Evaporator Section Research Articles

Effect of length ratios on the cooling performance of an inclined two-phase closed thermosyphon under negative temperature conditions

Two-phase closed thermosyphons (TPCTs) have been widely used in solar energy utilization. The work presents an optimization of the TPCT used in cooling foundation in permafrost regions. A series of experiments under negative temperature conditions were conducted to investigate the effect of length ratios (LRs, length ratio of the evaporator section to the condenser section) on the cooling performance of the TPCT. Experimental results show that there exists a best LR for each angle, and it varies with the inclination angle. As an example, for the TPCT with 5.0-cm inner diameter, the maximum efficiency can be decreased by 17.3% for the TPCT with the LR of 1.00 compared with the TPCT with the best LR of 1.65. Under the best LR, the efficiency can be raised by 30.2% for the TPCT with the inclination angle of 20° compared with that of 90°. Besides, the best LR also changes with the pipe inner diameter, e.g. the best LR varies from 1.65 to 1.27 when the inner diameter changed from 5.0 cm to 8.1 cm. The results suggest that the equivalent length of the evaporator section should be appropriately lengthened to enhance the cooling performance of TPCTs in permafrost engineering.

Resource-saving thermodynamic cycles in liquid hydrocarbon fuel storage technology

Resource-saving thermodynamic cycles for material and energy flows in the technology of storing liquid hydrocarbon fuel in tanks using a vapor compression heat pump are proposed, which reduce the loss of fuel resulting from evaporation. The heat pump is equipped with a two-section evaporator, the working and reserve sections of which alternately operate in condensation and regeneration modes, respectively. Vapors of hydrocarbon fuel from the tank are discharged to the evaporator section operating in condensation mode. The water contained in the fuel vapor condenses on the heat ex-change surface in the form of an ice crust, and the condensed fuel separated from the water is discharged into an interme-diate tank and returned to the storage tank. The condensation heat of the refrigerant in the condenser is used to heat the intermediate coolant, which is sent to defrost the section of the evaporator operating in the regeneration mode. After this section, the spent intermediate coolant is returned to the condenser in the closed thermodynamic cycle mode. The water formed during defrosting is sent to the biological treatment stage. Thus, real conditions are created for increasing the ener-gy efficiency and environmental safety of the technology for storing liquid hydrocarbon fuel in tanks with maximum con-densation of the vapors resulting from evaporation.

Experimental investigation on the thermal performance of air-cooled multi-port flat heat pipes

An experimental investigation is conducted to study the effect of the type of working fluid, liquid filling ratio (FR) and the cooling and heating conditions on the performance of air-cooled multi-port flat heat pipes (AMFHPs) designed for the thermal management of power battery. The results show that, under the same FR of 50%,the ammonia AMFHP owns the highest thermal performance, whose equivalent thermal conductivity is 2.21–3.30 times that of one filled with acetone and 1.05–1.31 times that of one using R134a as working substance. Evaporation thermal resistance of acetone AMFHP is significantly larger than those of the AMFHPs filled with ammonia and R134a, whereas their condensation thermal resistance values are comparative. Secondly, it is found that the equivalent thermal conductivity of the R134a AMFHP with 50% FR is 1.63–2.22 times that of one with 30% FR and 1.14–1.63 times that of one with 70% FR, respectively. Thirdly, result indicates that the effect of cooling air velocity on the equivalent thermal conductivity of AMFHP is insignificant, but the temperature of evaporation section is tightly connected to the cooling air velocity. There exists an economic air velocity for each AMFHP, the appropriate air velocities of the AMFHPs filled with R134a, acetone and ammonia at FR=50% are 3.5 m/s, 2.5 m/s and 3.5 m/s, respectively. In addition, analysis of heat transfer reveals that, the intensity of heat transfer mode of the AMFHPs in liquid pool ranges from R134a, ammonia and acetone, under the same working condition and filling ratio. The most direct conclusion is that the R134a AMFHP with appropriate FR is suitable to meet the thermal management requirements of lithium ion batteries for electric vehicles.

