Study on Flow Boiling Heat Transfer and Two-Phase Flow Pressure Drop in Flat Mini-Channel

Flow and the heat transfer characteristics of boiling two-phase flow of water in flat mini-rectangular-channels were examined. The cross-sections tested were 1.0×10 to 0.2×10 mm and the flow channel length was 250 mm. Single phase flow pressure drop was well expressed by the method for the usual size in the present experimental range. Boiling heat transfer of 0.5 mm high and 10 mm wide cross section was similar to that of the usual size. However, that 0.2 mm high and 10 mm wide cross section was a little different from that of the usual size. An increase in the heat flux after the onset of nucleate boiling on the boiling curve is milder than that of the usual size. Thus, the critical heat flux was lower than that of the usual size. Flow patterns observed in the present experiments were a little different from the Baker flow pattern chart. Consistent agreement was not obtained between the present results of the two-phase flow pressure drop and predictions by the methods for the usual size and also for a mini tube. Subcooled boiling was observed widely in the test section. This made it difficult to determine the local conditions such as quality that was necessary to calculate the Lockhart-Martinelli parameter for the two-phase flow pressure drop prediction.