Heat Pipe Radiator Research Articles

Transient study on heat transfer and flow performance of alkali metal heat pipe in space nuclear powered heat pipe radiator

The non-direct contact radiator has a simple structure and high reliability, making it more suitable for long-life nuclear powered spacecraft. This article is based on Fortran language and innovatively combines molecular dynamics models to establish a two-dimensional transient analysis program for thermo-hydraulic performance of rubidium heat pipes. The unsteady Navier Stokes control equation, heat conduction equation, and continuity equation is calculated by the finite difference method. This study adopt molecular dynamics theory for the first time to deal with condensation/ evaporation at the interface of alkali metal heat pipes under the background of space nuclear power. The delay method and multi grid method are used to ensure convergence and accelerate calculation speed. The transient thermo-hydraulic performance of different positions of heat pipes in non-direct contact radiators during start-up are analyzed. Current research can provide scientific reference for the upgradation of heat pipe radiators for nuclear powered spacecraft.

Performance evaluation of AMTEC/TEG coupling system for nuclear power space stations in space exploration

For deep space exploration, the performance of an alkali metal thermoelectric converter (AMTEC) can be improved by utilizing the thermoelectric generator (TEG) subsystem. In this work, a coupling system comprised of an AMTEC and a TEG is proposed, in which the waste heat produced by the AMTEC top cycle is used by the TEG bottom cycle cooled by a heat pipe radiator. A general mathematical model is built to analyze the output power and efficiency of each subsystem and the whole system. Finally, the effect of critical parameters on the output power and efficiency are evaluated, including the current density of AMTEC, dimensionless current i of TEG, geometrical structure, and operating environment. The results show that the combined AMTEC/TEG system is 4.35% and 15.39% higher than the efficiency and output power obtained when using the TEG subsystem to recycle the waste heat from the AMTEC condenser. The thermoelectric conversion performance of the AMTEC/TEG system is related to that of the AMTEC subsystem while less affected by the TEG subsystem. The present work could provide a new route for constructing long-distance nuclear space power stations, rovers, and lunar bases in extreme environments.

A multi-scale and multi-physical coupling method for the transient characteristics of space nuclear reactor

In the future of deep space exploration, space nuclear reactors (SNRs) are essential because they can provide a robust, sustainable energy supply independent of the environment. SNRs have complex multi-physics coupling effects, and their systems involve many modules. The traditional method uses the lumped parameter model, or single-filed, which cannot accurately describe the transient characteristics and has low spatial resolution and poor data representation. Thus, developing a multi-dimensional, multi-physics coupled method to analyze and design SNRs is necessary. This work proposes a multi-dimensional, multi-physics coupled method for the SNRs. A transient coupling code for the space thermionic reactor TOPAZ-II based on OpenFOAM was developed. The reactor neutron physics model, multi-region heat transfer model, thermoelectric conversion model, electromagnetic pump model, and heat pipe radiator model are included. Different scale models are imported by the code, including a three-dimensional reactor model and a two-dimensional heat pipe. Furthermore, the experimental data from the V-71 test unit were used to verify the developed code. The shutdown and startup of the improved TOPAZ-II system are simulated using the developed code. The results show that the calculated results agree well with the experimental data. During the startup and shutdown processes, the material temperatures remained within acceptable limits, so it can be considered that the developed 2D/3D system analysis for SNRs has successfully achieved a high-dimensional simulation of transient characteristics, accurately capturing the spatial distribution of SNRs at different scales.

Novel Lightweight Loop Heat Pipe Radiator for High-Power Space Systems

High-power space systems reject a large amounts of waste heat via medium- or high-temperature radiators. For this application, the heat pipe radiator is desired for its simplicity, efficiency, and reliability. It is commonly composed of cylindrical heat pipes and planar fins. Although typically made of advanced materials with low density and high thermal conductivity, the pipe–fin combination suffers from a series of drawbacks, such as large thermal resistance in component joints, thermal expansion rate incompatibility, and high acquisition cost. This study innovates the heat pipe radiator configuration by developing an all-metal loop heat pipe (LHP) radiator. The evaporator and compensation chamber are formed in a cylindrical container with traditional sintered wick layers and a plug. The LHP applies dozens of parallel capillaries arranged in two planar arrays as condensers to spread heat to radiating panels, realizing lightweightness and efficient heat transfer. A theoretical study was performed to analyze the nonuniform liquid–vapor distribution in multicondenser lines. Experimental studies were carried out to investigate startup performance, quasi-steady-state operation, and temperature hysteresis. The proposed design is proven to be capable of fulfilling the heat rejection requirement of space systems and exhibits technical benefits over existing ones.

