An active control strategy for reduction of pressure instabilities during flow boiling in a microchannel

Flow instabilities during boiling in a microchannel have been well studied and documented in the literature. However, passive/active ways to reduce their magnitude are less well explored. In this paper, we examine the effect of external pulsations on flow with respect to reduction in pressure instability during boiling. Both the frequency and the amplitude of superimposed pulsations are varied and the study is performed for different mass flow rates and heat flux values. It is observed that the pressure fluctuations reduce significantly at high frequencies for all the cases studied; however, small frequencies of external pulsations may or may not be helpful. Interestingly, the average pressure is also found to reduce in certain cases. Flow visualization reveals that the flow switches from bubbly to annular when external pulsations are applied, which leads to this reduction in the pressure fluctuation. These results demonstrate that it may be possible to simultaneously reduce both mean and fluctuating pressure drops by carefully choosing the operating parameters.