Thermal performance enhancement of air-cooled proton exchange membrane fuel cells by vapor chambers

In this study, five vapor chambers as heat spreaders are integrated into a 10-cell air-cooled proton exchange membrane fuel cell stack to improve the thermal management of the stack. The evaporation sections of the vapor chambers are embedded in the stack, while the condensation sections are exposed to the environment to release the heat generated in the stack. A series of experiments are performed, and the relevant thermal performance parameters are compared under different operating conditions. The experimental results show that the vapor chambers can enhance the heat transfer and homogenize the temperature within the stack. The maximum temperature difference between the cells at 0.64 A/cm2 is only 5.3 °C, and the temperature gradient within the active area is less than 1.5 °C. The results also indicate that the cooling conditions of the condensation sections of the vapor chambers and the air flow rate in the cathode channels have important effects on the thermal performance of the stack. Under proper cooling conditions, the vapor chambers can remove almost half of the heat in the stack. The results of this study demonstrate the feasibility of applying vapor chambers to the thermal management of small-sized air-cooled proton exchange membrane fuel cells.

Enhanced thermal performance of a thermosyphon for waste heat recovery: Microporous coating at evaporator and hydrophobic coating at condenser

An enhanced two-phase closed thermosyphon (TPCT) was experimentally investigated for waste heat recovery in heat pipe heat exchanger, which was capable with two different surface coatings: a microporous coating at the evaporator and a hydrophobic coating at the condenser. The TPCT was made of a copper pipe with an inner diameter of 25 mm and was comprised of three sections: evaporator, adiabatic, and condenser sections, which were 300, 300, and 325 mm long, respectively. Distilled water was used as the working fluid and the filling ratio was varied between 0.25 and 1.0, at four inclination angles; 90° (vertical), 60°, 45°, and 15°. The microporous structures of the evaporator section were coated using a sintering process, and the hydrophobic coating at the condenser section was formed by the electrostatic spraying of a perfluoroalkoxy alkane (PFA) resin. From the comparison of the overall thermal resistances of bare and coated TPCTs, it is concluded that the effect of the microporous coating was largest with a low filling ratio and the effect of the hydrophobic coating was largest with a high filling ratio. When both the evaporator and condenser were coated, the TPCT exhibited a maximum enhancement of 100% (filling ratio = 0.25) at a heat flux of 50 kW/m2 and an average 61% enhancement at a heat flux of 100 kW/m2, compared with the TPCT with bare surfaces.

Experimental investigation on the heat transfer performance and evaporation temperature fluctuation of a new-type metal foam multichannel heat pipe

Recent electronic industry developments require a variety of compact and high-performance heat sinks for the heat dissipation of electronic devices. In this paper, on the basis of a new type of heat pipe called the metal foam multichannel heat pipe (metal foam MCHP) proposed by our team, an experimental apparatus on its heat transfer characteristics was built. The heat transfer characteristics of the metal foam MCHP with the distilled water as the working fluid were experimentally investigated in a heat flux range of (18750-112500) W/m2, a filling ratio range of 0.1–0.6 and single-sided/double-sided heating modes. The experimental results showed that the working fluid could flow up and down in the metal foam MCHP, and thus the heat was transferred from the evaporation section to the condensation section during the operation. The thermal resistance of the metal foam MCHP decreased with the increase of the heat flux. When the heat flux was up to 112500 W/m2, the thermal resistance decreased to 0.142 °C/W. The optimal filling ratio of the metal foam MCHP charging with the distilled water was 0.2. During the experiment, the temperature fluctuations of each measuring point in the evaporation section were almost within 2 °C and the temperature differences of different measuring points in the evaporation section were within 8 °C. The thermal resistances of the metal foam MCHP under the single-side heating mode and the double-sided heating mode were compared, and the thermal resistance of the metal foam MCHP was found to be higher under the single-sided heating mode. In addition, compared with the traditional PHPs, the metal foam MCHP showed better heat transfer performance and better stability and uniformity of the evaporation temperature.

Performance Analysis of a Heat Pipe with Stainless Steel Wick

In this study, the influences of different parameters on performance of a heat pipe with stainless steel net as wick have been presented. Experiments have been carried out for an input power range from 80 W to 160 W, constant cooling water mass flow rate of 0.0515 liter/s, and constant temperature at the inlet to condenser of 11°C. The temperatures were recorded at different power level by using a laser thermometer of the heater block, evaporator and condenser end at 50 second interval. Variation in the input power was done by varying the input voltage. It was done by a variack. Considering all criteria the copper is selected as the material of the container, water is selected as the working fluid of the heat pipe, stainless steel net is used as wick material. As copper/water heat pipes are able to tolerate storage temperatures between -65°C and 250°C, and can effectively operate between 10°C and 250°C. So a .9144 m copper tube is used to construct the heat pipe. Inside this tube stainless steel net is used as wick material to aid the flow of fluid. In the observation it is observed that the temperature of the evaporator end increases at a greater rate of the copper pipe than the heat pipe at different power level. It has been shown the variation of temperature of the heater block and the evaporator section at 80V, 100V, 120V, 140V, 160V respectively of the heat pipe and copper pipe.

