Critical hydraulic gradient

Figure 1. The effect of volume concentration C on critical velocity VCr and critical hydraulic gradient ICR for sand-water mixture (1) and sand-glycol solution mixture (2)...

Critical Hydraulic Gradient, Quick Conditions and Hydrauiic Upiift Phenomena... 

The physical properties of the carrier liquid, especially density and viscosity, can essentially influence both main hydrodynamic parameters of the mixture flow, i.e. critical velocity VCr and the hydraulic gradient/. 

This ability of surfactants to solubilize NAPL components and coalesce into thermodynamically stable microemulsions is of critical importance in their selection for use in NAPL remediation. This is because microemulsions are highly fluid and can easily flow through permeable media and transport contaminants with them under the very low hydraulic gradients typical of shallow, unconfined aquifers. By contrast, macroemulsions, which are physical mixtures or dispersions of one liquid phase interspersed in another liquid phase are unstable, often very viscous, and do not flow easily or in a way that is predictable or easy to control, and thus are highly undesirable. 

The diffusion model and the hydraulic permeation model differ decisively in their predictions of water content profiles and critical current densities. The origin of this discrepancy is the difference in the functions D (T) and /Cp (T). This point was illustrated in Eikerling et al., where both flux terms occurring in Equation (6.46) were converted into flux terms with gradients in water content (i.e., VA) as the driving force and effective transport coefficients for diffusion, A), and hydraulic permeation,... 

Thomas A. D. 1979.Therole of laminar/turbulent transition in determining the critical deposit veloc ity and the operating pressttre gradient for long distance sltmy pipelines. Paper read at the 6th International Conference of the Hydraulic Transport of Solids in Pipes. Cranfield, UK BHRA Fluid Engineering, pp. 13-26. 

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