Experimental Study On Regularities Of Aerosol Particles Deposition In Rectangular Ventilation Ducts

It is intricate for ductwork to influence regularities of particle distribution in a building, and is worth being intensively studied. For studying regularities of particle distribution and depositon in ductwork, laboratory experiments were conducted to study on deposition of aerosol particles in ventilation duct systems.Particle deposition experiments were conducted with french chalk released in rectangular ductwork, which approximate to ventilation ducts using real HVAC materials. These ducts were fabricated from galvanised steel. Experiments with two particle sizes were conducted at different air speeds in three ventilation duct systems. Particle deposition fluxes to four panels at each of the floor, wall and ceiling surfaces of test ducts were measured in each experiment. Particle deposition velocities which dimensionless deposition velocities were calculated from, were calculated from the particle flux to the surface and the airborne particle concentration in the duct. Deposition velocities and dimensionless deposition velocities of aerosol particles with different sizes on the different location were contrasted and analyzed at different air speeds.In straight horizontal sections of the experimental duct with fully developed turbulent flow profiles, experiments showed that deposition velocities to duct ceiling, wall and floor surfaces increased with an increase in both particle size and air speed. And deposition velocities of aerosol particles to be highest at duct floors, intermediate at duct walls, and lowest at duct ceilings.In local connectors and in ducts with developing turbulent flow profiles, these experiments indicated that particle deposition rates to surfaces in a ventilation duct system vary depending on the specific location. Deposition rates in the locations were generally greater than rates to equivalent surfaces in ducts with fully developed turbulent flow profiles.On the basis of experiment results, the major factors influencing particle deposition rates are the air speed, the particle size, the orientation of the deposition surface and size of the duct.