Heat transfer in an annular space fitted with heating isothermal blocks: Numerical bifurcation for low blocks height

A numerical study of the thermoconvective effects induced by the placement of two heating blocks on the inner surface of an air filled cylindrical annular space is presented. The radii ratio is kept constant R=2. This study investigates the influence of initial conditions on the flow structure and the overall heat transfer rate, when the height of the blocks is varied up to h=0.10. The interval of variation of the Rayleigh number, Ra, is [103,104]. The main result is the existence of a bifurcation point separating two flows regimes: uni- and bi-cellular, corresponding to a critical value of the Rayleigh number Rac, close to 3598. For Rayleigh numbers higher than Rac, the bicellular flow allows substantial enhancement of the heat transfer rate up to 18% in the considered interval of Ra.