Visualization Experiment of Condensation in Expansion and Contraction Microchannels

This paper conducted visualization experiments on condensation heat transfer of three different types of microchannels with periodic expansion and contraction structures. The difference in microchannels lies in the relative lengths of the expansion and contraction sections. Using pure steam as the experimental working fluid, the visualization experiment observed dropwise condensation, annular condensation, injection condensation, and intermittent condensation. Besides, different phenomena of "gasping" and "breakpoint antedisplacement" were observed in the injection flow, which was different from those in straight microchannels. In addition, a two-phase flow map was established for three kinds of microchannels. The findings indicated that under the same steam mass flux, increasing the length of the expansion section of the microchannels and reducing the length of the contraction section led to an augmented annular flow area within the microchannels. Increasing the length of the microchannel expansion section and reducing the length of the contraction section are beneficial for reducing the frictional pressure drop of vapor condensation, but maintaining the same length of the microchannel expansion section and contraction section can achieve the best condensation heat transfer effect.