The effect of a drainage layer on filtration performance of coalescing filters

The effect of a drainage layer on the filtration performance of coalescing filters was evaluated experimentally. The “jump-and-channel” model was used to analyze saturation, pressure drop and efficiency of the filters with and without the drainage layer. The results showed that jump pressure drop dominated the wet pressure drop. The steady-state pressure drop was not proportional to filter saturation which was related primarily to the channel pressure drop. A liquid film was present between coalescing layer and drainage layer at steady state. The jump pressure drop was affected by the thickness of this liquid film. A thicker liquid film produced a higher jump pressure drop. When the drainage layer was assembled outside of the coalescing layer, pressure drop and penetration changed, and both saturation and efficiency increased significantly. A filter with a polyester drainage layer had the overall best performance. Furthermore, the dynamic thickness of the liquid film can be predicted using theoretical calculations, which allows qualitative analysis of the effect of the liquid film on filtration performance.