THERMAL ANALYSIS AND FLOW VISUALIZATION OF A FLAT LOOP HEAT PIPE

The realization of a high heat flux removal with a flat loop heat pipe at ambient temperature is of great importance for achieving thermal control within spacecraft electronic equipment. In this article, a flat bifacial evaporator loop heat pipe with two flat thermo-contact surfaces has been proposed, fabricated, and investigated. The shell of the flat evaporator was made of stainless steel, and ammonia was selected as the working fluid. The startup and operating characteristics of the single side, both sides, and switching working modes were analyzed, as well as the influence of heat consumption, orientation, wind speed, and environmental temperature. The experimental studies indicated that this novel loop heat pipe can start up and run successfully under different working modes, and that the heat dissipation capacity of a set of loop heat pipes can reach 250 W at room temperature. Based on this, a light-weight and small electronic device has been developed using a multi-functional (efficient ‘heat collection-heat dissipation-structural support’) flat bifacial loop heat pipe to realize a kilowatt level heat dissipation capacity. This work can provide reference for the future design of high heat flux, light-weight, and small payload for use in spacecraft.

Advanced thermal management system based on a novel flat evaporator loop heat pipe with high-efficiency condenser for electronic cooling

Experimental research on the thermal performance of a flat evaporator loop heat pipe with a new composite wick

In response to the heat dissipation and temperature control requirements of a certain type of spacecraft payload, this paper designs a set of ceramic core flat plate loop heat pipes and couples them with TEC for use. The start-up of the loop heat pipe with the assistance of TEC was tested in the air, and the loop heat pipe started quickly. Comparing the operating states of the loop heat pipe under different loads without TEC, without TEC, and when TEC is turned on, the experimental results show that TEC coupled loop heat pipe can offset the heat leakage from the evaporator and the environment to the reservoir, reduce the temperature of the reservoir, and improve the thermal conductivity of the loop heat pipe. When TEC is not turned on, TEC has a significant side effect on the operation of the loop heat pipe. The influence of different measuring point positions on temperature control accuracy during temperature control was compared. The experimental results showed that precise temperature control of the heat source can be achieved by using TEC temperature control. The placement of measuring points has a significant impact on temperature control accuracy. The measuring points placed on the heat conduction strip have higher temperature control accuracy, while those placed on the heat source have larger temperature fluctuations. A temperature control circuit can be arranged on the liquid storage tank to improve the temperature control accuracy of the heat source. The TEC-coupled flat plate loop heat pipe has been successfully applied on a certain model to dissipate heat and control temperature for a certain load. Analysis of in-orbit data shows that the loop heat pipe starts quickly, runs stably, and has high-temperature control accuracy.

Experimental investigation on thermal characteristics of a novel loop heat pipe for cooling high heat flux electronic chips

Novel hybrid structures to improve performance of miniature flat evaporator loop heat pipes for electronics cooling

Design, fabrication, investigation and analysis of a novel flat evaporator loop heat pipe for cooling high heat flux server chips

Novel battery thermal management system for electric vehicles with a loop heat pipe and graphite sheet inserts

The thermal properties (thermal transfer and thermal expansion coefficient) of the enhanced epoxy resin (MWCNT / x-TiO2) were studied by weight ratios with the values (0%, 3%, 5%, 7% and 10%) and a constant ratio of 3% of MWCNT. The ultrasonic technology was used to prepare the neat and composites which were then poured into Teflon molds according to standard conditions. Thermo-analyzer sensor technology was used to measure thermal transfer (thermal conductivity, thermal flow, thermal diffusion, thermal energy and heat resistance). The thermal conductivity, flow, and thermal conductivity values were increased sequentially by increasing the weight ratio of the filler while the results of stored energy values and thermal resistance decreased by increasing the percentage of salts. The thermal mechanical analysis was used to measure thermal expansion and elasticity coefficient. The scanning electron microscopy was used to interpret the results of thermal analysis and distribution of the nanoparticle within the polymer matrix.

