Design optimization of a loop heat pipe to cool a lithium ion battery onboard a military aircraft

The present paper proposes optimization procedures for loop heat pipe (LHP) designed to cool the lithium-ion battery for airborne high energy electric lasers (HEL) without power consumption. The LHP is more efficient than the air cooling device using bleed air. The battery temperature rising enlarges the permanent loss of its capacity and makes it unusable and unsafe. Cold speedy air around a flying aircraft becomes a good heat sink for dissipating the battery heat. The design objective is to reduce the weight of the LHP, considering the range of battery operating temperature and operational reliability. For numerical analysis, the total system of the LHP is analyzed through a thermohydraulic model and the heat transfer of the porous wick is predicted by the thin liquid film model. The thermal characteristics of the groove section are found by an analytical solution and a finite difference method. The design optimization is executed by using approximation models for the cases of (1) a fixed heat load, (2) a varied heat load without uncertainty consideration, and (3) a varied heat load with uncertainty consideration about the generated heat of the battery. As result of the optimization process, the weight of the LHP was reduced significantly. The optimized LHP for the varied heat load with uncertainty consideration case is most reliable and robust with slight increase of the weight.