Heat Pipe Evaporator Research Articles

Selective laser melting manufacturing and heat transfer performance study of porous wick in loop heat pipe

Porous wicks, characterized by high capillary pumping force, lightweight, and excellent permeability, have been widely used in heat transfer. Currently, porous wicks are fabricated using powder sintering, porous foaming, and solvent volatilization techniques. However, there is the problem that the shape, size, and pore distribution of the porous structure are difficult to control. This paper proposes a novel 3D printing method to fabricate porous wicks using selective laser melting. The unit diameter and length are optimized to obtain a porous wick with high porosity and capillary pumping force. The effect of laser power on the surface morphology and porosity of the porous wick is investigated by modulating the 3D printing process parameters. The results show that the porosity of the porous wick can be regulated by changing the diameter and length of the pore unit. Decreasing the laser processing power and attaching unmelted solid-phase particles to the pore surface can further increase the porosity. When the laser power is 125 W, the unit diameter is 0.4 mm, and the unit length is 0.6 mm, the porous wick has strong capillary pumping force. The 316L porous material is modified by heat treatment to obtain super-hydrophilic properties. The porous wick is applied to the evaporator of the loop heat pipe, which significantly improves the heat transfer performance. When the heat load is 200 W, the evaporator temperature is 57.09 °C, and the thermal resistance is 0.025 °C/W.

Investigation on performance enhancement of micro-channel separated heat pipe in data center: A coupled heat-mass-flow characterization approach

As data center continues to expand in scale and complexity, the demand for efficient heat dissipation solutions becomes increasingly critical. The utilization of micro-channel separated heat pipe is prevalent in data center cooling due to their low energy consumption and efficient cooling. This study aims to investigate the effects of different refrigerant flow rates, different inclination angles and different inlet vapor phase fractions on the heat transfer and flow characteristics of micro-channel separated heat pipe evaporator. Firstly, a simulation model of the heat pipe evaporator was established considering the heat-mass-flow coupling characteristics, and the fins were modeled and simplified without neglecting the enhanced heat transfer. Then, the experimental data are used to verify the established simulation model, and the error is within the acceptable range. Finally, scheme design and performance optimization research are conducted. Research on the inlet flow rate of R134a shows that when the inlet flow rate is 0.005 m/s, the outlet is superheated vapor. The presence of an inclination angle (0°-20°) in the evaporator not only significantly reduces the pressure difference between the outlet and the inlet (more than 30 %), but also improves the heat transfer coefficient and the refrigerant velocity magnitude. In addition, increasing the inlet vapor volume fraction promotes vapor bubble nucleation and reduces the pressure drop, but leads to the presence of outlet overheating. The findings of this study contribute valuable insights for advancing thermal management strategies in data center environments.

Numerical simulation analysis of high-temperature bent sodium heat pipes

Abstract High-temperature bent heat pipes are safety-level heat transfer components used in heat pipe cooled reactor, and their applications are becoming increasingly widespread. In this study, a comprehensive three-dimensional numerical model was established to evaluate the effects of different bending angles and radii on the performance of high-temperature heat pipes. The model solved for the temperature, pressure, and velocity fields in the wall, wick, and evaporator, considers the compressibility effect of the vapor. The study investigated parameters such as vapor pressure, vapor velocity, radial secondary flow field, wall temperature, wick temperature, and equivalent thermal resistance of powder sintered core sodium heat pipes with bending angles of 45°, 90°, 135°, 180°, and a bending radius under 90°. The results showed that when sodium vapor enters the bent pipe, the vapor flow deviates towards the outer side, resulting in higher vapor pressure at the outer side than the vapor pressure at the inner side, and the generation of radial secondary vortex. This leads to higher temperature in the evaporator and adiabatic sections of the bent heat pipe, while lower temperature in the condenser. Fractal patterns are observed in the outer and inner wall temperature curve in the adiabatic section, with lower temperatures on the inner side and higher temperatures on the outer side. The bent heat pipe exhibits higher equivalent thermal resistance than that of a straight heat pipe, and the equivalent thermal resistance increases with increasing bending angle, and the equivalent thermal resistance decreases with increasing bending radius.

