Development Of Heat Pipe Research Articles

Development of novel flexible heat pipe with multistage design inspired by structure of human spine

To improve the thermal performance and expand application scope of the flexible heat pipe, a novel flexible heat pipe with multistage design is proposed which inspired by the structure of human spine. The thermal performance of bionic flexible heat pipe under different working conditions was experimentally investigated. Our results show that bionic flexible heat pipe has lower thermal resistance and better stability after bending compared with the traditional flexible heat pipe. Moreover, the bionic flexible heat pipe with 25% filling ratio has low thermal resistance and strong anti-gravity ability. Furthermore, the thermal resistance of bionic flexible heat pipe keeps about 0.57 °C/W after bending multiple times because working fluid can realize two phase cycle in bionic flexible heat pipe. In general, the thermal resistance of bionic flexible heat pipe increases with the increase of bending angle, but the change of thermal resistance is closely related to the working position during the inclined bending process, because the height difference between the evaporator and condenser has a great effect on the thermal performance of flexible heat pipe. Moreover, the maximum height of the anti-gravity section of flexible heat pipe is derived to determine the maximum bending angle range of flexible heat pipe during three-dimensional (3D) bending. This study provides a new method for the design of flexible heat pipe with high performance.

RESEARCH AND DEVELOPMENT OF LOOP HEAT PIPE – A REVIEW

RESEARCH AND DEVELOPMENT OF LOOP HEAT PIPE – A REVIEW

Code development and analysis of heat pipe cooled passive residual heat removal system of Molten salt reactor

The high efficient and reliable Passive Residual Heat Removal System (PRHRS) is of great importance to the development of Molten Salt Reactor (MSR), whether the liquid fuel MSR or solid fuel MSR. In this research, based on the structure and operation performance of the new conceptual PRHRS, using high temperature heat pipe as heat transportation, a set of reasonable mathematical and physical models have been built, mainly including reactor core model, high temperature heat pipe model and PRHRS model. The new conceptual Passive Residual heat removal system Analysis Code (PRAC) has been developed using FORTRAN language. The verification and validation for PRAC is conducted by using existed Molten Salt Reactor Experiment (MSRE) data provided by Oak Ridge National Laboratory and the PRHRS experimental data in our previous work. The results show that the developed PRAC could predict the MSR transients reasonably and show high fidelity. The numerical results of reactor core neutronic and thermal–hydraulic model show a good agreement when compared with MSRE pump startup and shutdown transients. The numerical results by PRHRS model agree well with experimental data which the maximum error of the fluoride salt temperature and heat pipe wall temperature are within 1.2% and 2.8%. This research provides a valuable software basis for the design and analysis of PRHRS of MSR.

Development of Heat Pipes for Cooling Thermally Stressed Electronics Elements

An algorithm for the development of heat pipes involving the choice of the working fluid, materials for the casing and wick, and the methods of calculating the limits of heat-transmitting ability of heat pipes is suggested. This algorithm has been applied successfully for creating different types of wicks and heat pipes on the basis of which a cooling system has been created for a high-power light-emitting diode lantern.

Development and Study of a Loop Heat Pipe with Several Heat Sources of Different Power

The results of the development and experimental studies of a loop heat pipe designed for the simultaneous cooling of several heat sources that dissipate different power amounts is presented. The pipe has a cylindrical evaporator and a serpentine-shaped condenser that is connected via the vapor and liquid lines. The evaporator was in thermal contact with the main heat source. Two additional, less powerful heat sources were in contact with the heat exchangers located on the vapor line and liquid lines. Freon-152a and ammonia were used as the working fluids. The efficiency of the loop heat pipe is estimated according to the ratio of the maximum heat load on the additional sources to the heat load of the main source. A temperature of 90°C was the limiting condition for each source. The tests were performed at a condenser coolant temperature of 20°C. The maximum power of the pipe with ammonia, without additional heat sources, was equal to 350 W, and that with freon-152a was130 W. We show that the maximum load on the additional source located on the liquid line was 34 W (57%) for a freon pipe under a nominal heat load on the main source of 60 W and 10 W (16%) on the source located on the vapor line. For an ammonia loop heat pipe under a nominal load on the main source of 220 W, the respective values for the additional sources were 60 W (27%) and 13 W (6%).

