Heat Transfer Enhancements from Elastic Turbulence Using Sucrose-Based Polymer Solutions

Abstract

The influences of elastic turbulence on convective heat transfer, within a C-shaped passage of a viscous disk pump, are experimentally determined using viscoelastic fluids and Boger fluids, which are constant-viscosity Newtonian solvents. Different concentrations of polyacrylamide in 65% sucrose solutions are used, along with solutions with 65% sucrose only, as different magnitudes of shear stress and strain rate are imposed upon the flowfield. Transition and development of elastic turbulence are characterized, along with convective heat transfer enhancements. The resulting increased levels of mixing, transport, and diffusion from elastic turbulence give convective heat transfer coefficient enhancements that are as large as 240%, relative to the Newtonian, Boger fluids at the same shear rate, rotation speed, flow passage height, and flow temperature. Variations of spectra of static temperature fluctuations and mean-square magnitudes of fluctuating static temperature provide evidence of increased flow irregularities and unsteadiness (relative to Boger solution flows), which result from elastic turbulence-induced polymer twisting, convolutions, and interactions. Such observed enhancements are shown to not be due to increased viscosity values alone, nor to centrifugal instabilities associated with streamline curvature, because Dean numbers are not large enough to allow development of the associated centrifugal-instability induced secondary flows.