J. KSIAM Vol.18, No.3, 257–268, 2014 http://dx.doi.org/10.12941/jksiam.2014.18.257 THERMAL DIFFUSION AND RADIATION EFFECTS ON UNSTEADY MHD FREE CONVECTION HEAT AND MASS TRANSFER FLOW PAST A LINEARLY ACCELERATED VERTICAL POROUS PLATE WITH VARIABLE TEMPERATURE AND MASS DIFFUSION M. VENKATESWARLU 1,† , G. V. RAMANA REDDY 2 , AND D. V. LAKSHMI 3 1 DEPARTMENT OF MATHEMATICS, V. R. SIDDHARTHA ENGINEERING COLLEGE,KANUR,KRISHNA (DIST), ANDHRA PRADES,I NDIA 520 007 E-mail address: mvsr2010@gmail.com, mvenkateswarlu@vrsiddhartha.ac.in 2 DEPARTMENT OF MATHEMATICS,K.LUNIVERSITY,VADDESWARAM,GUNTUR (DIST), ANDHRA PRADESH, I NDIA 522 502 3 DEPARTMENT OF MATHEMATICS,BAPATLA WOMEN’ S ENGINEERING COLLEGE,BAPATLA,GUNTUR (DIST), ANDHRA PRADESH,I NDIA 522 102 ABSTRACT. The objective of the present study is to investigate thermal diffusion and radiation effects on unsteady MHD flow past a linearly accelerated vertical porous plate with variable temperature and also with variable mass diffusion in presence of heat source or sink under the influence of applied transverse magnetic field. The fluid considered here is a gray, absorbing/ emitting radiation but a non-scattering medium. At time t> 0, the plate is linearly accelerated with a velocity u = u0t in its own plane. And at the same time, plate temperature and concen- tration levels near the plate raised linearly with time t. The dimensionless governing equations involved in the present analysis are solved using the closed analytical method. The velocity, temperature, concentration, skin-friction, the rate or heat transfer and the rate of mass transfer are studied through graphs in terms of different physical parameters like magnetic field pa- rameter (M), radiation parameter (R), Schmidt parameter (Sc), Soret number (So), Heat source parameter (S), Prandtl number (Pr), thermal Grashof number (Gr), mass Grashof number (Gm) and time (t). 1. I NTRODUCTION The study of magnetohydrodynamics with mass and heat transfer in the presence of radiation and diffusion has attracted the attention of a large number of scholars due to diverse applica- tions. In astrophysics and geophysics, it is applied to study the stellar and solar structures, radio propagation through the ionosphere, etc. In engineering we find its applications like in MHD Received by the editors July 3 2014; Accepted August 19 2014; Published online September 5 2014. 2010 Mathematics Subject Classification. 76A02, 76D10, 76W05, 80A20. Key words and phrases. MHD, Analytical method, Vertical porous plate, Radiation parameter, Heat source or sink. † Corresponding author. 257