Heat Pipe System Research Articles

Novel design integration for advanced nuclear heat-pipe systems

A new design integrating heat-pipes into a nuclear cooling system is presented. The heat-pipes are presented as the primary mode of heat transfer. Analyzing the prevailing limits to determine suitability for predicting the performance of the heat-pipe concept. When the limits are determined for the design integration, steady-state behavior needs to be quantified. A model that accounts for 3D behavior is evaluated for use. Using the limits to evaluate the design integration, with sodium, the operating regime would still remain below the predicted limits. With potassium the operating regime would exceed the capillary limit. This is caused by the increase in pressure drop. With the 3D model, a validation shows that conduction can give very good results for both transient and steady-state behavior for sodium. It shows that water has poor transient prediction but accurately predicts the steady-state behavior. Both solutions were close to the reported experimental results for steady-state.

Research on Heat Transfer Performance of Micro-Channel Backplane Heat Pipe Air Conditioning System in Data Center

This paper deals with the heat transfer performance of a micro-channel backplane heat pipe air conditioning system. The optimal range of the filling rate of a micro-channel backplane heat pipe air conditioning system was determined in the range of 65–75%, almost free from the interference of working conditions. Then, the influence of temperature and air volume flow rate on the heat exchange system were studied. The system maximum heat exchange is 7000–8000 W, and the temperature difference between the inlet and outlet of the evaporator and the condenser is almost 0 °C. Under the optimum refrigerant filling rate, the heat transfer of the micro-channel heat pipe backplane system is approximately linear with the temperature difference between the inlet air temperature of the evaporator and the cooling distribution unit (CDU) inlet water temperature in the range of 18–28 °C. The last part compares the heat transfer characteristics of two refrigerants at different filling rates. The heat transfer, pressure, and refrigerant temperature of R134a and R22 are the same with the change of filling rate, but the heat transfer of R134a is lower than that of R22. The results are of great significance for the operational control and practical application of a backplane heat pipe system.

Heating and cooling capacity of phase change material coupled with screen mesh wick heat pipe for thermal energy storage applications

The thermal performance of a phase change material (PCM) heat pipe system is experimentally analysed using acetone as heat pipe fluid in a heat load range of 10-50 W at different flow rates of the condenser coolant. The evaporator of the heat pipe is enclosed in a chamber which filled with a PCM or water. Heat inputs are applied at the evaporator of the heat pipe through the PCM or water. In this study, the heat retention as well as cooling time of the PCM-water are estimated at different heat loads and flow rates of condenser coolant. Similarly, the thermal resistance, evaporator and condenser heat transfer coefficients are also estimated at different heat loads. It is observed that the PCM takes more time during heating and cooling cycles to reach the steady-state temperatures and the temperature values reached during heating are also higher for PCM compared to water. The use of PCM enhances the thermal storage capacity and shows a maximum enhancement of 200% in heat retention time compared to water at 50 W. Moreover, a maximum enhancement of 63.6% is observed in the steady-state temperature of the PCM compared to water. Similarly thermal resistance, evaporator wall temperature and heat transfer coefficients of the heat pipe also vary for PCM and water. The experimental results indicate that PCM or water can be used in this combined system depending upon requirement of thermal storage or electronics cooling.

Comparison of Heat-Pipe Cooling System Design Processes in Railway Propulsion Inverter Considering Power Module Reliability

In this paper, the effect of the heat-pipe cooling system design processes on the reliability of the power module in a railway propulsion inverter was investigated. The existing design processes for the heat-pipe cooling system guarantee that the junction temperature of power devices does not exceed the maximum allowable junction temperature when the railway propulsion inverter operates under its mission profile; therefore, each step of the design process was reviewed to analyze the effect of the heat-pipe cooling system. Based on the processes, in the calculation for the required thermal resistance of the heat-pipe cooling system, two difference losses were considered with the thermal resistances of the insulated gate bipolar mode transistor (IGBT) module and the thermal grease at an interface between the baseplate of IGBT module and heat-pipe cooling system. The control scheme and mission profile of the train were taken into account to calculate the power losses. Then, the designed heat-pipe cooling systems were compared in terms of the size and weight. In addition, the junction temperatures and lifetimes of the power module with heat-pipe cooling systems designed by different power losses were estimated and compared. Finally, guidelines for a heat-pipe system cooling design are proposed.