Heat Leakage Numerical Investigation of a Compound Parabolic Concentrator-Pulsating Heat Pipe Solar Collector

As a new type of equipment for solar medium temperature utilization, the compound parabolic concentrator-pulsating heat pipe solar collector (CPC-PHPSC) uses pulsating heat pipe (PHP) as an endotherm, which can realize efficient energy conversion. The design of proper concentration ratio of compound parabolic concentrator (CPC) ensures that the incident sunlight can be concentrated on the evaporator section surface of PHP without solar tracking system. The objective of the present work is to study the influence of solar radiation intensity, air speed, material thickness (glass and insulation board) and tilt angle on the thermal performance of the new collector, which is difficult to control in the experiment. The heat leakage process and characteristics of the CPC-PHPSC were numerically studied by establishing a 3D numerical model of the collector unit. The results show that the theoretical collector efficiency of CPC-PHPSC reaches 74.5%, which is consistent with the experimental results. During operation, the heat collection performance is the best when the tilt angle is 45° and the solar radiation intensity is 1000 W/m2, while the excessive air speed will increase the convective heat loss. Increasing the thickness of insulation board and glass has little effect on the collector efficiency.

Effect of non-condensable gas on thermal characteristics in two-phase closed thermosyphon

With the development of building energy saving technology, low-temperature two-phase closed thermosyphon (TPCT) will be widely used in building energy supply and storage. However, the non-condensable gas (NCG) can affect the performance of TPCT. In this paper, experiment, theoretical heat transfer model and CFD simulation model have been established to comprehensive analyze the operation performance of the TPCT with NCG (NTPCT). The research contents include the variation of TPCT wall temperature, heat transfer efficiency (η), thermal resistance (R) and NCG phase distribution. Experimental results showed that the temperature difference between the evaporator and condenser sections of the NTPCT was greater than that of the TPCT in the steady state, resulting in RexpNTPCT being higher than RexpTPCT, and the difference was widening with the decrease of input temperature (Tb), leading to serious adverse impact on heat transfer. When Tb was higher than 60 °C, the ηtheory difference with different mass of NCG (XNCG=0.0418%~0.0746%) was small, but when Tb was low, the difference became larger, and even whenTb = 27 °C, theηtheory = 44.02% forXNCG = 0.0418%, andηtheory = 0.04% forXNCG = 0.0746%, i.e., the heat pipe failed to work. In addition, with the decrease of inclination angle, NCG diffused downward and occupied more and more length of the condenser section, resulting in worse and worse heat transfer performance.

A comparative experimental investigation on thermal performance for two types of vacuum tube solar air collectors based on flat micro-heat pipe arrays (FMHPA)

Two types of solar air collectors (SACs), namely, a conventional-tube collector (C-TC) and a transparent-tube collector (T-TC), are designed on the basis of flat micro-heat pipe arrays (FMHPA) and are compared. FMHPA is used as the core heat transfer element for both collectors. Absorption coatings are located at different places. It is located at, namely, on the inner wall of vacuum tube and on the FMHPA evaporation section in the C-TC and the T-TC. A large volumetric flow rate of air contributes to high efficiency. Results of the comparative experiment show that even if the thermal efficiency of the C-TC (77.6%) is smaller than that of the T-TC (85.0%), the useful energy of the C-TC (641 W) is larger than that of the T-TC (497 W). Moreover, the COP values of the C-TC and T-TC are 11.4 and 8.9, respectively. The unit initial investments are 0.15 and 0.21 $/W. Hence, considering the heating capability and price advantage, the C-TC is a better collector form than the T-TC in the same collector gross area. The collector pressure drop does not exceed 19.1 Pa. These results can serve as a reference for the selection and design of SACs for heating applications and crop drying.