Numerical Investigation on Thermal Performance of Nanofluid-Assisted Wickless Heat Pipes for Electronic Thermal Management

Abstract Heat pipes are passive heat transfer systems and serve as an effective thermal management solution for electronic devices. The adaptability of heat pipes makes these suited for a wide application range, especially in the field of electronic thermal management. The current study highlights the transient numerical analysis of wickless heat pipes (thermosyphons) for the thermal management of electronic devices. The thermal performance of the thermosyphon is analyzed using both copper oxide (CuO) and aluminum oxide (Al2O3) nanofluids with their concentrations at 1% and 5%. Deionized (DI) water is employed as a reference case for comparison. The study is carried out for variable heat inputs to the thermosyphon ranging 10–50 W for a time interval of 30 s. The idea is to analyze the effect of the evaporator heat input and the nanoparticles concentration on the temperature, heat transfer coefficient, thermal resistance, and effective thermal conductivity of the heat pipe. The results indicate that CuO nanoparticles at a 5% concentration lead to a maximum thermal resistance reduction of 4.31% at 50 W, while alumina nanoparticles at the same concentration lead to a more substantial reduction of 6.66% at the same heat load. The evaporator temperature varies between 377.52 K to 374.99 K using deionized water, and 376.95 K to 374.29 K using CuO nanofluid (at 1% concentration). The heat pipe's evaporator attains its highest convective heat transfer coefficient (437.91 W/m2K) by using alumina nanofluid with 1% nanoparticle concentration at 50 W. Moreover, the effective thermal conductivity of the heat pipe is enhanced by 5% and 7% for copper oxide and aluminum oxide nanofluids (with 5% concentration), respectively, at 50 W. Thus, the nanofluids play a significant role in improving the efficiency and reliability of electronic components. These findings demonstrate the potential of using the nanofluids in thermosyphons to enhance their thermal performance in electronic cooling applications.

Wrap-around loop pulsating heat-pipe heat exchanger for enhancing the energy efficiency of high-tech cleanroom HVAC systems

Abstract To maintain strict temperature, humidity, and cleanliness requirements, the cleanrooms of high-tech semiconductor fabrication plants have heating, ventilation, and air conditioning (HVAC) systems, which require substantial amounts of energy. To reduce energy consumption, this study proposes using a wrap-around loop pulsating heat pipe (WLPHP) heat exchanger comprising a pulsating heat pipe for precooling high-temperature outdoor air to reduce relative humidity. The heat absorbed by the heat-pipe evaporator is then transferred to the condenser and released, reducing the energy required to subsequently reheat the air with an HVAC system. The experimental results reveal that the system reduces the required reheating energy and increased the moisture removal rate per unit energy consumption by an average of 24.8% and 33% compared with a typical heat exchanger. Hence, using the WLPHP heat exchanger in HVAC systems could provide large energy savings.

Experimental Study of the Wickless Heat Pipe Heat Exchanger by Using Nano Fluid

The use of wickless heat pipe heat exchangers has been improving a wide range of thermal applications such as solar water heaters. Therefore, more scientific research needs to be conducted to improve its performance. In the present study, a wickless heat pipe heat exchanger test rig has been designed and fabricated to investigate the effect of different parameters on its performance. Two different heat pipe working fluids have been used namely pure water and water with nanoparticles (Al2O3) using different fluid volume ratios (20%,40%,60%,80%, and 100%). The concentrations of the nanoparticles in water range between 1.3 and 7 % wt. For the heat exchanger, various inlet hot air temperatures (50, 55, and 60 oC) have been tested at the hot side (heat pipe evaporator) whereas the inlet temperature of the cold side (heat pipe condenser) has been maintained at 20 oC. The effect of airflow Reynolds number has also been examined with a range of 2583-20664. Results showed that the best heat exchanger effectiveness is achieved at a Reynolds number of 10332 and nanoparticles concentration of 7% wt. Also, the use of nanoparticles reduced the thermal resistance in the heat pipe due to the significant reduction in its surface temperature compared to that of pure water.