THERMOELECTRIC DEVICE FOR INTRACAVITARY HYPOTHERMIA

Objectives In this research, we aimed to develop a thermoelectric device (TED) for intracavitary hypothermia, to carry out experimental studies into its functional characteristics, as well as to develop treatment procedures using this device.Method A TED design for intracavitary hypothermia was developed, consisting of two thermoelectric batteries (TEBs) interconnected using an allmetal heat pipeline equipped with an influencing applicator and a liquid heat exchanger. Experimental studies of the device were carried out on a designed bench, which included a climatic chamber, a source of electrical energy and a temperature meter connected to a PC. Results Temperature changes at the control points of the device were recorded over time. Changes in the time taken to stabilise temperatures of the device tip, heat pipe and heat sink system at different TEB supply currents were investigated. Possible methods for treating some ENT diseases using the developed device are described.Conclusion It is shown that the temperature of the applicator is stabilised after approximately 4-4.5 minutes without load. At the same time, an increase in the current of the additional TEB from 5 to 12 A at the main TEB current of 23 A reduces the temperature from 237 K to 224 K. In the process of carrying out the procedures, the necessary level of a decrease in the temperature of a biological object can be reached at the supply current of the main and additional TEBs equal to 23 and 12 A, respectively, after 2.5 minutes. The full potential of the TED device will be realised through the developed of methods for treating ENT diseases.

Comparative experimental investigation of two evacuated tube solar water heaters of different configurations for domestic application of Baghdad- Iraq

Evacuated tube solar water heaters have drawbacks that limit their performance against local habits of hot water consumption, like slow water temperature rise and slow response to loading. A method to enhance their performance is using heat pipes as heat transport tools from the solar collectors to the storage water. The present work investigates the enhancement of thermal performance of evacuated tube solar water heaters subjected to (non- standard) load conditions and weather conditions of Baghdad- Iraq. Two identical evacuated tube solar water heaters (both of 120 l capacity and 20 evacuated tube solar collectors) are investigated experimentally. One system works with thermosyphon (natural convection); the other system incorporates 20 wickless heat pipes (closed thermosyphon tubes), of 16 mm diameter and 1750 mm length and are charged with methanol as working fluid at 50% fill charge ratio, as thermal conductors from the solar collectors to the storage tank. A comparison of performance of the two solar systems has been conducted by subjecting them simultaneously to different load conditions namely; no load, intermittent and continuous loading to simulate the hot water consumption habits in the local community. Extra experiments were conducted at sunny days and various weathers at no load to verify the thermal diode effect of heat pipes and the effect of weather conditions on the systems performance. Experimental results reveal an enhancement in overall daily efficiency of the heat pipe system over the thermosyphon system by 22.5% for no load, 42.5% for intermittent loading and 32.4% for continuous loading. The heat pipe system produced higher temperatures and better response at all load conditions and adverse weather conditions that make it more suitable for local domestic application. The thermosyphon system performs suitably with no load and intermittent load at small removal quantities. Results agree with those in the literature.

Thermal-hydraulic analysis of the thermoelectric space reactor power system with a potassium heat pipe radiator

The thermoelectric space reactor power system conceptual design incorporates fast reactor, liquid-lithium primary coolant loops that transfer heat to potassium-filled high temperature heat pipes and thermoelectric generators. An integrated system analysis model was developed to study the operating characteristics of the space power system, which consisted of reactor thermal-hydraulic model, neutron kinetics model, thermoelectric energy conversion assembly (ECA) model, heat pipe radiator model etc. One-dimensional thermal-hydraulic model was applied to model the coolant circuit. Quasi two-dimensional analysis models for heat transfer of fuel element, ECA and the heat pipe fin were established. Considering the thermoelectric conversion phenomena, an equivalent electric efficiency model was inserted in the ECA model. Both finite element method and thermal resistance network were applied to simulate the potassium heat pipe system. The normal operation condition and two demonstration accident scenarios (unprotected inadvertent movement of a sliding reflector and loss of heat pipes) were calculated to prove the capabilities of the new system model.

