Experimental study of a Capillary Pumped Loop for cooling power electronics: Response to high amplitude heat load steps

Among the challenges of future increases in electric terrestrial transportation, the Capillary Pumped Loop (CPL) and Loop Heat Pipe (LHP) are at the forefront of the solutions for cooling power electronics. In the present work, a CPL designed for ground applications is subjected to fast and large heat loads (up to 2 kW) as they occur in standard power cycles of vehicles. The loop time response is investigated versus the amplitude of the heat load step: the dynamics is dominated by the liquid redistribution between the condenser and the reservoir in which large (one order of magnitude above the steady state value) liquid mass flow rate overshoots and undershoots are observed. The first minute consecutive to the heat load change is thus a critical period for the wick in terms of mechanical solicitation and actually, this transient can lead to substantial loop performance limitations: effects on the stability of the evaporator temperature, failure mode. These results demonstrate that dimensioning based on a steady-state model will not guarantee loop performance in the event of sudden large amplitude heat loading.