Pore network simulation of loop heat pipe evaporator with different pore size distribution

To investigate the relationship between the loop heat pipe evaporator heat-transfer coefficient and wick pore size distribution, this work simulated the two−phase thermal hydraulics in the evaporator by pore network model in three dimensions. The simulation considered a liquid–vapor (L–V) two-phase state in the wick, which is induced by nucleate boiling and local pore-scale fluid dynamics. Some wick samples, while having the same macroscopic porous characteristics such as permeability, were created with different pore size distributions. Heat transfer and fluid flow of the evaporator were solved with ammonia and R134a as working fluids, along with stainless-steel and polytetrafluoroethylene (PTFE) porous materials. Each evaporator showed a different evaporator heat-transfer coefficient and maximum applied heat flux. Some characteristics with respect to the L–V phase distribution in the wick were selected to investigate their correlation with heat-transfer coefficients. As a result, the correlation coefficients with the three-phase contact line (TPCL) length ranged from 0.70 to 0.91. Only the TPCL showed a correlation with the heat-transfer coefficients in all conditions, as opposed to the vapor pocket maximum depth and liquid saturation. It was discovered that the TPCL length is proportional to the heat-transfer coefficients. In all cases, the TPCL length and heat-transfer coefficients reached a maximum at moderate pore size dispersion. In addition, The heat-transfer coefficients of the PTFE wick were more sensitive to the TPCL length than that of the stainless-steel one. The discovery helps enhance the thermal performance of the evaporator porous structural design by additive manufacturing.

Relationship between phase distribution and heat-transfer coefficient of loop heat pipe evaporator investigated by lateral observation of porous media

Loop heat pipes (LHPs) can be passively operated, require no electric power, and can be flexibly arranged, making them promising in thermal control systems for both terrestrial and aerospace applications. Understanding the two-phase state in the porous media of a capillary evaporator induced by nucleate boiling is key to enhancing the evaporator performance. This study visualized the liquid–vapor (L–V) phase distribution on the contact surface between the cylindrical evaporator casing and the wick to investigate the L–V phase distribution and to figure out its relationship with the evaporator heat-transfer coefficient. The visualization was successfully realized under conditions similar to those observed in a practical environment using a sapphire tube as the evaporator casing. The observation results showed that the wick underwent a phase transition from a liquid-saturated state to a two-phase state under the effect of nucleate boiling, and the evolution of the L–V phase distribution on the contact surface with varying heat load could be determined. The heat-transfer coefficient peaked immediately after the nucleate boiling and then decreased with increasing heat load. The three-phase contact line (TPCL) within the casing, liquid, and vapor phases showed a similar trend; however, the saturation on the contact surface was different, decreasing quickly after the nucleate boiling, followed by a gradual decrease. The correlation coefficients between the heat-transfer coefficient and the saturation/TPCL length were −0.61 and 0.83 under all heat load conditions, respectively. The characteristics of the heat-transfer coefficient as a function of the heat load were found to correspond to those of the TPCL length rather than the saturation. This finding can aid in the design of microscopically optimized porous media by additive manufacturing.

Performance evaluation of a solar desalination-hot water system using heat pipe vacuum tube parabolic trough solar collector – An experimental study with Taguchi analysis

The utilization of renewable energy to generate hot water and distilled water can considerably reduce pollution. This study looked at a hybrid system that used a parabolic-trough heat pipe solar collector to generate hot water while also providing drinking water. The system is constructed in two stages, the first producing distilled water and the second producing hot water. A concave mirror increases the temperature of a vacuum tube heat pipe's evaporator area and the condenser of the heat pipe, which is directly connected to the desalination system's saltwater tank. To improve the amount of drinking water generated and to transfer thermal energy to the hot water generation system, a condenser region at the top of the saltwater tank, as well as multiple heat pipes, were employed. The effect of the water flow rate (200, 300, 400 and 500 ml/min), number of heat pipes (0, 1, 2 and 4), and the filling porous medium (0, 0.3, 0.6 and 0.9 m) of the vacuum tube on the system performance were evaluated. In addition, Taguchi-Based design of experiments was used to determine the effect of independent input parameters on the energy and efficiency of the system. The results showed that the effects of water flow rate, porous medium length, and number of heat pipes on the energy efficiency were approximately 50.89%, 26.53%, and 20.6%, respectively. Furthermore, the cost of distilled water and the cost of hot water were approximately 0.0380 $/L and 1.01 $/m3, respectively. Additionally, the highest daily productivity of the system (4940 ml/day) was obtained with a water flow rate of 200 ml/min, a length of porous media of 0.6 m, and four heat pipes. The CO2 emission reduction based on the environmental and enviroexergoeconomic parameters of the proposed systems ware improved by 37.5% and 268.4%, respectively, resulting in returns of approximately $358.1 and $260.5, respectively.

