Meccanica DOI 10.1007/s11012-010-9321-0 ORIGINAL ARTICLE Unsteady MHD natural convection from a heated vertical porous plate in a micropolar fluid with Joule heating, chemical reaction and radiation effects Ali J. Chamkha · R.A. Mohamed · Sameh E. Ahmed Received: 10 May 2009 / Accepted: 25 May 2010 © Springer Science+Business Media B.V. 2010 Abstract The effects of Joule-heating, chemical re- action and thermal radiation on unsteady MHD nat- ural convection from a heated vertical porous plate in a micropolar fluid are analyzed. The partial differential equations governing the flow and heat and mass trans- fer have been solved numerically using an implicit finite-difference scheme. The case corresponding to vanishing of the anti-symmetric part of the stress ten- sor that represents weak concentrations is considered. The numerical results are validated by favorable com- parisons with previously published results. A para- metric study of the governing parameters, namely the magnetic field parameter, suction/injection parameter, radiation parameter, chemical reaction parameter, vor- tex viscosity parameter and the Eckert number on the linear velocity, angular velocity, temperature and the concentration profiles as well as the skin friction coef- ficient, wall couple stress coefficient, Nusselt number and the Sherwood number is conducted. A selected set A.J. Chamkha ( ) Manufacturing Engineering Department, The Public Authority for Applied Education and Training, Shuweikh 70654, Kuwait e-mail: achamkha@yahoo.com R.A. Mohamed · S.E. Ahmed Department of Mathematics, South Valley University, Qena, Egypt S.E. Ahmed e-mail: sameh_sci_math@yahoo.com of numerical results is presented graphically and dis- cussed. Keywords Unsteady flow · Natural convection · Micropolar fluid · MHD · Suction/injection · Radiation 1 Introduction Micropolar fluids are fluids of microstructure. They represent fluids consisting of rigid, randomly oriented or spherical particles suspended in a viscous medium, where the deformation of fluids particles is ignored (e.g. polymeric suspensions, animal blood, liquid crys- tals). In order to describe accurately the behavior of such fluids, the geometry and intrinsic motion of indi- vidual material particles have been taken into account, and the angular velocity field of rotation of particles and the conservation of the angular momentum are added in the theory of micropolar fluids discussed by Eringen [1]. In this case, many classical concepts such as the symmetry of the stress tensor or absence of cou- ple stresses are no longer existed. Owing to its rela- tively mathematical simplicity, the micropolar fluids model has been widely used in lubrication to investi- gate the polymer solutions in which the Newtonian lu- bricant is blended with small amount of long-chained additives. So far, there have been many studies fo- cusing on one- and two-dimensional non-Newtonian bearings by the micropolar fluids model [2–8]. For