Shell-and-tube heat exchangers (STHXs) are widely employed in industrial thermal systems, but conventional baffle designs often cause high pressure drops, stagnant flow regions, and suboptimal heat transfer. This study proposes and numerically evaluates a novel three-zonal porous baffle configuration, wherein porosity is varied radially to redistribute shell-side flow, suppress bypassing, and enhance turbulence. Using computational fluid dynamics (CFD) with the realizable k–ε turbulence model, the effects of baffle thickness (7.5–10 mm), zonal cut radius (21.00–22.00 mm), and baffle number (6–8) were systematically investigated. The optimized structure (a 10 mm thick baffle with 8 units at Zonal Cut Radius, Rc = 21.00 mm) obtained a maximum heat transfer coefficient of 13,008 W/m²·K and a heat flux rate of 423.21 kW, demonstrating a 28% improvement over conventional porous baffles. Simultaneously, the design reduced shell-side pressure drop by up to 49%, lowering pumping power requirements while maintaining high thermal efficiency. Parametric analysis revealed an optimal cut radius range (21.0–21.5 mm), beyond which heat transfer gains plateau due to flow saturation. The porosity gradient (inner ≈30%, middle ≈30%, outer ≈40%) proved crucial in minimizing stagnant zones and strengthening crossflow mixing near tube walls. These findings establish three-zonal porous baffles as a scalable and manufacturable enhancement for industrial STHXs, offering a practical route to improved energy efficiency, reduced operating costs, and extended equipment life. Future work should experimentally validate these results and explore advanced materials and alternative cut angles for broader industrial applicability.