Design and experimental validation of a high capacity loop heat pipe for avionics cooling

Abstract

With the rapid development of modern aviation industry, the power of avionics has been increasing continuously, bringing great challenge to thermal management. As an efficient two-phase heat transfer device, loop heat pipe (LHP) holds great application potential in avionics cooling. To address the issue of inadequate heat transfer capability, a set of kW-class LHP was specially designed and experimentally validated considering the airborne environment. A detailed introduction covering the entire design process was presented, in which some targeted design criteria were provided. Ammonia was chosen as the optimal working fluid, and stainless steel envelope with a nickel wick was adopted. Experimental validation showed that, at a heat sink temperature of 20 ℃, the designed LHP could achieve a maximum heat transfer capacity of 1021 W, confirming the efficacy of the design method. The average heat flux at the evaporator could reach 12.04 W/cm2. The LHP exhibited a maximum and minimum thermal resistance of 0.16 and 0.054 ℃/W, respectively, achieved at heat loads of approximately 50 W and 600 W. The maximum temperature fluctuation at the center of the saddle surface was no more than ±1.40 ℃. A method for estimating the heat leak between the evaporator and the compensation chamber was also developed, and the maximum heat leak rate was calculated to be approximately 5.2%. Moreover, the designed LHP also manifested excellent startup performance and operation stability.