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Question 7.P.5: For producing an oil-water emulsion, two portable three-blad...

For producing an oil-water emulsion, two portable three-bladed propeller mixers are available; a 0.5 m diameter impeller rotating at 1 Hz and a 0.35 m impeller rotating at 2 Hz. Assuming turbulent conditions prevail, which unit will have the lower power consumption?

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Under turbulent conditions, the power requirements for mixing are given by:

P =k N^3 D^5                  (equation 7.13)

In this case: P _1=\left(k 1^3 \times 0.5^5\right)=0.03125 k and P _2=\left(k 2^3 \times 0.35^5\right)=0.0420 k

∴                        P _1 / P _2=(0.03125 k / 0.0420 k)=0.743

Thus the 0.5 m diameter impeller will have the \underline{\underline{\text { lower power consumption}}}; some 75% of that of the 0.35 m diameter impeller.

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