heat Mass Transf. 52 (2014) 1–7. [22] R. Cheung, Silicon carbide microelectromechanical systems for harsh environments, Imperial College, 2006. 3. [23] P.K. Namburu, D.P. Kulkarni, A. Dandekar, D.K. Das, Experimental investigation of viscosity and specific heat of silicon dioxide nanofluids, Micro Nano Lett. 2 (3) (2007) 67–71. [24] M. Kole, T.K. Dey, Viscosity of alumina nanoparticles dispersed in car engine coolant, Exp. Therm. Fluid Sci. 34 (6) (2010) 677–683. [25] J. Eapen, R. Rusconi, R. Piazza, S. Yip, The classical nature of thermal conduction in nanofluids, ASME Trans. J. Heat Transf. 132 (10) (2010) 102402–102414. [26] R.K. Shah, Thermal entry length solutions for the circular tube and parallel plates, Proceeding of the 3rd National Heat Mass Transfer Conference, 1, Indian Institute of Technology, Bombay, India, 1975, (Paper no. HMT-11-75). [27] Y.M. Xuan, Q. Li, Investigation on convective heat transfer and flow features of nanofluids, Trans. ASME C 125 (1) (2003) 151–155. [28] W. Yu, D.M. France, D.S. Smith, D. Singh, E.V. Timofeeva, J.L. Routbort, Heat transfer to a silicon carbide/water nanofluid, Int. J. Heat Mass Transfer 52 (15–16) (2009) 3606–3612.

U

421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 464

7

Please cite this article as: N. Nikkam, et al., Experimental study on preparation and base liquid effect on thermo-physical and heat transport characteristics of α-SiC nanofluids, Int. Commun. Heat Mass Transf. (2014), http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.04.011

444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463