Heat Pipe Research Articles

Editor's Note for article entitled “Prediction of battery thermal behavior in the presence of a constructal theory-based heat pipe (CBHP): A multiphysics model and pattern-based machine learning approach”

Editor's Note for article entitled “Prediction of battery thermal behavior in the presence of a constructal theory-based heat pipe (CBHP): A multiphysics model and pattern-based machine learning approach”

An experimental study on evaporator heat transfer performance of radially rotating heat pipes with water as working fluid

The utilization of radially rotating heat pipes (RRHPs) provides a novel method for gas turbine cooling due to the high thermal conductance and simple structure. Centrifugal force is utilized to return the condensate from the condenser to the evaporator. In this paper, the evaporator heat transfer performance of a RRHP, including heat transfer regime and the effect of centrifugal acceleration on heat transfer, are investigated experimentally. The RRHP evaporator with 45 % filling ratio was heated by electric heating wire with heat input ranging 50 W to 200 W and the condenser was cooled by air. Centrifugal acceleration at the evaporator center ranged from 117 g to 1457 g. Temperature distribution along the RRHP was measured by thermocouples. Experimental results revealed that non-boiling regime and boiling regime could occur in the RRHP evaporator according to heat input while natural convection and nucleate boiling were the dominating heat transfer mechanisms respectively. Geyser boiling phenomenon at 117 g to 344 g and temperature overshoot at 682 g to 1457 g were first observed in RRHPs as the transition stage at which boiling started to occur and the heat transfer performance was enhanced by 23 % in average. The evaporator heat transfer coefficient ranged 5180 to 9866 W/(m2·K) in non-boiling regime and 10,621 to 15438 W/(m2·K) in boiling regime with a boundary around 10000 W/(m2·K). With increase of centrifugal acceleration, transition stage was delayed to higher evaporator temperature and heat input. Nucleate boiling was suppressed by 20.3 % while natural convection was enhanced by 14.9 % as accelerations increased from 117 g to 682g. Interestingly, it was first observed that boiling was not entirely suppressed at 1457 g and the RRHP evaporator showed high heat transfer coefficient of 13065 W/(m2·K) at 200 W under such a high acceleration.

Experimental study on the flat loop heat pipe with minichannel wick under low heat flux

Stable operating under low heat flux condition is crucial for loop heat pipe. To investigate the performance of the flat loop heat pipe under low heat flux, a visual structure of evaporator with longitudinal replenishment characterized by minichannel wick is proposed and fabricated. The minichannel wick increases the permeable area and reduces flow resistance to enhance the heat transfer capacity. However, under low heat flux condition, excessive liquid permeation into the vapor line and the local reverse vapor flow may deplete the liquid storage in the compensation chamber, resulting in a wick temperature increase of 4.7 °C under extreme condition. Lowering the heat sink temperature does not necessarily lead to a lower stable wick temperature in specific cases but rather poses operational challenges and further raises the stable wick temperature by 9 °C. By visualizing the flow structure, it is found that arduous vapor–liquid prestart distribution leads to prolonged circulation establishment time and higher wick temperature, resulting in a higher stable wick temperature. As the heat flux increases, the effect of prestart distribution on the stable wick temperature weakens as the redistribution capability improves.

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Heat transfer characteristic of an alumina oscillating heat pipe

Oscillating heat pipes (OHP) are a promising and highly efficient heat transfer technology especially in the field of power electronics thermal management. However, conventional metal OHP do not meet the need for insulation or low coefficients of thermal expansion. In order to expand the application field and break the application limitation of the OHP technology, alumina ceramic oscillating heat pipes was designed and investigated in this paper. The alumina OHPs combine the excellent insulating, oxidation-resistant, corrosion-resistant and low thermal expansion properties of alumina ceramic with the efficient heat exchange mechanism of oscillating heat pipe technology, exhibiting great application potential. An alumina flat-plate oscillating heat pipe was prepared, 6 internal microchannels were examined using micro-CT, and the microstructure was characterized using scanning electron microscopy. The heat transfer characteristics of the OHP charged with water were investigated using a heat transfer test system. Increasing heat loads were employed to the OHP, and the operating temperature of 20 °C and 60 °C as well as the orientation varied between 0° and 90° were also introduced. The oscillation motion of the alumina OHPs were investigated, including temperature oscillations before and after startup of the OHPs, and a comparison effective thermal conductivities at various tilt angles and operating temperatures was carried out. The experimental results revealed that the heat transfer performance of the alumina oscillating heat pipe significantly increased with the increased heat loads and reached to 861.7 W/(m∙K) at 56 W. The effective thermal conductivity of the OHP was 6 times higher than that of the empty OHP at heat load of 16 W. When the orientation was 30°, the temperature oscillation instability increased, the oscillation amplitude increased, and the heat transfer performance of the oscillating heat pipe decreased. As the operating temperature increased, the stability of temperature oscillations improved, the amplitude decreased, and heat transfer performance was enhanced.

