Question

A journal bearing 200 mm in diameter and 250 mm long is supporting a load of 15 KN at 1000 rpm. The radial clearance is 0.08 and the bearing dissipates 100 KJ/min in friction; What is the viscosity of oil at the operating temperature?

• A. 0.006 Pa-sec
• B. 0.05 pa-sec
• C. 0.002 pa-sec
• D. 0.08 pa-sec

Answer 1

The correct option is A 0.006 Pa-sec

Heat generated = Heat dissipated

Heat generated = fWV

f = co-efficient friction; W = radial load

$\therefore 100\frac{KJ}{min}=f\times 15\times \pi \times \frac{200}{1000}\times 1000$

$\therefore f=0.0106$

By using Mckee equation

$f=0.326\times \left(\frac{\mu N}{p}\right)\left(\frac{d}{C_d}\right)+K$

Bearing pressure 'p' = $\frac{Load}{projectedArea}=\frac{W}{l\times d}=\frac{15\times {10}^{3}N}{\left(\frac{250}{1000}\right)\times \left(\frac{200}{1000}\right)m^2}$

$\therefore p=3\times {10}^5\frac{N}{m^2}$

$Now0.0106=0.326\times \left(\frac{\mu \times 1000}{3\times {10}^5}\right)\times \left(\frac{200}{2\times 0.08}\right)+0.002$

$\Rightarrow \mu =0.006Pa-sec$