Experimental investigation of energy and exergy efficiency of a pulsating heat pipe for chimney heat recovery

Sustainable Energy Technologies and Assessments 16 (2016) 11–17

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Original Research Article

Experimental investigation of energy and exergy efficiency of a pulsating heat pipe for chimney heat recovery R. Khodami a,b, A. Abbas Nejad a,⇑, M.R. Ali Khabbaz a a b

Department of Mechanical Engineering, Shahrood University of Technology, P.O. Box 3619995161-316, Shahrood, Iran AbarSazandegan Shahvar knowledge-based Company, Shahrood, Iran

a r t i c l e

i n f o

Article history: Received 30 December 2015 Revised 10 April 2016 Accepted 11 April 2016

Keywords: Heat exchanger Heat recovery Pulsating heat pipe Exergy analysis

a b s t r a c t A prototype heat exchanger is proposed for exhaust heat recovery by means of pulsating heat pipe. The device is made up of an exhaust channel, an air channel, and a row of pulsating heat pipes with the filling ratio of 40% and ethanol and silver nano-fluid as working fluids. The exhaust hot gas from the combustion of natural gas feeds the device. For exergy analysis of the device, the inlet and outlet temperatures of the hot gas and cold air were measured with appropriate devices. Having the exergy of each flow, the exergetic efficiency of the system was calculated at different inlet temperatures. The calculations were carried out for two distinct working fluids within the heat pipes. The energy analysis results show that ethanol, at an inlet smoke temperature of 120 °C, has the best functionality. Exergy analysis also demonstrated the better performance of silver nano-fluid compared to ethanol. The use of silver nano-fluid instead of ethanol increases exergy efficiency as much as 1–3% and decreases exergy losses as much as 8–14%. Ó 2016 Elsevier Ltd. All rights reserved.

Introduction Over the past few centuries, the world economy has been dependent on non-renewable fossil fuels. Until the oil crisis of 1973, the necessity of long term rethinking and plans to address energy optimization was not felt. After the crisis, attention was focused on ways to reduce fossil energy consumption and to replace it with the new renewable energies. Of course, there are some other reasons as well, such as climate changes, global warming due to the greenhouse effect, energy security, rising fuel prices, and strict environmental regulations for gas emissions that drove a comprehensive research on clean technologies. One of the main ways to reduce fuel consumption is to recycle the exhaust heat from the combustion of fossil fuels. This reduces carbon dioxide emissions as well as fuel consumption, which would positively affect environmental preservation [1–12]. Heat pipes are one of the best options for heat transfer in most cases and are considered to be effective for heat loss recovery. The advantage of using heat pipe over other conventional methods is that this system can transfer huge amounts of heat through a small cross section and along a considerable distance without receiving any power. In addition, simple manufacturing and design, low temperature drop along the heat pipe, application in a wide range of ⇑ Corresponding author. Tel.: +98 23 32300258; fax: +98 23 32340111. E-mail address: [email protected] (A. Abbas Nejad). http://dx.doi.org/10.1016/j.seta.2016.04.002 2213-1388/Ó 2016 Elsevier Ltd. All rights reserved.

temperatures (4–2000°K), and the ability to control and transfer high heat flow rates at different temperatures are considered as other advantages [13,14]. The new generation of heat pipes, called pulsating heat pipes, were invented by Akachi in 1990s [15,16]. Due to the use of a combination of sensible and latent heat transfer, the pulsating heat pipes are more efficient than conventional heat pipes. Simple design and low price are also among other superiorities of the pulsating heat pipe in comparison with other heat transfer equipment. Alawi et al. [17] presented an overview of different research works and recent developments in the field of heat transfer enhancement using nanofluids in various types of heat pipes. Their review showed that adding nanoparticles to the working fluids can increase the heat transfer and reduce the heat resistance of the heat pipes. Lin et al. [18] experimentally investigated the thermal performance of pulsating heat pipes using nano-fluids. They used water-based silver nano-fluid in various volume percents (100 ppm, 450 ppm), as well as different filling ratios (20%, 40%, 60%, 80%). Silver nano-particles were 20 nm in diameter. The results showed that using nano-fluid instead of water improves the thermal efficiency of pulsating heat pipes. The best filling ratio was reported to be 60% and the best volumetric concentration 100 ppm. These results were obtained with the input power of 85 W. Furthermore, the mean temperature difference between the evaporator inner wall and saturated vapor was

