Bubble Dynamics and Boiling Heat Transfer in Microsystems

Understanding of micro boiling systems requires multiscale modeling, linking nanoscale fluid-surface interactions and micrometer channels. We present a multiscale model, successfully used for analysis of boundary conditions in microchannels. Slip lengths are found to be mainly dependent on the surface-fluid interactions, weakly on the channel sizes from nanometer to micrometer. The multiscale model is expected to be extended for bubble dynamics in microsystems, considering wall surface roughness, nano bubbles tripped in the cavities of the surface, etc. The second part gives a review on the micro bubble dynamics of pool boiling under pulse heating conditions. The third part reviews boiling heat transfer in silicon microchannels. Bubbles are being nucleated in the channel corners. Flow patterns are repeated in millisecond time-scale. Explosive boiling was found to be triggered by the higher liquid superheat, pushing liquid plugs out of microchannels. Depending on boiling numbers, three distinct heat transfer regions are identified. Heat transfer displays the nucleate boiling behavior at medium boiling numbers, and the convective heat transfer one at higher boiling numbers. The available heat transfer correlations over-predict the heat transfer performance in silicon microchannels, due to lack of nucleation sites in smooth silicon microchannels.