Experimental study of heat transfer in double-loop plate pulsating heat pipe

Experimental study of heat transfer in double-loop plate pulsating heat pipe

Expression of Concern for article entitled “Thermal management systems based on heat pipes for batteries in Electric and Hybrid Electric Vehicles”

Expression of Concern for article entitled “Thermal management systems based on heat pipes for batteries in Electric and Hybrid Electric Vehicles”

Heat dissipation design and performance optimization of high speed train PMSM based on coupled electromagnetic-thermal field

The permanent magnet synchronous motor (PMSM) has been widely recognized as the most promising driving system. This research presents a hybrid cooling system to improve the cooling effect of high speed train PMSM. At first, the cooling system includes the water jacket, heat pipes, Aluminum Nitride Ceramic sheets (AINC) inserted in the stator teeth, potting material at both ends of winding, and fins bonded to the evaporation section of heat pipes. In addition, the 3D model of PMSM is constructed with the error between experiment and simulation less than 5 %. Subsequently, using the Response surface method (RSM), this study investigates the sensitivity and the coefficient of correlation by varying AINC size on the electromagnetic properties. Finally, Particle Swarm Optimization (PSO) is employed to establish the mathematical optimization model of this cooling system. The results show that the optimized cooling system reduces the maximum temperature (Tmax) for each component of the PMSM while achieving a more uniform temperature field without compromising its electromagnetic properties. This significantly enhances the reliability and contributes to advancements in multi-physical field optimization for PMSM cooling.

Experimental Study on the Impact of Lubricant on the Performance of Gravity-Assisted Separated Heat Pipe

Gravity-assisted separation heat pipes (GSHPs) are extensively utilized in telecommunications base stations and data centers. To ensure year-round cooling, integrating GSHPs directly with a vapor compression refrigeration system is a viable solution. It is unavoidable that the refrigeration system’s lubricant will infiltrate the heat pipe loop, thereby affecting its thermal performance. This paper examines the performance of a GSHP, which features a water-cooled plate heat exchanger as the condenser and a finned-tube heat exchanger as the evaporator, when the working fluid (R134a) is contaminated with a lubricant (POE, Emkarate RL-46H). The findings are compared with those from a system free of lubricant. The experimental outcomes indicate that the presence of lubricant degrades the heat transfer efficiency, particularly when the filling ratio is adequate and no significant superheat is observed at the evaporator’s outlet. This results in a 3.86% increase in heat transfer resistance. When the charge of the working fluid is suboptimal, the average heat transfer resistance remains relatively constant at a 3% lubricant concentration yet increases to approximately 5.27% at a 4–6% lubricant concentration, and further to 12.32% at a 9% lubricant concentration. Concurrently, as the lubricant concentration fluctuates between 3% and 9%, the oil circulation ratio (OCR) varies from 0.02% to 0.11%.

Experimental study and numerical simulation of concrete pavement electrical heating for snow melting

Road snow accumulation can lead to severe traffic delays, and commonly used deicing agents may pose potential environmental risks. Electrically heated concrete pavement systems utilizing heating pipe technology offer a safe and environmentally sustainable alternative. The snow-free ratio was frequently used as an evaluation index to evaluate the snow-melting performance in road infrastructure. However, the unique wavy temperature distribution during the snow-melting process of the heating system results in discontinuous melting, making the existing snow-free ratio inadequate for accurately assessing its performance and effectively guiding the operational strategy of the heating system. Therefore, this study analyzed the special temperature distribution and proposed a new calculation method for snow-free ratio based on the average temperature and the temperature non-uniformity coefficient of the pavement surface. First, the effects of factors such as heating pipe spacing, embedded depth, heating power, and wind velocity on average temperature and the temperature non-uniformity coefficient were analyzed using finite element simulation. Prediction models for average temperature and the temperature non-uniformity coefficient were then established and validated using the response surface method and experiments. Subsequently, using average temperature and the temperature non-uniformity coefficient as intermediate variables, a new functional relationship between the snow-free ratio and the four factors was established, allowing for satisfactory snow-melting performance to be achieved by adjusting the relevant factors of the heating system. The results show that the error rate between the proposed new calculation method and simulation results is only 4.44 %. Moreover, it was concluded that adjusting spacing and heating power is the most effective strategy for heating systems to achieve optimal snow-melting performance.

