Jinguo Yang

Experimental Investigation of New Flat-Plate-Type Capillary Pumped Loop

A capillary pumped loop is a two-phase heat transfer device which has been increasingly applied in thermal control of satellite or spacecraft and electronic cooling. However, startup performance of a normal capillary pumped loop is poor and hydrodynamic oscillation in the system appears sometime during its operation. A flat-plate-type capillary pumped loop is constructed and tested in the present study, which combines the advantages of a capillary pumped loop and a loop heat pipe by improving both system and components. In the present capillary pumped loop, both evaporator and condenser are designed as a type of flat plate with porous wick, and a reservoir is used to control and adjust operation temperature of the system. In addition, a subcooler is adopted to improve the quality of working fluid flowing back to the evaporator. A plane type of evaporator with a cross channel for the liquid supply was made to reduce the probability of a dry-out point caused by strong evaporation in the case of high heat flux, and therefore to enhance the stability of the system. Also, a plane type of condenser with a porous wick is designed, which is of the three ports for vapor-pipe inlet, liquid-pipe outlet, and an adjusting pipe connected to a reservoir. The startup performance of the system benefits greatly from this three-port design, as liquid in the system can be easily pressed into a reservoir due to resistance reduction. The performance of a capillary pumped loop prototype was tested in startup, persistence operations, and different vacuum. Startup experiments under different heat loads and working conditions were conducted. Excellent startup performance, being stable and easy, has been shown for the plane-type capillary pumped loop system, which validates the new configuration. Pressure oscillation and temperature fluctuation in the system were reduced largely owing to the induction of a porous wick in the plane condenser. During experimental processes lasting more than 10 h, the new type capillary pumped loop shows outstanding thermal behavior and no dry-out phenomena were observed. The testing results indicate that 1) the new capillary pumped loop system shows excellent startup performance without pressure priming and liquid clearing of vapor line; and 2) the new capillary pumped loop system is stable under very severe operational conditions, such as low load, sudden power step, etc.

High Thermal Conductivity of Flake Graphite Reinforced Polyethylene Composites Fabricated by the Powder Mixing Method and the Melt-Extruding Process

The thermal conductivity of flake graphite (FG) particulates reinforced high density polyethylene (HDPE) composites was systematically investigated under a special dispersion state of FG particles. The effects of particle size, weight filling ratio and proportion of various sizes were discussed in detail. A special composite (15 wt % 500 μm/10 wt % 200 μm/10 wt % 20 μm/5 wt % 2 μm FG + 60 wt % polyethylene (PE)) with a high thermal conductivity about 2.49 W/(m·K) was produced by combining the synergistic effect of several fillers. The component material size distribution was employed to analyze the effect of particle size. And scanning electron microscope (SEM) was adopted to observe the FG network in the composites. Thermogravimetric analysis (TGA) revealed the good thermal stability of composites. Differential scanning calorimetry (DSC) indicated that all composites own a similar melting temperature. Sample compression experiment indicated that all composites still exhibit high mechanical strength. Consequently, the easy-making flake graphite reinforced polyethylene composites with a high thermal conductivity would have a wide application in the new material field, such as a thermal interface material, a heat exchanger, voltage cable, etc.

Experimental Investigation of Temperature Oscillation in Miniature Loop Heat Pipe

Temperature oscillations are a rather wide‐spread phenomenon accompanying the mLHP operation, which depend on the charging ratio of the working fluid, the device orientation in the gravity field and the conditions of the condenser cooling, and so on. Intense oscillation, whose amplitude may exceed tens of centigrade degrees and the period maybe equal to tens of minutes, arise from the lack of a working fluid in a mLHP when a hot condensate or vapor bubbles periodically penetrate into the compensation chamber and act on the vapor phase in it, which increasing its temperature and volume. Changes in the external conditions, for instance, the LHP arrangement in an unfavorable orientation or applied heat load with respect to the conditions for which the filling volume is optimal, also contribute to the initiation of intense temperature oscillation. All in all, the heat leak from the evaporator to the compensation chamber, the heat loss to ambient and the temperature and rate of subcooled liquid dictate the vap...

An Experimental Investigation of Miniature Loop Heat Pipe with Flat Evaporator

This paper specifically addresses the thermal characteristics of the miniature loop heat pipe (mLHP) with flat disk shaped evaporator for the thermal control of the compact electronic devices. The loop was made of stainless steel with sintered nickel wick and ammonia as the working fluid. Detail study was conducted on the start-up reliability of the mLHP and the operating characteristics under different heat loads. In the horizontal orientation, the device was able to transfer maximum heat-flux of 7W/cm2 with evaporator temperature below 55degC limit. The experiments conformed that the mLHP could achieve steady state in very short time and adapt the different heat-flux loads very well. The effect of the sink temperature was studied in detail, and decrease of the sink temperature was useful to the start-up of the mLHP but useless to decrease the temperature of the evaporator wall.

Numerical Simulation of Two Phase Flow and Heat Transfer in CPL Condenser With Porous Wick

In the present paper, the Volume of Fluid (VOF) method is introduce to model the two phase flow and heat transfer with phase change in CPL condenser with porous element and the effect of different wall temperature and inlet vapor velocity to condensation phase change interface was studied with numerical simulation method. The results present that a fixed condensation physical interface can be formed on the face of porous wick, which can restrain, even eliminate the pressure oscillation. The reason of the effects are also analysed in this paper.Copyright