Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Jianshun Zhang

Keywords

Particle Deposition, Surface Roughness

Subject Categories

Mechanical Engineering

Abstract

The purpose of this work was to quantify the deposition rate constants of size-classified particles on typical indoor surface materials as affected by the degree of surface roughness. The experiments were conducted in a small-scale acrylic chamber. The particle size range was from 0.723 to 5.048 £gm with 28 size bins. The air change rates were 6, 11 and 13 h-1. The TSI large particle aerosol generator 8108 was used to generate potassium chloride as test particles, and the TSI aerodynamic particle sizer (APS3321) was used to measure the particle number concentrations. Particle deposition rate constants were determined by regression fitting of the measured time and size-resolved particle number concentrations. The air change rates (ACH) were measured by photo acoustic field gas monitor (Model 1412, Innova, AirTech Instruments).

The tested materials were acrylic (as a smooth surface reference), finished hardwood floor surface (FHFS), vinyl tile and four carpets with different surface textures. Based on the surface roughness measurements (Sz), the surface materials tested were divided into three categories smooth (Sz<140 fÝm), slightly rough (140 fÝmfÝm) and rough (Sz>2020 fÝm). Results showed that the particle deposition rate constants were significantly larger for the rough surface than for the smooth and slightly rough surfaces, and differed little between smooth and slightly rough surfaces. The results also showed that the air change rates (ACH) did not affect the deposition rate constant significantly for the particle size range and ACH range studied due to the similar flow regime involved. The calculated particle deposition rate constants were dependent on the sizes. The small particles had low deposition rate constants because of the relatively small gravitational settling effect, and the weak Brownian motion. The sedimentation of the large particles was mainly affected by the gravity. The experimental results were also compared with the predictions by previous empirical model for particle deposition, confirming the validity of this model.

Inside the small-scale chamber, the instantaneous airflow field was obtained by using Particle Image Velocimetry (PIV). The friction velocities were determined by analyzing the experimental data and used as the input of an empirical model that describes deposition rate constant as a function of friction velocity, air kinematic viscosity, particle Brownian diffusivity, particle diameter and terminal particle gravitational settling velocity, room area and volume.

The study also proposed a new dimensionless deposition rate constant k+, defined as the ratio between the deposition rate constant of a given particle size to the maximum deposition rate constant among all particle sizes from the same test. Analysis of the results from different experimental conditions show that k+ exhibits a consistent function of particle size, and hence can be used to estimate the particle deposition rate constant for a given particle size based on the measured deposition rate constant at a different particle size under the same experimental condition.

Access

Open Access

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