Thermal analysis of interaction between buoyancy induced flow under parallel rotation and rib induced vortices: Experimental and numerical study

This paper performing both experimental and numerical approaches underlines the aiding and opposing effects of secondary vortices resulting from parallel mode rotation on convective heat transfer coefficient in a rectangular channel in smooth and rib roughened channels. The Nusselt number is obtained by measuring the wall and fluid temperature at the Reynolds number ranging from 5118 to 10,677 and 0.07 < Delta rho/rho < 0.42. In addition, the Nusselt number is investigated in ribbed channels with one wall being perpendicularly ribbed at pitch ratio (P/e) and blockage ratio (e/Dh) equal to 15 and 0.088, respectively. Numerical simulations also allow to consider the effects of rotational induced secondary flows caused by centrifugal and the Coriolis forces in high rotation numbers (0 < Ro < 0.56) and Buoyancy numbers (0 < Buo < 1). The numerical results with non Boussinesq approximation for density variation show good agreement with experimental results, while it is revealed that the Nusselt number is underestimated if Boussinesq approximation is used. As the Reynolds number increases, the larger Buoyancy number is required to affect the Nusselt number. That is, under certain conditions which is expressed in terms of Gr(alpha)(omega)/Re the rotational buoyancy effects may be negligible and the Nusselt number is equal to stationary case. However, in rib roughened channels the rotational buoyancy causes the reattachment point to occur closer to upstream rib while physical presence of ribs reduce the enhancing effects of rotation. Thus, for practical use in rotating cooling systems such as turbo-generators or electrical machinery, rib roughened channels are not recommended.

Automated summary

This study examines the effects of rotation on convective heat transfer coefficient, demonstrating that rotational buoyancy effects may be negligible under certain conditions, while in rib roughened channels, rotational buoyancy causes the reattachment point to occur closer to the upstream rib and reduces the enhancing effects of rotation.