Experimental and Numerical Investigation of Thermosyphon Heat Pipe Performance at Various Inclination Angles

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1 Journa of Adanced Research in Fuid Mechanics and Therma Sciences 44, Issue 1 (2018) Journa of Adanced Research in Fuid Mechanics and Therma Sciences Journa homepage: ISSN: Experimenta and Numerica Inestigation of Thermosyphon Heat Pipe Performance at Various Incination Anges Open Access Baa Abduahi 1,2,, Ahmed E-Sayed 1, Raya Khaid A-Dadah 1, Sa ad Mahmoud 1, Abde Fateh Mahrous 3, Nura Mu az Muhammad 2, Sa idu Beo Abbakar Schoo of Mechanica Engineering, Uniersity of Birmingham, Birmingham, B15-2TT, United Kingdom Mechanica Engineering Department, Kano Uniersity of Science & Technoogy, Wudi, Kano, Nigeria Mechanica Power Engineering Department, Menoufiya Uniersity, 32511, Shebin E-Kom, Egypt ARTICLE INFO Artice history: Receied 9 March 2018 Receied in reised form 6 Apri 2018 Accepted 25 Apri 2018 Aaiabe onine 27 Apri 2018 Keywords: Thermosyphon, Computationa Fuid Dynamics, Incination ange ABSTRACT Interest in the use of heat pipes in soar appications is increasing due to their roe in improing the heat transfer performance of soar coectors. In order to effectiey utiise heat pipes, their performance under arious operating conditions and incination anges need to be inestigated. In this work, numerica and experimenta studies were carried out to inestigate the effects of heat input and incination ange on the wa temperature distributions and therma resistance of thermosyphon heat pipe. A Computationa Fuid Dynamics (CFD) mode was deeoped using ANSYS Fuent to simuate the fow and mass transfer using oume of fuid (VOF) approach together with user - defined function (UDF) to simuate the phase change processes at arious incination anges. Experiments were carried out to aidate the CFD mode at heat inputs of 81.69W and W with temperature distribution resuts showing good agreement of ±4.2% aerage deiation. Aso the predicted therma resistance at different incination anges showed good agreement with the experimenta ones with maximum deiation of ±5.7%. Resuts showed that as the heat input increases, the heat pipe wa temperature increases and the therma resistance decreases. Experimenta and numerica resuts showed that increasing the incination ange wi improe the thermosyphon heat pipe performance to reach its maximum aue at 90o, but this effect decreases as the heat input increases. Copyright 2018 PENERBIT AKADEMIA BARU - A rights resered 1. Introduction Heat pipe is an effectie heat transfer deice inoing simutaneous eaporation and condensation processes. It consists of eaporator and condenser sections with or without adiabatic section in between them. Heat is suppied to the eaporator section where the working fuid eaporates and fows to the condenser section where it condenses to iquid using cooing medium. The condensate returns to the eaporator by capiary effects in case of wicked heat pipe and by graity in case of wickess heat pipe (thermosyphon). Corresponding author. E-mai address: baabduahi@yahoo.com (Baa Abduahi) 85

