An experimental study on the frosting characteristics of heat pump system in pure electric vehicle.

Due to the excellent features of environmental friendly and energy saving, pure electric vehicles are getting more and more attentions and incentive promotions all in the world. Because of the great difference between engines and driven motors, there will not be engine waste heat as a heat source for the air-conditioning system of a pure electric vehicle. Though a direct heating device can be used to solve this problem, its low heating efficiency and high energy consumption unavoidably makes the cruising mileage problem serious. Therefore, differently from the cooling air-conditioning system in traditional vehicles, it is obviously a good way for an electric vehicle to use a heat pump type air-conditioning system with high heating efficiency. For a heat pump air-conditioning system used in an electric vehicle, the frosting of evaporator greatly influences its heating performance. The frost characteristics of a micro-channel heat exchanger are experimentally studied under different working conditions. The influences of temperatures and humidity on the frost thickness and the increment of ice crystals on the heat exchanger surface were studied in this paper. The structure of frost layer was investigated with CCD imaging technology. A program based on MATLAB was made to study the growth pattern of frost layer structure, the addition of ice crystals and the height of frost layer, with wavelet transform and gray scale threshold. The results show that, the lower the ambient temperature, the more the amount of ice crystals is and the more the frost thickness is; keep the ambient temperature constant, when the humidity increases, the average density of the frost layer is correspondingly increased and the distribution of the ice crystals in the spatial position is more intensive.