Theoretical And Experimental Study On The Performance Of The Gravity Feeding Refrigeration System Used In Refrigerated Warehouse

Gravity-flooded evaporator,increasing the refrigerant flow as a method of the augmentation of evaporator heat transfer,taking advantage of thermal-siphon principle to make refrigerant recycled,can exchange evaporator heat transfer performance.In this way,the coefficient of heat transfer and efficiency of evaporator can be improved.With the step of substituted refrigeration is speeding up,R404A is considered as a better refrigerant that substituted R22 and R502 in middle and low temperature commercial refrigeration equipments.So considering the gravity feeding refrigeration system for the application,we used R404A as a refrigerant to make further theoretical and experimental study on the system in the low temperature condition.In this paper,the resistance equilibrium analysis of two-phase flow for gravity feeding systems were done,a heat transfer model of gravity-flooded evaporator was established.Four correlations for boiling heat transfer were analyzed and the predicted values by the correlations were compared with the experimental data.The result shows that Shah correlation can well predict in-tube boiling heat transfer coefficient of gravity-flooded evaporator with small error. Based on the experimental data,the mathematical model of the gravity-flooded evaporator was proved.The experimental installation was set up by ourselves,and the existing problems as the oil reture and level control were resolved.Room heat balance method was adopted to test the gravity feeding system operating performance in different feed liquid height,heat transfer characteristics of the system was obtained.Contrast experiments between gravity feeding and direct expansion refrigeration system were carried on,performance characteristics difference of the two refrigeration systems were found out.Investigations presented in this paper indicate that circulating rate is improved by increasing the feed liquid height,meanwhile,the opposite law of the heat transfer coefficient and temperature difference of heat transfer along with the circulating rate has been found out.In the right feed liquid height,the maximum heat transmission performance of evaporator can be achieved.Comparing to the direct expansion evaporator,gravity-flooded evaporator has much better heat transfer characteristics and efficiency under the low temperature condition,moreover, it has not additional energy consumption.