Question

A Hydrodynamic journal bearing of diameter 250 mm and length 400 mm carries a load of 250 kN. The average bearing pressure is:

• A. $0.25 \text{ N/mm}^2$
• B. $2.5 \text{ N/mm}^2$
• C. $25 \text{ N/mm}^2$
• D. $50 \text{ N/mm}^2$

Hint:

When calculating bearing pressure, always use the Projected Area ($D \times L$), not the surface area ($\pi D L$). Just think of it as the rectangular "shadow" cast by the bearing.

Answer 1

The Correct Option is B

1. Identifying the Variables: Given data:

• Diameter of bearing ($d$) = 250 mm

• Length of bearing ($L$) = 400 mm

• Load on the bearing ($W$) = 250 kN = $250 \times 10^3$ N

2. Calculating Projected Area: The projected area ($A$) for a journal bearing is the product of its diameter and its length: $$A = d \times L$$ $$A = 250 \text{ mm} \times 400 \text{ mm}$$ $$A = 100,000 \text{ mm}^2 = 10^5 \text{ mm}^2$$

3. Calculating Average Bearing Pressure ($p$): Bearing pressure is the load divided by the projected area: $$p = \frac{W}{A}$$ $$p = \frac{250,000 \text{ N}}{100,000 \text{ mm}^2}$$ $$p = 2.5 \text{ N/mm}^2$$