Heat transfer characteristics in a Quadrilobed tube
Purpose
 |
From the viewpoint of energy saving, the application of heat pump system to hot water supply is spreading.
For residential heat pump hot water supply system, since water is heated with large temperature rise, a single double tube heat exchanger is widely used as water heaters.
When a high-critical point refrigerant is used as the refrigerant, the water heater operates as a condenser. In condensing flow, condensate liquid film causes heat resistance and leads to reduction in heat transfer coefficient.
The purpose of this study is to clarify heat transfer and flow characteristics of condensing flow in a horizontal Quadlilobed tube used in an actual heat pump water heater. The effect of the channel cross-sectional shape on heat transfer coefficient and pressure loss.
Research content
 |
The quadrilobed tube has five separate refrigerant channels, four leaf-like channels and one core channel, as shown in the figure. The leaf like channel with triangular shape will make a large contribute to heat transfer because the heat transfer wall directly faces to water flow. In our previous studies, it was shown that the decrease in heat transfer coefficient with increasing wetness was suppressed under the low mass flux and moderate quality conditions. The reason might be liquid accumulation in the corner by surface tension, and the accumulation might make the liquid film thickness thinner. Therefore, condensation heat transfer experiments in a triangular channel simulating the leaf channel is investigated. The effect of the channel shape on the heat transfer characteristics has been experimentally studied. The arrangement of the triangular tube to gravity is changed, and the local wall temperature at the top and bottom of the triangular tube is measured with a thermocouple. In addition, the void fraction was measured by the capacitance sensor at the adiabatic section. Flow observation is conducted at the observation section downstream of the heat exchange section, and the correlation between the liquid film structure during condensation and the heat transfer characteristics is evaluated.
Back