Experimental investigation of loop heat pipe with a large squared evaporator for multi-heat sources cooling

A heating area of 190 mm × 90 mm large flat-plate loop heat pipe was designed for the heat dissipation problem of multi-heat sources. The design process was also briefly introduced. The evaporator was made of aluminum alloy, and heat dissipation fins were arranged on the back side of the compensation chamber to enhance the heat transfer between the compensation and the ambient. The stainless steel wire mesh worked as the porous wick, and the acetone was chosen as the working fluid. Six ceramics heating blocks were used as the heat sources. The results showed that the system could start up and work normally between 20 W–140 W, and maintained the heating surface temperature below 90 °C. The system behaved as a zigzag start below 20 W, and the condenser inlet temperature oscillated periodically, and the system could start up stably between 25 W and 140 W. When the heat load was increased, there occurred periodic temperature fluctuation in condenser outlet. The system could establish a new balance quickly during variable heat loads operation, which reflected the good reliability of the LHP. The experiment of changing the heat dissipation condition on the condenser side and the evaporator side was carried out. When the heat load was 120 W and the ambient temperature was constant, the system equilibrium temperature difference caused by the air ventilation of the condenser was changed, which was less than the heat dissipation of the evaporator under the same conditions. The evaporator thermal resistance decreased with the increase in heat load, and the minimum thermal resistance of 0.032 °C/W was achieved at the heat load of 120 W. The total thermal resistance of the LHP was distributed between 0.312 °C/W and 0.212 °C/W. It was also pointed out that it was very important to improve the thermal uniformity of the heated surface of a large-plane loop heat pipe system with multiple heat sources.

Mutual Influence of Capillary Pumps in Heat-Pipe Systems with Different Evaporator Loads

Thermal management systems that are not hermetically sealed have been developed for use in spacecraft; in such systems, scientific equipment and instruments operate in open space. Accordingly, new methods of thermal regulation have been developed: axial and loop heat pipes; and honeycomb thermal panels with embedded axial heat pipes. Heat transfer in heating systems with heat pipes is based on evaporation and condensation in a two-phase loop. The working fluid moves under the action mainly of capillary forces that appear in capillary channels or honeycomb structures for axial heat pipes and in the porous heated medium (capillary pump) of the loop heat pipes.

Experimental study on transient performance of heat pipe-cooled passive residual heat removal system of a molten salt reactor

Abstracts A heat pipe-cooled passive residual heat removal system (PRHRS) of a molten salt reactor (MSR) is proposed by employing high-temperature heat pipe technology. This system can significantly improve the passive safety of an MSR during abnormal transients. In the study, an experimental system is constructed to verify the feasibility of using a PRHRS in molten salt reactors. A eutectic salt mixture of 46.5 mol%LiF-42 mol%KF-11.5 mol%NaF composition, termed as FLiNaK, is selected as the working fluid because it has similar thermo-physical properties to real salt 67 mol% LiF-33 mol%BeF2, termed as FLiBe. The transient responses of the designed PRHRS for an MSR are studied from the following two aspects. 1) The temperature distribution of molten salt in the drain tank with different heat pipe cooling schemes during transients is analyzed. 2) The effect of key parameters such as height of the air stack, number of heat pipes, initial salt temperature, and different decay power on the transient performance of the PRHRS is investigated. Experimental results indicate that the heat pipe system significantly removes the residual heat of molten salt in the drain tank, although part of the heat pipes does not operate normally. The residual heat is released in 5–10 h until the molten salt reaches its freezing point, thereby indicating the feasibility of the designed PRHRS for an MSR. The study provides valuable experimental data and suggestions for the design and analysis of a PRHRS for an MSR.

Field study on the self-adaptive capacity of multi-split heat pipe system (MSHPS) under non-uniform conditions in data center

The multi-split heat pipe system (MSHPS) is an efficient cooling system, since it mainly belongs to two-phase heat transfer and closes to the heat source. The self-adaptive capacity including operation performance under various heating loads, refrigerant distribution characteristics and anti-failure capability are important factors to determine the thermal safety of the data center using MSHPS. This paper focused on the onsite test about self-adaptive capacity of a MSHPS in a real data center under 25%, 50%, 75% and 100% heating loads and various fan failures. The results show that the MSHPS abnormally operated under low heating loads, but it still met the cooling demands due to its superior self-adaptive capacity. It was also found that abnormal operation was deteriorated by refrigerant side unbalanced pressure and heat leak. Further, the influence of fan failures on the airside heat transfer performance was limited, but the influence on refrigerant side was obvious due to the deteriorating of heat leak. For racks, the air velocity reduction caused by fan failures will increase the risk of servers overheating. For the whole computer room, owing to its superior self-adaptive capacity, the MSHPS ensured the thermal safety under serious fan failures in single rack and mild fan failure in row racks. Those results can give good guidance to improve the operational availability and reliability of MSHPS application.

