On the Prediction of Pressure Fluctuations and Pressure Drop Caused by Confined Bubble Growth During Flow Boiling in a Rectangular Mini/Micro-Channel

Heat-sinks based on flow boiling in microchannels have the potential to mitigate temperature rise in high heat flux devices such as electronic equipment. One of the major challenges is the instability associated with pressure fluctuations caused due to the confined bubble growth during boiling in a microchannel. This paper presents a comprehensive model to estimate the dynamic pressure fluctuations in a channel of rectangular cross-section and compares with the experimental results. The time-averaged pressure drop obtained from the transient model has been verified with the experimental results and the steady two-phase flow pressure drop correlations. Effects of various parameters such as heat flux and mass flux on the time-averaged pressure drop and the transient pressure fluctuations are presented. The paper also provides an approximate methodology to estimate the nucleation frequency derived from the waiting period of the bubble. The calculated frequency is validated qualitatively with the experimental observation available in the literature. The current work also demonstrates that the transient pressure drop models, which, with suitable inputs, predict the local pressure fluctuations during confined bubble growth, can also be used to predict the steady- flow pressure drop.