EXTRUSION AND LUBRICATION FLOWS OF VISCOPLASTIC FLUIDS WITH WALL SLIP

The simplest model flow which approximates the extrusion (shallow scre w channels) and lubrication flow is the steady, laminar flow occurring between two infinitely long parallel plates i.e., the generalized pla ne Couette flow. Here we develop an analytical model of the generalize d plane Couette flow of viscoplastic fluids. The deformation and flow behavior of viscoplastic fluids can be realistically represented with the Herschel-Bulkley constitutive equation, which we have utilized as the basis for the development of our analytical model. Furthermore, as also demonstrated here, the deformation behavior of viscoplastic flui ds is generally complicated by the presence of wall slip at solid wall s, which occurs as a function of the wall shear stress. The wall slip versus the wall shear stress behavior of viscoplastic fluids can be ex perimentally characterized using viscometric flows, including steady t orsional and capillary flows. Thus determined Navier's wall slip coeff icient can then be utilized in modeling of processing flows. In our an alytical model of the generalized plane Couette flow of viscoplastic f luids the Navier's wall slip boundary condition was included. This mod el should be an important engineering tool, which provides design expr essions for the extrusion and lubrication flows of viscoplastic fluids , with or without wall slip occurring at the walls.