Two-phase flow patterns for condensation of ethanol-water mixtures in triangular microchannels

An array of isosceles triangular microchannels with sidewalls inclined at 54.7° were fabricated by the wet etching method. The condensation of water and ethanol binary mixtures was visualized with additional measurements to investigate the condensation flow patterns in the silicon microchannels with hydraulic diameters of approximately 155 μm. The visualization study indicated that the flow patterns were influenced by the inlet ethanol concentration and the mass flux. Annular, injection, droplet-injection and bubble flow patterns were observed along the channels. The condensation instability effects were stronger with increased equivalent surface free energy differences. The increasing equivalent surface free energy differences caused droplets to form in the microchannel that moved from the condensing surface to the top corner due to the Marangoni effect, which led to fluctuating flow patterns. The frequency of the injection flow increased with increasing Rev and input ethanol concentration. The mass flux and the steam quality during condensation were measured at various locations in the experiments. Two phase flow pattern maps were developed for various inlet ethanol concentrations.