SHEAR RATE-DEPENDENT THERMAL-CONDUCTIVITY MEASUREMENTS OF NON-NEWTONIAN FLUIDS

An investigation was carried out to experimentally determine the therm al conductivities of non-Newtonian fluids in a shear field. Time-indep endent purely viscous and viscoelastic fluids were considered. A coaxi al cylinder apparatus with a rotating outer cylinder was used to estab lish the velocity field in the test fluid. First, the thermal conducti vity of distilled water was measured to validate the instrument. The e xperimental water data agreed within 1% of literature values, and ther e was no effect of outer cylinder rotation (shear field). However, for non-Newtonian fluids such as aqueous carboxymethylcellulose and Separ an solutions, there were significant increases in thermal conductiviti es of as much as 70% for CMC and 50% for Separan, depending on the she ar rate, polymer concentration, and temperature. The effect of shear r ate dependent thermal conductivities on the study of heat transfer in non-Newtonian fluids could be important. As in natural convection, the momentum and energy equations could no longer be solved separately bu t would have to be solved simultaneously. (C) Elsevier Science Inc., 1 997.