Method of improvement of air flow uniformity to reduce the evaporator frosting of a passenger car

For an efficient automotive HVAC system it is very essential to ensure uninterrupted and consistent airflow and temperature at the vent exit to help achieve the comfortable cabin space. This certainly requires temperature sensor to position at lowest possible temperature on heat exchanger and uniform flow distribution over it. However the uneven distribution of airflow on evaporator entry face leads to lowest temperature and sometimes goes undetected. This causes the condensate to get freezed and then frosting occurs at the core surface. Eventually a substantial portion of evaporator face gets choked and gradually airflow reduces and evaporator exit air temperature shoots up. Hence it is very important to prevent the frosting on evaporator core so to have uninterrupted airflow and adequate cooling in the passenger compartment. The present paper investigates the reasons for frosting occurring in one of the hatchback vehicle in bench test. The investigation consists of conducting anti-freezing tests under some test conditions. Further numerical simulation was performed to understand the flow pattern over the evaporator. Flow simulation was carried out in STAR CMM+ software. The numerical results of evaporator flow distribution exhibit almost the same area where the frosting was occurring. In order to improve the flow uniformity over the evaporator further design iterations were done and flow analysis was executed. Once the desired level of uniformity is achieved, prototypes were made and tested in bench under same conditions. The numerical simulation results were in good agreement with that of experimental results and eventually the frosting was avoided. Hence involving numerical simulation at early stages of design cycle really helps in robust design.