Formation of Vortex Structures in a Vertical Enclosure with Finning of Its Both Walls

Abstract

One of the efficient methods of controlling heat transfer is the installation of barriers or fins on heat transfer surfaces. A numerical model of a free-convective flow and heat transfer in a high closed enclosure in the presence of fins on its isothermal side walls has been developed. The Navier-Stokes equations in two-dimensional statement were solved numerically. The influence of the height of the fins and of the spacing between them on the flow structure, local and average heat transfer was investigated. Calculations were carried out in the range of Rayleigh numbers Ra = 103−105 , when there exist laminar and multicellular regimes of convection. Two types of fins have been considered: adiabatic and with an infinitely high thermal conductivity. The effect of heat transfer rate decrease is equal to about 30% as compared to smooth walls. For heat-conducting fins heat transfer enhancement may reach 200% and above. Their influence on the aerodynamic and thermal structure was investigated in a number of experimental and computational works. It was shown earlier that installation of partitions in a square cavity may lead to a great decrease in the heat transfer rate. The effect of this decrease is attained due to the decrease in the intensity of air vortex flow in the cavity, therefore the enhancement of heat release is observed for both nonconducting and conducting partitions. The installation of fins on the side walls of high vertical enclosures leads to a substantially more complex structure of flow inside an enclosure. The average heat transfer rate for such conditions depends on a large number of parameters: the Rayleigh numbers, aspect ratio of an enclosure (A = H/L), spacing between fins (h), number of fins (n), as well on the fin height (l). The aim of the present work was to numerically investigate a two-dimensional flow and heat transfer in a vertical finned enclosure and determination of the regimes with a lowered and intensified heat release. Since the thermal conductivity of fins has a strong effect on heat release, two-extreme cases are investigated in the work: nonconducting (adiabatic) fins and fins with an infinitely high thermal conductivity (λf → ∞). Thus, the limits of the influence of finning on the change in heat transfer with fins installed on the side surfaces in a vertical slit were determined.