Mixed convection in an open cavity has been growing into one of the most attractive topics of investigation for years, owing to its importance in many engineering applications. In this study, the effect of different inflow conditions on mixed convective flow inside an open cavity of T shape is investigated thoroughly to find the optimum condition for efficient heat transfer. Three different inlet conditions (uniform, Poiseuille, and Couette) have been considered, and a comparative study has been conducted to assess their performance of mixed convection heat transfer enhancement. Moreover, the presence of water-Al2O3 nanofluid over conventional fluid (water) to improve thermal performance is examined by varying solid volume fractions from 0 to 0.04. The Galerkin Weighted Residual based finite element analysis is used to resolve the current problem. Numerical solutions are obtained by varying Grashof number (Gr) from 0.1 to 104 and Reynolds number (Re) from 0 to 1000. Pure mixed convective heat transfer is also emphasized by keeping Richardson number (Ri) at unity while varying Gr and Re simultaneously. A profound effect for the uniform inflow condition has been observed on the rate of heat transfer inside the cavity with the variation of Gr and Re. In addition, the nanofluid increases the heat transfer performance, particularly at higher values of Grashof number (Gr > 103) at Ri = 1.