2 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Heat pipes hae many adantages incuding high heat conduction, ight weight, efficient heat transfer and design fexibiity. Due to these adantages, the technoogy has undergone rapid deeopment in the past decades [1] eading to their appications in spacecraft therma contro [2], heat exchangers [3] and soar energy systems [4, 5]. Thermosyphon heat pipes are highy durabe and cost effectie which make them suitabe for arious appications such as soar heating of buidings [6] and cooing of turbine bades, transformers, eectronics, interna combustion engines and nucear reactors [7, 8]. This is due to their abiity to dissipate and transfer arge amount of energy from sma area without any significant oss. Some appications of thermosyphon require that the pipe be incined to an ange from the horizonta [4, 6, 9, 10]. There are many numerica modes deeoped to simuate the performance of thermosyphon under arious operating conditions, Experimenta and CFD modeing of fow and heat transfer in thermosyphon using oume of fuid (VOF) approach was presented by Asghar et a., [11]. The effects of heat inputs and fi ratio on the performance of the heat pipe were inestigated using 1000mm ong pipe. Resuts showed that the performance of the thermosyphon increases with the increase in heat input between 350W and 500W, but it decreases when the heat input is aboe 500W. Aso for the fi ratios tested; 0.3, 0.5 and 0.8, the best performance was found at the fi ratio of 0.5. A two- phase mode for the fow and heat transfer in a thermosyphon was deeoped by Asmaie et a., [12] by using de ionized water and mixture of copper(ii)oxide with water as working fuid. Temperature distributions on the wa and the heat transfer coefficients of both the eaporator and condenser were predicted. The CFD resuts were aidated with the experimenta resuts reported by Liu et a., [13] and were in good agreement especiay at the adiabatic and condenser sections. The effects of working fuid type, concentration of nanofuid and inet heat fux were inestigated and resuts reported showed that the wa temperature of the pipe decreases with increase of the concentration of nanofuid. Aso the maximum heat fux of the nanofuid was found to be 46% higher than that of the water. A three dimensiona CFD mode to simuate the fow boiing process of hydrocarbon feedstock heat exchanger of a steam cracker was deeoped by De Schepper et a., [14]. VOF together with user defined function (UDF) were used in modeing the conection section of the cracker. Aso the authors proposed correations for the interphase mass source term used in the goerning equations for simuating the eaporation and boiing phenomena in the cracking furnace. CFD mode using VOF together with UDF was buit to simuate the fow and heat transfer in a two phase cosed thermosyphon by Fadh et a., [15]. The temperature profies obtained from the simuation was in agreement with the experiment at high heat input ranging from to W. But there is arge deiation between the experimenta therma resistances and the simuation especiay at the ow heat inputs around 60% at W. It can be seen that a the reported CFD simuation of thermosyphon heat pipes were carried out with the pipe in ertica orientation, hence none of them consider the situation when it is incined. Aso ANSYS software has argey been used in simuating heat transfer processes in different channes such as in turbuent circuar pipe [16], circuar channe with constant heat fux [17] and in rectanguar microchanne heat sink [18]. Howeer, considerabe experimenta research works were pubished on the inestigation of the effects of parameters ike the geometry, working fuid, fi factor and incination on the thermosyphon heat pipe performance [19-23]. Regarding the effect of incination ange on heat pipe performance, conficting resuts were reported ike anges between 15 o and 60 o [22], between 40 o and 45 o [23] and 60 o [24] gae the best performance. Others reported higher anges ike 90 o [25] and 83 o [26] as the best performing anges whie some reported that incination ange has no 86

3 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) effect [27]. Various appications ike soar systems require the use of heat pipes in incined positions from the horizonta which makes the inestigation of the incination ange on heat pipe performance of paramount importance. With the contradictory experimenta resuts in the iterature and the ack of any numerica studies on the effect of incination, this work aims to address these issues by deeoping a CFD mode that takes into account the effect of incination anges (10 o to 90 o ) and experimentay aidated the modeing. Hence, this research coses the gap of the effects of the incination ange of a thermosyphon on its performance and the therma resistance. This wi eads to the seection of best incination ange for an improed performance of the system. 2. Methodoogy Figure 1 shows the experimenta test faciity consisting of a two phase cosed thermosyphon heat pipe heated eectricay at the eaporator section and water cooed at the condenser section. The thermosyphon used is a 400mm ong, 22mm outer diameter, 0.9mm thick cosed copper tube with water as the working fuid (0.65 fi ratio). It has 200mm ong eaporator, 200mm ong condenser and no adiabatic section. Uniformy wrapped eectrica wire was used to heat the eaporator section using TSx1820P Programmabe DC PSU 18V/20A power reguator with accuracy of ± (0.5% + 1 digit) for the current. The otage was measured using a digita mutimeter from Mastech (MAS 343) of 3 3/4 digita dispay and maximum accounts of 3999 (AC otage 400V ± 0.5%) which was connected cose to the pipe to account for otage drop. The eaporator section is insuated with 25mm thick pipe insuator to reduce the heat osses to the ambient. The condenser section was cooed using water jacket. The cooing water fow rate was controed by a ae and measured using an Omega FLR1009ST-I fow meter ( ml/min) with measurement uncertainty of ±2.09% of fu scae. Six thermocoupes were paced at different ocations on the pipe; four and two on the eaporator and condenser sections respectiey to measure the wa temperatures. Three thermocoupes were used on the water jacket and one on the insuation surface to measure the effectieness of the insuation. Two probe thermocoupes were used to measure inet and outet temperatures of the cooing water in the condenser section. The readings were ogged using Pico TC - 08 data oggers connected to a PC. Seen different heat inputs ranging from 20W to 110W were used with an aerage fow rate of kg/s for the thermosyphon at the ertica position. The aues of the heat inputs were obtained from optica simuations on different geometries of compound paraboic concentrators [28, 29]. The power input to the eaporator is cacuated from the product of the current, I and otage, V suppied thus Q in = VI (1) The effectieness of the performance of thermosyphon is determined by its oera therma resistance, R th gien by R th Tae T = Q in ac (2) 87

