Dave Dickey Forum Moderator 295 Posts
Re: How can we improve our mixing?11 August 2011 at 1:29pm
Reviewing the description of your installation, the biggest problem involves the impeller dimensions. Their location is as good as practical, but you have impellers with many (8) blades that are very narrow (1/16 of the diameter). The narrow blades are especially bad with a 16,000 cp viscosity. As viscosity increases, the flow pattern, even from an axial-flow, pitched-blade turbine, becomes radial flow. With narrow blades the effective capacity of the impeller to move the fluid is dictated by the vertical height of the blades.
Your application could be improved considerably if the current impellers were replaced by 45 degree pitched-blade turbines (PBTs) with four (4) blades and blade widths about 1/5 of the impeller diameter. By my estimates, 800 mm diameter impellers with four 160 mm wide blades may require about 10 kW. Slightly smaller impellers, 750 mm diameter with four 150 mm wide blades may require 8 kW. Those power estimates may be a bit high, since the interaction between the mixers in a rectangular basin are difficult to predict from standard results for cylindrical vessels. I don't want you to overload your motor. My estimate for your 800 mm impellers with eight 50 mm wide blades is 6.5 kW.
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We have a rectangular tank 3.3m x 2.1m x 1.6m deep. It has two 45-degree PTB stirrers located 1.0m from each end of the tank and 0.3m from the tank bottom. Each stirrer has 8 blades 50mm wide and 400mm long (diameter 800mm). Each stirrer has a max rpm of 130. The liquid we are mixing is latex paint with a viscosity of 16000 cp. Can you give any suggestions on how to improve our mixing.
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