Outdoor testing of an evacuated tube closed two phase thermosyphon solar water heater charged with Nano-fluid

This paper reports the performance of two types of evacuated tube heat pipe solar water heater systems that have been experimented outdoors under the local meteorological conditions of the capital of Iraq. Tests were conducted using two systems made of the same materials but with different design specifications. To build each of the two trail system, a single evacuated tube to two phase thermosyphon is used to make the investigation of the experiments simpler. With the absence of loading conditions, experiments with the first system were conducted. Graphene water Nano-fluid (GW) was used as the working fluid in this system. The water storage tank system capacity was varied, to analyze the performance for different storage capacity. The system was operated with a flat reflector plate and without this reflector. A modified second system was built with a longer evaporator section for higher performance and with tank that enables hot water removed from it. The hot water from the storage tank was withdrawn intermittently and continuously. Graphene water (GW), Graphene acetone( GA) and distilled wate( d-W) were used as the working fluids in this second system. Energy stored at the water storage tank and overall efficiencies were calculated and found to be comparable to those obtained using natural circulation solar water heating systems. A comparison between the obtained Results and other works was made. The comparison showed that the present systems were just as good in performance. An improvement in the overall efficiency was found when operating the system under load conditions. This improved value is about 10% higher than that without load condition.

Finding the Thermal Characteristics of a Heat Pipe using Hybrid Nano Fluid

In this experiment, work was carried out to infer the thermal characteristics of a heat pipe containing nano fluid inside in it. Various Parameters were considered in this experiment, some of them are inlet temperature at one end, mass flow rate (mfr) to evaporator section and inclination angle of heat pipe. In this work three numbers of heat pipes were used and hybrid nanofluid of Al2O3 – TiO2 has been used as cooling fluid in all three heat pipes. The thermal efficiency of the usage of hybrid nanofluidic working system is found to be highest and also this makes the system to get worse in terms of thermal resistance. The flow rate of condenser section was modified to the various ratios from 1:1 to 1:3 as that of evaporator section. To find the thermal characteristics of the heat pipe, many experiments have been carried out by considering many operating conditions. Evaluation on the heat pipe effectiveness was made on basis of gravity assistance to the condenser. The better productiveness of heat pipe when using the hybrid nanofluid has attained when Ch/Cc = 2 and 100 LPH for all operating conditions.

Effect of Pure and Binary Fluids on Thermal Performance of Closed Loop Pulsating Heat Pipe

Pulsating heat pipe is the raising methodology of cooling systems in many areas. CLPHP is a passive mode of phase change heat transfer device having potential to transfer heat from source to sink in less span. Heat transfer performance of this method is improving day by day as giving less thermal resistance. Number of experimentations are conducting to increase the efficiency of pulsating heat pipes in many aspects i.e. varying lengths, working fluids, number of turns, different fill ratios, heat inputs and orientation. As taking part of these research a five turn closed loop pulsating heat pipe (of tube inner diameter 2mm, outer diameter 3mm; adiabatic section length 170mm, condensation section length is50mm, evaporation section length is 42mm) working with pure and binary fluids (water-acetone, water-ethanol) compared with water, Acetone, Ethanol with heat inputs 20w, 40w, 60w, 80w, and fill ratio 50%, also the orientations are horizontal and vertical. The analysis from the results obtained was the thermal resistance of all working fluids is drastically diminishing from 20w to 40w heat input and slowly from 40w to 80w.

Experimental and Simulation Study of Micro-Channel Backplane Heat Pipe Air Conditioning System in Data Center

This paper mainly studies the heat transfer performance of backplane micro-channel heat pipes by establishing a steady-state numerical model. Compared with the experimental data, the heat transfer characteristics under different structure parameters and operating parameters were studied, and the change of heat transfer coefficient inside the system, the air outlet temperature of the back plate and the influence of different environmental factors on the heat transfer performance of the system were analyzed. The results show that the overall error between simulation results and experimental data is less than 10%. In the range of the optimal filling rate (FR = 64.40%–73.60%), the outlet temperature at the lowest point and the highest point of the evaporation section is 22.46 °C and 19.60 °C, the temperature difference does not exceed 3 °C, and the distribution gradient in vertical height is small and the air outlet temperature is uniform. The heat transfer coefficient between the evaporator and the condenser is larger than the heat transfer coefficient under the conditions of low and high liquid charge rate. It increases gradually along the flow direction, and decreases gradually with the flow rate of the condenser. When the width of the flat tube of the evaporator increases from 20 mm to 28 mm, the internal pressure drop of the evaporator decreases by 45.83% and the heat exchange increases by 18.34%. When the number of evaporator slices increases from 16 to 24, the heat transfer increases first and then decreases, with an overall decrease of 2.86% and an increase of 87.67% in the internal pressure drop of the evaporator. The inclination angle of the corrugation changes from 30° to 60°, and the heat transfer capacity and pressure drop increase. After the inclination angle is greater than 60°, the heat transfer capacity and resistance decrease. The results are of great significance to system optimization design and engineering practical application.

