Bachelor's thesis Tobias Burgholz


Evaluation of the influence of register vent geometry on air flow field and thermal comfort in car cabins

In the context of vehicle air conditioning, the provision of a comfortable environment and healthy air quality is crucial. The thermal comfort of the passenger strongly depends on the distribution of local air velocities and temperatures within the cabin. Various air outlets deliver conditioned air into the car cabin. Passenger vents are usually integrated into the car’s dashboard and play a key role in terms of air distribution.With conventional passenger dash vents, maximumair velocities are likely to occur in the immediate vicinity of the passengers. Along with low temperatures, high velocities are mainly responsible for draughts. In order to successfully reduce local air velocities and hence the draught rating while keeping the volume flow at a constant level, the structure of the airflow has to be altered. To achieve this, applying swirl to the airflow is a promising approach.
In this thesis two different types of passenger dash vents are compared experimentally: a conventional model with strictly linear flow pattern as frequently used by Ford on the one hand, a newly developed swirl inducing model on the other. In addition to stationary ventilation and air conditioning of the cabin, heat-up and cool-down performances are examined. It is discussed to what extent local air velocities depend on both orientation and induced flow pattern of the employed passenger dash vents. Using the swirl inducing models an important question is how long it takes to provide a state of thermal comfort within the cabin despite possibly smaller flow velocities. Subject to further experiments is both the saving potential of fan power and the reduction of noise emission through a selective air conditioning of single seats and the use of radiation surfaces within the cabin. Trials with test persons serve the validation of previous findings and the evaluation of the climate within the car cabin.
The results show that swirl inducing air vents allow for a siginficant reduction of both local air velocities and draught rating at head and breast level. As the link between orientation of the passenger air vents and local velocities is less pronounced, swirl inducing models provide a more uniformdistribution of local air velocities and temperatures within the cabin. Employing radiation surfaces within the cabin and merely supplying air to the immediate vicinity of seats that are actually occupied enable the achievement of the same air velocities despite a smaller volumetric airflow. Consequently, both noise emission and the energy required to drive the fan can be reduced substantially. Results of a survey among 30 participants reveal great popularity of passenger air vents with considerably reduced risk of draughts and a higher degree of satisfaction when radiation surfaces are employed in addition to the vehicle’s air conditioning system.