Particle deposition near ceiling induction outlets

Particle deposition on ceilings close by ventilation outlets is a well-known and bothersome problem in the ventilation industry. This paper reveals the mechanisms causing the soiling of induction outlets and offers countermeasures. Experimentally verified CFD-calculations are performed to gain insight into the processes leading to particle deposition. It shows that the room air that is being induced by the entering airflow transports particles from the room to the ceiling where they deposit due to turbulent interaction forces. Other forces such as electro- and thermophoresis are negligible. An experimental technique is proposed to visualize the soiling patterns of an outlet by photographing deposited sodium chloride crystals. These tracer-particles stem from an atomizer and aerodynamically behave like the particles responsible for the soiling of ceilings in reality. Using image processing, suitable statistics describing the tendency of an outlet to attract particles can be derived from the pictures.