Laminar Forced Convection of a Pseudoplastic Thermo dependent Fluid in an Annular Horizontal Duct

Abstract

In this work, the problem of thermal development for laminar forced convection of a pseudoplastic thermo dependent fluid in a concentric annular horizontal duct is numerically addressed. Three thermal conditions are assumed: inner cylinder subjected to an imposed heat flux while the outer is insulated; then the inverse; and finally both cylinders are heated with the same heat flux densities. All computations are carried out from the entrance up to the thermal fully developed stage for a flow already developed dynamically. The study objective is to illustrate the effects of the rheological index (n), aspect ratio (r1), thermodependency (Pn) and heating mode on velocity profiles and Nusselt number evolution in addition to thermal entrance length. The results show an improvement in heat exchange with the shear-thinning of the fluid. The outer Nusselt decreases as r1 decreases while the inner one improves. Overall, the thermodependency has a similar effect to that of the shear-thinning. A very important result shows the reduction in thermal length with increasing n and/or Pn. Simple, accurate and widely valid correlations are provided for Nusselt number and thermal entrance length under different conditions.