Non‐Newtonian heat transfer in the thermal entrance region of uniformly heated, horizontal pipes

Abstract

Abstract Experimental data were obtained for laminar forced flow in the thermal entry region of a uniformly heated pipe with fluids exhibiting a range of non‐Newtonian behavior. The Graetz number range was between 240 and 38,000. Contributions to heat transfer made by non‐Newtonian fluid behavior, temperature‐dependent fluid properties, viscous heating, and secondary flow due to buoyancy were evaluated. Results indicate that heat transfer is controlled by local wall shear rates. Local wall shear is affected much more by temperature variation of fluid rheological properties than by the degree of pseudoplasticity. Viscous heating was not detected in any of the tests. Natural convection effects were apparent in all cases; however, the heat transfer rates showed contributions due to buoyancy only at the lowest flow rates with low viscosity fluids.