Experimental Study and Visual Observation of a Loop Heat Pipe with a Flat Disk-Shaped Evaporator under Various Orientations

In this study, visualization treatment was applied to the flat disk-shaped evaporator of a loop heat pipe. By observing the liquid/vapor behavior inside the evaporator and compensation chamber, the effects of orientation on the performances during startup and during a step-increase in heat load were investigated. With water as the working fluid, the loop heat pipe was tested under three typical orientations of φ = −90°, φ = 0°, and φ = +90°. The startup time was the shortest for the φ = −90° orientation but there could be a slight temperature overshoot, resulting in an unsmoothed startup process. The startup speeds under the φ = 0° and φ = +90° orientations were similar, both without any significant temperature overshoot. The orientation could significantly change the heat leak and, therefore, the operating temperature and the heat-transfer limit. For the φ = +90° and φ = −90° orientations, the heat-transfer limits were about 71% and 157% of the value at the φ = 0° orientation, respectively. Based on visual observations, for the loop heat pipe operating in gravity-driven mode, there could be two different paths for the working fluid to return to the evaporator, namely, along the vapor line for low heat loads and along the condenser and liquid lines for relatively large heat loads, respectively.

Heat transfer coefficient and thermal performance of heat pipe with R134a/mineral oil nanodiamond+Fe3O4 hybrid nanorefrigerant

Experimental research has been done on the heat transfer coefficient and thermal performance of heat pipe operating with R134a/mineral oil (5:1% weight percent) based nanodiamond+Fe3O4 hybrid nanorefrigerants. The in-situ growth approach was used to create the hybrid nanoparticles, which were subsequently characterized by X-ray diffraction. Using a vibrating sample magnetometer, the prepared sample magnetic measurement was determined. The studies were conducted with varying heat inputs of 100, 150, and 200 W and with particle loadings of 0.1%, 0.5%, and 1.0%, respectively. The results show that when using hybrid nanofluids instead of base fluid, the wall temperatures at the evaporator and condenser sections of heat pipe are lower. At a heat supply of 200 W, the average temperature in evaporator and condenser sections are reduced by 30.08% and 19.21%, respectively. At [Formula: see text] = 1.0% vol. loading and 200 W, the thermal resistances in the evaporator and condenser sections drop to 24.58% and 21.74%, respectively. In comparison to the base fluid, the heat transfer coefficients of the evaporator and condenser are greater to 37.08% and 30.24%, respectively, at a heat input of 200 W. The thermal performance of the heat pipe is enhanced by employing the hybrid nanoparticles based nanorefrigerant, and it is also increased with increasing particle loadings.

Experimental and numerical investigation of solid-solid phase change material assisted heat sink with integrated heat pipe for electronic cooling

Advancements in phase change materials (PCM) technology offer adaptable solutions for challenging high heat dissipation problems in electronic devices. In this work, the influence of Neopentyl Glycol (NPG) as PCM having solid-solid phase transition on the functioning of heat pipe assisted heat sink is studied. Experimental and numerical investigation was performed on the transient thermal performance of heat pipe integrated PCM-assisted heat sink application with forced air cooling. The heat pipe's evaporator section is in contact with PCM- assisted heat sink, while condenser section is exposed to the ambient. Investigations were carried out at power levels of 9–13 W, corresponding to an equivalent heat flux range of 2.5–3.5 kW/m2 and with PCM filling of 33, 66 and 99 % of the heat sink volume where without integration of PCM and heat pipe in heat sink as the reference configuration. PCM-assisted heat sink and heat pipe configurations outperformed other configurations based on charging period for all experimental parameters with a maximum enhancement ratio of 3.29. Heat sink assembly comprising 99 % PCM with heat pipe gives the most significant results on comparison with all other configurations, whereas the assembly without heat pipe showed the best results for 66 %.

Modification and pool boiling performance elevation of copper foam wicks for high power applications

Surface modification is an effective method to improve boiling heat transfer performance and has the feasibility of application in enhancing equipment cooling and energy conversion efficiency. A magnetron sputtering (MS) method is employed to modify the skeleton surface of copper foam for further maximizing the boiling performance in this study. After modification, the heat transfer coefficient (HTC) and critical heat flux (CHF) of copper foam wicks have been significantly improved, with a maximum increase of 75.6 % and 17.3 % compared to the original copper foam, respectively. The greatly enhanced boiling performance is attributed to the structure of “cauliflower-like” and gradational wettability along the thickness direction, which provide more nucleation sites and increase the bubble detachment frequency. Meanwhile, the heat transfer correlation for modification samples is developed, and the results show an average error equal to 11.2 %. In addition, the beat sample is assembled in the evaporator of heat pipe (HP) as wick which increased the heat transfer coefficient by 144.3 ∼ 333.4 %. All results demonstrated that the surface modification of copper foam based on MS can greatly increase heat and mass transfer performances, which is promising in the high power applications.

