Dynmic Simulatiom Of Evaporator For Indirect Cooling Refrigeration Under Frosting Conditions

In many fields of national economy which closely related to people's life, the refrigeration installation with air forced convection cooling(i.e. Indirect Cool Refrigerator, ICR) has been widely used, and now it is becoming an important develop direction of small-scale refrigeration installation. The finned-tube evaporator is always used as cold source and supplies capacity to cooled space in ICR. When the outside air temperature of evaporator is below dew point and zero simultaneously, frost will deposit on the surface of finned-tube. The frost formation acts not only as a thermal insulator between surface and the humid ambient air, but also significantly reduces the performance of the heat exchanger, since the air passages become narrower and pressure drop generated becomes higher. Therefore, a study of performance of evaporator for indirect cooling refrigerator under frosting conditions is essential. Meanwhile, main development method for indirect cooling refrigerator are combined the experiential and the experimental method. To experiential principles, the reliability is affected by many factors, and the validity is limited. To experimental method, the results are reliable and it is necessary to find out the essential principles for refrigeration equipments. But the experiments normally mean high cost, long duration. Also, it is difficult to get an optimized result by pure experiments. Therefore, simulation based on computer is a good compensation for experiments. This dissertation uses the theory of Thermodynamics of Refrigeration System, i.e., the viewpoint of dynamic, distributed parameters and parameters quantitatively coupled to study the following problems which must be solved in the simulation of ICR.This dissertation establishes the evaporator dynamic distributed parameters mathematics models and directly solves control conservation equations with math software to study the frosting and heat transfer characteristics of finned-tube evaporator for ICR. The model considers the water vapor at frost surface was supersaturated. This dissertation improves the equation for calculating the water vapor supersaturation degree at frost surface, and describes a numerical model which uses supersaturated water vapor at the frost surface to predict the frost growth for finned-tube heat exchangers. The mass of frost accumulated on the heat exchanger surface, airside pressure drop, the overall energy transfer coefficient, frost density and thickness are calculated.In order to verify the exactitude of model of finned-tube evaporator dynamic frosting and heat transfer, some experimental research data was used to compare to the simulation results.Based on the dynamic simulation model for frosting, this dissertation also addresses the optimization of fin-tube evaporator for ICR under frosting conditions using the Taguchi method.Finally, the dissertation summarizes the open issues in this research and further study topics related to this field in future.