In this paper, a theoretical analysis was carried out for optimum designing of the leading edge of centrifugal compressor blades. The effect of change in specific heat capacity ratio on the optimal design of impeller blades' leading edge was investigated theoretically considering the inlet pre-whirl. It was found that with the growth in heat capacity ratio, the maximum achievable mass flow function was reduced, while the optimum blade angle at the leading edge was increased. Results showed that the maximum achievable mass flow function for γ = 1.13, was about 0.77 and occurred at a pre-whirl angle (α) of 60.3° and blade angle (β) of 48.2°. For γ = 1.4, the maximum achievable mass flow function was about 0.64 and occurred at α=59°, β=51°. For the case of γ = 1.67, the maximum mass flow function was obtained at about 0.55 and took place at α=57.9°, β=52.7°. It was found that there is a limitation for the hub to shroud radius ratio in impeller designing. The interval between hub to shroud radius is reduced by increasing the angle of inlet guide vanes.