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Nomenclature A cp D Ex g h m Q s T V W

Area [m2] Specific heat [kJ/kg K] Diameter [m] Exergy ratio [W] Gravity [m/s2] Specific enthalpy [kJ/kg] Mass [kg] Heat transfer [kJ] Specific entropy [kJ/kg K] Temperature [k] Velocity [m/s] Work [kJ]

reduced to 7.8 K. This reduction is equivalent to a 15% reduction in the final heat pipe thermal resistance. The heat transfer of a closed two-phase thermosiphon using pure water and different nanofluids was compared by Khandekar et al. [19] and Noie et al. [20]. Wang et al. [6] carried out a comprehensive review on different techniques for exhaust heat recovery from internal combustion engines. They came to the conclusion that the most widely used method for this task is using the Rankin cycle. Moreover, they reported up to 30% energy consumption saving in an internal combustion engine. Srinivasan et al. [7] investigated exhaust heat recovery in a dual fuel low-temperature combustion engine by means of anorganic Rankin cycle. They showed that the amount of carbon dioxide produced can be reduced up to 18% in this method. A new combined cycle to recycle the heat in the internal combustion engines was introduced by He et al. [8]. The new cycle was a combination of a Kalina cycle for low-temperature recovery and an organic Rankin cycle for high-temperature recovery. By examining a variety of cycles for direct and indirect heat recovery, Liu et al. [10] concluded that the indirect method is the better one. Messerer et al. [21] investigated thermal recovery in combustion engines, in which fossil fuels were replaced by wood, and reported the recovered heat rate. An increment in thermal efficiency (2.9–3.7%) was reported for heat recovery by Rankin cycle in hydrogen internal combustion engines by Yamada et al. [22]. Srimuag and Amatachaya [23] discussed the applications of heat pipes in thermal recovery and factors affecting the conventional, pulsating, and closed thermo syphon types. They believed that one of the best ways to save energy is using heat pipe heat exchangers. Shabgard et al. [24] demonstrated the effect of using heat pipes on latent heat storage in solar systems through exergy analysis. By means of exergetic analysis in air conditioning systems, Fang et al. [25] illustrated that the use of heat pipes in ice storage systems enhances exergy efficiency as much as 9.55% compared to ‘‘iceon-coil” ice storage systems. Naphon [26] carried out several exergy studies on horizontal micro-fin tube heat exchangers. The effect of exergy transfer in heat exchangers on finite pressure drop was studied by Wu et al. [27]. They presented a relation for exergy transfer efficiency, both in isobar and finite pressure drop cases. As stated above, the most papers in the literature considered the heat transfer enhancement, advantages and disadvantages of using nanofluids in different types of heat pipes. The past research

x

w ep

q g

Mole percent [%] Specific exergy [kJ/kg] Exergy transfer efficiency Density [kg/m3] efficiency

