Experimental And Numerical Study On Particle Deposition Characteristics In A Square Duct

The deposition of aerosol particles in air-conditioning ducts can cause microbial and bacterial growth,producing harmful substances,which can cause indoor air pollution.Therefore,studying the deposition characteristics of particulate matter in air-conditioning ducts is of great significance for air duct cleaning,improvement of indoor air quality,and protection of human health.So far,there have been some investigations on the theory of migration and deposition of particulate matter in ducts,yet there are relatively few studies on the particle matter in real air-conditioning ducts,e.g.,valves.Therefore,this paper experimentally and numerically investigate the movement and deposition characteristics of the particles near the elbow and valve in the square duct.First,this paper introduced the experimental bench,test methods,steps,data and error handling methods.For models,by analyzing the force characteristics of the particles in the duct,a correction formula for the turbulent fluctuation velocity near the wall was proposed.By comparing the numerical simulation results with the present and previous experimental results,it was revealed that the modified Reynolds stress average model(RSM model)can accurately predict the characteristics of the flow field and the particle movements.Subsequently,for the 90° elbow of the duct,the nearby flow field,pressure field and particle movement characteristics were studied.The results show that there was a secondary flow phenomenon inside the elbow.That is,there were two symmetrical vortices along the horizontal center cross section,the penetration rate of the particles in the elbow is only related to the Stokes number,and then a formula of the particle penetration rate was fitted.As the particle size increases,the deposition velocity of the particles on the inner wall surface of the elbow gradually decreases,while that on the outer wall surface increases.Compared with the straight pipe,the deposition velocity of the particles in the elbow increases about 2 ~ 5 times,yet for the larger particles,the particle deposition velocity increases relatively slower.After issuing the elbow,the particle deposition on the duct occurs mainly in the 5 times hydraulic diameter downstream region.Finally,the paper studies the particle motion characteristics of butterfly valves and parallel bilobed valve with different opening degrees.The results show that the downstream high wind speed and high kinetic energy region of the butterfly valve are located in the near wall area.The high wind speed and high kinetic energy area downstream of the double leaf valve are biased toward the center of the pipe section.The particle penetration rate increases with the opening angle of the valve.When the valve opening degree is large,the particle penetration rate changes little.When the opening degree of the damper is small,the particle penetration rate drops rapidly.When the valve opening degree is the same,the particle-to-butterfly valve the penetration rate is lower than for the double leaf valve.Compared with the straight pipe section,the deposition velocity of the particulate matter in the downstream of the valve is increased by 1 ~ 2 orders of magnitude,which is more obvious for small particle size particles.The deposition of the downstream particles of the valve occurs within the range of 5 times the hydraulic diameter downstream of the valve.The butterfly valve is downstream of the valve.The deposition velocity increases more than the double leaf valve.In addition,the deposition velocity sequence of the straight pipe section after the valve from high to low is floor,wall,and ceiling.