Experimental Research on Flow and Heat Transfer in Microchannel with Refrigerant HFO1234yf

Abstract

An experiment was carried out to study the effect of refrigerant mass flow rate, heat flux density, and saturation temperature on boiling heat transfer coefficient and frictional pressure drop in microchannel. Flow patterns are captured by a high-speed camera. HFO1234yf was used in rectangular microchannels with a hydraulic diameter of 0.5 mm. The results showed that there were eight flow patterns in the experiment, and the change of flow pattern is closely related to the change of heat flux and mass flow rate. The higher the heat flux and mass flow rate, the more the flow patterns appear. Different flow patterns have different heat transfer mechanisms. The heat transfer mechanism is mostly nuclear boiling at the region of bubble flow, slug flow, elongated slug flow, and agitated flow; the heat transfer mechanism is film convection boiling at the region of annular flow, and it is vapor convection at the region of dryout flow. When the dryness is about 0.4, the heat transfer mechanism changes from nuclear boiling to film boiling. The friction resistance decreases with the increase of dryness and saturation temperature.