Ryuta Misumi

Drag and lift forces acting on a spherical bubble in a linear shear flow

The effects of fluid shear on drag and lift forces acting on a spherical bubble are studied for high particle Reynolds numbers of 0.5⩽Rep⩽200 by means of a three-dimensional numerical simulation, and the effects are compared with those for a solid particle. The results show that the fluid shear increases the drag acting on a bubble. On the other hand, the lift always acts from the lower fluid-velocity side to the higher fluid-velocity side, and tends to approach a constant value for high particle Reynolds numbers. Further, the asymptotic value of the lift increases with increasing fluid shear rate. Although the trend of the drag on a bubble against the fluid shear is similar to that on a solid particle, the trend of the lift is quite different. For a solid particle the direction of the lift changes from the higher fluid-velocity side to the lower fluid-velocity side with the increasing particle Reynolds number. The difference in the lift between a bubble and a solid particle can well be explained by taking account of pressure and viscous contributions to the lift.

Resolution enhancement of electrical resistance tomography by iterative back projection method

An iterative back projection method (i-BP) has been developed to improve the resolution of reconstructed images produced by electrical resistance tomography (ERT). This solution is based on an iterative calculation of the electrical fields and it is possible to reconstruct clearer images than those reconstructed by the conventional back projection method without divergence. However, it does take several minutes to finish the iteration process, and therefore this solution can be applied to flow fields that require high spatial resolution rather than short processing times, such as the accumulation of noble metals in glass melters. Numerical simulations and experiments using a simple model are performed in this study. The numerical simulations show that clear images are reconstructed both near the wall and at the center by i-BP. The conductivity correlation coefficient between the genuine distribution and the reconstructed image is improved from 0.4 to 0.9. The validity of the i-BP method is also confirmed by the experimental results. As a result, it is confirmed that ERT and i-BP are capable of reconstructing acceptable images and have potential for use in the visualization of the accumulation of noble metals in a glass melter.Graphical Abstract