Study On Mechanism Of Particle Deposition Influenced By Rising Hot Air From Near-wall Heat Sources

The presence of particle deposition has received extensive attention due to the closerelationship with the electronic equipments, mechanical equipments, chemicalequipments, heritage conservation and indoor environments. The research on particledeposition mechanism influenced hot air is still rare. In this paper, a set of environments,simulations and measurements are carried out to probe the mechanism of particledeposition influenced by rising hot air from near-wall heat sources. The main researchcontents are as follows.First, an experiment on particle dimensionless concentrations and size distributionsabove a near-wall heat sourse and in the air far away from the heat sourse is performed.The influences of the heat sourse temperatue, the distance from the wall behind the heatsource and the distance from the upper-edge of the heat source on particle decay rateloss coefficients are discussed. The results reveal that the deposition mechanism and thesize distribution of particles in the air above the near-wall heat sourse both haveparticularities.Second, particle deposition in a chamber with a near-wall heat source is studied byCFD (computational fluid dynamics) modeling. The Discrete Phase Model (DPM) isadopted to investigate deposition fractions, deposition velocities and particle depositionnumbers of particles ranging from2.5μm to10.0μm. The results indicate that thenear-wall heat source surface temperature, near-wall heat source length and the gapbetween the near-wall heat source and the wall have varying degrees of an effect forparticle deposition on surfaces. It is also found that the particle deposition number onthe wall areas above the near-wall heat source is a function of the particle size and the deposit position.Third, the particle concentrations above radiators, temperatures, air velocities andrelative humidity are measured in42places and the data is analyzed by usingcorrelation analysis and multiple linear regressions in SPSS. The correlations of particleconcentrations above radiators and temperatures, air velocities or relative humidity arediscussed. Three multiple linear regression equations are established to obtain theconcentrations of PM10, PM2.5and PM1above near-wall heat sources.Finally, the effects of deflectors above the near-wall heat source on reducing particledeposition on the wall behind the near-wall heat source are discussed. To exploresuitable width and position of the deflector, the particle deposition numbers on the wallbehind the near-wall heat source with different deflectors are compared. The resultsshow that the deflector is effective in reducing particle deposition on walls behind heatsources. The width and position of deflectors both have significant effect on particledeposition control.