An Experimental Study of Particle Deposition on Micro-ribbed Surface in a Chamber

Abstract

Nowadays, because people spend more time indoors than outdoors, their health is being influenced by the indoor air quality. Particles smaller than 10 μm (PM10) can be easily inhaled by human beings, leading to serious lung diseases. Therefore, it is necessary to develop a highly efficient particle removal system to improve indoor air quality. Aerosol removal systems are widely used in indoor environments but many of them are not efficient for small particles, especially in the submicron range (0.1-1m). For example, HEPA filters can remove some of them but they are expensive to maintain because they need to be replaced on a regular basis. Aerodynamics type air cleaners, e.g. cyclones, are lower in cost and easier to maintain, but they still face the low removal efficiency for submicron particles. So it is expected to find a simple and low-cost way to enhance their efficiency. On one hand, it has been found that the particle collection performance on some air cleaners, such as electrostatic precipitators, can be significantly enhanced by an arrangement of repeated surface ribs. On the other hand, it is well known that roughness in micrometer scale increases the particle deposition rate and certain experiments have revealed that a ribbed surface in millimeter scale on the wall can also enhance the deposition. Inspired by this, it is expected that the removal efficiency, especially for submicron particles, can be further enhanced by adding ribs in micrometer scale on surfaces of the air cleaning system to enhance particle deposition. In this study, the relationship between the particle deposition effect and the geometrical parameters of the rib was studied experimentally. Two different rib shapes, convex semi-circular and concave semi-circular, and for each shape, five different ratios of rib height to rib pitch were investigated. All samples were fabricated by 3D printing and the smallest ribs are in micrometer scale. In each experiment, only one sample was put on the bottom surface of a well-sealed chamber. Dust particles with diameters ranging from 0.3 to 5 μm were injected to the chamber until a specific concentration was achieved. A fan in the middle of the chamber produced a turbulent flow, thoroughly mixing the air inside. The number concentration of different particle sizes inside the chamber was measured during the experiments. The particle deposition rate due to the ribbed surface was calculated by the concentration decay method. Relative deposition rate, which is defined as the deposition rate on micro-ribbed surfaces divided by the deposition rate on a non-patterned surface, was introduced to evaluate the enhancement effects. The results show that both the shape and aspect ratio have obvious effects on particle deposition for different particle sizes. For submicron particles, the enhancement effects are positive, showing a strong correlation with the particle size. The mechanism of particle deposition on different micro-ribbed surfaces was also compared and discussed. The results of this study suggest a possible particle deposition enhancement approach using micro-ribbed surfaces which could be a reference for considering efficiency enhancement of aerosol removal systems.