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A significant route for water ingress into passenger cars is through the Heating, Ventilating, and Air-Conditioning (HVAC) system. The penetration of rainwater through the HVAC unit and the subsequent rise in moisture levels within the passenger compartment directly affect the provision of thermal comfort to the cabin occupants. It is speculated that up to 80% of water ingress into the cowl or engine bay is from water film movement over the bonnet of the car, and only the remaining 20% is from direct rain impact from above. Using a full-scale Climatic Wind Tunnel (CWT) facility, which incorporates accurate rain distribution modeling, it has been possible to study the movement of rainwater film over the exterior surface of the vehicle to ascertain the flow distribution of the film moving into the engine bay, into the cowl, advancing up and over the windscreen and shed to the sides and front of the vehicle.

The role of the Heating Ventilation and Air Conditioning (HVAC) system of passenger vehicles is to maintain the ambient environment within the vehicle at a temperature and humidity comfortable for the occupants, regardless of the external weather conditions. A commonly occurring problem in vehicles incorporating an HVAC system is that of unwanted water ingress into the cabin space. This occurs mainly in wet weather conditions, and is caused by the penetration of water through the cowl box and air filter. Large droplets are broken up by the blower motor into a fine mist that can collect in the interior of the car, causing window fogging, damage to carpets and passenger discomfort. Numerous solutions have been implemented by the automotive industry ranging from the placement of baffles within the cowl box of the vehicle to the use of variable area ducts.

Maintaining adequate visibility at all times, through a vehicle windshield, is critical to the safe usage of the vehicle. The ability of the windshield defrosting and demisting system to quickly and completely melt ice on the outer windshield surface and remove mist formed on the inner surface is therefore of paramount importance. The objectives of this paper are to investigate the fluid flow and heat transfer on the windshield as well the effect of the air discharge from the defroster vents on passenger comfort. The results presented are from numerical simulations validated by experimental measurements both carried out a model and full-scale. The numerical predictions compare well with the experimental measurements at both scales. The effects of the defrosting and demisting air on occupants' comfort and safety are examined.

The penetration of rainwater through the heating ventilation and air conditioning system, HVAC, of a vehicle directly affects the provision of thermal comfort within the vehicle passenger compartment. The first element of a typical HVAC system, namely the cowl box is considered. The purpose of the airway from the cowl grille openings to the air filter, immediately before the blower, is to ensure proper water separation from the incoming air stream before entry onto the air filter and onwards into the rest of the HVAC system. This is achieved by ensuring standing water within the cowl is quickly drained and that water rain droplets or water flows from the windshield and body are separated from the air stream, hence minimising the effect on the total system volumetric flow rate. An experimental study is conducted to examine the effect of plane baffles on the airflow filed within a rectangular duct. A set of plane baffle plates is placed within the cowl duct.

This paper describes an investigation into the fluid flow and heat transfer on the windshield as well the effect of the air discharge from the defroster vents on passenger comfort. The investigation is both experimental and computational. Full-scale tests are conducted on a current vehicle model using non-intrusive diagnostic methods. The results presented are from numerical simulations validated by experimental measurements. The numerical predictions compare well with the experimental measurements. The locations of maximum velocity and pressure, as well as width and length of re-circulation regions, are correctly predicted.

The analysis of airflow in a road vehicle HVAC splitter duct is complicated by the cross sectional variations and abrupt changes in airflow direction. In this study, the complex three-dimensional turbulent airflow found in a generic automotive HVAC splitter duct is investigated experimentally and computationally. An optical anemometer is used to acquire the experimental data within the HVAC duct. The results are then used to validate and tune a Computational Fluid Dynamics (CFD) numerical model.

The ventilation flow inside a one-fifth-scale model of a typical mid size passenger compartment with a driver present has been investigated experimentally and computationally. In this study only one ventilation mode has been evaluated, namely the defrost mode in which air is discharged from two vents in the form of slits located along the top of the dashboard. The fluid measurements were taken using the Particle Image Velocimetry (PIV) technique to acquire the velocity distribution of the model interior. The Computational Fluid Dynamic (CFD) analysis have been implemented and simulated by using the commercial CFD code FLUENT as a tool to investigate the flow of the compartment's interior. Comparisons of the predicted velocity field with experimental data show good agreement and were qualitatively consistent.

The penetration of rainwater through the heating ventilation and air conditioning system (HVAC) of a vehicle directly affects the provision of thermal comfort within the vehicle passenger compartment. Present vehicle designs restrict considerably the air-management processes due to reduced space and tighter packaging. The motivation for the study is to get an insight into factors affecting the water ingress phenomenon when a stationary vehicle is subjected to water loading such as heavy rain when parked or waiting in a traffic light or when in a car wash. The test programme made use of a compact closed circuit full-scale automotive climatic wind tunnel that is able to simulate wind, rain and road inclination. The tunnel was developed as part of the collaborative research between the Flow Diagnostics Laboratory (FDL) of the University of Nottingham and Visteon Climate Control Systems [1].

This paper examines the prevailing fluid flow and heat transfer on the windshield of a full–scale vehicle and examines ways of promoting efficient de–icing and demisting. It establishes that present methods of defrosting and demisting windshields are inefficient; since the first area cleared is below the driver's eye level and even this result only occurs some considerable time after the blower has been switched on. The complexity of the windshield topography and the defroster nozzle geometry yield inadequate flow mixing, poor momentum interchange and consequently dead flow zones in critical visibility areas. This study explores ways of improving the defrosting and demisting process through passive means and using the existing air handling system of the vehicle. The results presented are from numerical simulations validated by experiment.