Numerical simulation of oscillatory flow and heat transfer in pulsating heat pipes with multi-turns using OpenFOAM

The oscillatory flow and the heat transfer in two-dimensional pulsating heat pipes (PHPs) with multi-turns were simulated using OpenFOAM. The volume of fluid method was used for the phase change, and the behavior of the working fluid was achieved by considering the mass transfer balance between the evaporation and the condensation. Ethanol was used as the working fluid, and the liquid phase and the vapor phase were assumed to be incompressible. The result revealed that the temperature variation curves did not converge to one pattern according to the number of grids in the symmetric shape of the PHP because the starting time of the working fluid circulation was different. In the PHP with the asymmetric shape, the circulation started earlier than in the PHP with symmetric shape. When the bond number was 0, which means being in zero gravity, the working fluid dried out in the evaporator section of the PHPs with 5 and 10 turns. However, the working fluid still remained in the PHPs with 15 and 20 turns. The numerical analysis performed in this article is expected to help to simulate the flow phenomenon in PHP.

Investigation of Start-Up Characteristics of Thermosyphons Modified with Different Hydrophilic and Hydrophobic Inner Surfaces

In this paper, the influence of wettability properties on the start-up characteristics of two-phase closed thermosyphons (TPCTs) is investigated. Chemical coating and etching techniques are performed to prepare the surfaces with different wettabilities that is quantified in the form of the contact angle (CA). The 12 TPCTs are processed including the same CA and a different CA combination on the inner surfaces inside both the evaporator and the condenser sections. For TPCTs with the same wettability properties, the introduction of hydrophilic properties inside the evaporator section not only significantly reduces the start-up time but also decreases the start-up temperature. For example, the start-up time of a TPCT with CA = 28° at 40 W, 60 W and 80 W is 46%, 50% and 55% shorter than that of a TPCT with a smooth surface and the wall superheat degrees is 55%, 39% and 28% lower, respectively. For TPCTs with combined hydrophilic and hydrophobic properties, the start-up time spent on the evaporator section with hydrophilic properties is shorter than that of the hydrophobic evaporator section and the smaller CA on the condenser section shows better results. The start-up time of a TPCT with CA = 28° on the evaporator section and CA = 105° on the condenser section has the best start-up process at 40 W, 60 W and 80 W which is 14%, 22% and 26% shorter than that of a TPCT with smooth surface. Thus, the hydrophilic and hydrophobic modifications play a significant role in promoting the start-up process of a TPCT.

A comparative empirical investigation on the thermal performance of gravity-assisted double-bent, double-ended cooling, and single-bent, single-ended cooling heat pipes

Abstract Using of heat pipes is one of the best practical solutions that are considered for cooling processors and heat sources. A comparative study on the thermal performance of gravity-assisted double-bent, double ended cooling (DBDC) and single-bent, single-ended cooling (SBSC) heat pipes having sintered copper felt wick was proposed and evaluated experimentally. The DBDC and SBSC heat pipes are bendable post fabrication. Cooling blocks were elevated upper than the evaporator section of the heat pipes. The effects of heat input, bending angle, and using double condenser on the thermal performance were evaluated. The results showed that the minimum evaporator surface temperature for the DBDC and SBSC heat pipes occurred in the 60° and 45° bending angles respectively. Also the evaporator surface temperature of the DBDC heat pipes was less than SBSC heat pipes for bending angles lower than 60° while for bending angles more than 60° it was vice versa. The results indicated that the bending angle had a significant effect on the heat pipe's thermal performance. The minimum thermal resistance and maximum Nusselt number witnessed were 0.23857 °C/W and 7.51 × 105 respectively for DBDC heat pipe at the 60° bending angle, for the 70 W and 80 W heat inputs.

