Calculation of pressure drop in the tube flow of sewage sludges with the aid of flow curves

Abstract

The layout of pumps for the transport of sewage sludges in sewage plants is of great importance. The understanding of pressure drop plays a decisive role. In this paper, a method, existing in the literature, which was developed within the framework of treating the frictional behaviour of viscoelastic fluids, will be presented for the calculation of the pressure drop in pipes. Sewage sludges belong to the class of nonNewtonian fluids. They exhibit intrinsically viscous behaviour and elastic properties. Due to the variation of the viscosity across the cross-section of flow, a representative Reynolds number at the operating point of the flow is defined with the aid of a representative viscosity, in order to determine the type of flow. Exact statements about the pipe friction coefficient in laminar flow are facilitated knowing the correlations for Newtonian fluids. For the case of the turbulent region, a modified formula for Newtonian fluids is taken as a basis. The validity of the method of calculation for sewage sludge flow is compared and discussed with and with respect to numerous experiments in research plants and actual sewage plants.