HEAT TRANSFER IN FLOWS OF NON-NEWTONIAN VISCOPLASTIC FLUIDS THROUGH SUDDEN EXPANSIONS AND CONTRACTIONS IN A PIPE

摘要

The heat transfer phenomena associated with the flow of non-Newtonian viscoplastic Bingham fluids over sudden expansions and through contractions in a circular pipe are studied by numerically solving the fully elliptic governing continuity, momentum, and energy equations. Solutions are obtained for a wide range of the governing Reynolds, yield, and Prandtl numbers in the laminar flow regime and under the assumption of constant fluid properties. The influence of the yield number on the thermal field, for both geometries, is more pronounced at high Reynolds and Prandtl numbers. In the sudden expansion case this influence takes the form of a localized peak in the Nusselt number distribution downstream of the reattachment point. The magnitude of the peak Nusselt number increases with the Reynolds, yield and Prandtl numbers. The effect of the contraction on the thermal field is more significant at high Reynolds and Prandtl numbers, and takes the form of a sharp reduction in the Nusselt number values right before the contraction plane.