Abstract
In this study, the experiments were performed to observe vertically upward vapor-liquid two-phase flow of HFE-7000 in the parallel microchannel whose hydraulic diameter was 0.93 mm per a path by using a high-speed camera. The experiments were conducted by heating the microchannel portion for use as evaporator. The saturation temperature was 30 °C. In order to investigate the influence of the inlet qualities of the test section on the flow pattern, the experiments were conducted to keep exit quality at xout = 0.9 and mass flow rate W = 0.0022 kg･s-1, set inlet qualities at xin = 0, 0.2 0.7. From the results of the observation, it was clear that the cause of drift flow was unevenness of the vapor and liquid distribution in the inlet header. Moreover, back flow which is thought to degrade the heat exchanger performance was observed as well, and it was found that the cause was rapid expansion of the vapor plug. Therefore, when the inlet header part was made a modified shape narrowing the flow path area as it goes away from the test section inlet part, drift flow and back flow were suppressed. Furthermore, in order to investigate the influence on the heat exchanging performance by drift flow and back flow, the downstream side of the test section was photographed and measured using an IR camera. In the case of a vapor-liquid mal-distribution in the inlet header section, temperature rise accompanying dryout had been constantly occurring on the downstream side in the flow path near the test section inlet. However, in the case of the modified inlet header shape, it was found that the mal-distribution of the heat distribution on the downstream side due to the drift was reduced.
