Effect of Oscillatory Heat Load on Pressure Drop Oscillation

Abstract

Microchannel and minichannel evaporator cooling systems can help remove large heat fluxes with high heat transfer coefficients. However, flow instabilities during microchannel boiling, like pressure drop oscillation (PDO), can deteriorate the cooling performance. In this study, we numerically analyze the effect of an oscillatory evaporator heat load on PDO characteristics occurring in a pumped liquid cycle (PLC). Our model indicates that a specific range of heat load oscillation amplitude and frequency can suppress the PDO amplitude significantly. For the PLC considered in this study, the PDO amplitude can be reduced by 60% when the baseline heat load of 300 W is superposed with an oscillating component of amplitude 100 W and frequency 6 Hz. The study finds that a smaller heat load oscillation amplitude would show a weaker effect on PDO suppression. For an oscillation amplitude of 60 W, the PDO amplitude reduction was only 40% for a wide range of heat load frequency. When the combined effect of heat load oscillation amplitude and frequency was investigated, results showed that the PDO would reach a state of invariance for all heating amplitudes when the frequency was large enough. We believe this could be utilized as an active control strategy to suppress flow oscillation and optimize the overall cooling performance. Furthermore, the PDO characteristics under oscillatory evaporator heat load are compared with the forced Van der Pol oscillator. The similarities between the two systems noted in this study are initial steps towards understanding the effect of various oscillatory system parameters on PDO occurring in a two-phase system.