Effect of halocarbon refrigerants as working fluid of the heat pipe for thermoelectric power generation

This study investigates the effect of a refrigerant in a heat pipe for thermoelectric power generation (TEG). R22, R32, R134a, and R410a were used as working fluids. A water bath was used to heat the hot side of the TEG, and a heat pipe was used to cool the cool side of the TEG. Eight high-performance TEGs connected in series were used in this study. The heat-absorbing section of the heat pipe was the evaporator while at the top section was the condenser. The experiment tested ten conditions of the hot-side temperature of the TEG as 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 °C. In each testing condition, the necessary parameters were collected, such as the hot-side and cool-side temperature of the TEG, the inlet and outlet of the cooling air of the heat pipe condenser, the temperature of the heat pipe condenser and heat pipe evaporator, the voltage, and the current generated by the TEG. The necessary parameters were used to investigate the power generation of the TEG module, which is related to the hot-side temperature of the TEG. Multiple linear regression was used to investigate the relation of TEG power generation. The result was found that the power generation of the TEG was in direct relation to the hot-side temperature of the TEG, for which the correlations are reported. The average power generation of R410a, R22, R134a, and R32 is 45.4, 46.3, 49.5, and 62.7 mW, respectively. Finally, it can be concluded that the halocarbon refrigerant of the heat pipe has a significant effect on the TEG power generation.

Relation between triple phase contact line and vapor groove width for enhancing thermal performance of a loop heat pipe evaporator

• The effects of changing vapor groove width of a porous wick and improving wettability of a LHP evaporator on heat transfer performances were evaluated experimentally and theoretically. • The micro-grooves processed on the heating plate improved heat transfer performances regardless of the vapor grooves width. • The micro-grooves increased heat transfer performances more greatly as the vapor grooves width increased. • Numerical model explained that the length of triple phase contact line has a great influence on the evaporative heat transfer coefficient. In this study, the effects of an increased evaporation area known as the triple-phase contact line (TPCL), of the porous wick and improved evaporator wettability on the loop heat pipe (LHP) heat transfer performance were evaluated experimentally and theoretically. An infrared camera and a microscope were used to observe the thermo-fluid behavior of porous wicks with different vapor grooves widths and evaporator heating plates with different inner wall structures in the experiment. The porous wick's vapor groove widths were 1.0 mm, 0.5 mm, and 0.2 mm. A normal heating plate and a micro-grooved heating plate were used as the evaporator case. As a result, it was clarified that processing the micro-grooves on the heating plate improved the evaporative heat transfer coefficient and maximum heat flux, regardless of the vapor grooves width of the porous wick. Furthermore, it was proposed that both of them increased significantly as the vapor grooves width increased. The thermal-hydraulic numerical model that predicted the heat transfer coefficients for each case was developed. The calculation results showed a significant increase in the heat transfer coefficient as the TPCL appearance rate, which expresses how much the TPCL appears in the micro-grooves, increased, and this increasing tendency was in good agreement with the experimental results. Furthermore, it was proposed that the TPCL appearance rate at a high heat flux was reduced as the vapor grooves width decreased. The results indicate a new promising approach for improving the heat transfer performance of LHP evaporators.

Parametrical Study on the Capillary Flowing Characteristics of the Parallel Microchannel Array

The flow mechanism within a silicon-based micro heat sink plays a crucial role in two-phase thermal dissipation technology. In this study, the effect of geometrical properties on the flow behavior within a silicon-based array parallel microchannel as the evaporator of a silicon-based micro loop heat pipe (s-mLHP) is experimentally and numerically investigated. Here, three arrayed microchannels with different aspect ratio (AR) parameters (depth of 180 μm and AR of 6, 9, and 15) are specially fabricated. A visual experiment platform is established to observe and measure capillary properties of microchannels characterized by the suction distance. In addition, a validated numerical model (the maximum deviation less than 38.3%) is applied to simulate the flow characteristics of microchannels with different ARs. Numerical solutions show that the microchannel with ARs taken between 3 and 4 achieves the best capillary pumping performance within the studied range (suction distance up to 0.8 mm), which provides a theoretical basis for further exploration of silicon-based microchannel array with the optimal flow and thermal performance.

