SHAFT SPEED. SELECT THE CORRECT ANSWER USING THE CODE GIVEN BELOW

3. Shaft speed.

Select the correct answer using the code given below:

(a) 1 and 2 only

(b) 1 and 3 only

(c) 2 and 3 only

(d) 1, 2 and 3

IES-30Ans. (b) 2 is false Petroff’s law says

μ

_×

⎜

⎞

⎛

r

N

_S

Co efficient of friction (f) = 2

π

⎟⎟

⎠

⎝

P

c

f

↑

if (i)

μ

↑

; (ii) c

↓

; (iii) N

s

↑

IES-31.

A journal bearing with hydrodynamic lubrication is running steadily with

a certain amount of minimum film thickness. When the load and speed are

doubled, how does the minimum film thickness vary?

[IES-2008]

(a) Remains unchanged

(b) Gets doubled

(c) Gets reduced to one-fourth of original value

(d) Gets reduced to half of original value

IES-32Ans. (a)When the load and speed is doubled, the minimum film thickness remains

⎛

⎞⎛ ⎞

μ

unchanged. Since,S =

^N

^r

²

⎜

⎟⎜ ⎟

⎝ ⎠

p

c

⎝

⎠

Since S remains the same even after doubling the speed as well as load and film

Thickness depends on the Sommerfeld number.

IES-33. What is the main advantage of hydrodynamic bearing over roller bearing?

(a) Easy to assemble

[IES-2005]

(b) Relatively low price

(c) Superior load carrying capacity at higher speeds

(d) Less frictional resistance

IES-33Ans. (c)

IES-34. Consider tile following statements:

[IES-1993; 2002; 2006]

Radius of friction circle for a journal bearing depends upon