Experimental Study of Composite Heat Pipe Radiator in Thermal Management of Electronic Components

Conventional straight fin (SF) radiators have difficulties meeting the cooling requirements of high-power electronic components. Therefore, based on the structure and technology of the detachable fin radiator, this paper proposes a kind of radiator embedded in the heat pipe base and uses the roll-bond flat heat pipe (RBFHP) to replace the traditional fin. The radiator has the advantages of modularity, easy manufacturing, low cost and good heat balance. In this study, the heat pipes (HPs)-RBFHPs radiator was tested in natural convection and forced convection to mimic the actual application scenario and compared with the conventional aluminum radiator. Heating power, angle, wind speed and other aspects were studied. The results showed that the cooling performance of the HPs-RBFHPs radiator was improved by 10.7% to 55% compared with that of the SF radiator under different working conditions. The minimum total thermal resistance in the horizontal state was only 0.37 °C/W. The temperature equalization of the base played a dominant role in the performance of the radiator at a large angle, and the fin group could be ineffective when the angle was greater than 60°. Under the most economical conditions with an inclination of 0° and a wind speed of 2 m/s, the input power was 340 W, the heat source temperature of the HPs-RBFHPs was only 64.2 °C, and the heat dissipation performance was 55.4% higher than that of SFs.

Lightweight Heat Pipe Radiator for Nuclear Reactor Power Systems on Lunar Surface

Heat rejection radiators of nuclear reactor power systems for space exploration and for planetary surface power are the largest component by volume and mass, depending on the radiator’s design and surface average temperature. This work developed designs for lightweight radiator modules for waste heat rejection on the lunar surface at a surface average temperature of 600 K. The modules each have a cesium (Cs)–titanium (Ti) heat pipe (HP) and highly oriented pyrolytic graphite (HOPG)/Ti heat spreading fins. The assembled panels of 10 Cs-HP modules hydraulically coupled in parallel are armored with carbon-carbon composite to protect against impacts by micrometeoroids and space debris for 10 years. The performance of the developed armored radiator panels is much superior to the current state of the art, with an areal density of 2.98 to 3.6 kg/m2, specific power of 3.36 to 3.98 kW/kg, rejected thermal power of 56.3 to 96.3 kW, and rejected power density of 7.56 kW/m2.

Performance analysis of indirect contact heat pipe radiator for space nuclear power system

The heat pipe radiator, with excellent thermal conductivity and anti-collision performance, is expected very suitable for heat emission in nuclear-power spacecraft. Indirect contact heat pipe radiator could operate longer life with lower capital cost. In this paper, the fluid-solid coupling heat transfer method is integrated to solve the energy model and S–S radiation model based on the k-epsilon model. Optimization objectives, heat dissipation performance and temperature uniformity are adopted to optimize the radiator structure. A comparison analysis between the ordinary and optimized radiator is conducted based on energy and entropy variation. The results show that the temperature uniformity and heat dissipation characteristic of the radiator after the optimization of connection mode of heat pipe and coolant pipe, fin shape, and fins welding direction have been improved without changing the area of fins and the weight of radiator. Through the comparative of radiators after changing the working conditions, some useful conclusions are drawn, which provide the theoretical foundation for the experimental research and engineering practice.

Preliminary analysis of in-orbit operation accidents for an ultra-small Lithium-cooled space reactor power system

To study the safety characteristics of an ultra-small (5.2 MWt) lithium-cooled space reactor power system (ULCR) under postulated accidents, a transient analysis code for the ultra-small space reactor coupled with a closed Brayton cycle dynamic conversion and heat pipe radiator was established. A preliminary analysis of four typical postulated accidents occurring at 100 percent power in-orbit operation of the ULCR system was conducted to define postulated problem areas and establish safety requirements. The postulated accidents mainly include (1) reactivity insertions, (2) coolant partial flow loss, (3) turbomachinery failure, and (4) radiator partial failure. The results showed that: a) since the ULCR system was designed to operate at high-temperature conditions (coolant temperature greater than 1500 K), the safety margin of the ULCR system was small. Emergency shutdown control or reduced power operation action should be taken proactively to ensure ULCR's safety in different accidents. b) When the control rod was misoperated and large reactivity was inserted, the maximum temperature of the lithium coolant was very close to the saturation temperature (the difference was 24 K), and the system was operated at extremely high temperatures (the average temperature of the core coolant was 1750 K); c) In coolant flow loss accident, when the coolant flow of the system dropped below 40% of the rated mass flow, the lithium coolant boiling would occur in the primary loop system, and the emergency shutdown control action was required to ensure the safety of the system.