Evaporative heat transfer analysis of a micro loop heat pipe with rectangular grooves

Thermal requirements of today’s spacecraft and instruments exceed the heat transport capacities of conventional heat pipes. Accordingly, spacecraft engineers have turned to the Loop Heat Pipe (LHP) technology as a high-performance replacement. Like heat pipes, a LHP is also a passive capillary-pumped device having no mechanical moving part to wear out or break down. Hence it is reliable, durable, and more importantly maintenance-free for space applications. But while heat pipes can be treated as linear conductors in most thermal analyses, LHP thermal characteristics are not easy to predict for they are highly dependent upon the loop operational conditions. A few examples are given here: power input, sink and ambient temperatures. Even the past history of the aforementioned parameters can have an effect on the LHP performance. Previous LHP modeling efforts focused primarily on the prediction of the loop temperature and pressure drop for steady state or transient operation. For the most part, the model simulations agreed very well with test data from various LHPs. However the “health” of the secondary wick was conveniently ignored for two reasons: (i) to simplify the numerical method and (ii) the secondary wick design was a “trade secret” of the LHP vendor and was not divulged to the general public. In other words, the secondary wick was assumed to have “infinite” liquid transport capability and would not fail under any operating scenario. In truth, available test data had shown that the secondary wick might be the weakest link of the LHP. In an attempt to model the secondary wick fluid transport (without the knowledge of its actual design), a simplified geometry of the LHP pump core that functions like a conventional heat pipe was imposed in the analysis. In this paper, theoretical aspects of mass/heat transfer and fluid dynamics in the pump core will be given along with the model assumptions/simplifications. Discussion of the numerical method and prediction of the secondary wick transport requirements will also be given.

한국에서 삼원촉매 내구성은 1988년에 5년/80,000 km 이지만 2002년 이후로 10년/120,000 km이 요구된다. 국내의 삼원촉매는 배출가스 정화효율이나 압력강하 등이 만족하지만 열적 내구성은 만족시키지 못하고 있다. 삼원촉매는 내부에서 높은 온도를 유지하지만 외부 표면에서는 낮은 온도를 유지한다. 본 연구는 열유동과 구조해석 및 다음과 같은 과정에 의해서 열적 내구성을 평가하였다. 열유동 매개변수 범위는 차량시험과 열유동 해석에 의해 결정하였다. 후면 촉매 온도에 대한 반응 표면은 열유동 매개변수에 대한 실험계획법을 이용해 구성되었다. 차량시험에서 후면 촉매 온도에 대한 열유동 매개변수는 만족도 함수에 의해 예측하였다. 삼원촉매의 온도분포는 예측된 열유동 매개변수에 대한 열유동 해석에 의해 평가하였다. 【Three-way catalyst durability in the Korea requires 5 years/80,000km in 1988 but require 10 years/120,000km after 2002. Domestic three-way catalyst satisfies exhaust gas conversion efficiency or pressure drop etc. but don't satisfy thermal durability. Three-way catalyst maintains high temperature in interior domain but maintain low temperature on outside surface. This study evaluated thermal durability of three-way catalyst by thermal flow and structure analysis and the procedure is as followings. Thermal flow parameters ranges were determined by vehicle test and basic thermal flow analysis. Response surface for rear catalyst temperature was constructed using the design of experiment (DOE) for thermal flow parameters. Thermal flow parameters for rear catalyst temperature in vehicles examination were predicted by desirability function. Temperature distribution of three-way catalyst was estimated by thermal flow analysis for predicted thermal flow parameters.】

Thin diffusion bonded flat loop heat pipes for electronics: Fabrication, modelling and testing

In design phase, it is difficult to evaluate the influence of heat density distribution by non-uniform current density on temperature distribution of conductive parts. Therefore, we are developing an electromagnetic field ? thermal flow coupling analysis system. In this research, we developed a physical quantity mapping technique for electromagnetic field - thermal flow coupling analysis. Conventionally, temperature distribution of conductive parts is evaluated by thermal flow analysis under the condition of uniform heat density. In this research, heat density is calculated by finite element method, and thermal fluid field is calculated by voxel method. We developed a technique of mapping heat density onto thermal fluid field. In the technique, defining points and units of finite element are converted to defining points and units of voxel. We compared temperature evaluated by thermal flow analysis under the condition of non-uniform heat density with uniform heat density. As a result, it is confirmed that we can evaluate the influence of heat density distribution on temperature distribution of conductive parts.

Experiments have been conducted on a flat rectangular loop heat pipe with water and methanol at heat loads from 40 to 320 W at three orientations of the heat pipe (0°, 45°, 90°) and two filling ratios (33% and 50%). Performance parameters such as thermal resistance, effective thermal conductivity and capillary limit are calculated from the experimental data. The results exhibited that the thermal performance of water is better than methanol with least thermal resistance 0.13 K/W, maximum capillary limit 2626.72 W and an effective thermal conductivity 84490.48 W/mK at a heat load 320 W in horizontal position for 33% filling ratio.