JCE_V4_N2_RP4 Kamlesh pandey V. Kumar Journal on Civil Engineering 2249 - 0779 4 2 25 38 Crack, Momentum Equation, LCL Equation, Crack Wall Geometry, Self-affine, Quintic law, Hydraulic Conductivity, Two-Phase Flow Present review discusses the scope and limitations of basic equations of continuity and momentum used in the study of flow behavior in single crack. The continuity equation for liquid flow used in the literature does not account for source and sink which occurs during crack wall leakages. In two-phase continuity equation, inter-phase transfer terms have been identified to be used as source or sink terms. Navier-Stokes momentum equation and its simplifications under various assumptions, leading to derivations of Stokes and Reynolds equations, and their limitations along with computational difficulty in crack flow problems is discussed. Emergence of Local Cubic Law (LCL) equation and its limitations has been indicated. Validity of LCL equation has been tested in the literatures under the influence of various factors. The relative importance of inertial and viscous forces show that LCL equation is valid for Reynolds number of 10 and a non-linear relation between pressure gradient and volumetric flow rate need to be used when Reynolds number is between 10 and 100. The use of scaling law used in the fracture mechanics shows that in smooth walled fracture, the volumetric flow rate vary with fifth power of crack aperture and so this law is termed as 'quintic' law. There are few published works in literature to study the effect of slip boundary condition in deriving the correction factor in hydraulic conductivity of fracture using Beaver-Joseph slip boundary conditions in case of smooth permeable fracture walls. Some works have shown that formulation of momentum equation for different flow regimes of two phase flow in cracks is a difficult task. March - May 2014 Copyright © 2014 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=2987