Abstract:

ESDU 91025 discusses models used to describe the rheology of time independent pseudohomogeneous non-Newtonian fluids (power- law, Bingham, Herschel-Bulkley and a generalised model due to Metzner and Reed); they are used to calculate the laminar flow pressure drop (which is independent of pipe roughness in this regime). Values of generalised critical Reynolds numbers are suggested to define transitional and turbulent flow. For turbulent flow in smooth pipes, pressure loss is estimated on the basis of an experimentally determined flow curve using either the Dodge-Metzner or Bowen approach depending on the available measurements. Bowen requires results for at least two pipe diameters. The choice of Dodge-Metzner when data are limited is discussed; seven possible methods are assessed against five sets of experimental results drawn from the literature. While it is suggested that transitional flows should be avoided, if the regime is required the use of a turbulent correlation is recommended because it will yield an overestimate. Suggestions are made for the treatment of roughness effects. Several worked examples illustrate the use of the methods. Six additional estimation methods are provided for cases where the flow curve has a complicated form that cannot be fitted to any of the rheological models. Guidance on the experimental determination of rheological data and the calculation of the flow curve is given in ESDU 95012. Two programs are provided: ESDUpac A9125 implements the Dodge-Metzner method and ESDUpac B9125 implements the method of Bowen.