The study of coalescence filtration and drainage design

The objective of this work is to study the effect of fiber orientation and drainage angle of non-woven media on filtration performance. This work will improve filtration performance by changing only the fiber structure in filter media. In industrial processes, the demand of high-purity air supply can be achieved by using of air cleaning such as cyclones, sedimentation tanks, scrubbers, and electrical precipitators. When there is need of higher than 95% efficiency for the 0.1 to 1mum range of diameter, the fibrous filters are often employed.This study is done on both Microscale and Macroscale. The visual observation of the oil droplets in the fibrous filter media during the coalescence process by using microscope is conducted to understand the mechanism of the process. The study shows that there are three main steps in the coalescence process: the attachment of the small oil drops on the fibers, drop size growth, drop detachment and drainage from the fibers.In the second step, the drop growth can be by two mechanisms: (1) collision with other drops in the carrier gas stream or (2) two drops held on a fiber merging together. The theoretical models are derived and compared with the experimental results for both mechanisms. The results show that the vapor deposition diffusion mechanism in creeping flow can be responsible for the growth of drop on a single fiber. For the second mechanism, the merging time of two drops is on the order of 10-4 sec.The drag coefficient of a small drop migrating along a fiber is modeled as a function of the angle between fiber and flow direction. The results show that the drag coefficient is higher when the angle is lower.For the macro scale study, the filter media are made by gravitational filtration. The parameters, which are included in this study, are fiber angle, cake layer, and the presence of polymer scrim sheet. The sample media are characterized and tested performance tested in a coalescence filter media test system. The results show that the fiber structure significantly affects the filter performance.