Subscripts h Hot flow c Cold flow i Inlet o Outlet ° Ambient condition

seldom addressed the exergy components of heat pipes and the probable differences were studied using energy-based analyses. Moreover, to determine the characteristics of the working fluid, exergy analysis has not been considered in previous studies. The performance of a pulsating heat pipe for heat recovery is investigated experimentally from both energy and exergy points of view. Finally, according to the experimental results, the exergetic efficiency and exergy transfer efficiency are compared for two different working fluids, namely ethanol and silver nano-fluid. Experimental setup Pulsating heat pipes There are two types of pulsating heat pipes, namely closed-loop and open-loop as illustrated in Fig. 1. The closed-loop type is more efficient, since it provides the possibility of fluid flow in the pipes. When the heat pipe is partially filled with a proper working fluid, the fluid will be distributed in pipes as slug-plug due to the adhesion effect in small diameter pipes (according to Fig. 1). The heat flux at the start of the process is not sufficient for the movement of the working fluid. With a further increase in heat flux, the working fluid in the heat pipe starts moving and heat transfer is greatly improved [28]. A unique feature of the pulsating heat pipe is that the evaporated fluid in the evaporation section flows toward the condenser under its own increasing pressure force and moves the fluid in the condenser toward the evaporator in the adjacent pipe. This phenomenon, as will be explained later on, will make the performance of pulsating heat pipe less dependent on gravity. Pulsating heat pipe fabrication Pulsating heat pipes made for this study consist of two rows of closed-loop pulsating heat pipes with an internal diameter of 2 mm and an external diameter of 4 mm. Each row consists of 18 turns of pipes, in a way that the total height of 56 cm was considered for the pulsating heat pipe. There was a 27-cm evaporator, 27cm condenser, and 2 cm for the adiabatic section, which is negligible. To achieve maximum heat transfer, copper pipes were selected. Then, in order to create an pulsating heat pipe, copper pipes were bent to a U-shaped pipe by a pipe bender. In this case, 18 turns were made in a distance of 100 cm. First, the air was evacuated from the pipe. To ensure complete evacuation of air in a closed-loop pulsating heat pipe, the air inside the closed-loop pulsating heat pipe was evacuated for approximately 30 min using a vacuum pump to get to the set pressure of less than 15 Pa. This relatively long time duration was set

R. Khodami et al. / Sustainable Energy Technologies and Assessments 16 (2016) 11–17

13

Fig. 1. Various types of pulsating heat pipes [25].

because pipes were thin-walled and helical. Then, the working fluid with the filling ratio of 40% was injected. At this moment, the heat pipe was partially filled with the proper working fluid. In this experiment, two types of working fluid were used, ethanol with a purity of 96% and silver/water nano-fluid with a size of 18 ± 1 nm.

enable forced convection on both sides of the channel. In this experiment, different mass flow rates were investigated with different fan speeds, which were controlled by a dimmer. Hot output gas of Mahya Gas Heater (Model 10000), with minimum and maximum thermal powers of 1500 and 8500 kcal/h, was used as the driving power of the heat exchanger.

Heat exchanger fabrication

Equipments and experiment procedure

The heat exchanger body, exhaust gas and air channels are made of a galvanized steel sheet with a thickness of 0.7 mm, whose characteristics are as follows: The experimental setup includes a rectangular box with dimensions of 100
60
10 cm and four conical caps with the length of 30 cm, which in fact, are the inlet and outlet of cold and hot gases as depicted in Fig. 2. An interface divides the box into two channels with the width of 30 cm for air and exhaust gas. Pulsating heat pipes passed through the holes punched on the interface in a manner that half of the pulsating heat pipes were positioned in the hot gas channel (evaporator) and the remaining are in the air channel (condenser). In order to prevent the infiltration of hot gas into the air channel, the void area around each pulsating heat pipe on the interface was sealed with a proper thermal resistant sealing adhesive. Two fans with the maximum power of 16 W were used to

After the exchanger was assembled, it was placed on a suitable base. Gas heater outlet was connected to the inlet gas channel of the exchanger with appropriate connector pipes. To record temperature at the smoke and air inlet and outlet, four PT100 sensors were used. A schematic view of the device and how to install the equipment is illustrated in Fig. 3. Sensors at the inputs and outputs of the exchanger were fixed in the center and perpendicular to the flow direction. To measure the fan speed, an anemometer was utilized. After about thirty to forty minutes of turning the heater on and reaching the steady state, the measurement started. To establish a stable condition after each time of changing the input smoke temperature and the air mass flow rate, a time interval of approximately 15 min was considered. Two experiments were run for two modes; once with a row of pulsating heat pipes with ethanol as the working fluid and a filling ratio of 40%, when the device was placed at an angle of 90° to the horizon. The next experiment was conducted using silver/ water nano-fluid with the same filling ratio and device angle as the first experiment. In both cases, the effect of the input smoke temperature and changes in the mass flow rate of air was taken into consideration. In these experiments, flow in the exchanger is opposite, the fan has a sucking function, and the device body is insulated with fiberglass. To review and ensure that no heat is transferred from the interface of the exhaust and air channels where pulsating heat pipes passed, an experiment on a mere sheet (the interface surface with no pulsating heat pipes) was performed. The results showed that when the speed is less than 0.7 m/s, outlet air temperature increases by 2 °C. But, when a speed higher than 0.7 m/s is considered, no change is observed in the outlet air temperature. So, in order to focus more and more on the performance of pulsating heat pipes, it is assumed that the smoke flow velocity magnitude is constant and equal to 1 m/s, and the air velocity is variable and higher than 1 m/s. To prevent the heater temperature from affecting smoke input and air exhaust sensors, the heater was

Fig. 2. Experimental heat recovery system.