Finite time thermodynamic analysis and optimization of water cooled multi-spilit heat pipe system (MSHPS)

• Energy saving in data centers is increasingly with the developing IT industry. • An accurate performance and evaluation model based on time cycle is proposed. • An periodic integral energy efficiency model is proposed. • The refrigerant flow distribution characteristic of MSHPS was built and tested. • The proposed method is fit for analysis of MSHPS and the real pipe-net systems. This study focuses on the heat transfer characteristics of the evaporation terminal, the cool distribute unit (CDU) and refrigerant flow distribution of a water cooled multi-spilit heat pipe system (MSHPS) used in data center. The finite time thermodynamic analysis, the exergy method and the software SIMULINK was employed to build the simulation model of the combined system. The results show that the IT servers should concentrate on arranging at the location below 1.3 m. The CDU has a heat transfer of about 74 J in a period of 6 s. And the optimum flow rate of the CDU is 0.82 kg/s. The flow distribution characteristic of a CDU which connect 2 heat pipe evaporator terminals of 6 kW was calculated, and the working fluid is R22. Then the free cooling time,part time free cooling and energy saving potential in major cities of China were analysised. The energy saving potential is from 61% to 25%. The results are of great significance for the operational control and practical application of a MSHPS and other pipe-net systems.

Effect of phase change temperatures and orientation on the thermal performance of a miniaturized PCM heat sink coupled heat pipe

ABSTRACT This study reports the results of experimental and numerical investigations on the thermal performance of a miniaturized phase change material (PCM) heat sink coupled with heat pipe. Initial studies are conducted on two different configurations of PCM heat sink with heat pipe (i) HSHP (i.e., PCM coupled at evaporator of heat pipe) (ii) HPHS (i.e., PCM coupled at condenser of the heat pipe). The results showed a superiority of HSHP over HPHS by up to 98.8% in the charging cycle. Experiments are conducted on HSHP with different melting temperature PCMs. The HSHP with high melting temperature PCM showed high thermal performance.

Thermal-hydraulic analysis of heat pipe reactor experimental device with thermoelectric generators

Heat pipe reactor relies on heat pipes to transfer the fission energy generated in the core to the secondary loop or thermoelectric conversion system. In our group's design, thermoelectric generators (TEGs) are selected to convert fission energy to electricity. In this paper, we established a heat pipe reactor experimental device with TEGs. To verify the heat transfer performance of the heat pipes and the thermoelectric conversion efficiency of TEGs, steady-state experiments were carried out. The minimum temperature drop between the evaporator and condenser sections of heat pipes can reach 6.4 °C. The maximum output power of TEGs can go 74.4 W. The thermoelectric conversion efficiency is about 8.0%. The Computational Fluid Dynamics (CFD) method is used to simulate the steady-state operation of the experimental device. After comparing the simulation results with the experimental data, the temperature error of the heat pipes is less than 26.8 °C, and the temperature error of the TEGs is less than 17.3 °C. A CFD simulation method for heat pipe reactor steady-state operation is presented based on the verification and validation.

The Solving of the Inverse Thermal Conductivity Problem for Study the Short Linear Heat Pipes

The results of studies by solving the inverse thermal conductivity problem of the heat capacity of evaporator of the short linear heat pipes (HP’s) with a Laval nozzle-liked vapour channel and intended for cooling spacecraft and satellites with strict take-off mass regulation are presented. Mathematical formulation of the inverse problem for the HP’s thermal conductivity in one-dimensional coordinate system is accompanied by the measurement results using the monotonic heating method in a vacuum adiabatic calorimeter the HP’s surface temperatures along the longitudinal axis over the entire temperature load range, thermal resistance, and arrays of thermal power data on the evaporator Qev and vortex flow calorimeter Qcond for the condensation surface allow us to estimate the average value of the evaporator heat capacity Cev by solving the inverse thermal conductivity problem in the HP’s evaporator region. Since at the beginning of working fluid boiling for a certain time interval, the temperature of the capillary-porous evaporator remains close to constant, and with the continuation of heating and by solving the inverse thermal conductivity problem, it becomes possible to calculate the heat capacity of the working evaporator and the evaporation specific heat of the boiling working fluid and compare it with the table values.