Thermal characteristics in the annulus with an inner rotating rib-roughness cylinder

This work experimentally investigates the heat transfer characteristics in the annulus with an inner rotating rib-roughness cylinder, whose flow and thermal behaviors are associated with Taylor number (Ta) and centrifugal buoyancy parameter (GrΩ/Ta). The operating range of Ta is from 4.90 × 102 to 5.80 × 105, while the surface of the inner cylinder is heated up with several constant heat fluxes (279, 425 and 597 W/m2) to obtain various values of GrΩ/Ta. Besides, three modes of the inner cylinder without/with longitudinal ribs are considered. The end of the annular channel is connected to a side chamber to fit practical applications (such as in the rotary blade coupling of a four-wheel-drive vehicle). The experimental results show that the average Nusselt number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ (\overline{{Nu}} ) $$\end{document} was almost constant at low Ta, but increased rapidly with Ta when Ta exceeded some critical value (3,000–5,200 for present study). Additionally, the GrΩ/Ta effect on the heat transfer was negligible herein. Furthermore, by comparing with the inner cylinder without longitudinal ribs, stalling ribs on the inner cylinder increases the transport of heat by a factor of 1.22 at 105 < Ta < 106, and embedding cavities into the ribs increases the transport of heat by a factor of 1.16 at 105 < Ta < 106. Finally, the relationships between the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \overline{{Nu}} $$\end{document} and the Ta for various modes of test sections were proposed.