Development of hybrid loop heat pipe using pump assistance for cooling application on high heat flux device

Loop heat pipe (LHP) is an effective two-phase heat transfer device that utilizes evaporation and condensation of a working fluid. LHP is widely used in a passive cooling system, highly reliable and a very high thermal conductive device. However, extreme power density can cause dry-out in the evaporator section of LHP and might hinder the performance of the cooling system. The purpose of this research is to design and manufacture a new prototype of LHP by modifying the conventional LHP. The modification was performed by adding a diaphragm pump, called hybrid loop heat pipe (HLHP). The experimental results show that the installation of pumps in the modified LHP was able to prevent the occurrence of a dry out and reduce the operating temperature. Under a constant conductance mode, the pump was activated for 20 minutes and succeded in forcing the system to a new stable condition with a significant temperature drop. These results indicate that HLHP is very promising as a two-phase cooling system that can be proposed for devices that produce high heat flux.

Development of Flat-Plate Loop Heat Pipes for Spacecraft Thermal Control

This paper describes the development, ground experiment results and on-orbit test plan of stainless steel-ammonia flat-plate loop heat pipes for space applications. The pressure-proof evaporator with reinforced structure was designed to endure the high pressure of the working fluid. The cylindrical compensation chamber and the primary sintered nickel wick were connected by the secondary wick for liquid supply under microgravity. To validate the startup and operation capability in space, the on-orbit tests of two FLHPs (flat-plate loop heat pipes) will be carried on in the reentry capsule of the Chinese next generation spaceship. The FLHPs will be used to transfer the dissipated heat of the laser gyro and fiber optic gyro to the cold capsule wall. Extensive ground experiments were conducted to investigate the startup and operation characteristics and the heat transfer capability. Test results indicate that there are only two startup situations for the FLHP. A superheat degree of above 10 °C is required to initiate the nucleate boiling in the evaporator when the vapor channels are flooded by liquid. The auxiliary startup measure by locally heating on the top surface near the evaporator outlet is effective to obtain the required superheat, not affecting the equipment’s temperature. Orientation of the evaporator and the CC (compensation chamber) has negligible effect on the startup and operation of the FLHP, and the secondary wick can provide effective liquid supply to the primary wick even at an unfavorable position. The heat transfer capacity of the evaporator is greater than 330 W and the critical heat flux is greater than 20 W/cm2.

A mathematical study of water migration in heat pipe from plants

Heat pipe is being widely used nowadays in industry as a high efficiency heat transfer device. For the development of heat pipe, many attempts have been made to enhance its performance by mimicking biology, including the optimization of structure and flow patterns in heat pipe wicks. Constructing biporous, composite, and nanopillar wicks with aim of achieving hierarchical structure has been found through the learning of natural solutions. And bionic approach studying plant water migration provides another path to the fluid flow enhancement inside heat pipe as well. Forces involved in the water migration process in plants include the capillary effect, friction, gravity and transpiration effect, and all these happen in heat pipe as well. The investigation through plant water migration can provide a guidance to the heat transfer performance analysis and wick structure design. Magnetic Resonance Imaging (MRI) technology is used in this paper to scan live plants, providing the possibility of visualizing the internal structures in vivo and obtaining water transport velocity in xylem vessels. In addition, a novel mathematical model on the forces in plant water migration and heat pipe is proposed in this paper. The result from mathematical calculation is compared with the experimental measured result. This paper also successfully put transpiration effect and friction into consideration, as our innovation syntheses of a low level of hierarchical structure and integrates integral wicks includes evaporator, adiabatic, and condenser as well.

Development and tests of a loop heat pipe with several separate heat sources

The paper presents the results of development and experimental investigations of ammonia loop heat pipe (LHP) intended for a simultaneous cooling of several heat sources dissipating a variable capacity. The LHP was equipped with two heat exchangers located on the liquid line and one heat exchanger on the vapor line, which were in thermal contact with some additional heat sources. The LHP evaporator was in thermal contact with the main, the most powerful heat source. It has been shown that at a nominal heat load of 120 W on the main heat source the total heat load on the additional heat sources located on the liquid line may reach 34 W. The maximum heat load on an additional heat source located on the vapor line, in the same conditions, was 9 W. It has also been shown that a thermal action on the liquid line has a considerable effect on the temperature of the main heat source, whereas a thermal action on the vapor line does not influence it.

