To transport the energy efficiently without much dissipation, first and second law analyses of mixed convection heat transport from an array of nonisothermal rectangular vertical plate-finned heat sink are made using purely computational fluid dynamics (CFD) analysis on the governing equations. Report provides the dependence of Nusselt number, entropy production, pumping power ratio (PPR), and flow bypass factor (BF) on the inlet velocity, fin conductance parameter, thermal Grashof number (Gr), dimensionless clearance (C*), and dimensionless fin spacing (S*). Total nondimensional entropy production is found to decrease continuously with clearances for all fin spacings, except at the lowest fin spacing involving lowest Gr (= 1.8 × 105). On the other hand, at higher inlet velocities, Nusselt number indicates an optimum value with clearances. Optimum Nusselt number is found to observe in a range of S* = 0.2–0.3 for all Gr. For smaller fin spacing, PPR is noticeably higher, but at the optimum value of fin spacing, PPR reduces roughly by an order of magnitude. Interestingly, flow bypass is remarkably lower at the optimum clearance. Finally, correlation of friction factor, PPR, and entropy generation is presented.