The Effects of Liquid Compressibility on the Nucleation and Growth of Bubbles in Forced Convective Flow Boiling Within Microchannels

Forced convective flow boiling in microchannels is characterized by the nucleation and rapid growth of vapor bubbles in confined geometries. Experimental studies of these flows have been limited to the measurement of wall temperature, inlet liquid velocity, inlet and outlet pressures, and high speed imaging forcing analysts to infer the conditions inside the channel from measured external values. The present study examines the evolution of the pressure field during bubble growth prior to bubble departure using a one-dimensional fully compressible Lagrangian-Eulerian model. Numerical results for a single bubble growing from a nucleation site for both constant pressure and constant volumetric flow rate conditions demonstrate the magnitude of the pressures generated and bound the magnitude of the reflected pulses from the channel ends. The reflected pulses can locally decrease the pressure in the channel below the levels predicted by incompressible models. Additional simulations predict nucleation and growth of bubbles at sites that would be inactive if liquid compressibility is neglected. The results indicate the acoustic characteristics of microchannels for flow boiling can not be neglected and will be important in the optimization of microchannel designs.