An optical measurement system was used to investigate the effect of microchannel length on adiabatic gas-liquid two-phase flow characteristics. Experiments were conducted with 146 mm and 1,571 mm long, circular microchannels of 100 micron diameter. Two-phase flow patterns, void fraction, gas and liquid plug lengths and their velocities were measured for two inlet configurations and gas-liquid mixing, i.e., (a) reducer and (b) T-junction. The test section length was found to have a significant effect on the two-phase flow characteristics measured at the same axial location in the microchannel test section typified by the void fraction data. The mean void fraction data obtained in the shorter (146 mm) microchannel with the reducer inlet agreed well with the equation by Kawahara and Kawaji which was previously proposed. On the other hand, the mean void fraction obtained at 36 mm from the inlet in the longer (1,571 mm) microchannel corresponded well with the homogeneous flow model and Armand’s equation for both reducer and T-junction inlet configurations. In the present experimental ranges of superficial gas velocity, jG = 0.03 ∼ 14 m/s, and superficial liquid velocity, jL = 0.04∼0.7 m/s, the gas and liquid plugs obtained in the longer microchannel had relatively shorter lengths and higher velocities than those in the shorter channel. Thus, both the microchannel length and inlet geometry were found to affect the two-phase flow characteristics in a microchannel.

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