Crisis of the Laminar Flow of a Non-Newtonian Liquid in a Pipe

Abstract

The laminar-turbulent transition of flows of Newtonian (viscous) and non-Newtonian liquids in pipes was investigated on the basis of the combined analysis of the generalized equation of the first and second laws of thermodynamics for a simple system and the Darcy–Weisbach equation. It is shown that a reason for the crises of the laminar flows of such liquids in pipes is the disturbance of the balance between the positive entropy production and the negative entropy flow in them. An analysis of calculation and experimental data on the disturbance of the laminar flow of a non-Newtonian liquid in a pipe and the transformation of this flow into a turbulent flow has shown that the crises of a laminar flow of an elastoviscoplastic liquid in a pipe happens at a larger critical Reynolds number compared to that of a laminar flow of a viscoplastic liquid at one and the same values of the Hedstrom parameter.