Transient natural convection in vertical annuli with rotating inner walls

The problem of transient laminar natural convection in open ended vertical concentric annuli with rotating inner walls is investigated numerically A finite-difference scheme and a computer code are developed for solving the governing boundary-layer equations. Two kinds of thermal boundary conditions are studied. In the first case, the inner wall is heated isothermally or at constant heat flux while the outer wall is maintained adiabatic (insulated). In the second case, the inner wall is heated isothermally or at constant heat flux while the outer wall is maintained at the inlet (ambient) fluid temperature.; Transient torque required to rotate the inner wall is presented for a fluid of Pr=0.7 in an annulus of radius ratio 0.5 over a wide range of the controlling parameter Gr2/Ta. Furthermore, the effect of Gr 2/Ta on the volumetric flow rate, heat absorbed and steady-state time is discussed.