Study of heat transfer in horizontal bare and finned annuli

A numerical study is presented for the laminar natural convection in a diff erentially heated horizontal bare and finned rhombic annulus filled with ai r. An adaptive finite-element method is adopted to predict the complex reci rculating buoyancy driven flows. Simulations were conducted for cavity widt hs Eg ranging from 0.25 to 0.875, for two different fin configurations with fin lengths l varying from 0.3 to 0.7 and Rayleigh numbers Ra ranging from 10(3) to 10(7). Results indicate that the heat transfer is maximized for a narrow cavity Eg = 0.25 with fin length l = 0.7 (configuration 1). In this case, conduction prevails over convection. On the other hand, when convect ion is dominant, the heat transfer is maximum for Eg = 0.875 and l = 0.7. T he equivalent thermal conductivity k(equ) was correlated in terms of Ra for all geometries via k(equ) = CRan. (C) 1999 Elsevier Science Ltd. All right s reserved.