Simulation of dynamic changes in fluid parameters and flow patterns during condensation

Abstract

The three-dimensional numerical simulation of the R32 flow condensation is conducted in a circular microchannel with a hydraulic diameter of 1 mm, and the setting of two phase inlets is applied to the transient simulation. The temporal process of flow patterns, velocity contour and temperature contour are obtained for inlet vapor quality of 0.5 and mass flow rate of 100, 150 and 200 kg/(m2·s), respectively. The corresponding relationship between each flow pattern and its internal parameters along the flow direction during condensation are studied in detail. The fluid in the microchannel undergoes annular, slug, bubbly and shrinking bubbly flow in sequence. The fluctuations of wall shear stress (WSS) and turbulent intensity (TI) caused by the oscillation of velocity gradient are the most intense near the transition point of flow regimes. Revealing the relationship between WSS, TI and flow patterns is an excellent supplement to the existing condensation flow. The local heat flux reaches its extreme value at the head of downstream of the annular flow, injection flow and slug flow. Similarly, the fluid temperature fluctuates violently at the same location. The time-average heat transfer coefficient of annular flow is higher than that of other flow patterns, and the peak value of heat transfer coefficient is located at the head of annular flow downstream under different mass flow rates.