Power Correlation for Paddle Impellers in Spherical and Cylindrical Agitated Vessels

Abstract

Power consumption for paddle impellers in both spherical and cylindrical agitated vessels was measured over a wide range of Reynolds number from laminar to turbulent flow regions. By using the friction factor f and the modified Reynolds number ReG, which were defined by Hiraoka and Ito, a power correlation was expressed as
f=C_L/Re_G+C_t {(C_tγ/Re_G+Re_G) ^-1+ (f_∞/C_t) ^1/m} ^m
where C_L, C_t, C_tγ, f_∞ and m were empirically correlated with impeller size and the number of impeller blades. The power correlation was applicable to both spherical and cylindrical vessels, when the apparent diameter of the spherical vessel was equal to the diameter of the cylindrical vessel which had a height equal to its diameter and had the same volume as the spherical vessel. The power consumption was well correlated with the experimental results of Nagata, et al. and Hixson-Baum. The critical Reynolds number, which was used for a simple estimation of power number in fully baffled conditions N_p, _max by Nagata, was directly related to the coefficient C_tγ characterizing transition from a laminar to a turbulent flow region in the correlation proposed here.