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Fig. 3. Schematic view of the system.

_ ¼ mw _ ¼ m½ðh _ Ex o  hi Þ  T 0 ðso  si Þ

ð4Þ

placed at a distance of approximately two meters away from the exchanger (transducer). To achieve high accuracy and reduce measurement errors, the device was mounted far away (sheltered) from undesirable environmental conditions such as wind flow and sunlight.

where DH and DS values can be calculated according to the above assumptions and from Eqs. (5) and (6) [29]:

Exergy analysis

Ds ¼ so  si ¼ cp ln

Exergy is the maximum work that can be derived from a system, from the beginning state until the ambient state (dead state). This concept was first proposed at the beginning of the 1970s with the aim of finding an optimal amount of energy consumption. This optimization is to simultaneously reduce fossil fuel consumption and increase energy efficiency [29,30]. The exergy of an exergy system is directly linked to the second law of thermodynamics. In fact, based on the exergy destruction principle, exergy destruction and entropy production occur in a system and entropy is partially engaged in the exergy calculation formula, as expected. This entropy survey as well as enthalpy, requires mass, energy, and exergy balance equations to be written for each component of the system [29]. To analyze the device in terms of exergy, it is first considered as a heat exchanger. The exergy equation is summarized with the following assumptions: 1. 2. 3. 4.

Changes in potential and kinetic energy were ignored. Pressure magnitudes at the inlet and outlet are the same. Gas is assumed ideal and compressible. Density of both fluids is considered identical.

_i¼ m

X

_o m

ð1Þ

The first law of thermodynamics for a stable system can be written as follows [29]:

_ þ Q_  W

X

ho 

X

hi ¼ 0

_ exhaust ¼ Ex

X

_ air þ Ex

X

  To Ti

ð6Þ

The value for input smoke was calculated by the following assumptions [29]: 1. Input smokes are assumed as emissions resulting from the complete combustion of methane. 2. Combustion is considered with ten percent excess air. With these assumptions, the equation of methane combustion, gives the molar ratio of each of the products as listed in Table 1. Then, cp is obtained as follows [29]:

cp ¼ xN2 cpN2 þ xH2 O cpH2 O þ xO2 cpO2 þ xCO2 cpCO2

ð7Þ

Moreover, exergetic efficiency is as follows [29,30]:

P_ ExAir

gex ¼ P _

ð8Þ

ExExhaust

According to our understandings, when the temperature at the input and output of the exchanger is given, the heat transfer efficiency concept is used to facilitate the determination of the rate of the exchanged heat. Similarly, the concept for exergy is defined as below [27]:

ee ¼

actual amount of exchanged exergy of target fluid maximum amount of exchanged exergy of target fluid

ð9Þ

ð2Þ

The exergy balance equation of the device would be as follows [29,30]:

X

ð5Þ

Exergy transfer efficiency

Mass balance in a stable system is as follows:

X

Dh ¼ h o  h i ¼ c p DT

_ dest: Ex

ð3Þ

P_ P_ Exexhaust and ExAir denote the exergy changes of the inlet where smoke air, respectively. The exergy equation would be written as follows [27]:

Table 1 Mole percent of methane combustion productions. Combustion gas

Mole percent

N2 H2O C2O O2

72.1 17.43 8.71 1.74

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ee ¼

T co  T ci  T 0 ln T hi  T ci  T co ln

  T co T ci

 

ð10Þ

T hi T ci

80

75

70

Exdes(W)

This concept is an alternative criterion for exergy exchange rate and demonstrates the exchanger capacity to exchange exergy. Furthermore, this value provides the possibility to compare the two exchangers. It is noteworthy that the actual amount of exchanged exergy plus exchanged m equals the exergy changes of the target fluid. The target fluid is the exhaust air from the device. Exergy transfer efficiency for non-aligned flow exchangers that have no pressure drop and the target fluid is at a temperature above the ambient temperature is as given below [27]:

65

60

Results

Texhaust_in=120c Texhaust_in=125c Texhaust_in=130c

55

To obtain exergy in the device, the results were recorded at a variety of temperatures in the air and smoke inlet and outlet. It is assumed that burning methane produces the smoke exhaust. In calculations of the experimental results, some data that failed to match the theoretical results owing to measurement errors were removed. Inlet air velocity is variable from 1 m/s to 2.5 m/s and input smoke velocity is constant end equal to 1 m/s. First, energy and exergy efficiency coefficients for ethanol as the working fluid were calculated in different velocities of intake air and the results were illustrated in Fig. 4. As can be seen, energy efficiency increases by increasing the speed. In fact, increased speed results in an increased heat transfer rate, and this increases energy efficiency [31]. On the other hand, the exergy efficiency coefficient decreased. In fact, increased speed increases heat transfer rate and the amount of exergy improves on the one hand. On the other hand, it leads to increased exergy losses the effect of which is greater than increased heat transfer rate. As a result, exergy efficiency decreases. Moreover, both in energy efficiency or exergy efficiency, the best performance was achieved at 120 °C. Fig. 5 shows the diagram of exergy loss in terms of air mass flow rate. This figure illustrates exergy loss increase with increased speed, in diverse temperatures of inlet smoke. When speed increases, irreversibility and exergy destruction due to the changes

50 0.01

0.015

0.02

0.025

0.03

0.035

Air mass flow rate(kg/s) Fig. 5. Exergy loss in terms of air mass flow rate for different temperatures of inlet smoke.

in flow rate increase, which led to the reduction of exergy efficiency in the previous section. These results are in good agreement with those obtained by Pandey et al. [32]. On the other hand, this figure shows that exergy destruction has the least value in the inlet smoke temperature of 120 °C, which, in fact, shows the best performance at this temperature. Fig. 6 demonstrates exergy efficiency changes in terms of air mass flow rate at different temperatures of inlet smoke. As can be seen, with increased speed, exergy efficiency has decreased, which is caused by increased exergy loss, as in decreased exergy efficiency. Maximum exergy efficiency is for the exhaust temperature of 120 °C. The comparison between ethanol and silver nano-fluid as the working fluids within the heat pipe and its effect on exergy variables is depicted in Figs. 7–9. As can be seen, silver nano-fluid has a better performance compared to ethanol. This is due to the

9.5

0.25

8.5

0.2

8

Texhaust_in=120c Texhaust_in=125c Texhaust_in=130c

7.5 7

0.15

ex

Exergy & Energy transfer effectiveness

9

,Texhaust_in=120c ,Texhaust_in=130c ,T =120c ex exhaust_in ex,Texhaust_in=130c

0.1

6.5 6 5.5 5 4.5

0.05

4 3.5

0

0.01

1

1.5

2

Exhaust to Air mass flow rate

2.5

Fig. 4. Energy and exergy efficiency in terms of exhaust to air mass flow rate.

0.015

0.02

0.025

0.03

0.035

0.04

Air mass flow rate(kg/s) Fig. 6. Exergy efficiency in terms of air mass flow rate for different temperatures of inlet smoke.

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0.05

Nano Fluid,Texhaust_in=130c Ethanol,Texhaust_in=130c Nano Fluid,Texhaust_in=120c Ethanol,Texhaust_in=120c

9 8.5

0.045

8 7.5

0.04

7

ex

Exergy transfer effectiveness

9.5

Nano Fluid,Texhaust_in=130c Ethanol,Texhaust_in=130c Nano Fluid,Texhaust_in=120c Ethanol,Texhaust_in=120c

0.035

6.5 6 5.5

0.03

5

0.025

4.5 4

0.02 0.5

1

1.5

2

Exhaust to Air mass flow rate

2.5

3

Fig. 7. Exergy efficiency of the exchanger in terms of exhaust to air mass flow rate for different temperatures of inlet smoke, for ethanol and nano silver-fluid as working fluids.

