2021 Volume 38 Issue 2 Pages 73-
When the inlet temperature of water in a water heater used in a heat pump water heater becomes higher, the use of a refrigerant with a high critical point is effective for the improvement in the coefficient of performance. In this case, the water heater operates as a condenser. This study deals with condensing flows of HFC-245fa in a horizontal mini triangular channel with the hydraulic diameter of 1.44 mm, simulating a part of the channel of a quadrilobed tube used in an actual heat pump water heater. Flow and heat transfer characteristics of condensing flows were examined using a short heat transfer section with a length of 200 mm. The cross-sectional average void fraction was measured by an electrostatic capacitance sensor at an adiabatic observation section downstream of the heat transfer section. Flow behaviors were observed at the observation section, simultaneously. The effect of the channel orientation, i.e., vertex up and inverted vertex down, on condensing flow characteristics was evaluated. As a result, it was confirmed that liquid was kept in the top corner for the vertex up orientation. The effect of channel orientation on the flow pattern transition to annular flow, void fraction, and heat transfer coefficient was a little because the flows were dominated by surface tension and inertia force.