A numerical approach to a very fast thermal transient in an air cooling evaporator

A numerical study of the performance of an air cooling evaporator inserted in a climatic chamber in the presence of a very fast thermal transient is considered. The climatic chamber is a confined environment that allows one in the presence of air, to submit for a short time a certain product to a particular thermal stress. In fact, according to some international standards, it is necessary to analyse the response of some type of products, that then will be used under severe condition, such as a sudden heating and cooling, to obtain an acceptable future operative life. Heating and cooling cycles are obtained in the confined environment respectively by means of an electrical resistance and of an air cooling evaporator linked to a vapour compression system. To study the cooling thermal cycle an air cooling evaporator numerical model has been obtained according to the hypotheses of a homogeneous model for the refrigerant and of an incompressible and one-dimensional flow for the air flowing onto the evaporator. Finally, the numerical model results have been compared with the experimental ones in terms of the evaporator outlet refrigerant temperature, the air temperature and of the evaporator outlet air relative humidity. This comparison is very satisfactory, as it shows that this study is very useful to permit proper design of the vapour compressor plant and its particular control system.