Loop Heat Pipe Operating Temperature Research Articles

Flat-evaporator-type loop heat pipe with hydrophilic polytetrafluoroethylene porous membranes

This paper describes an experimental study of a flat-evaporator-type loop heat pipe (LHP) with wicks made from hydrophilic polytetrafluoroethylene (PTFE) porous membranes, which have small pore sizes but high porosity and permeability. To demonstrate the applicability of these membranes, the LHP was designed completely and fabricated, after which the performance was experimentally investigated under a 0.52 m anti-gravity condition at a constant heat sink temperature of 80 °C. Two types of membranes were used, possessing different pore diameters and permeabilities. The pore diameter and permeability of wick 1 were 0.44 µm and 2 × 10−14 m2, respectively, while wick 2 had a pore diameter and permeability of 1.40 µm and 5 × 10−14 m2, respectively. A special wick support was designed and fabricated to ensure contact between the wick and the groove fins and to prevent the shrinkage of the PTFE membranes. Pure water was used as the working fluid. The effect of the PTFE wick characteristics on the LHP thermal performance was investigated by measuring the temperature at each point and the compensation chamber pressure. The LHP achieved steady-state operation at heat loads up to 1000 W, with a minimum thermal resistance of 0.052 K/W. Wick 2, which had a larger pore size and higher permeability, exhibited better performance than wick 1. The LHP operating temperature decreased by 10 °C, and the thermal resistance decreased by approximately 20% between wick 1 and wick 2.

Experimental study and steady-state model of a novel plate loop heat pipe without compensation chamber for CPU cooling

In this study, a new type of loop heat pipe (LHP) without compensation chamber is designed and manufactured, meanwhile the liquid line is fitted with a sintered wick to enhance startup and steady operation capacity. Specifically, the thermal characteristics of the LHP are studied experimentally. The results show that the LHP can start up smoothly at any heat load and the highest temperature of LHP does not exceed 90 °C. The fluid at the liquid line is subcooled, which is beneficial for the startup and steady operation of LHP. When the heat load is in range of 10 W to 50 W, the LHP works at variable conductance mode, and the system thermal resistance and the loop thermal resistance both decrease sharply with the increasing heat load. When the heat load is in range of 50 W to 150 W, the LHP enters a constant conductance mode, and the system thermal resistance and the loop thermal resistance remain basically constant. Besides, the steady-state model of LHP used to predict the operating temperature of LHP is established. The simulation results were compared with the experimental data, and the maximum relative error of evaporator, vapor, condenser outlet and liquid line wick inlet temperature are less than 15%.

Operating temperature and distribution of a working fluid in LHP

One of the main factors that influence the operating temperature of a loop heat pipe (LHP) is the distribution of a working fluid in the device. The paper presents the classification of LHP operating modes on the basis of the criterion of presence or absence of the working-fluid vapor phase in the compensation chamber (CC). It gives a description of method of calculating the LHP operating temperature for every operating mode and shows the characteristic features, advantages and disadvantages of every mode.

Mathematical Modeling of Loop Heat Pipes and Experimental Validation

A mathematical model to calculate the steady-state performance of a loop heat pipe (LHP) is presented. The mathematical model is based on the steady-state energy conservation equations and the pressure drop calculations along the fluid path in the LHP. The LHP operating temperature is calculated as a function of the applied power at a given LHP condition. The beat exchange between each component of the LHP and the surroundings is taken into account. Both convection and radiation environments are modeled. Experimental validation of the model is attempted by using two different LHP designs. The validity of the mathematical model is investigated for different sink temperatures and elevations. The comparison of the calculations and experimental results showed good agreement (within 5% ). The proposed method proved to be a useful tool for reliable prediction of the steady-state performance characteristics of the LHP.