Recently, development of a small and high efficient heat exchanger, which is utilized in a fuel battery and a heat pump system for CO 2 refrigerant and so on, is strongly required. In author's previous study, a prototype of stacked high pressure resistance microchannel heat exchanger manufactured with diffusing bond technique has been proposed. In the present study, the objective is to reveal flow and heat transfer properties of this microchannel heat exchanger when water and vapor are employed as low-and high-temperature fluids, respectively. Pressure drop and heat transfer rate are measured as flow and heat transfer properties, respectively. As the results, it is identified that the cross-flow heat exchanger operates as a condenser with small pressure drop of less than 60 kPa. Heat transfer rate of it is approximately 7500 W despite the weight of 240 g. Counter-flow heat exchanger indicates high heat transfer properties as heat transfer rate of approximately 9000 W.

At present, a microchannel heat exchanger is requested to achieve high efficiency in small size energy equipments. In order to clarify the heat transfer mechanism in a microchannel heat exchanger, knowledge on the thermal hydraulic characteristics of condensation flow in channels is essential. However, study on the thermal hydraulic characteristics of steam condensation flow in a microchannel is hardly conducted except visualization of flow patterns. Especially, the number of study on the correlation between the flow structure and heat transfer is small. The objective of the present study is to clarify the thermal hydraulic characteristics of condensation flow in a microtube through the observation of condensation behavior. In order to achieve the purpose, overall heat transfer coefficient in annular flow and slug flow is measured. As the results, the observed flow pattern is transformed from annular flow to bubbly flow through injection flow in a single capillary glassy tube as simulated unit microchannel. And the local overall heat transfer coefficient at slug flow is 10 to 25% lower than that at the annular flow under the particular condition in the present study.

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