Based on its potential to develop more sustainable and energy efficient systems, process intensification is of increasing importance in various processing industries. The process intensification vs efficiency is carried out for natural convection in square enclosure and curved (concave/convex) wall enclosures filled with both fluid and fluid saturated porous bed via heatlines and entropy generation analysis for the development of sustainable process equipment design. As the selection of an optimal cavity is the main objective for the increase in efficiency, a comparative study has been carried out among the enclosures with equal dimensionless area ( = unity) and equal heater length (= 1 unit). (i) Case 1: isothermal heating at bottom straight wall and cold side curved walls and (ii) Case 2: isothermal heating at left straight wall with cold horizontal curved walls. Numerical simulations have been carried out for various values of Prandtl number (Pr = 0.015 and 7.2) and Rayleigh (103 ≤ Ra ≤105) numbers involving fluid media and Prandtl number (Prm = 0.015 and 7.2), Darcy numbers (10−5 ≤ Dam ≤ 10−2) at Rayleigh number, Ram= 106 involving the fluid saturated porous bed. The streamfunctions (ψ), heatfunctions (Π) associated with local entropy generation (Sψ,Sθ), are further estimated using finite element method. The total entropy production (Stotal), average Bejan number (Beav) and average Nusselt number (Nub or Nul)re computed. Flow and thermal maps are significantly influenced by convex or concave walls for Case 1 or Case 2 heating strategies. For enclosures with fluid media the heatline trajectories illustrate that convex cavities with Case 1 or Case 2 may be chosen based on higher thermal mixing for various R