4 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) where Taeand T ac are the aerage temperatures on the eaporator and the condenser respectiey and Q in is the heat suppied. The performance of the thermosyphon can aso be eauated in terms of the rate of heat transfer to the cooing water as [11] Q η = out Q in (3) The rate of heat transfer to the cooing water can be determined by Q out =. mc p ( T T ) out in. where mis the mass fow rate, kg/s and Cpis the specific heat capacity of water, kj/kg-k. Whie T in and T out are the aerage inet and outet cooing water temperatures respectiey. (4) Fig. 1. Schematic diagram of the experimenta test rig for thermosyphon characterization Figure 2 shows the performance of the thermosyphon aigned erticay at different heat inputs. It can be seen from such figure that the performance of the pipe increases as the heat inputs increases from 20 to 81.69W, but it tends to decrease as more heat is suppied showing the imit of this pipe has been reached under these operating conditions. At ow heat input, the apour generated from the eaporator section is sma, so there wi be significant dry areas in the condenser section; hence heat transfer is argey by free conection. As the heat is graduay increased, more apours wi rise to the condenser section, there wi be high condensation rate on the condenser wa and the dominant heat transfer mechanism wi be condensation. But at certain high heat input, thick ayer of iquid can be formed on the wa of the pipe causing high therma resistance and hence ower the heat transfer to the cooing water, hence reduction of performance. 88

5 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Fig. 2. Performance of thermosyphon aigned erticay at different heat inputs Figure 3 shows the eaporator and condenser wa temperatures respectiey. It can be seen that the temperature distribution is amost uniform for each heat input and this is due to the constant temperature phase change process taking pace in the eaporator section (Figure 3 (eft)). But on the condenser section, there is rise in the temperature at the top of the condenser which is due to the rise of the saturated steam to the top of the tube and the formation of iquid fim ayer on the pipe wa. The thickness of this ayer increases downward hence creating more resistance at the ower tube part which reduces the wa temperature compared to the top section. It can aso be deduced from the figures that there is gradua increase in the wa temperature as the heat input increases up to certain aue when the performance imit of the pipe is reached. It can be seen that at the condenser section, the temperature of the 109W is higher than that of 101W showing that ess energy is transferred to the cooing water when the pipe reaches its operation imit as shown in Figure 2. Fig. 3 Experimenta temperature distributions on the eaporator and condenser sections of the thermosyphon, (eft) Eaporator section, (right) Condenser section Three different heat inputs; 31.18, and W at constant aerage cooing water fow rate of kg/s were used in experimenta inestigation of the effects of incining the thermosyphon heat pipe reatie to the horizonta (10 to 90 o ). Figure 4 shows the ariation of the performance of the thermosyphon with the incination anges at different heat inputs. It can be deduced from the figure that the heat transfer to the cooing water increases with the increase in the incination in a the cases making 90 o the best. But the effects is more pronounced at sma 89

6 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) heat input giing enhancement from 10 o to 90 o of 17.8%, 13.9% and 3.4% for 31.18W, 51.7W and 109W respectiey. The effect of the incination anges on the thermosyphon performance is caused by the graitationa force effects on the two-phase fow patterns, return of the condensate to the eaporator and the conectie heat transfer coefficient. The resuts shown in Figure 4 indicate that the incination ange has an effect on the performance of the thermosyphon heat pipe, but this effect decreases as the heat input increases. 3. CFD Modeing Fig. 4. Variation of the thermosyphon performance with incination ange at different heat inputs The aim of this section is to carry out a CFD anaysis on the fow and heat transfer characteristics of a thermosyphon in both ertica and incined orientations using VOF approach in ANSYSFLUENT VOF is one of the modes aaiabe in ANSYSFLUENT which is used for modeing two or more immiscibe fuids by soing a singe set of momentum equations and tracking the oume fraction of each fuid in the computationa ce throughout the domain. The motion of the working fuid inside a thermosyphon is described by continuity, momentum and energy equations. The continuity equation of the VOF for the secondary phase () is described as [30]. α ρ u = + t ( α ρ ) Sm (5) S m, is the source term, used in the cacuation of the mass transfer during eaporation and condensation. But for the primary phase, the continuity equation can be soed based on the constraint beow n = 1 α = 1 (6) The energy equation is shared among the primary and secondary phases and is expressed as [30]: 90

