Texture tortuosity

Commonly used GDL materials are made of porous carbon fibers, including carbon cloth and carbon paper. Carbon cloth is more porous and less tortuous than carbon paper and has a rougher surface. Experimental results showed that carbon cloth GDL has better performance under high-humidity conditions because its low tortuosity (of the pore structure) and rough textural surface facilitate droplet detachment. " However, under dry conditions, carbon paper GDL has shown better performance than carbon cloth GDL because it is capable of retaining the membrane hydration level with reduced ohmic loss. 

Currently, the tortuosity, r, and the quotient, D/r, are assumed constant. However, r may depend on the habit and texture of the particular precipitated mineral. Also, the assumption is made that precipitation is uniform over the fluid-porous medium interface, rather than concentrated in small pores or in bottlenecks connecting large pores. However, non-uniform deposition may be expected in natural systeoLS. Both assumptions are first approximations and are subject to refinement when experimental data become available that provide more detailed information about effects of precipitation/dissolution on tortuosity and about uniformity of precipitation. 

As can be deduced from Eq. (14.78), the CO2 flux of DPMs is controlled not only by the intrinsic carbonate and oxygen ionic conductivities of the MC and perovskite phases but ako by the carbonate and perovskite porosity-to-tortuosity ratios. These textural parameters are influenced to an important extent by the sintering temperature. 

In fliis work, porous glasses in the sh e of beads and ultrathin membrane with controlled mesoporosity in the range between 2 and 20 nm were used as model catalyst supports. The hydrogrmation of braizene over nickel catalysts on the basis of the porous ass beads was used to invratipte the transport characteristics of the mesopores inside the primary particles of silica supports. The tortuosity fectors of the supports were obtained from measurements of the permeability of membranes with comparable texture properties. 

The right-hand side of the equation indicates that the term k/4> is controlled by specific internal surface or pore size, tortuosity, pore shape, and pore-throat to pore-body ratio. Thus, it covers all textural properties that control permeability except porosity. A reservoir quality index (RQI) can be defined as (Altunbay et al, 1997) ... 

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