Multichannel Effect of Condensation Flow and Heat Transfer in Horizontally Positioned Silicon Microchannels With the Channel Depth Down to Thirty Microns

Multichannel effect is an important issue in micro condensers. In the present paper, we fabricated a silicon chip, consisting of three rectangular microchannels, with each width of 800 microns but depth down to 30 microns. Saturated vapor of water enters the entrance of microchannels which were horizontally positioned. There are two types of flow patterns: (1) the annular flow at high inlet pressures; (2) the quasi-stable bubble slug in the microchannel upstream followed by the isolated bubbles downstream, at moderate or low inlet pressures. For the second flow pattern, the downstream isolated bubble is formed by breaking up: (1) the single vapor thread connecting the upstream bubble slug and the detaching bubble; (2) the dual vapor threads synchronously in the center microchannel; (3) the dual vapor threads non-synchronously in the side microchannels. The flow patterns in the two side channels are symmetry against the center microchannel. The upstream bubble slug is shorter in the side channels than in the center channel. The temperature gradient across the chip width direction accounts for the non-synchronously break-up of the dual vapor threads connecting the bubble slug and the detaching bubble, in the side channels, indicating the multichannel effects.