Thermal Drive In Rotating Cylinders

The primary objective of the present work is to reveal some physical phenoma about thermal drive under centrifugal field, or combined gravitational and centrifugal fields. A numerical investigation of the flow and heat transfer of air in the annulus between horizontal concentric cylinders with one cylinder heated and rotating has been carried out. The mechanism of the suppresion of natural convection by fluid rotation is advanced. Thermal drive in a vertical rotating cylinder, and in a vertical annulus with outer cylinder and ends rotating is analyzed and discussed. It is found that the mean equivalent conductivity (K_eqm) for end drive increases at first and then decreases with rotating Reynolds number (Re), and K_eqm is approximately kept constant at low Re and then decreases with Re. It shows that the heat transfer can be weakened by fluid rotation under some conditions. Based on the analysis and numerical results, the physical mechanism of thermal drive in centrifugal fields is advanced, and a dimensionless parameter group is suggested to measure the relative importance of buoyancy and rotation to the mean equivalent conductivity. An iterative simultanous solution method is first developed to efficiently solve liner equation set for velocity, pressure and temperature. The proposed method was demonstrated for several cases of the thermal drive in a vertical rotating annulus, and was shown to be insensitive to dimensionless time step, requiring significantly less computational effort to coverge to the desired accuracy than did SIMPLEC. The test apparatus on thermal drive of air in a rotating vertical anuulus was established for experiments of mixed convection in the annulus with inner cylinder heated and outer one rotating. The changes in flow patterns and heat transfer provide evidence for the conclusion of the suppresion of natural convection by fluid rotation.