An investigation of unsteady hydromagnetic natural convection heat and mass transfer flow of an electrically conducting, viscous, incompressible and optically thick radiating fluid past an impulsively moving infinite vertical plate embedded in a uniform porous medium in a rotating system with Hall effects in the presence of homogeneous first order chemical reaction is carried out when temperature of the plate has a temporarily ramped profile. Exact solution of the governing equations is obtained in closed form by Laplace transform technique. Expressions for skin friction due to primary and secondary flows and Nusselt number are derived for both ramped temperature and isothermal plates. Expression for Sherwood number is also derived. The numerical values of primary and secondary fluid velocities, fluid temperature and species concentration are displayed graphically whereas those of skin friction are presented in tabular form for various values of pertinent flow parameters. In order to highlight the influence of ramped temperature distribution within the plate on the flow-field, the fluid flow past a ramped temperature plate is compared with the one past an isothermal plate.

The unsteady hydromagnetic flow due to torsional oscillations of a rotating disc in a viscous incompressible electrically conducting fluid which is also rotating is studied taking the effects of the Hall current and ion-slip into consideration. The governing equations are solved analytically. The results show that the inclusion of the Hall current and ion slip have important effects on the velocity distributions as well as shear stresses at the disc. The flow is characterized by two opposite circularly polarized waves, travelling with different velocities. It is found that there is a formation of two-deck boundary layers, thicknesses of which increase with increase in either Hall parameter or ion-slip parameter. The radial velocity increases with an increase in Hall parameter and the azimuthal velocity increases with an increase in either Hall parameter or ion-slip parameter. Further, it is found that the amplitude of the transverse shear stress at the disc decreases with an increase in either Hall parameter or ion-slip parameter.