Local and Spatially Averaged Heat Transfer Distributions in a Curved Channel with40 to 1 Aspect Ratio for Dean Numbers from 50 to 200

摘要

The effects of curvature and the resulting centrifugal instabilities on localheat transfer distributions are studied in a curved channel at Dean numbers ranging from 50 to 200. The channel has a rectangular cross section of 1.27 cm by 50.1 cm giving an aspect ratio of 40 to 1. Flow is heated in a straight portion of the channel prior to the curved portion in order to obtain flow which is hydrodynamically and thermally fully developed. All baseline tests confirm techniques employed and qualify flow behavior. These consist of energy balance checks and comparison of results from the straight section to numerical and analytic solutions. Nusselt numbers in the curved section initially show an abrupt decrease after the imposition of the stabilizing influences of convex curvature. These are followed by a gradual increase as centrifugal instabilities and Dean vortices form and develop. Spatially resolved results also show significant surface Nusselt number variations across the span of a vortex pair, especially on the concave surface. On the convex surface, local Nusselt numbers are much more apt to be spanwise uniform. Keywords: Curved heating channel, Heat transfer coefficients, Nusselt numbers, Dean vortices, Centrifugal instabilities, Thesis. (jhd)