Wetted perimeter concept

For a rectangular jet the wetted perimeter concept must be used (Marple, 1970). That is, the opening width A to be used in computing the Reynolds number is defined as A = 4 (area/perimeter). For a rectangle of length L and width W, A = 2WLI (W + L). When Lf> W,... 

S is the ratio of the surface area of the medium to its pore volume and stands for equivalent diameter of the pores. The hydraulic (mean) radius m is defined as the ratio of the average pore cross-sectional area to the average wet perimeter, in line with the concept of the equivalent loads (as explained in Section III). All the geometrical parameters from Eq. (19) can be estimated for particulars of the porous media. For example, in the case of aligned fibers, hydraulic radius and equivalent diameter can be expressed by ... 

The presence of the transition zone between a drop or a bubble and thin liquid interlayers can be described in terms of line tension, x, a concept first introduced by Gibbs (see for example [22]). In the case of surface tension, the transition zone between the liquid and vapor is replaced by a plane of tension with excess surface energy, y. By analogy, the transition zone between a drop or a bubble and the thin liquid interlayer may be replaced by a three-phase contact line with an excess linear energy, x. In contrast to surface tension defined always as positive, the value of the line tension may be positive and negative. When positive, it contracts the wetting perimeter, whereas the perimeter expands if the line tension is negative [33-36]. 

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