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Studies on Impeller Design on Power Consumption from Temperature Rise Data in a Stirred Tank

Damaraju P. Rao and Chander S. Mahey. Chemical Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi, India

Power Consumption for Mixing in Stirred Tanks depends on impeller design. Reduction in the power consumption is a key requirement of industry to make it competitive and cost effective. Since 1950's attempts have been made to study and improve impeller design. In the recent literature, Kumarsan and Joshi [1] studied the effect of impeller design on flow pattern and mixing. However their study was focused on flow patterns and impellers used by them were standard available impellers .Raghav Rao and Joshi [2]studied liquid phase mixing where in power consumption was measured by using a torque table for DT (disc turbine) and pitched turbine impellers. This study was also focused on two types of standard impellers and it used torque table for measuring power consumption. In the present study, experiments on power consumption and mixing time were made with two new “CME” impellers which are modified versions of hydrofoil impellers. Power consumption was measured by applying the temperature rise method of Panja and D.Phaneswara Rao[3] as well as by measuring electrical power input with the help of VFD meter of Dan Foss Make. Panja and Rao studied power input to mechanically agitated homogeneous liquid and gas-liquid systems by using temperature rise method and employing a 164 mm dia. vessel. In the present work, the feasibility of the above method was tested with 500 mm dia. flat bottom vessel made of perspex. In addition, electrical power input was measured and corrected for frictional and other losses in the motor and shaft bearing by measuring power input to the vessel with no water taken in the tank. The Baffle width( Bw=T/10), Baffle thickness, and the clear liquid height ( H=T) used in the present study were chosen equal to 50 mm, 4.5 mm, and 500 mm respectively and kept constant in all the experiments. RO Water was used as the working fluid. A 2 HP variable speed motor supplied necessary power for the system. It was observed that Power Consumption measured by using the temperature rise method and the power input measured by using electrical power meter corrected for frictional and other losses were in close agreement.. Experiments on power input were performed by using the normal pitched blade impeller and CME hydrofoil impellers to study the effect of impeller design on the power consumption. Comparison of the Power consumption values have shown that CME hydrofoil impellers were more efficient as compared to the normal pitched blade impellers.

References:

[1]: T.Kumarsan and J.B.Joshi : Effect of impeller design on the flow pattern and mixing in stirred tanks , Chemical Engineering Journal 115(2006) 173-193.

[2]: K.S.M.S.Raghav Rao,J.B.Joshi, Liquid-phase mixing and power consumption in mechanically agitated solid liquid contractors, The Chemical Engineering Journal 39 (1988) 111-124.

[3]: N.C. Panja and D.P. Rao, Power input measurement from temperature rise data in mechanically agitated contractors, Institution of Chemical Engineers, (1992) 24-27.