Rushton turbine having an impeller diameter of 20 cm and operating at a stirrer speed of 200 rpm is used in a mixing tank. If the tank receives air at a volumetric flow rate of 0.2 m³·min⁻¹, the non-dimensional Froude Number, N_Fr is ______. [round off to 2 decimal places]
Official Answer Key:
0.21 to 0.31
Step-by-Step Solution & Explanation
Froude Number for a stirred tank: N_Fr = N²D/g, where N is in rev/s and D in m. N = 200/60 = 3.333 rev/s; D = 0.20 m. N_Fr = (3.333)²×0.20/9.81 = 11.11×0.20/9.81 = 2.222/9.81 = 0.227. (The air flow rate is a distractor — it is relevant to the aeration or gas-flow number, Na = Q/(ND³), not to the Froude Number.)
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