Two-Phase Flow Instability of Boiling in Two Parallel Microchannels

The present work investigates experimentally the two-phase flow instability of convective boiling heat transfer in a system of two parallel trapezoidal microchannels. The test section employed in this work is fabricated by silicon bulk micro machining and anodic bounding processes. Both channels are trapezoidal with a hydraulic diameter of 47.7 μm. The topside width of the central island between two channels is 20 μm. The forced flow of de-ionized water is provided by a syringe pump. The two-phase flow visualization under boiling conditions is made possible by a high-speed digital video camera. The temperatures at the heating surface, inlet and outlet reservoirs and the inlet pressure during the experiments are recorded and analyzed with flow visualization. The results of the study demonstrate clearly that two-phase flow instabilities with significant oscillations in two-phase flow properties can be developed in the system of two parallel microchannels at low mass fluxes and relatively high heating powers. Flow visualization confirms the presence of flow reversal. In particular, large magnitude, aperiodic oscillations appear with alternative presence of two-phase flow period and dryout period at a high heat flux. The time interval for each cycle is from 1800 to 4000 sec. Such a large magnitude oscillation may be a kind of flow excursion. At an even higher heat flux, dryout and so vapor flow prevails in both channels and oscillations ceased.