HEAT-TRANSFER IN VERTICAL ROTATING ANNULI - A NUMERICAL STUDY

Heat transfer in vertical rotating annuli. A numerical study. Mixed convection between coaxial rotating cylinders has been numerically studied both for steady pow and heat transfer in a vertical, differentially heated annulus, and for transient heating of a fluid enclosed in an annulus with adiabatic horizontal plates and outer cylinder. Two cases of shear induced flows were considered : the first is produced by the axial rotation of the inner cylinder while the second is caused by the rotation of the horizontal plates and outer cylinder. A parametric study has been conducted to investigate the effects of the rotational Reynolds number, Rayleigh number, aspect ratio and radius ratio. It is shown that rotation of the inner cylinder leads to an enhancement of the heat transfer between the differentially heated cylinders. On the other hand, rotation of the outer surfaces produces a decrease in heat transfer due to the opposite effects of the gravitational and centrifugal forces. As a result, axial rotation of the inner cylinder is shown to be a viable means for reducing the heating time of a cold fluid while rotation of the outer surfaces allows a slowing down of the heating.