I need to calculate the horsepower required to agitate a solution with viscosity of 0.3 cps and density of 839 kg/m3 at 60 rpm. The tank has an inner diameter of 1,500 mm and tangent-to-tangent length of 4,500 mm. The agitator has three impellers (pitched turbine, I do not know the number of blades) with 900-mm diameter. The tank has four mixing baffles. Using equations from a handbook, I found that the power required is about 1 hp. However, I am not sure if this equation considers the use of multiple impellers.
Have an insight or suggestion?
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Re: Horsepower calculations for a specific viscosity
23 October 2007 at 1:29pmI am not sure which equation or handbook you used, but that is not the correct answer. The calculated power for three impellers is almost always just three times the power for one impeller. My calculation for three impellers with the fluid density and viscosity given is 0.80 hp. However, since the tank might be filled with water, even just for a test, I would always design for a density of 1,000 kg/m3, which gives a result of almost exactly 1.0 hp. In any case, even if I knew how many blades and the blade widths for the turbines, I would not size a motor at 1 hp. The minimum motor size for this application should be 1.5 hp.
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