Theoretical and numerical investigation of entropy for the variable thermophysical characteristics of couple stress material: Applications to optimization

Abstract Transportation of heat and mass along with irreversibility analysis for the flow of Couple stress fluid past over a nonlinear stretched surface is reported in this exploration. The novel features and purpose of this report is to notice the involvement of variable thermophysical characteristics i.e. (variable magnetic field, thermal conductivity, diffusion coefficient) for the couple stress model. Flow is produced over a non-linear stretched surface under constant pressure. Variable wall temperature, wall concentration and variable magnetic field are observed. Thermal transport is influenced by thermal radiation. Conducting mass in the light of Fick's second law is derived by adding a chemical reaction. Flow presenting partial differential equations describing the conservation laws are modelled under boundary layer approximation in Cartesian coordinate system. Similarity transformation is used to convert these coupled nonlinear fluid flow equations into ordinary differential equations. The converted nonlinear coupled system of differential equations is solved analytically using optimal homotopy procedure. Mathematical software Mathematica 11.0 is used to handle the computational complexity. Solution for velocity, temperature, concentration and entropy generation is displayed and it is discussed for the flow against numerous influential parameters. Numerical values for the dimensionless stresses, rate of heat and mass transfer is computed and tabulated. Moreover, limiting case of present exploration is compared to that of existing literature and an excellent agreement in results is noted. Also, it has been drafted that magnetic parameter retards the flow, whereas, the increment in ratio parameter and fluid parameter upsurges the velocity field.