7 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) t ( ρe) +. ( ρe + p) =. ( keff T ) + S E (7) S E, is the energy source term for cacuating the heat transfer during eaporation and condensation. The momentum equation for the VOF can be written as [31] ( ρ) t where +. ρ = p + µ + u 2 µ. I + ρg + 3 F (8) ρ = α ρ + α ρ (9) k = α k + α k (10) µ = α + µ α µ α ρ E + α ρ E E = α ρ + α ρ (11) (12) E E ( T T ) = C p, sat (13) ( T T ) = C p, sat (14) F acts as the source term in the momentum equation gien by [31] F = σ α ρk α + α ρk α 0.5 ( ρ + ρ ) (15) where σ, is the surface tension between the iquid and the apour and k is the surface curature. A user-defined function (UDF) is used for cacuating the mass and heat transfer between the iquid and apour associated with the phase change processes. Both eaporation and condensation processes require two mass source terms for the iquid and apour phases whie heat transfer requires ony one source term for the phases during eaporation and condensation. Mass and energy source terms in the continuity and energy equations respectiey are defined in the UDF and inked to the FLUENT goerning equations. Correations proposed by De Schepper et a., [14] for source terms are used in this work to cacuate the mass and energy transfer as shown in Tabe 1. 91

8 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Tabe 1 Correations for mass and energy source terms [14] Energy Phase change Temperature State Correation Mass Eaporation T m T sat Liquid Tm Tsat Sm = 0.1ρ α Tsat Vapour Tm Tsat Sm = 0.1ρα Tsat Condensation T m T sat Liquid Tsat Tm Sm = 0.1ρ α Tsat Tsat T Vapour Sm = 0.1ρ α T Heat transfer Eaporation Condensation T m T sat T m T sat S S E E Tm T = 0.1ρα T sat Tsat T = 0.1ρ α T sat m sat LH LH sat m 3.1 Mode Description and Vaidation A 2D geometry of the 400mm ong thermosyphon used in the experiment was deeoped in Gambit software to simuate the fow and heat transfer in the pipe using VOF approach. The simuation was carried out using COUPLED scheme for the pressure eocity couping, first order upwind for the momentum, oume fraction and energy whie first order impicit is used for the transient formuation. The soution is considered to be conerged when the residua scaes of mass and eocity is beow The graity was taken as 9.81 m/s 2 in the y- axis for the ertica orientation cases. For the incined heat pipe simuation, the graitationa force was determined on both x and y axes for each ange according to Figure 5 and the equations were updated in ANSYSFLUENT. Fig. 5. Forces on an incined thermosyphon heat pipe Water-apour and water-iquid are considered as primary and secondary phases respectiey and phase interaction is defined in the surface tension force modeing using poynomia function of temperature (eq. 16) as deried using data from the steam tabe [15]. 92

