Experimental study on thermal performance of loop heat pipes with flat evaporator for LSI package
Thermal performance of a loop heat pipe (LHP) equipped with a flat evaporator and a compensation chamber integrated onto the evaporator and separated from the evaporator was experimentally investigated. The heat leak in the flat evaporator is a critical problem as it results in the degradation of the heat transport characteristics of the LHP. In this paper, the heat leak quantity during the steady-state operation of the LHP was calculated by carrying out a thermal energy balance analysis for the flat evaporator. From the results, the heat conduction along the case sidewall of the evaporator dominated the heat leak on the evaporator, and it was found that the heat leak from the heat source to the compensation chamber decreased to 5% or less of the applied input power due to the reduced heat conduction of the evaporator casing.
Submillimeter-thick loop heat pipes fabricated using two-layer copper sheets for cooling electronic applications
Abstract A new submillimeter-thick loop heat pipe (LHP) fabricated using two copper sheets is proposed as a cooling solution for thermal management of electronics. The experimental investigation was conducted by measuring the temperature of each part of the surface of the thin LHPs for its heat input, to evaluate the heat transport characteristics of the LHPs discussed in this paper. Submillimeter LHPs with thicknesses of 0.6 and 0.4 mm were fabricated using chemical etching and diffusion bonding processes on two thin copper sheets. A design is exhibited that achieves efficient heat transfer under a variety of operating orientations with a thin LHP, by using a half-etching process on a thin copper sheet to form a grooved structure that generates capillary force. A thermal resistance of 0.09 K/W between the evaporator and the condenser is achieved at 5 W in the top heat orientation, using a nonwoven fabric consisting of copper fibers located inside the flow path of one of the copper sheets. Moreover, it is demonstrated that heat transport can be achieved up to a heat input amount of 7.5 W without orientation dependence for an ultrathin LHP of 0.4 mm thickness.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.