Experimental study and numerical simulation Concerning fogging characteristics and Improvement of return air utilization for electric vehicles

Abstract

Anti-fogging treatment is a key task associated with the thermal management of electric vehicles, which focuses on utilizing the cabin return air to reduce heating load and save battery power. The present study analyzes the interior climate characteristics of the vehicle with an improved thermal and humidity model (T&H model), which considers a thin air layer between the windshield and the interior air so as to enhance the accuracy of the model. A test bench is constructed to investigate the fogging characteristics of the windshield under various environmental conditions, based on which two relevant factors are experimentally measured, i.e., the difference between the critical moisture content (CMC) of the surface air layer and the corresponding saturation moisture content (SMC) associated with the windshield surface temperature, as well as the impact of air velocity on the convective heat transfer coefficient. The results obtained here are leveraged to improve the T&H model, which is in turn validated with an additional experimental test, showing errors below 10%. Finally, numerical simulation is conducted to analyze the maximum return air ratio, which shows that with an elevated driving speed, an increased convective heat transfer coefficient leads to a subdued windshield temperature, which in turn causes the return air ratio to drop. This driving-speed-dependency of return air ratio becomes more pronounced as the relative humidity of exterior air increases.