higher coefficient of heat transfer in the nano-fluid temperatures tested. Fig. 7 represents a comparison between the exergy efficiency of an exchanger with two working fluids in terms of exhaust to air flow mass rate. This diagram displays an enhancement of 15–48% in the exergy efficiency coefficient if silver nano-fluid was utilized. Fig. 8 depicts a comparison between exergy destruction of a device with two distinct fluids as working fluids in terms of exhaust to air flow mass rate. This diagram shows that the amount of destruction is less when the working fluid is silver nano-fluid. The exergy destruction also decreases between 8% and 14%, but the direct relationship between destruction and velocity is still there. A comparison between the exergy efficiency with two distinct working fluids in terms of exhaust to air flow mass rate is shown in Fig. 9. 80

75

Nano Fluid,Texhaust_in=130c Ethanol,Texhaust_in=130c Nano Fluid,Texhaust_in=120c Ethanol,Texhaust_in=120c

Exdes(W)

70

65

60

0.5

1

1.5

2

Exhaust to Air mass flow rate

2.5

3

Fig. 9. Exergy efficiency in terms of smoke and air inlet flow rates at different temperatures of inlet smoke, for ethanol and silver nano-fluid as working fluids.

In the case of silver nano-fluid, the trend of exergy efficiency is similar to that of ethanol, but the diagram shows an improvement of 1–3% in efficiency when silver nano-fluid is the working fluid.

Conclusion The use of pulsating heat pipes for heat recovery from chimneys was investigated experimentally to reduce the fuel consumption. The main objective of the research was the evaluation of the proposed system from the exergy point of view. The exergy transfer efficiency was studied for different working fluids including pure and nanofluids. As stated earlier, the inlet and outlet temperatures of the device were measured at first. Then, using exergy analysis, exergy efficiency and exergy transfer efficiency were calculated as well as exergy destruction. Furthermore, these factors were used to compare the performance of the two working fluids, namely ethanol and silver nano-fluid. The results showed that the energy analysis alone may not represent the performance of the device. Therefore, exergy devices should be used to achieve a better analysis because the irreversible effect on the device performance is ignored in energy analysis. On the other hand, the study showed that silver nano-fluid as the working fluid in the heat pipe exchangers has a better performance compared to ethanol in terms of exergy analysis. This indicates the great importance of nano-fluids. In the end, it is proposed that the device be examined from the thermo-economic perspective to provide a criterion for the economic analysis of the device. References

55

50 0.5

3.5

1

1.5

2

Exhaust to Air mass flow rate

2.5

3

Fig. 8. Exergy loss in terms of smoke and air inlet flow rates in different temperatures of inlet smoke, for ethanol and silver nano-fluid as working fluids.

[1] Hu J-L, Kao C-H. Efficient energy-saving targets for APEC economies. Energy Policy 2007;35:373–82. [2] Tolón-Becerra A, Lastra-Bravo X, Bienvenido-Bárcena F. Proposal for territorial distribution of the EU 2020 political renewable energy goal. Renew Energy 2011;36:2067–77. [3] Bunse K, Vodicka M, Schönsleben P, Brülhart M, Ernst FO. Integrating energy efficiency performance in production management – gap analysis between industrial needs and scientific literature. J Clean Prod 2011;19:667–79. [4] Baños R, Manzano-Agugliaro F, Montoya FG, Gil C, Alcayde A, Gómez J. Optimization methods applied to renewable and sustainable energy: a review. Renew Sustain Energy Rev 2011;15:1753–66. [5] Denny E. The economics of tidal energy. Energy Policy 2009;37:1914–24.

