Unsteady natural convection of water adjacent to the sidewall of a differentially heated cavity with multiple fins

The unsteady thermal flow and heat transfer adjacent to the sidewall of a differentially heated cavity with single and multiple nonconductive fins are investigated utilizing the finite element method. The transition to the unsteady flow, as well as flow oscillations, is described for the water-filled cavity and Rayleigh numbers ranging from 1 x 10(7) to 1 x 10(10), including the critical Rayleigh number. Characteristics of unsteady flows are investigated for early, transitional, and quasi-steady stages. For all cases, heat transfer from the finned sidewall to the interior fluid is quantified and compared with the cavity without the fin. Results show that the volumetric flow rate along the vertical axis in the middle of the cavity rises by increasing the number of fins (up to 13.41% for the cavity with two fins for Ra = 1.84 x 10(9)) in transitional and quasi-steady stages. Moreover, the increment of fin number and Ra leads to a higher enhancement factor (epsilon) that shows the heat transfer enhancement or depression. For Ra = 1.84 x 10(9), the maximum e for the cavity with one and three fins is calculated about 17.5% and 34% respectively.