Abstract
Keywords - Demisting, de-icing, water layer, evaporation, condensation.
Abstract - The performance of the vehicle HVAC system during demisting operation has an immediate effect on the global security, towards both the passengers and the pedestrians. From this point of view, ensuring the proper visibility for the driver is, in fact, of crucial importance and more critical than preserving thermal comfort.
FIAT Auto regulation sets the performance required for the HVAC systems in order to assure windshield demisting. The actual performances are evaluated by means of experimental tests in climatic chamber. Such climatic chambers tests usually are quite expensive and time consuming. Eventually, and only if this first test is satisfied, thermal comfort performances of the vehicle are analysed .
The goal of the present work is to describe a CFD virtual model developed to predict the demist performance of an HVAC system. CFD simulations can be carried out as soon as the cabin CAD surfaces are available (draft surfaces are enough), while experiments require complete vehicle manufacturing.
The numerical procedure involves the computation of the fluid and thermal fields in the vehicle cabin, by means a finite volume commercial code, the solution of the three-dimensional thermal conduction equations through the windshield domain (using a specific in-house code), and the simulation of the heat and mass transfer phenomena in the misted water layer. The model for the misted layer simulation is derived from a numerical method developed for the aeronautical de-icing systems. Fluid domain, solid domain and liquid film are simultaneously solved, and the conjugate heat transfer coupling between solid and fluid domains is obtained via an exchange of boundary conditions information and the use of proper interpolations.
Finally this model has been successfully validated with experimental data.