Performance analysis and optimization of insulation layers on a novel building-integrated photovoltaic system

Conventional photovoltaic-thermoelectric generator (PV-TEG) systems are hindered by significant heat transfer losses, which impair power generation throughout the year. Addressing this challenge, a novel PV-MCHP-TEG system is proposed, integrating photovoltaic (PV) cell, microchannel heat pipe (MCHP) array, and thermoelectric generator (TEG) module components with strategically placed insulation layers to facilitate year-round, day-and-night power generation. This study primarily investigates the impact of insulation layers on heat transfer processes, employing a comprehensive analysis and optimization approach. Utilizing Simulink software, the multifaceted influence of insulation layer variables, including locations, thicknesses, and materials, on TEG efficiency across various conditions was examined. Further, a comparative analysis was undertaken to evaluate the dynamic payback period across different modes. The optimization of these insulation parameters revealed that incorporating Polyisocyanurate Foam (PIR) as the insulation material in the optimized PV-MCHP-TEG system achieved an efficiency of 19.32 %, marking a 2.41 % improvement over conventional PV-TEG systems without insulation. Furthermore, the dynamic payback period was reduced to 11.34 years, representing a decrease of 1.05 years compared to conventional PV-TEG systems. These findings underscore the potential of our proposed system to outperform existing solutions by optimizing thermal management through insulation, thereby offering a promising avenue for enhancing photovoltaic-thermoelectric energy conversion.

Review on Research Progress of Pulsating Heat Pipes

Since their invention by Akachi in 1990s, pulsating heat pipes (PHPs) have attracted widespread interest and application in practice, e.g., grinding, chip cooling, the thermal management of batteries, etc., owing to their notable efficiency in heat transfer and their simplicity and flexibility in structure. Key factors influencing the heat transfer efficacy of pulsating heat pipes are mainly attributed to the thermophysical properties of the working fluid, the structural parameters, and the operating conditions. Research on pulsating heat pipes is conducted through theoretical investigations, numerical simulations, and visual experiments. In this paper, the research on PHPs in recent decades is reviewed with the consideration of the heat transfer performance mechanism and application of pulsating heat pipes, especially research under operation conditions such as with “status with motion” and with “inconsistent heat flux”.

Environmental and economic assessment of industrial excess heat recovery collaborations through 4th generation district heating systems

The external use of excess heat from industrial processes is an important factor in the energy transition and 4th generation district heating is an enabling technology. This paper presents a calculation tool for assessing the economic feasibility and the environmental impact of collaborations between potential industrial sources and users. The tool supports the sizing of district heating pipe diameters, pumps, heat pumps, and heat storage systems. A distinctive feature of the model is the possibility of calculating carbon and blue water footprints, alongside economic indicators, for both existing stand-alone systems and potential collaborative configurations. Excess heat recovery from water-cooled condensers of refrigeration systems is evaluated for two case studies involving the space heating of offices in a food logistics hub and the heating of a greenhouse from a frozen pizza factory, respectively. Only the second collaboration is profitable with the baseline price of natural gas (0.04 €/kWh) and electricity (0.12 €/kWh), provided that the distance between the source and the user is less than 2 km. For higher gas prices, distances of approximately 8 km would be viable. However, for source-user distances above 5 km, the water footprint of the collaboration would be higher than that of stand-alone systems.

Preparation and thermal properties of biomimetic polymer-based flexible ultra-thin flat heat pipe

Inspired by the structure of the human spine, a flexible ultra-thin flat heat pipe featuring a biomimetic human spine design has been devised. This flat heat pipe, equipped with a biomimetic human spine structure, is capable of undergoing repeated bending at large angles. An experimental study was conducted to investigate the primary influencing factors. The results revealed that the optimal liquid filling ratio for the flexible ultra-thin flat heat pipe is 0.3. The dip angle is positively correlated with the heat transfer performance of the flexible ultra-thin flat heat pipe, and the bending angle is negatively correlated with the heat transfer performance of the flexible ultra-thin flat heat pipe. The maximum thermal conductivity of the flexible ultra-thin flat heat pipe can reach 1457.68 W/(m·K). The flexible ultra-thin flat heat pipe with liquid filling rate of 0.3 and bending angle of 0 degree has the fastest start-up speed. A visualized experimental platform was further designed to observe the internal flow of the working fluid within the flexible ultra-thin heat pipe in various bending states. The visual experimental results demonstrate that bending initiates the premature condensation of steam within the flexible section, and the condensed working medium subsequently generates resistance to the flow of subsequent steam, leading to an inability for the latter to be smoothly transported to the condensing section, thereby creating a vicious cycle.

