Effect of pore size and wettability of multilayered coalescing filters on water-in-ULSD coalescence

Coalescing filters are generally used to increase the size of the small drops for their separation from gases and liquids. Many studies have been performed on coalescing filter media. The performances become much more complicated for multilayered media having different properties and systematic studies are needed. Wettability, pore size, face velocity and wetting properties are among the important factors controlling performance. In this work, microscopic studies were performed to visually observe coalescence of water droplets on hydrophilic Nylon and hydrophobic Polypropylene woven sheets in a water-in-diesel emulsion at different face velocities and spacings between the sheets. The combination of hydrophobic sheet followed by hydrophilic sheet had the best performance. Statistical analysis of variance showed that the variations of distance between sheets and the face velocity were not significant factors. To better understand the effects of multilayers in filter performance, pilot scale experiments of stacked layers of woven sheet media of different thicknesses and wetting properties were conducted. Thin media had poor performance, but the performance improved and reached a plateau as the thickness increased. Effects of fiber surface wettability and pore size variations in the layers were also evaluated. Similar to microscope results, the coalescence performance was better for dual layer media with different wetting properties of each layer compared to dual layer media having the same wetting properties of each layer. The pore size was a dominant parameter affecting the performance. When pore size was similar to the average drop size of the water in the upstream, the best performance was observed. For dual layer filters having one layer of small pores and the other of large pores, the observed performance was lower than that of dual layer filters having only large pores but higher than the filters having only small pores.