An experimental study on the heat transfer performance of a loop heat pipe system with ethanol-water mixture as working fluid for aircraft anti-icing

Owing to the increasing demand of an energy-saving aircraft anti-icing technology and cooling of hydraulic system, loop heat pipes are gradually becoming efficient heat transfer mediums that can meet both anti-icing and heat dissipation requirements. To fundamentally investigate the heat transfer performance of a loop heat pipe used for aircraft anti-icing, a stainless steel-nickel one was fabricated and tested at three typical inclination angles under both steady and transient states, with the system performance as the final evaluation index. Additionally, to address the freezing problem under negative temperature flight conditions, ethanol-water mixture with four concentrations was specially used as the working fluid. The steady-state results showed that, 60% concentration of mixture enabled the loop heat pipe to obtain a lower operating temperature as 178.1 °C, and a smaller thermal resistance as 0.26 °C/W at 300 W. In transient tests, the loop heat pipe with 60% concentration of mixture operated robustly and stably, and reduced the total response time by 30.18%, about 26 mins, than in pure ethanol group. It also achieved the highest temperature distributions on the wing at −20°, which were about 31.8 °C higher than those in pure ethanol group. This study aims to effectively guide the utilization of ethanol-water mixture in loop heat pipes, and shows highly practical value in further applications of loop heat pipes in aircraft anti-icing.

Experimental and theoretical study of thermoelectric generator waste heat recovery model for an ultra-low temperature PEM fuel cell powered vehicle

An energy recovery method for ultra-low waste heat temperature Proton Exchange Membrane (PEM) fuel cell is presented utilizing a combined thermoelectric generator (TEG), heat pipe and heat sink system. The aim is to analyze the fundamental characteristics through experimental works and obtain a steady-state model of the system under the scenario of a mini hydrogen fuel cell vehicle. A test bench was developed consisting of a 2 kW open-cathode PEM fuel cell and a single TEG. A thermal resistance network model was also developed and validated. The main variables were the TEG cooling modes and orientation of the TEG towards the heat flow. At 37 °C waste heat temperature, the highest voltage and power output of 25.7 mV and 218 mW respectively were obtained via forced convection cooling and normal flow orientation. The results obtained are unique as it positively showed that the combined use of TEG, heat pipe and heat sink on a vehicle would offset the ultra-low waste heat temperature from a PEM fuel cell. Successful characterization of this system and validation of the model would also allow the system to be further developed for higher performance and contribute to sustainability of PEM fuel cell systems.

Multi-objective optimization using response surface methodology and exergy analysis of a novel integrated biomass gasification, solid oxide fuel cell and high-temperature sodium heat pipe system

A combined system including a biomass gasifier and a solid oxide fuel cell (SOFC) is studied. The heat is transferred from the afterburner to the biomass gasifier reactor by heat pipes. After model verification, response surface methodology (RSM) is utilized in order to investigate and optimize the process. The steam to biomass ratio (STBR), the current density and the inlet temperature of the SOFC are chosen as the input parameters while exergy efficiency and electrical power are considered as the responses. Regression models in order to predict the responses based on the considered input variables are obtained using analysis of variance (ANOVA) tool of the RSM method. The results indicate that the proposed regression models have high accuracy. The exergy efficiency improves by increasing the inlet temperature of the SOFC and decreasing the current density, as the results are illuminating. An optimum point (the current density of 5308 A/m2, the inlet temperature of SOFC of 1037 K and STBR of 1.6) is anticipated and the outputs and the exergy destruction rate of the combined system components are investigated. The power of 535 kW and the exergy efficiency of 44.22% are obtained in the optimum state.

Long-term thermal analysis of an airfield-runway snow-melting system utilizing heat-pipe technology

Snow removal is a critical security issue in airports, where heat-pipe technology can be an environmentally friendly and efficient alternative to traditional approaches for snow removal. This study investigated the long-term thermal regime of airfield-runways equipped with a heat-pipe system, using data collected over several recent years from two full-scale snow-melting systems, one located in Beijing, and the other in Harbin, China. The findings showed that the heat-pipe system automatically increases the airfield-runway surface temperatures by up to 17 °C utilizing geothermal energy in winter for preventing icing. Surface temperature levels up to 0 °C were observed to increase by over 25% when a shallow pipe embedded depth and a longer pipe evaporation section were selected. However, the surface temperature was less affected by the diameter of the heat-pipe. Field experiments indicated that, the heat-pipe technology threshold value for the airfield-runway snow-melting performance was an ambient air temperature exceeding −10 °C. Using the heat-pipe technology, the snow-melting rate on an airfield-runway was about 3–8 mm/h within the working range, and there was therefore a decrease in the snow-cover durations. Particularly, the heat-pipe airfield-runway was always free of snow when the average ambient air temperature exceeded −4 °C. The statistical results illustrated that the heat-pipe airfield-runway snow-melting system is applicable in more than 78% of the cities in China, indicating that this technology is feasible and practical in China and can be applied in other countries.