Conceptual design and optimization of heat rejection system for nuclear reactor coupled with supercritical carbon dioxide Brayton cycle used on Mars

During the conceptual design of the Mars surface nuclear reactor coupled with supercritical carbon dioxide Brayton cycle, the heat rejection system occupies most of the weight, and reducing the weight of heat rejection system can effectively cut down the transportation cost from Earth to Mars. This paper explored the feasibility of adopting a combination of heat pipe cooling device and convective heat exchanger to design the heat rejection system for the Mars surface nuclear power station, established flow and heat transfer model and weight model, developed a thermal-hydraulic design program for the heat rejection system, and verified its accuracy; then, the NSGA-II multi-objective optimization method is used to optimize the weight of heat rejection system. Pareto front shows that with higher heat rejection proportion of convective heat exchanger, corresponding inlet velocity of Mars' atmosphere should also be increased. As the optimization result of heat rejection system, the ratio of weight to heat rejection is between 0.94 kg/kW and 2.92 kg/kW, and the maximum power consumption of convective heat exchanger accounts for 3.29% of the total power generation.

Performance Analysis of Water Heat Pipe for Application of the Passive Cooling System in Nuclear Power Plants

Incorporating heat pipes into passive cooling systems in nuclear reactors offers the benefits of passive operation without external power, a simple design, and high thermal capacity. Accurate thermal performance prediction of the heat pipe is crucial for ensuring safe reactor design and operation. Prior studies on nuclear reactor systems utilizing heat pipes have focused on thermosyphons, which operate by gravity. However, to expand the range of heat pipe applications in reactor systems, experimental investigations of large-scale heat pipes driven by capillary pumping force are required. In this study, a water heat pipe with a 25.4-mm diameter and 4-m length was manufactured to provide thermal experimental results under extreme conditions, such as system rollover or loss-of-cooling accidents. A three-dimensional (3D) printing technique was used to fabricate the high-performance lattice capillary wick structure by combining cubic and diamond lattice structures. The 3D printed wick structure showed 21 to 165 times higher capillarity and enhanced surface properties compared to the screen mesh wick structure. Compared to wickless thermosyphons, the 3D printed wick heat pipe exhibited higher thermal conductivity, stable operation in both vertical and horizontal orientations, and faster startup under extreme conditions.

A numerical study on the influence of fin numbers and material embedded with heat pipe for thermal charging in a trapezoidal container

This study delves into the thermal charging of a PCM accommodating thermal energy storage system within a trapezoidal enclosure, incorporating variable-length fins and heat pipes, through numerical analysis. The investigation employs multiple variable-length fins, and Steel, Aluminum (Al), and Copper (Cu) are considered potential fin materials. The study utilizes six key benchmarks—completes melting duration, enhancement ratio, total accumulated energy, average PCM temperature, mean power, and cost per mean power to comprehensively assess the impact of varying fin numbers and materials. The findings reveal that while an increased number of Al fins results in a higher enhancement ratio, this effect diminishes with a further increase in the number of fins. The scenario featuring 12-Steel-fins demonstrates the most uniform temperature distribution. Furthermore, an augmentation in the number of fins and their thermal conductivity corresponds to an improvement in mean power. Notably, the cases of 12-Cu-fins and 12-Al-fins exhibit equal and the lowest cost per mean power among all scenarios.

Experimental Investigation of Evaporation of Methanol and n‐Pentane on a Submerged Capillary Structure

AbstractThe heat transfer limit of heat pipes is investigated by pool boiling experiments in a standard apparatus with a capillary layer placed on a copper tube. The capillary layer is a hollow cylinder made of bronze with a wall thickness of 2 mm and the test fluids are methanol and n‐pentane. The setting is comparable to high‐flux tubes already investigated in the literature. In dependence on the heat flux, three to four sections with different characteristics are identified. Compared to plain copper tubes, the heat transfer is partially increased by a factor of 12 until the limit is reached at around 70 kW m−2.

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.

Multi-criteria decision analysis and experimental study on heat pipe thermoelectric generator for waste heat recovery

In the realm of heat conversion and utilization, gravity heat pipes have garnered significant attention due to their exceptional heat conduction efficiency. As a strategy to effectively enhance the efficiency of thermoelectric generator (TEG) systems through shallow geothermal heat recovery, optimizing the performance of gravity heat pipes holds significant implications for their widespread application in the field of sustainable energy. Experimental evaluations comprehensively assessed the performance of a 6 m gravity heat pipe within a temperature difference power generation system, employing multi-criteria decision-making to test thermal performance, efficiency, reliability, stability, and working fluid studies. The study demonstrates that the heat transfer efficiency of gravity heat pipes is highest under film boiling conditions at 250 °C to 350 °C. By adjusting the inclination angle to 60° to 90° and the filling ratio to 30 %–60 %, the power generation efficiency can be improved to 9.71 %. With an increase in wind speed to 8 m/s, the cold end temperature decreases by 30 %, resulting in a peak power generation efficiency of up to 11.3 %. Additionally, CHIME connection methods reduce energy losses to 8.1 %, providing crucial scientific foundations for the design and optimization of temperature difference power generation systems. These findings not only elucidate the heat transfer mechanisms of gravity heat pipes but also offer technical guidance for efficient energy conversion in thermoelectric generator systems.