CONVECTIVE HEAT-TRANSFER IN THE DEVELOPING FLOW REGION OF A SQUARE DUCT WITH STRONG CURVATURE

Abstract

A comprehensive numerical study is made of the velocity and convective heat transfer characteristics of developing laminar flow in a 90-degrees curved square duct. Straight inlet and outlet tangents are attached to the duct. The fully elliptic, three-dimensional, steady, incompressible Navier-Stokes equations are solved numerically over wide ranges of Reynolds number Re (and corresponding Dean number). A body-fitted coordinate system is utilized. Two thermal boundary conditions at the bend were adopted: a constant wall temperature condition, and a constant wall heat flux condition. The elaborate numerical results are consistent with the available flow field data. The details of the temperature field as well as the Nusselt number in the curved region are depicted. The influence of Re on local heat transfer in various parts of flow field is scrutinized. The impact of the thermal boundary condition at the bend is examined. In the vicinity of the entrance of the curved region, heat transfer is higher on the inner wall due to the presence of local accelerating flows near the inner wall. However, at further downstream, heat transfer is higher on the outer wall, since the maximum of the mainstream is shifted toward the outer and side walls by the action of centrifugal force. As the Reynolds number increases, a region of reverse flow appears in the corner area between the outer and side walls near the inlet of the bend. Heat transfer is reduced in this region of reverse flow. The present computational results clearly illustrate the variations of the Nusselt numbers, both in the peripheral and streamwise directions.