Experimental Study On Deposition Velocity Of Particles In Rectangular Ventilation Ducts

Particle contamination is one of the key factors that endanger of endangering human health by affecting the indoor air quality. As the increasing pollution of outdoor and indoor air nowadays, the indoor air quality issue draws more and more attentions from government and individuals. The distribution of the indoor particulate alters due to the particle intruding through ventilation ductwork from the outdoors. So the research into the law of the particulate matter's movement and sedimentation provides a theoretical foundation and experimental evidence for evaluating exposure of contaminators inside buildings.In this paper, french chalk is adopted to simulate the particle activities. An investigation is conducted into the sedimentation of the French chalk in ventilation ductwork, by means of releasing the French chalk in horizontally rectangular ventilation ducts made of HVAC materials, which approximates the actual project. There are two duct systems which differ in the cross section. One is 200 mm×400mm, and the other is 200mm×200mm. Each duct system consists of straight ducts, bends, ventilation valves and abrupt contraction section. The length of the straight duct section is 2000mm, and the length of the abrupt contraction section is 180 mm. The bend section forms from four 90°bends with different curvature.18 experiments are performed in three different wind speeds, using two kinds of French chalk differing in size in two duct systems. Firstly, sample the surface deposition of particles by means of tin foil sheets on the duct. Secondly, calculate their sedimentation velocity and non-dimensional sedimentation velocity. Thirdly, compare and analyze the two velocities of the different duct sections under different air speeds and different particle sizes. Fourthly, calculate the penetration of bend and compare with the previous model predictions.The experimental result shows that the deposition velocities on a given duct surface increased with the increase of the particle size or the air speed. For the straight horizontal sections, the deposition velocity reached the highest peak at the duct floor, intermediate at the duct walls and lowest at the duct ceilings. Compared with the straight horizontal sections, the deposition velocities experienced a significant rise in the bend sections, the outside side wall and the ceiling, and a decline in the inside wall. The penetration of bend section, under the influence of the curvature of the bend, decreased corresponded with the increment of the parameter Stk. Compared with the straight sections, the deposition velocity of the floor, the wall and the ceiling surface in the abrupt contraction section is higher, and markedly higher at the cross section of ventilation valve. Consequently, the floor and the local component of the ventilation ductwork are the primary drifting dust parts, and also the key parts of the cleaning work of the ventilation ductwork.