9 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) σ = x10 T 2.3x10 T (16) where σ, is the surface tension between the iquid and the apour and T is the temperature shared by the phases. The boiing temperature of 373K was considered at which the phase change occurred. The atent heat of 2455 kj/kg was used in the UDF and the saturation temperature was taken as the aerage of the eaporator and condenser temperatures for each case as obtained from the experiment. Cacuations were carried out with the time step size of sec and number of time step between 120,000 and 180,000 depending on when the soution reaches a steady state (usuay between 60 and 90 seconds). Grid independence test was conducted by generating three different mesh sizes of 23,998, 38,278 and 120,794 ces in Gambit software and their properties are shown in Tabe 2. Temperature distributions aong the wa of the pipe were monitored and shown in Figure 6 to test the grid independence of the resuts. The resuts show amost the same temperature distributions aong the wa of the pipe for the mesh sizes of 38,278 and 120,794 ces. To reduce the computationa time, the mesh size of 38,278 Quad, Map ces was used in the simuation of this work. Figure 7 shows the apour oume fraction in the eaporator section indicating gradua generation of bubbes at different computationa time. The top section (red coour) shows the presence of ony apour with oume fraction of one. Beow such region there is mixture of apour and iquid with bue coour indicating the iquid which has apour oume fraction of zero. The iquid in the eaporator section is first heated and eaporation occurs when it reaches the boiing point eading to the bubbes generation which moe to the condenser section. The apour is condensed on the wa of the condenser due to the cooing appied to such wa and transport back to the eaporator section for the next cyce. The boiing temperature of 373K was considered at which the phase change occurred. The atent heat of 2455 kj/kg was used in the UDF and the saturation temperature was taken as the aerage of the eaporator and condenser temperatures for each case as obtained from the experiment. Cacuations were carried out with the time step size of sec and number of time step between 120,000 and 180,000 depending on when the soution reaches a steady state (usuay between 60 and 90 seconds). Grid independence test was conducted by generating three different mesh sizes of 23,998, 38,278 and 120,794 ces in Gambit software and their properties are shown in Tabe 2. Temperature distributions aong the wa of the pipe were monitored and shown in Figure 6 to test the grid independence of the resuts. The resuts show amost the same temperature distributions aong the wa of the pipe for the mesh sizes of 38,278 and 120,794 ces. To reduce the computationa time, the mesh size of 38,278 Quad, Map ces was used in the simuation of this work. Figure 7 shows the apour oume fraction in the eaporator section indicating gradua generation of bubbes at different computationa time. The top section (red coour) shows the presence of ony apour with oume fraction of one. Beow such region there is mixture of apour and iquid with bue coour indicating the iquid which has apour oume fraction of zero. The iquid in the eaporator section is first heated and eaporation occurs when it reaches the boiing point eading to the bubbes generation which moe to the condenser section. The apour is condensed on the wa of the condenser due to the cooing appied to such wa and transport back to the eaporator section for the next cyce. 93

10 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Tabe 2 Mesh information Mesh information Run 2 Run 7 Run 8 Ces 23,988 38, ,794 Faces 47,463 75, ,893 Nodes 23,474 37, ,098 Ce zone Face zone Fig. 6 Temperature distributions aong the ength of the thermosyphon for different mesh sizes Fig. 7. Contours of apour oume fraction at different computationa time 94

11 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) The simuation was carried out at fie different aues of heat inputs of 39.5, 60.2, 81.7, and W appied to the eaporator section for the thermosyphon at the ertica position. Whie constant aerage heat inputs of 51.7W and 109.7W respectiey were used for the incination anges of 50 o to 90 o. Conectie therma condition was appied to the condenser section by specifying the heat transfer coefficient, hcw/m 2 K of the cooing water according to the foowing equation h c = π DL cond Q out ( T T ) cond cw (17) where D and L cond are the pipe diameter and condenser ength respectiey. T cond and T cw are the aerage temperatures on the condenser wa and the cooing water respectiey. A the parameters in equation 17 are obtained from the experiment and used to cacuate the conectie heat transfer coefficient for each case which is used in the ANSYSFLUENT as input. As part of the boundary conditions, the inner wa of the tube is considered as stationary and with no sip condition appied. The CFD predicted temperature distributions on the thermosyphon wa is compared with the experimenta resuts for different heat inputs when the pipe is at ertica position (90 o ) as shown in Figures 8 (a and b). The figure shows good agreement between the simuation and the experimenta resuts for the arious heat inputs with maximum deiation of ±4.2%. Figure 9 shows the ariation of the therma resistances with the seected heat inputs for both CFD and experiment with deiation of ±5.8%. Figures 8 and 9 indicate the aidity of the CFD modeing technique used in this work. Figures 10 (a and b) compare the predicted and measured temperature distributions for different incination anges (50, 70 and 80 o ) and heat inputs of 51.7W and 109.7W with deiation ranging from ±1.2% to ±2.8%. Figure 11 compares the experimenta and predicted therma resistance at different incination anges ranging from 50 to 90 o with heat input of 109.7W. It can be seen from such figure that the owest therma resistance was reached at the 80 o and 90 o incination anges. Fig. 8. Comparison of the experimenta and CFD resuts for different heat inputs at ertica orientation, (eft) Temperature distributions at Q = 81.69W, (right) Temperature distributions at Q = W 95