Comparison work about different empirical formulas for the boiling heat transfer coefficient in separated heat pipe system

Comparison work about different empirical formulas for the boiling heat transfer coefficient in separated heat pipe system

CFD analysis of a dual heat recovery system

This paper presents a CFD Heat Transfer Analysis of an originally designed system for heat recovery in the building sector. The heat exchanger has a dual role, which means it will produce simultaneously hot water and warm air. The key to the efficiency of the heat exchanger is the heat pipe system which recovers thermal energy from residual hot water and transfers it to the secondary agents. The paper includes a case study structured by different mesh distributions and flow regimes. The purpose of the heat exchanger is to reduce the costs of producing thermal energy and to increase the overall energy efficiency of buildings.

Transient Modelling of Rotating and Stationary Cylindrical Heat Pipes: An Engineering Model

Rotating wickless and stationary capillary cylindrical heat pipes are widely used heat transfer devices. Transient behavior of such heat pipes has been investigated numerically with computational fluid dynamics and lumped parameter models. In this paper, the advantages of both methods are combined into a novel engineering model that is low in computational cost but still accurate and rich in the details it provides. The model describes the interior dynamics of the heat pipe with a 2D representation of a cylindrical heat pipe. Liquid and vapor volumes are coarsely meshed in the axial direction. The cells are allowed to change in size in the radial direction during simulation. This allows for tracking the liquid/vapor interface without having to implement fine meshing. The model includes the equations for mass, momentum and energy and is applicable to both rotating and stationary heat pipes. The predictions of the model are validated with other experimental, numerical, and analytical works having an average deviation of less than 4%. The effects of various parameters on the system are explored. The presented model is suitable for the simulation of heat pipe systems in which both the level of detail and the computational cost are crucial factors.

Numerical model of heat transfer characteristics for sintered-grooved wick heat pipes under non-uniform heat loads

A sintered-grooved wick heat pipe, which is a passive two-phase heat transfer device, is widely used in the thermal control and electronic cooling system inside laptops because of its high thermal performance. These devices are mainly confronted with non-uniform heating and cooling loads during operation. In this study, the development of a numerical model for the sintered-grooved wick heat pipe operation was conducted to predict thermal resistance under non-uniform conditions for approaching the real heat transfer mechanism of the heat pipe thermal module. Finite element analysis (FEA) was used to develop the numerical model of the heat pipe. In the model, the non-Darcian transport and convection–diffusion equations were used for the wick region, while the capillary pressure model was used for the vapor–liquid interface. The FEA model was verified with experimental data, which found that the model formulation was in good agreement with the experimental results of the temperature profiles at both the top and bottom of the heat pipe walls. A quantitative comparison was also carried out, which showed that the predicted wall temperatures and thermal resistances deviated from the corresponding experimental data by an average of 4.25% and 3.63%, respectively. Thus, this developed model can provide adequate predictions for heat transfer in order to design a sintered-groove wick heat pipe system.

Battery thermal management system for electric vehicle using heat pipes

Thermal management of battery systems in electric vehicles is critical for maintaining energy storage capacity, driving range, cell longevity and system safety. In this paper, heat pipe based thermal management system for high power battery, with eight prismatic cells, has been proposed, designed and tested for heat load up to 400 W. The heat pipe system consists of two parts: heat pipe cooling plates to extract heat from the individual prismatic cells of the battery module, and remote heat transfer heat pipes to transport heat from the module to liquid cooled cold plates located 300 mm away. As compared to a conventional liquid cooled system, two-phase heat pipe based thermal control will provide better cell/module temperature uniformity, less complicated design and a safer system (no leakage issues in high voltage areas). Modeling of the complete system was done based on two-phase analysis for the heat pipe portion, and single phase analysis for the cold plate portion. The system manufacturing and evaluation method has been covered in detail. Based on controlled experimentation using a dummy battery module, it was estimated that the proposed system is able to successfully dissipate 50 W heat load from each cell while keeping their temperature below the given 55 °C limit using water coolant with a 25 °C inlet temperature and 1 lit/min flow rate.