HVAC defrost system assessment through 1D and 3D simulation during concept development 2019-01-0911
The windshield defrosting performance is a very important requirement for the vehicle safety because it affects directly the driver’s visibility during driving. The vehicle windshield defrosting performance has direct influence under driver safety. Some countries have specific standards describing the test procedure for windshield defrosting and demisting performance. The defrosting process in the windshield should not take too long while driving the vehicle and must guarantee a fog-free area to increase driver’s visibility within the short time. The defrosting process in the vehicle is carried out by blowing hot air from the HVAC through the defrost duct system. Computational Fluid Dynamics (CFD) is used to numerically simulate the vehicle defroster performance with the available defrost duct outlet temperature and coolant temperature data from the vehicle testing. It is difficult to simulate the defroster performance during early stages of the program, since the vehicle physical testing data will not available at that time and the simulation can be carried out only at the later stage of the program. This paper describes the 1D modelling of complete HVAC system configuration to find out the defrost duct outlet temperature and through the CFD, transient defrost simulation was carried out to simulate the ice melting process over the windshield at various time step with the input conditions from 1D simulation results. In the CFD simulation, shell modelling analysis method is followed to predict the de-icing phenomenon over the vehicle windshield. The wind tunnel vehicle de-icing testing was carried out to check the system performance. The validation results are presented by comparing the CFD predicted windshield de-icing patterns with the windshield de-icing tunnel test. The present CFD windshield de-icing simulations demonstrated reasonable agreement with available test data within the error of 10%. The prediction of defrost duct outlet temperature through 1D simulation numerical method will aid in getting the results quickly without carrying out the vehicle testing during early design cycle. By employing this methodology, CFD simulation results could be analyzed and it helps to optimize the defrost duct in a robust way during the early design stages of the program.