Forced convective flow of alumina-water nanofluid with different shapes of nanoparticles through pin-fins of circular cross-section aligned in an equilateral triangular array was analyzed using finite volume methodology. The effect of the shape of alumina nanoparticles on heat transfer across the periodic equilateral triangular array has never been studied in the past. Four different shapes of nanoparticles were considered: spherical, cylindrical, bricks, and platelets. Using non-spherical (cylindrical, bricks, and platelets) nanoparticles resulted in a thinning thermal boundary layer, which resulted in a significant enhancement in heat transfer rates across the array. The mean Nusselt number was augmented by 22% when platelet shaped nanoparticles were utilized in place of spherical shaped nanoparticles. Likewise, the mean Nusselt number was augmented by 17% when cylindrical nanoparticles were used, in place of spherical nanoparticles, at the highest values of other parameters. The increment in effective viscosity of the nanofluid was the highest for platelet-shaped nanoparticles, which resulted in a greater pressure drop compared to other shapes of nanoparticles such as cylindrical, bricks, and spherical for all values of particle concentration. The results in the present article are validated extensively with accessible experimental and numerical studies.