Entropy generation analysis for viscoelastic MHD flow over a stretching sheet embedded in a porous medium

In this paper it is intended to analyse entropy generation by applying second law of thermodynamics to magnetohydrodynamic flow, heat and mass transfer of an electrically conducting viscoelastic liquid (Walters B′) past on a stretching surface, taking into account the effects of Joule dissipation, viscous dissipation and Darcy dissipation, and internal heat generation. The boundary layer equations are solved analytically by using Kummer's function. The entropy generation has been computed considering Darcy dissipation besides viscous and Joule dissipation. Results for some special cases of the present analysis are in good agreement with the existing literature. Increase in viscoelastic and magnetic parameter reduces the velocity. Increase in elastic parameter causes a greater retardation in the velocity. Presence of porous matrix enhances temperature whereas increase in Prandtl number decreases the temperature. One striking result of the present study is that Darcy dissipation favours higher level entropy generation in all the cases except the flow of liquid with low thermal diffusivity assuming the process to be irreversible.