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The evaluation of pressure loss in gas-liquid two-phase flow through singularities is important for designing compact heat exchangers such as cooling devices in electronic equipment. However, the accurate evaluation methods are scarce especially for mini-channel flow. In the present study, air-water twophase flow and water single-phase flow experiments were conducted at room temperature using three kinds of horizontal rectangular mini-channels each with a U-bend, sudden expansion, and sudden contraction. The width and depth of the rectangular cross-section of the channel with U-bend were 3 mm by 3 mm, while those with sudden expansion and/or sudden contraction were 3 mm by 3 mm and 6 mm by 3 mm. The flow regimes covered were bubble, slug and annular flows. Reynolds number range for water was from 240 to 9300, while that for air from 17 to 3200. The local pressures upstream and downstream from the singularity were measured with calibrated pressure sensors to determine the frictional pressure drop in the channels upstream and downstream from the singularity, together with the pressure drop at the singularity. Video photography of flows was also conducted to determine flow regime, bubble velocity and void fraction. In the analysis, the frictional pressure drop data and the pressure drop data at the singularity were compared with calculations by various correlations in literatures. Results of such experiment and analysis are described in the present paper.

Air-water two-phase flow through U-bend, sudden expansion and sudden contraction in rectangular mini-channels