Macroporous membrane liquid transport

Meso- and Macroporous Membrane Liquid Transport The volumetric mechanical permeance for pure liquids is obtained as a variation of Darcy s law for both mesoporous and macroporous structures as... 

The viscous diffusion mechanism is also valid for transport process in the liquid phase. Then, if we have a liquid filtration process through a porous (i.e., macroporous or mesoporous) membrane, the following form of the Carman-Kozeny equation can be used [9]... 

In liquid filtration using micro-, ultra-, and nanofiltration porous membranes, the driving force for transport is a pressure gradient. Solvent permeability and separation selectivity are the two main factors characterizing membrane performance. Convective flux is predominant with macroporous and mesoporous membrane strucmres, the selectivity being controlled by a... 

Several investigators have demonstrated the feasibility of immobilized liquid membrane gas separations in applications where large pressure differences are encountered such as acid gas removal from synthetic natural gas. The immobilized liquid membranes prepared by Kimura et al. (16) using 100 pm cellulose acetate supports withstood CO2 partial pressure differences of up to 6.89 10 N/m. Matson et al. (15) used mlcroporous cellulose acetate and polyethersulfone films of 25-75 pm thickness to successfully immobilize potassium carbonate solutions for H2S transport at pressure differences of up to 2.07 10 N/m. The ILMs were supported by macroporous non-wetting polymer films such as polypropylene and polytetrafluoro-ethylene to increase the resistance to high transmembrane pressures. 

The GDL of PEM fuel cells connects between the bipolar plate/flow channel and catalyst layer. It provides the pathways for mass, heat, and electron transport, and also acts as the physical support of CL and membrane. The present state-of-the-art GDL consists of both a macroporous substrate and a micropo-rous layer (MPL). The macroporous substrate is a porous network of graphite fibers, which is usually carbon paper, carbon felt or carbon cloth. The substrate is often coated with hydrophobic materials such as PTFE for better liquid water removal. The MPL is coated on one side of the substrate which faces the catalyst layer. A typical MPL is a composite layer mixed by carbon particles and PTFE. The MPL usually has lower porosity and permeability but higher hydrophobicity and electrical/thermal conductivity than its substrate layer. The MPL enhances the water management and thermal/electricity connection between the substrate layer and CL to better cell performance. Unlike the membrane and catalyst layer, researches focusing on developing new materials and/or revolutionary design are scarce. Therefore, this subsection only focuses on the macroporous substrate/MPL GDL. 

All these methods lead to a set of parameters (membrane thickness, pore volmne, hydraulic radius) which are related to the working (macroscopic) permselective membrane properties. In the case of liquid permeation in a porous membrane, macro- and mesoporous structures are more concerned with viscous flow described by the Hagen-Poiseuille and Carman-Kozeny equations whereas the extended Nernst-Plank equation must be considered for microporous membranes in which diffusion and electrical charge phenomena can occur (Mulder, 1991). For gas and vapor transport, different permeation mechanisms have been described depending on pore sizes ranging from viscous flow for macropores to different diffusion regimes as the pore size is decreased to micro and ultra-micropores (Burggraaf, 1996). 

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