The condensation heat transfer, frictional pressure drop and refrigerant charge characteristics of R290 in minichannels with different diameters

In order to enhance the heat transfer performance and decrease the refrigerant charge of R290 in condensers, this paper numerically studied the condensation and refrigerant charge of R290 in minichannels (not the entire system) with different diameters to analyze the effect of diameter on them. The VOF multiphase flow model and SST k - omega turbulence model were used for 3D transient calculation in the simulation. The simulation results show that the diameter has a remarkable effect on the flow pattern, heat transfer coefficient, friction pressure drop and refrigerant charge. When the mass flux is small, a remarkable eddy current appears between vapor and liquid on the circular section, which can sharply enhance the heat transfer. At high vapor quality (x>0.8), the heat transfer coefficient and frictional pressure drop do not almost increase and even decrease with the increase of vapor quality under some working conditions, which is due to the influence of wall effect. Under the same heat transfer rate and heat transfer temperature difference, with the decrease of diameter, the maximum reduction of refrigerant charge reaches 94.8%. But when the diameter is reduced to a certain value, continuing to reduce the diameter will have little effect on the refrigerant charge. (C) 2020 Elsevier Ltd. All rights reserved.