Particle Deposition In Air Conditioning And Ventilating Duct Fittings

In order to make comfortable indoor air qualities, one of the most important problems in air condition systems is how to control the variation of the temperature, humidity and air flow rate indoors in the past few decades. But more and more concern is focusing on the indoor particle pollution and its effect on human health in the current days, because outdoor aerosol particles can come into the interior of buildings through ventilating ducts if the air conditioning and ventilating systems are not well designed and operated, this phenomena can lead to particle concentration rise in indoor air, and threaten the human healthy.The most results on particle motion and deposition in ventilating duct fittings of ducts were carried on bends(or called "elbows") with circular cross-sections, and the main concerning on bifurcations (or called "wyes" and "tees") are the human upper respiratory tracts, but there is not a complete study on ventilating duct fittings with rectangular cross-sections. In the present study, the characteristics and features of aerosol deposition in such fittings are investigated and analyzed.Based on the aerosol particle dynamic equation, the FLUENT code is employed to simulate the particle motion and deposition in duct fittings, and the main configurations are rectangular elbow, converging and diverging wyes. With the variation of particle sizes, flow parameters, fittings' inlet and boundary conditions, the features or characteristics of aerosol particle deposition are evaluated and estimated.The results of the simulations show that the deposition rates in elbows are primarily affected by the inlet geometrical structure of the elbow, the curvature of the bow and particle Stokes numbers, the deposition rate increased with the increase of the curvature and Stokes numbers. Deposition features in an actual elbow is most the same as in an ideal one when the curvature is small, but when the curvature is increased, the deposition rate in the former is less than in the latter, for the collecting area in an actual elbow is less than an ideal elbow. The particle deposition pattern in bifurcations are more complex comparing with bends, the factors affecting particle deposition in such duct fittings are also more than in bends. The same factor can cause different deposition pattern in diverging and converging wyes, respectively. The variation of air velocity can enhancing or reducing the deposition rate of coarse particles (>10μm) in wyes, but has no effect on the deposition of fine aerosols. The angle of a wye is also a main factor affecting aerosol deposition, small angle can results an increase of deposition rate, when a converging and a diverging wye have the same angle, the former can collect more aerosol on the wall.