Dynamic simulation of a space lithium-cooled reactor system coupled with a He–Xe closed Brayton cycle

The lithium-cooled reactor with Brayton conversion power system mainly consists of fast reactor, intermediate heat exchanger, closed Brayton cycle (CBC) loops filled with Helium–Xenon (He–Xe) binary gas mixtures and heat rejection loop which radiate residual heat through heat pipes to outer space. In this study, a dynamic model of 100-kWe lithium-cooled reactor with Brayton conversion power system was established based on RESYS code, which include reactor core thermal-hydraulic model, six-group neutron kinetics model and decay heat model, heat exchanger model, Closed Brayton cycle model including turbine, compressor and rotating shaft, heat pipe radiator model etc. The nominal steady-state simulation is carried out to verify the correctness and accuracy of individual component model the integrated system model. Four typical transient conditions including accidental reactivity insertion, loss of coolant flow of primary loop, partial and total external load loss and a step reduction in the mass flow rate of heat rejection loop are simulated to analysis the transient characteristics and prove the safety features for those simulated scenarios. The results are helpful for the design, evaluation and operation of space liquid-lithium-cooled reactor power system with He–Xe closed Brayton cycle.

Research on fluid heat transfer characteristics of heat pipe radiator directly driven by heat pump

The heat pipe radiator directly driven by heat pump heating system has the advantages of fast heat transfer and high energy efficiency. Based on the empirical heat transfer formula, the heat and mass transfer process in the heat pipe radiator was studied. The key parameters in the empirical heat transfer formula were derived by combining with the experimental data. The distribution of the thickness of the condensate film and the heat transfer coefficient in the height direction of the heat pipe radiator was analysed. The influence of the working fluid condensate mass and vapour mass in the heat pipe radiator was investigated. The results showed that the thickness of the liquid film changes from the bottom of 0.1110 mm to the top of 0.0594mm along the height of the heat pipe. The minimum charge of working fluid is 1.78 kg to 1.81 kg and the heating COP of the system still reach to 3.14 even at the outdoor temperature of -12.6 ?.

Simulation and analysis of a noval thermal management system integrated with heat pipe radiators for 4680 battery module

Simulation and analysis of a noval thermal management system integrated with heat pipe radiators for 4680 battery module

Experimental and simulation study of a U-shaped water-cooled sleeve heat pipe radiator for high heat flux density

Effective heat dissipation methods are desperately needed to ensure heat transfer of the large quantity of heat generated by radioactive isotopes in restricted places. This study employs the Bell-Delaware method to design a U-shaped water-cooled sleeve heat pipe radiator (UWC-HP) intended for heat dissipation on a 16 cm2 surface area with a heat flux density of 200 W/cm2. We have established a 3D model, which was experimentally validated, showing an error within 5 %. Subsequently, as the refrigerant and structural design of the condenser segment are crucial factors leading to the limitations of UWC-HP, this study aims to evaluate the impact of the condenser segment on the heat dissipation performance. Specifically, we investigated the effects of different cooling water temperatures, flow rates, and fin designs on the heat dissipation performance of the UWC-HP. Based on this, We found that the rib height, the number of ribs, and the rib material can strengthen the performance of the heat sink by a maximum of 12.3 %, 10.1 %, and 3.7 %, respectively. The heat sink optimized by orthogonal experiments has a maximum heat source surface temperature of 506.22 K and Nu of 101.85, which reduces the maximum surface temperature of the heat source by a maximum of 22 K and strengthens the heat sink capacity of heat pipes by 20 %. This article achieves efficient heat transfer for isotopic decay heat in a confined space by designing a heat pipe heat exchanger. It reduces the equipment's temperature and enhances the safety of the nuclear reactor.

Study on load tracking characteristics of closed Brayton conversion liquid metal cooled space nuclear power system

It is vital to output the required electrical power following various task requirements when the space reactor power supply is operating in orbit. The dynamic performance of the closed Brayton cycle thermoelectric conversion system is initially studied and analyzed. Based on this, a load tracking power regulation method is developed for the liquid metal cooled space reactor power system, which takes into account the inlet temperature of the lithium on the hot side of the intermediate heat exchanger, the filling quantity of helium and xenon, and the input amount of the heat pipe radiator module. After comparing several methods, a power regulation method with fast response speed and strong system stability is obtained. Under various changes in power output, the dynamic response characteristics of the ultra-small liquid metal lithium-cooled space reactor concept scheme are analyzed. The transient operation process of 70 % load power shows that core power variation is within 30 % and core coolant temperature can operate at the set safety temperature. The second loop's helium-xenon working fluid has a 65K temperature change range and a 25 % filling quantity. The lithium at the radiator loop outlet changes by less than ±7 K, and the system's main key parameters change as expected, indicating safety. The core system uses less power during 30 % load power transient operation. According to the response characteristics of various system parameters, under low power operation conditions, the lithium working fluid temperature of the radiator circuit and the high-temperature heat pipe operation temperature are limiting conditions for low-power operation, and multiple system parameters must be coordinated to ensure that the radiator system does not condense the lithium working fluid and the heat pipe.

