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Can any one help with this Fluid mechanics question please?

by jami8337
Tags: fluid, mechanics
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Jan8-13, 08:47 AM
P: 9
1. The problem statement, all variables and given/known data
A shaft of diameter 74.9mm rotates at 1400rpm in a bearing which is of diameter 75.03 mm and 75mm in length. The annular space between the shaft and the bearing is filled with oil of viscosity 0.096 kg/ms.By assuming a uniform velocity gradient in the oil, determine the power required to overcome the viscous resistance in the bearing.

2. Relevant equations

Thats the equation i have been using, where l is the difference between the radius of the outer ring and inner ring (i.e. bearing and shaft)

3. The attempt at a solution

When i plug in the values i get:
0.096* ((146.61*37.45*10^-3)/0.065*10^-3)*2∏*(37.45*10^-3)(75*10^-3)

this gives 143.12N

Presuming that this is all ok i then have no idea how to get to a power?
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Jan8-13, 09:10 AM
Sci Advisor
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PF Gold
P: 6,733
How much torque would this force produce on the shaft when it is turning at 1400 rpm? Once you know the torque, you can find the power.
Jan8-13, 09:22 AM
P: 9
Ah yeah thanks got the right answer :)

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