The Study Of Finned-tube Evaporator Performance Test Under Low-temperature Frosting Conditions

Frost on the surface of finned-tube evaporator is a common phenomenon in thelow temperature refrigeration system. On the one hand, The emergence of the frostincreases the heat transfer resistance. On the other hand, the emergence of the frostreduces the area of air flow through the evaporator, which leads to the deterioration ofthe heat transfer performance on the evaporator. Especially in the low temperature andhigh humidity environment, the frost on the surface of the evaporator affects the safeand stable operation of the evaporator and the system directly. So the experiment andsimulation research of the dynamic performance on evaporator under the frostingcondition is particularly important.The heat exchanger performance test system under frosting condition at lowtemperature Includes the steam compression refrigeration system and a closed windcirculation system with heated, humidified and wind speed controlled. At differentinlet air temperature, humidity, velocity and other environmental parameters, thechange of the frost quantity, refrigerating capacity, COP, air side pressure drop at theinlet and outlet of the evaporator and the energy transfer coefficient of finned-tubeevaporator could be measured under low-temperature frosting conditions in the article.And the change of the refrigerating capacity, COP, air side pressure drop and energytransfer coefficient along with the frost layer growth of finned-tube evaporator couldbe obtained. The effect of the environment parameters on the finned-tube evaporatorperformance was analyzed. Then defrosting time of the evaporator specimen wasdetermined under different working conditions.The simulation model of distribution parameters of finned-tube evaporator airside flow and heat transfer was set up under frosting condition. The influence of theparameters which vary along the airflow direction such as the structure of evaporator,thickness of the frost layer and the state of wet air were taken into account in themodel. The dynamic frosting process simulation program of the finned-tube evaporator suitabling for different air flow patterns and structures of evaporator was written. Theperformance parameters such as the frost quantity, refrigerating capacity, air sidepressure drop at the inlet and outlet of the evaporator and the energy transfercoefficient of the evaporator were calculated. The comparison and analysis of theresults of the experiment and simulation showed that maximum error between theexperimental value and simulation value was within14%in6hours frosting process.Both of them was in good agreement. The accuracy of the established distributionparameters models was verified powerfully. And the model could be used for correctprediction and optimization analysis of finned-tube evaporator performance underfrosting condition. The effect of the the structure parameters of the evaporator on theevaporator performance was analyzed further. And the change law of the density andthickness of the frost layer was studied. How to restrain the frost to improve thecomprehensive heat transfer performance on evaporator were analyzed. Then fourimprovement suggestions were put forward.The study of the finned-tube evaporator under low-temperature frosting conditionsprovides important experimental basis and design reference for the optimization of theenvironment parameters, the structure design of the evaporator and the determinationof defrosting cycle.