Review on Development of Aluminium Water Heat Pipe

Review on Development of Aluminium Water Heat Pipe

A Plate Heat Pipe Design with Micro-rectangular Groove

At present, micro-groove flat heat pipe has become the focus of study and development of heat pipe. This paper introduces mainly its design features and manufacturing processes. The conclusions of the study are as follows: The plate heat pipe has good start-up and performance characteristics. We should pay attention to the compatibility between working medium and shell material in the design. At the same time, we should control strictly the cleaning, leak detection, and filling in the process to ensure the manufacture quality.

Modelling of Heat Transfer in the Evaporator and Condenser of the Working Fluid in the Heat Pipe

ABSTRACTThe aim of this paper is to point out possible solutions to the further development of heat pipes by numerical modelling of phase-change heat transfer. Numerical modelling has now become a standard method that helps to reduce the economic costs of research and development of new and innovative devices. The article describes the procedures for using numerical simulation in phase-change heat transfer that occurs due to evaporation and condensation of the working fluid. The suggested procedure enables modelling of gravitational heat pipe under different changes in its geometry or under changes in the working fluid. From the simulation results we can find out how the heat pipe behaves under different geometric changes and how much heat output it transfers. The paper presents results obtained from modelling of heat pipes, such as classical gravitational heat pipe, heat pipe with capillary geometry, and closed loop pulsating heat pipe. The results gathered from numerical simulation of heat pipes were compared with measurement results.

Experimental Analysis on Thermal Performance of Fabricated Flat Plate Heat Pipe Using Titanium Dioxide Nanofluid

An effective design of flat plate heat pipe is developed for electronic equipment cooling. Due to its heat transferring nature, light weight and high effective thermal conductivity, flat plate heat pipes (FPHP) has been recognized as potential devices in this challenging part of thermal control of high density electronic devices. This present paper is a report of such an experiment which is a development of smaller size flat plate heat pipes (60x60x30mm), made up of copper as body material, sintered copper as wick structure and the working fluid used is a Nano fluid prepared from Titanium dioxide nanoparticles dissolved in DI water. Elaborative experiments were conducted to ascertain the thermal performance of the fabricated heat pipe and detailed analysis is discussed from the outcomes of the experiments. The FPHP charged with the nanofluid has been tested for thermal performance and found to be improved with the rise in temperature. The condenser section has been tested with the two types of cooling arrangements as natural and forced convection. Comparatively the results of forced convection experiment are showing extremely good performance. The thermal resistance at forced convection side is reduced considerably upto 80 Watts of power input and showing gradual increment with higher power inputs which is stabilized at 0.25 °C/W. The thermal resistance reduction is also showing better results in the forced convection setup. The thermal performance results have been analyzed and found to be in good agreement with the previous studies. This research work can be further proceeded to analyze the heat transfer coefficient of various nanofluids and to optimize the minimum size requirement of the FPHP.

Progress of cryogenic pulsating heat pipes at UW-Madison

Space agencies continuously require innovative cooling systems that are lightweight, low powered, physically flexible, easily manufactured and, most importantly, exhibit high heat transfer rates. Therefore, Pulsating Heat Pipes (PHPs) are being investigated to provide these requirements. This paper summarizes the current development of cryogenic Pulsating Heat Pipes with single and multiple evaporator sections built and successfully tested at UW-Madison. Recently, a helium based Pulsating Heat Pipe with three evaporator and three condenser sections has been operated at fill ratios between 20 % and 80 % operating temperature range of 2.9 K to 5.19 K, resulting in a maximum effective thermal conductivity up to 50,000 W/m-K. In addition, a nitrogen Pulsating Heat Pipe has been built with three evaporator sections and one condenser section. This PHP achieved a thermal performance between 32,000 W/m-K and 96,000 W/m-K at fill ratio ranging from 50 % to 80 %. Split evaporator sections are very important in order to spread cooling throughout an object of interest with an irregular temperature distribution or where multiple cooling locations are required. Hence this type of configurations is a proof of concept which hasn’t been attempted before and if matured could be applied to cryo-propellant tanks, superconducting magnets and photon detectors.

