This comment jointly addresses experimental observations related to the functioning of coalescence filters with or without added drainage layer and their interpretation, put forth in the following papers by Chang, C., Ji, Z. and Liu, J.:.
The effect of a drainage layer on filtration performance of coalescing filters. Separation and Purification Technology 170, 370-376, 2016
The effect of a drainage layer on the saturation of coalescing filters in the filtration process. Chemical Engineering Science 160, 354-361, 2017
Pressure drop and saturation of non-wettable coalescing filters at different loading rates. AIChE Journal 64, 180-185, 2018
The effect of a drainage layer on saturation and liquid distribution of oleophobic coalescence filters. Separation and Purification Technology 194, 355-361, 2018
These papers concluded that the addition of a drainage layer alters the behavior of a coalescence filter in terms of pressure drop evolution, saturation profile, as well as internal oil distribution pattern, in ways that necessitates significant modifications to the “Film-and-Channel-Model”. Notably, the jump-Δp is supposed to be reduced in presence of a drainage layer.
We were able to reproduce most of these experimental observations and find that the observed phenomena (especially those related to the shape of the Δp curve during loading) can be explained within the realm of capillary effects in fibrous media and without recourse to modifications of the Film-and-Channel-Model. Certain other data (e.g. those related to unusual oil distribution patterns) appear to have been impacted by experimental artifacts. We also show in this context that the mechanical compression of non-wettable coalescence media can lead to significant changes in apparent wettability.