Self-driven Liquid Metal Mollusk Oscillations

Abstract Room temperature liquid metal (galinstan, made up of gallium, indium and tin) is driven to oscillate by the phase change of water in the self-excited oscillating heat pipe (OHP) charged with liquid metal and water. The cross section of the channel is square with the dimension of 3×3 mm2. Liquid metal is a high-performance coolant with ultrahigh thermal conductivity (nearly 27 times higher than water). During the operation of OHP, liquid metal is pushed up by the vapor expansion in the evaporator section, and moves back by the vapor contraction and gravity effects. Then, liquid metal is driven to oscillate continuously between evaporator and condenser in the OHP. Surface tension of galinstan is 10 times higher than water, resulting in a ball shape of liquid metal in the channels. And there is a thin water film existing between liquid metal and inner surface. During the oscillating motion, liquid metal presents the characteristics of a mollusk. Soft liquid metal is extended into metal filament, or breaks up into small liquid metal balls. Then, small liquid metal balls coalesce into a long liquid metal slug, resulting in surface waves due to the released surface energy during the coalescence process. The deformation and deformation recovery of the liquid metal is the result of competition between deforming pressure forces and the reforming surface tension forces. Oscillations of liquid metal will generate flow field disturbance in the base fluid of water and further enhance the heat transfer performance in two-phase flow systems. [This research work was supported by the National Natural Science Foundation of China under Grant No. 21606034 and Office of Naval Research under Grant No. N00014-19-1-2006.]

Experimental investigations of single-slope solar still integrated with a hollow rotating cylinder

The main objective of the current study is to increase the productivity rate of conventional solar still by increasing the surface area of heat transfer in the evaporation section within solar still. Lightweight rotating hollow metal cylinder made of galvanized iron layer (0.06 cm thickness and diameter of 32 cm) with a length of 90 cm was used as evaporation section within the improved single slope solar still. The tests were carried out for 3 months (Jun, July and August) at the Ural Federal University of Yekaterinburg/Russia, the experimental results taken for a perfect day on 12 Jun 2019. The impact of different parameters on the productivity of freshwater has been investigated using the new improved solar still. Study results reveal that environmental factors such as the intensity of solar radiation, ambient temperature, relative humidity and wind speed have the greatest impact on freshwater productivity. The analyses of results show that the ratio of water productivity enhancement found to be about 161% than that of the conventional solar still over the long day period.

A case study on internal flow patterns of the two-phase closed thermosyphon (TPCT)

This study investigates types of two-phase flow patterns that affect the heat transfer rate which occurs within the two - phase closed thermosyphon (TPCT) made of heat-resistant glass tube with inner diameters of 7 and 25.2 mm. Aspect ratio was 5 while the inclination angels were 0°, 80° and 90°, and the evaporator temperature were 50, 70 and 90 °C. Furthermore, the addition rate of chemical reactants was 50% by volume of the evaporator component whilst the water temperature within the condensation unit was maintained at 20 °C. From the experimental results, the TPCT's inner diameter was 7 mm, the inclination angels were at 80° and 90°. There were four types of flow pattern including; bubble flow pattern, slug flow pattern, churn flow pattern and annular flow pattern. Churn flow pattern and the annular flow pattern affected the heat transfer rate of the TPCT with the inner diameter of 7 mm at the inclination angels of 80 and 90° respectively. As for the TPCT test, the inner diameter of 25.2 mm with the inclination angels of 80° resulted in four types of the flow patterns, including the bubble flow pattern, slug flow pattern, churn flow pattern and stratified flow pattern respectively. According to the results, churn and stratified flow patterns, were the types of flow that affected the heat transfer rate. According to the experiment of TPCT with inner diameter of 25.2 mm at the inclination angels of 90°, four flow patterns including the bubble pattern, slug flow pattern, churn flow pattern and the vortex flow pattern were found. The vertex flow pattern was initiated when the temperature of the evaporator section was raised from 70 to 90 °C. According to this experiment, the churn flow and the vortex flow patterns were able to affect the heat transfer rates. Furthermore, the experiment revealed that heat flux that was obtained from the experiments of TPCT with the inner diameter of 7 and 25.2 mm showed the highest heat transfer rate at evaporation temperature of 90 °C and the inclination angels of 80° which were 31.88 and 58.15 W, respectively.