Capillaiy number

These expressions include k, the filter cake permeability (m ) P , the thrediold pressure below v hich air will not penetrate the filter cake pores (N/m ) the equilibrium, irreducible cake saturation, a fimction of the capillaiy number iV (defined below) s the porosity of the filter cake. 

There have been a number of attempts to revise and elaborate Brown s description of the film formation process [11,30]. For an overview of these approaches the reader is refmed to Mazur s review [25]. Perhaps the most important insight is that in a strict thermodynamic sense, there is no distinction betweai the osmostic pressure, II, and the mean capillaiy pressure, pc, which develops when the meniscus intercepts the surface of the particles. As the system becomes more concentrated, there will be some contribution of capillary forces to 11 before the particles come into contact and before the particle-water meniscus develops. Ultimately, n must converge to pc once the particles are in contact This continuity of n and Pc is the main point of the theoretical analysis by Crowley et al. [31], and they showed that when the osmotic pressure rises to little as 1% of the equilibrium vapour pressure of water, the force should be sufficirait to densify the film. 

The ratio of the particle diameter to the capillaiy length is evaluated by the Edtvos number" ... 

---