Investigation on heat transfer characteristics of outside heat exchanger in an air conditioning heat pump system for electric vehicles

Abstract

The development of thermal management systems in electric vehicles challenges new understandings of outside heat exchangers. The increasing heat load of electric vehicles requires a corresponding improvement in their heat exchanger characteristics. The purpose of this work is to modify the classical Nusselt number correlation model through experiments to check and predict the heat transfer characteristics of such a heat exchanger. In this paper, a parallel flow microchannel outside heat exchanger was studied with experiments and numerical simulations. Heat transfer correlations on the air side were modified by experimental data obtained from a newly designed test bench. Experimental results show that the heat transfer rate increases with increasing inlet pressure and inlet airflow. Furthermore, a numerical model for predicting heat exchanger characteristics was also proposed with the modified Nusselt number correlations. The comparison between modeling and experimental heat transfer rate shows good agreement, in which the absolute errors of the corresponding heat transfer characteristics for the heat exchanger are within 25%. The typical heat transfer model with the j-factor was also applied to predict the heat transfer rate. Comparison between results of modeling and experiment shows that models with the modified Nusselt number correlations demonstrate advantages when predicting the outside heat exchanger characteristics in an air conditioning heat pump system. The Nusselt number correlation model has good applicability for various environmental conditions.