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Topic: Power of a pump  (Read 3373 times)

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Offline vhpk

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Power of a pump
« on: February 27, 2010, 03:44:01 AM »
Hi everyone,
I've got a question regarding the energy calculation:
Estimate the power required to pump milk at 20°C at 2.7 m s-1  through a 4 cm diameter steel tube that is 130 m long, including the kinetic energy and the friction energy. The viscosity of milk at 200C is 2.2x10-3, density is 1030kg/m3.The roughness for steel is from 0.9mm to 9mm
At first, I calculated the potential and kinetic energy,
Ep =hg= 1275.3(J)
Ek = v2/2 = 3.645(J)
Reynold number = density x velocity x diameter/viscosity = 50563.6 so the flow here is turbulent
The tube here is made of steel, I chose 9mm for the roughness e.
For turbulent flow:
Cf = 0.001375(1+(20000e/d+106/Re)0.33) = 0.0235
The energy of friction loss:
Ef = 2Cfv2L/D = 1112.6(J)
So the total energy for pumping is :
E = Ep + Ek + Ef = 2391.55J
So the total energy required:
E x mass flow rate = E x velocity x cross sectional area x density = 8380.12Js-1
The result in textbook is just 297.05J
I'm confused since I don't know where and when I was wrong. Plz help me with this .
Thanks a lot :D
Genius is a long patience

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