Study on the thermal-mechanical coupling characteristics and influencing parameters of heat pipe radiator under accident conditions

Space reactors, due to their strong environmental adaptability, high power output, small size, and long lifespan, are the most important direction for the development of nuclear energy systems in space. The waste heat of the space reactor system needs to be dissipated through a radiative heat exchanger. The current numerical analysis of the heat exchanger predominantly emphasizes heat transfer phenomena while neglecting the effect of mechanical properties. This study utilizes a self-developed, highly accurate thermal-mechanical coupling calculation program to conduct a numerical analysis of the heat pipe radiator. The main objective is to acquire a comprehensive understanding of its thermal-mechanical coupling characteristics and evaluate the effects of various accident conditions on the radiator. The results indicate that the heat dissipation power obtained from the thermal-mechanical coupled calculation is 0.42% higher than that obtained from the standalone heat transfer calculation. Single axial heat pipe failure leads to a 9.13% decrease in heat dissipation power for the affected module, while two axial heat pipes failure results in a 21.17% decrease. The ability of the heat pipe radiator to meet the heat dissipation power requirements under different failure conditions indicates its capacity to effectively respond to a wide range of incidents, thereby emphasizing its superior safety level.

Development and experimental study of a 3-dimensional enhanced heat pipe radiator for cooling high-power electronic devices

A 3-dimensional enhanced heat pipe radiator (HPR) is developed to meet the requirements of heat dissipation and temperature uniformity in the cooling of high-power electronic components. The radiator is composed of a conventional flat heat pipe base and roll-bond flat heat pipe fins, which can enhance heat transfer in three dimensions. By means of experiments, the heat transfer characteristic is firstly studied under different filling ratios for a single roll bond flat heat pipe. Then, a comparison is performed of the heat transfer performance between the HPR and the conventional aluminum fin radiator (CAFR) under different heating powers and wind speed conditions experimentally. In this research, HPR demonstrates obvious advantages in the heat transfer. Results show that the optimum filling ratio is 35% for the roll-bond flat heat pipe. The start-up time of HPR is shorter (25 mins), and the start-up performance is not affected by power variation. HPR has a low thermal resistance of less than 0.48 °C/W compared with CAFR, which can effectively control the heat source temperature difference is about 1.7 °C–1.8 °C. The maximum heat dissipation of HPR and CAFR is almost the same under natural convection condition. But when the wind speed is 4 m/s, the maximum heat dissipation of HPR increased by 58.2% compared to the maximum heat dissipation of CAFR.

Analysis of the Impact of Parameters of Gravity Heat Pipe Radiator on the Temperature Control of Gangue Hill and Engineering Test

ABSTRACT Deep within coal gangue hills, there is a substantial amount of wasted thermal energy. Prolonged accumulation of these hills leads to significant damage to the atmosphere and soil. Gravity heat pipes, as efficient heat transfer components, can safely, efficiently, and conveniently extract the accumulated heat in gangue hills to achieve effective thermal control. In this study, we first analyzed the optimal height of the heat dissipation fins through a single fin heat dissipation model. Then, we determined the optimum spacing between the heat dissipation fins through analysis with multiple fins. The results showed that when the height of the heat dissipation fins was 80 mm and the spacing between fins was 80 mm, the heat dissipation performance and economic costs were most reasonable. Through an engineering trial conducted for 143 days at the Maotergou coal mine gangue hill, it was found that the average heat dissipation rate of a single gravity heat pipe ranged from 243.52W to 494.32W. The total heat dissipation during the entire experimental process was 54.39 kJ, and the total heat dissipation at the elevation of 890 meters was 1087.71 kJ. This indicates that managing the internal temperature accumulation in coal gangue hills using gravity heat pipes is entirely feasible.

