Heat transfer in a swinging rectangular duct with two opposite walls roughened by 45° staggered ribs

This paper describes an experimental study of heat transfer in a rectangular channel with two opposite walls roughened by 45° staggered ribs swinging about two orthogonal axes under single and compound modes of pitching and rolling oscillations. A selection of heat transfer measurements illustrates the manner by which the swinging oscillations with and without buoyancy interaction modify local heat transfer along the centerline of rib-roughened surface in the range of 0.75–2.25 times of the static channel value. The compound rolling and pitching forces with harmonic and non-harmonic rhythms interacting with buoyancy exhibit synergistic effect to reduce heat transfer. An adverse buoyancy effect that reverses the buoyancy interaction from improving to impeding heat transfer when the relative strength of swinging force increases could develop in the channel that swings with compound mode oscillation. An empirical heat transfer correlation, which is physically consistent, has been developed that permits the individual and interactive effects of single and compound modes of swinging forces with and without buoyancy interaction on forced convection to be evaluated and quantified. This work has been motivated by the need to understand the general effect of swinging oscillation on the performance of the cooling passage in a rib-roughened plate-type heat exchanger under sea-going conditions.