纯R23及其混合工质管内蒸发数值模拟研究

Numerical Simulation of Pure R23 and Mixed Medium Tube Evaporation

针对自复叠制冷系统中非共沸工质不能完全被分离而有少量高沸点工质混入蒸发器的问题,采用FLUENT软件分别对纯R23制冷剂及含有质量分数为8%R134a的R23混合制冷剂进行了U形蒸发器内的数值模拟。结果表明:纯R23的管内蒸发速率明显大于含有8%R134a混合制冷剂的管内蒸发速率;相比于纯制冷剂,混合制冷剂分界面上易挥发组分的蒸发导致界面的饱和状态温度升高,从而传递给气泡热量的有效温差变小;混合工质的传质阻力也使气泡的生长速率降低,导致核态沸腾变弱,故混合工质更易到达完全抑制状态,传热恶化致其蒸发速率小于纯制冷剂。

To solve the problem that the non-azeotropic working medium cannot be separated completely and a small amount of working medium with high boiling point is mixed with the evaporator,FLUENT two-phase flow model was used to simulate the pure R23 refrigerant and the R23 mixed refrigerant with mass fraction of 8%R134 a in a U-tube.The simulation results show that the evaporation rate of pure R23 is significantly higher than that of mixed refrigerant containing 8%R134 a.The results show that compared with pure refrigerants,refrigerant mixture is prone to boundary surface evaporation of volatile components,leading to the saturated state of the interface temperature and decrease in the effective temperature difference passed to the bubbles.Meanwhile,the mass transfer resistance of the mixed working medium also results in reduced bubble growth rate and weakened nucleate boiling.Therefore,the mixed working medium is easier to reach complete inhibition and heat transfer deterioration,causing the evaporation rate to be less than that of pure refrigerants.