Influence of convective heat transfer and wall thermal capacity on dynamic interactions between wall temperature and pressure drop oscillations during microchannel flow boiling

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Flow boiling in microchannel heat sinks is attractive for use in industrial thermal management applications owing to highly effective heat dissipation and compactness. However, flow boiling is subject to two-phase flow instabilities, specifically pressure drop oscillations, that may deteriorate performance by causing transient wall temperature oscillations or initiating premature critical heat flux. While there has been extensive model-based investigation of the stability and flow dynamics associated with pressure drop oscillations in microchannels, prior work has not focused on the coupled interactions between these flow oscillations and the dynamic heat transfer processes, as is required to predict thermal performance degradation and ensure reliable operation. This study predicts the influence of wall thermal capacity and heat transfer coefficient on the dynamic interaction between pressure drop oscillations and wall temperature. First, we demonstrate and explain how added wall thermal capacity acts to reduce the amplitude of pressure drop oscillations due to coupling between the thermal and flow dynamics. Whereas previous work has attributed this effect to a thermal time constant of the wall, the amplitude of the pressure drop oscillations is shown to scale with the Biot number by scanning various combinations of wall thermal capacity and heat transfer coefficient. A Biot number threshold is thereby suggested as the criterion for judging whether the thermal wall capacity must be considered in dynamic models, based on the strength coupling between the wall temperature and pressure drop oscillations.