R. Khodami et al. / Sustainable Energy Technologies and Assessments 16 (2016) 11–17 [6] Wang T, Zhang Y, Peng Z, Shu G. A review of researches on thermal exhaust heat recovery with Rankine cycle. Renew Sustain Energy Rev 2011;15:2862–71. [7] Srinivasan KK, Mago PJ, Krishnan SR. Analysis of exhaust waste heat recovery from a dual fuel low temperature combustion engine using an Organic Rankine Cycle. Energy 2010;35:2387–99. [8] He M, Zhang X, Zeng K, Gao K. A combined thermodynamic cycle used for waste heat recovery of internal combustion engine. Energy 2011;36:6821–9. [9] Fu J, Liu J, Feng R, Yang Y, Wang L, Wang Y. Energy and exergy analysis on gasoline engine based on mapping characteristics experiment. Appl Energy 2013;102:622–30. [10] Liu JP, Fu JQ, Ren CQ, Wang LJ, Xu ZX, Deng BL. Comparison and analysis of engine exhaust gas energy recovery potential through various bottom cycles. Appl Therm Eng 2013;50:1219–34. [11] Bojic M, Mourdoukoutas P. Energy saving does not yield CO2 emissions reductions: the case of waste fuel use in a steel mill. Appl Therm Eng 2000;20:963–75. [12] Hoffmann T JB, Reports. Energy in a Finite, World: Paths to a Sustainable Future; The World Energy Triangle: A Strategy for Cooperation; International Energy Futures: Petroleum Prices, Power, and Payment. Energy Systems Program Group of the International Institute for Applied Systems Analysis. [13] Pluta Z, Pomierny W. The theoretical and experimental investigation of the phase-change solar thermosyphon. Renew Energy 1995;6:317–21. [14] Faghri A. Heat pipe science and technology. Global Digital Press; 1995. [15] Akachi H. Structure of a heat pipe. Google Patents; 1990. [16] Akachi H. L-type heat sink. Google Patents; 1996. [17] Alawi OA, Sidik NAC, Mohammed H, Syahrullail S. Fluid flow and heat transfer characteristics of nanofluids in heat pipes: a review. Int Commun Heat Mass Transfer 2014;56:50–62. [18] Lin Y-H, Kang S-W, Chen H-L. Effect of silver nano-fluid on pulsating heat pipe thermal performance. Appl Therm Eng 2008;28:1312–7. [19] Khandekar S, Joshi YM, Mehta B. Thermal performance of closed two-phase thermosyphon using nanofluids. Int J Therm Sci 2008;47:659–67.

17

[20] Noie S, Heris SZ, Kahani M, Nowee S. Heat transfer enhancement using Al2O3/ water nanofluid in a two-phase closed thermosyphon. Int J Heat Fluid Flow 2009;30:700–5. [21] Messerer A, Schmatloch V, Pöschl U, Niessner R. Combined particle emission reduction and heat recovery from combustion exhaust—A novel approach for small wood-fired appliances. Biomass Bioenergy 2007;31:512–21. [22] Yamada N, Mohamad MNA. Efficiency of hydrogen internal combustion engine combined with open steam Rankine cycle recovering water and waste heat. Int J Hydrogen Energy 2010;35:1430–42. [23] Srimuang W, Amatachaya P. A review of the applications of heat pipe heat exchangers for heat recovery. Renew Sustain Energy Rev 2012;16:4303–15. [24] Shabgard H, Robak CW, Bergman TL, Faghri A. Heat transfer and exergy analysis of cascaded latent heat storage with gravity-assisted heat pipes for concentrating solar power applications. Sol Energy 2012;86:816–30. [25] Fang G, Liu X. Exergy analysis of ice storage air-conditioning system with heat pipe during charging period. Energy Sustain Dev 2010;14:149–53. [26] Naphon P. Study on the exergy loss of the horizontal concentric micro-fin tube heat exchanger. Int Commun Heat Mass Transfer 2011;38:229–35. [27] Wu S-Y, Yuan X-F, Li Y-R, Xiao L. Exergy transfer effectiveness on heat exchanger for finite pressure drop. Energy 2007;32:2110–20. [28] Khandekar S. Thermo-hydrodynamics of closed loop pulsating heat pipes. Stuttgart: Universitätsbibliothek der Universität Stuttgart; 2004. [29] Auracher H. Thermal design and optimization: Adrian Bejan, George Tsatsaronis and Michael Moran John Wiley & Sons, Inc. (1996) 542 pp., $64.95, ISBN 0-471-58467-3. Int J Refrig 1996;19:482. [30] Rosen IDMA. EXERGY: Energy, Environment and Sustainable Development. Oxford: Elsevier; 2012. [31] Abd El-Baky MA, Mohamed MM. Heat pipe heat exchanger for heat recovery in air conditioning. Appl Therm Eng 2007;27:795–801. [32] Pandey SD, Nema VK. An experimental investigation of exergy loss reduction in corrugated plate heat exchanger. Energy 2011;36:2997–3001.