Fig. 4

a Concentration profiles for different values of Nb and Nt with Pr = 0.72, Le = 0.66, β = 0.02, γ = 0.01, ε ₁ = ε ₂ = 0.1, \( {\theta}_{\mathrm{r}}^{\hbox{-} 1} \) = −5, Mn = 10.0, S = 10. b Concentration profiles for different values of ε ₂ and Le with Pr = 0.72, S = 10, β = 0.02, γ = 0, ε ₁ = 0.2, A = 0.2, \( {\theta}_{\mathrm{r}}^{\hbox{-} 1} \) = −5, Mn = 10