Machine learning and computational fluid dynamics based optimization of finned heat pipe radiator performance

This study integrates machine learning, genetic algorithm and computational fluid dynamics to explore the influence of geometry on the finned heat pipe radiator performance. It also proposes an optimal geometry that enhances the heat transfer of the radiator significantly. Firstly, orthogonal test were designed, coupled the thermal resistance network method and the CFD method to model the finned heat pipe heat sink. The analysis of variance yielded the following qualitative conclusions: the height, number and thickness of the fins had different effects on the heat source temperature in descending order; the heat source temperature decreased with increasing number and thickness of the fins and increased slightly with increasing height. Secondly, a prediction model of the heat source temperature under different heat source distributions was built using four MLAs. The artificial neural network was chosen as the optimal model by comparison. The model was analysed with correlation analysis, SHAP and PDP analysis and consistent conclusions with the orthogonal test were obtained. Finally, GA was used to obtain the optimal geometric structure. The results showed that the heat source temperature was reduced to 41.75 °C and the heat sink mass was only 0.2231 kg when the number of fins was 18, the length was 38 mm, and the thickness was 0.6 mm. This solution decreased the heat source temperature by 8.7% and the heat sink mass by 18.42% compared with the optimal solution from the orthogonal test. This study demonstrated the advantages of machine learning methods in computational fluid dynamics.

Steady-state performance analysis of loop heat pipe radiator in space reactor

The loop heat pipe has a good application prospect in the field of space reactor radiator because of its characteristics of the separation of gas/liquid pipelines and the long-distance efficient heat transfer. The comprehensive performance analysis of loop heat pipe radiator for space reactor is carried out by the heat balance calculation method based on energy coupling iteration proposed in this paper. The loop heat pipe radiator models of different configurations were developed using the mass and energy conservation theory. The models were validated by experimental data of the loop heat pipe under various heat loads. The model in this paper can correctly simulate the steady-state operation characteristics of loop heat pipe, and evaluate the design of loop heat pipe radiator for space reactor. The performance of loop heat pipe radiator was analyzed in this paper under various design conditions such as power, evaporation temperature, and heat sink temperature. The results show that the thermal operating parameters have significant effect on characteristics of loop heat pipe radiator. The design length of the condenser pipe was considered as an important factor to achieve steady state heat balance under different design power. Meanwhile, the operation characteristics of loop heat pipe radiator with different configurations were compared, which demonstrated that the performance of panel-type radiator was better than fin-type radiator.

Experimental investigation of an air source heat pump with multigroup heat pipe radiators

As a clean and sustainable electrified heating technology, air source heat pump (ASHP) has been widely used in household in China. However, some problems occurred with the commonly used water loop system, such as low efficiency, complicated structure, more likely to be frozen and burst as well as high electric energy consumption, etc. In this paper, a new air source heat pump with multigroup heat pipe radiators (ASHPMP) was presented. In ASHPMP system, the condenser and heat pipe were coupled together to form a new type of heat radiation terminal, which was named as heat pipe radiators, multiple terminals driven by the compressor provided heat for several rooms. An experimental apparatus of the ASHPMP system was developed and the experiment was carried out in residential buildings also, and R410A was used in the heat pump and R134a was used in heat pipes. The influence of temperature, pressure of heat pump and heat pipe on the heating performance of ASHPMP under frosting/defrosting condition was analysed. The results showed that the new system can operate stably under outdoor temperatures of −12.7 °C to 6.5 °C. As the indoor temperature was set at 20 °C, the heating coefficient of performance (heating COP) could reach up to 3.15 with outdoor temperature −12.7 °C, and it was 6.73 with outdoor temperature 6.5 °C.

Shutdown safety analysis of megawatt-class space gas-cooled reactor system

Among the numerous space nuclear power sources, high temperature gas-cooled reactor with closed Brayton cycle has the advantages of both high power and high energy conversion efficiency. An Open-grid MEgawatt Gas-cooled spAce nuclear reactor (OMEGA) is investigated. Furthermore, a system Transient Analysis code of scheduled Shutdown and emergency Shutdown (TASS) is developed, including core, turbine-generator-compressor, regenerator, condenser, heat pipe radiator and other modules. TASS was verified by comparing prediction value with designed value, and transient performances of system shutdown were simulated. Over the course of shutdown, emissivity of fuel cladding is closely related to cladding peak temperature. Firstly, there is no overlay coating on fuel cladding whose emissivity equals to 0.18, the peak temperature of fuel cladding during scheduled shutdown and emergency shutdown reaches melting point at 7.8 h and 3.6 h respectively. Secondly, there is overlay coating on fuel cladding and emissivity is increased to 0.80. Radiation heat transfer can be greatly enhanced, and peak temperature of fuel pellet and cladding do not exceed the melting point of relevant material, which reflects the importance of fuel cladding surface processing. This paper provides a valuable analysis support for the design of megawatt-class space gas-cooled reactor system.