Heat (Mass) Transfer Characteristics in Rectangular Ducts with a Sharp 180-Degree Turn

Abstract

Experimental study has been conducted on forced convection heat (mass) transfer in the rectangular duct with a sharp 180-degree turn. Detailed distributions of local heat (mass) transfer rates over the all duct walls have been measured using the naphthalene sublimation technique, directing special attention to the influence of turn clearance and Reynolds number on the mass transfer characteristics. It has been found that, in case of smaller turn clearance, the flow separated at the tip of the inner wall reattaches on the outer wall of the duct and the local mass transfer rate becomes the local maximum at the reattaching location. On the other hand, in larger turn clearance, the local maximum mass transfer rate caused by the flow reattachment is observed not on the outer wall but on the inner wall after the turn. The characteristics of the flow reattachment after the turn is also influenced by the Reynolds number in the ducts with a large turn clearance.