Unsteady heat transfer in an enclosure with a time-periodic rotating cylinder

Unsteady mixed convection heat transfer in a differentially heated square enclosure is studied in this article. A conductive circular with rotational speed varying periodically with time is embedded in the center of the enclosure. The governing equations are modeled in the COMSOL, with a partial differential equation (PDE) solver being based on the Galerkin finite element method (GFEM). The governing parameters considered are the rotary amplitude, -1000 ≤ AΩ ≤ 1000, the rotary frequency, 0 ≤ FΩ ≤ 300π, the cylinder radius, 0 ≤ R ≤ 0.2, and the thermal conductivity ratio, 0.5 ≤ Kr ≤ 10. It was found that the recirculating cells exist for a positive rotary amplitude and it increases with the rotational speed. Fast rotation and a high frequency combined with a low thermal conductivity ratio was found to be most effective in enhancing the performance of the overall heat transfer rate.