12 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Fig. 9. Comparison of the predicted oera therma resistance with experiment Fig. 10. Comparison of temperature distributions between experimenta and CFD at different incination anges for two different heat inputs, (eft) Temperature profie for Q = 51.7W, (right) Temperature profie for Q = 109.7W Fig. 11. Comparison of the oera therma resistance between experimenta and CFD resuts 96

13 Journa of Adanced Research in Fuid Mechanics and Therma Sciences Voume 44, Issue 1 (2018) Concusion In the present work, a CFD mode was deeoped to simuate the eaporation and condensation processes in thermosyphon in ertica and incined positions using together with UDF subroutines. For the first time, the effect of the thermosyphon incination ange was incorporated in the modeing of thermosyphon by resoing the graitationa force in x and y axes. Experiments were carried out for wide range of operating conditions to study the effects of the heat input and the incination ange on the thermosyphon performance. The resuts of the experiments were compared with that of the simuation and good agreement was found on the temperature distributions aong the axia ength of the pipe and the therma resistance. Resuts of both CFD and experiments showed that as the heat inputs increases, the wa temperature on both eaporator and condenser section increase, whie the therma resistance decreases. The effect of the incination ange was modeed and the predicted resuts were found to be in good agreement with the experimenta ones. Experimenta and numerica resuts showed that increasing the incination ange wi improe the thermosyphon heat pipe performance to reach its maximum aue at 90o, but this effect decreases as the heat input increases. This work highights that the compex eaporation and condensation processes in the thermosyphon heat pipe were successfuy modeed and can be used to enhance the performance of thermosyphon heat pipes. Acknowedgement The first author acknowedged the financia support receied from Kano Uniersity of Science and Technoogy, Wudi, Kano Nigeria and Tertiary Education Trust Fund (TETFUND), Abuja Nigeria. References [1] Peterson, George P. "An introduction to heat pipes: modeing, testing, and appications." (1994). [2] Reay, Daid, Ryan McGen, and Peter Kew. Heat pipes: theory, design and appications. Butterworth-Heinemann, [3] Vasiie, Leonard L. "Heat pipes in modern heat exchangers." Appied therma engineering 25, no. 1 (2005): [4] Chow, T. T., Wei He, and Jie Ji. "Hybrid photootaic-thermosyphon water heating system for residentia appication." Soar energy 80, no. 3 (2006): [5] Abreu, Samue Luna, and Sergio Coe. "An experimenta study of two-phase cosed thermosyphons for compact soar domestic hot-water systems." Soar Energy 76, no. 1-3 (2004): [6] Pouad, M. E., and Aan Fung. "Potentia benefits from Thermosyphon-PCM (TP) integrated de-sign for buidings appications in Toronto." In Proceedings of esim: the Canadian conference on buiding simuation, pp [7] Hartnett, James P., Thomas F. Irine, George A. Greene, and Young I. Cho. Adances in heat transfer. Vo. 31. Academic press, [8] Japikse, D. "Adances in thermosyphon technoogy." In Adances in Heat Transfer, o. 9, pp Eseier, [9] Chami, Nada, and Assaad Zoughaib. "Modeing natura conection in a pitched thermosyphon system in buiding roofs and experimenta aidation using partice image eocimetry." Energy and Buidings 42, no. 8 (2010): [10] Wongtom, Sompon, and Tanongkiat Kiatsiriroat. "Effect of incined heat transfer rate on thermosyphon heat pipe under sound wae." Asian Journa on Energy and Enironment 10, no. 04 (2009): [11] Aizadehdakhe, Asghar, Masoud Rahimi, and Ammar Abduaziz Asairafi. "CFD modeing of fow and heat transfer in a thermosyphon." Internationa Communications in Heat and Mass Transfer 37, no. 3 (2010): [12] Asmaie, L., M. Haghshenasfard, A. Mehrabani-Zeinabad, and M. Nasr Esfahany. "Therma performance anaysis of nanofuids in a thermosyphon heat pipe using CFD modeing." Heat and Mass Transfer 49, no. 5 (2013): [13] Liu, Zhen-Hua, Yuan-Yang Li, and Ran Bao. "Therma performance of incined grooed heat pipes using nanofuids." Internationa journa of therma sciences 49, no. 9 (2010):

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