COMPUTATION OF AIRFLOW-DRIVEN RE-ENTRAINMENT OF FINE PM IN CONVENTIONALLY-VENTILATED CLEAN ROOM

Detailed airflow pattern and particulate contamination characteristics, induced by dump-type air supplyin a full-scaled conventionally-ventilated clean room, are investigated numerically. Standard k- epsilonturbulence model is applied to calculate velocity vector, turbulent intensity etc. mainly due to theadoption of large ACH which results in high turbulence indoors. Based on the criterion proposed byMurakami et al, small-slip model in Euler framework advanced by S. L. Soo is applied to characterizeparticulate diffusion. Test data from an in-site observation are used to define boundary conditions, andreleasing rate of contaminant on interior surface from literature is used to define source strength.In general, floor surface is an important sink of airborne particles and re-entrainment is rare due to largeadhesion force, especially for micron-sized aerosol particles generating indoors through a variety ofmechanisms. However, under the condition of strong supply jet flow required for dilution purpose inclean room, phenomenon of deterioration in cleanliness is confirmed both by numerical investigationand by experimental test.The airborne cleanliness of a conventionally-ventilated clean room is dependent not only on thequantity and quality of air supplied to the room but also the interrelationship between airflow andgeneration mode of contamination. For some specific location and strength of contaminant source, itshould be recognized that the type and layout pattern of air supply devices will influence the airmovement in clean room and hence its cleanliness.