Heat pipes with variable thermal conductance property for space applications

The activities presented in this paper focus on a new approach to provide passive regulation of the electronic unit thermal regime of the MASCOT lander (DLR) onboard the NEA sample return mission Hayabusa 2 (JAXA), by using heat pipes. It provides information on the development and testing of heat pipes with variable thermal conductance in a predetermined temperature range. Such heat pipes acts as thermal switches, but their construction does not include additional elements inherent to gas loaded heat pipes (GLHP) and thermal diode heat pipes (TDHP). Copper heat pipes with metal fibrous wick were chosen as baseline design. We have obtained positive results by choosing heat carrier and structural parameters of wick (i.e. pore diameter, porosity and permeability). A rising of heat pipes thermal conductivity from 0.04 to 2.1 W/K was observed in the temperature range between -20°C…+55°C. The heat pipes transferred predetermined power not less than 10 W within the temperature range of +20°C… +55°C. These heat pipes are in flight since December 2014 and the telemetric data obtained in September 2015 showed normal operation of the thermal control system.

Development and on-orbit operation of loop heat pipes on chinese circumlunar return and reentry spacecraft

This paper describes the development and result of ground experiment and analyzes the on-orbit operation of Loop heat pipes (LHP) for the Chinese circumlunar return and reentry spacecraft. A novel LHP was developed to satisfy the thermal control requirements of Inertial measurement units (IMU). The LHP consisted of an integrated evaporator subassembly, a cambered condenser, and an electric explosion valve. Ground experiments were conducted to investigate the startup characteristics, and heat transfer and heat insulation performance of the LHPs. During a flight mission, the LHPs work as a thermal switch and perform both heat transfer and insulation functions. Before returning to the earth’s atmosphere, the valves of the reentry capsule are opened to discharge working fluid and prevent heat transfer from the capsule wall to the devices. In the flight mission, the LHPs performed all the required functions, and the IMU temperatures were maintained within an allowable range.

Experimental Development and Computational Optimization of Flat Heat Pipes for CubeSat Applications

Due to the compact and modular nature of CubeSats, thermal management has become a major bottleneck in system design and performance. In this study, we outline the development, initial testing, and modeling of a flat, conformable, lightweight, and efficient two-phase heat strap called FlexCool, currently being developed at Roccor. Using acetone as the working fluid, the heat strap has an average effective thermal conductivity of 2149 W/m K, which is approximately five times greater than the thermal conductivity of pure copper. Moreover, the heat strap has a total thickness of only 0.86 mm and is able to withstand internal vapor pressures as high as 930 kPa, demonstrating the suitability of the heat strap for orbital environments where pressure differences can be large. A reduced-order, closed-form theoretical model has been developed in order to predict the maximum heat load achieved by the heat strap for different design and operating parameters. The model is validated using experimental measurements and is used here in combination with a genetic algorithm to optimize the design of the heat strap with respect to maximizing heat transport capability.

Development and examination of switchable heat pipes

The well-directed transmission of heat flux enables an efficient and demand-actuated temperature control of technical systems. By the combination of heat pipes and shape memory alloy actuators, an adaptive, passively working switch concept is developed and implemented, which automatically activates the heat flux through the heat pipe when reaching a certain temperature limit. Furthermore, the created numerical calculation model provides the opportunity to theoretically describe the behavior of the designed system. Measurements show the proof of the concept and validate the model for further optimizations of switchable heat pipes to be applied in various technical applications.

自動車の排熱利用を目指した kW 級ループヒートパイプの構築と過渡的熱流動特性の評価

自動車の排熱利用を目指した kW 級ループヒートパイプの構築と過渡的熱流動特性の評価

Development and tests of loop heat pipe with multi-layer metal foams as wick structure

A plate-type loop heat pipe (LHP) with multi-layer metal foams as wick structure was fabricated. In the LHP, the multi-layer metal foams and vapor channels with high depth-to-width ratios were integrated into a flat evaporator, which is beneficial for cycling the working fluid and enhancing the evaporation process. Subsequently, the operational parameters, such as the types of working fluid inventory, wick material and heat load with ethanol as the working fluid, were varied to investigate the effect on the heat transfer performance of LHP. The experimental results show that obvious three stages were observed in the start-up and running process of the LHP including the rising temperature stage, start-up stage and steady running stage. In the fluid inventory range of 20~60 ml, it is found that 40 ml of ethanol was the optimized working fluid inventory for the designed LHP. Compared to the nickel foam, the LHP with multi-layer copper foams with wick structure showed better performance with different heat loads because of the higher thermal conductivity and smaller pore size.