Heat Transfer MCQs

Question 1

For a laminar flow of fluid in a circular tube, 'h 1 ' is the convective heat transfer co-efficient at velocity 'V 1 '. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is

Accepted Answer

0.794 h 1

Answer

1.26 h 1

Answer

0.574 h 1

Answer

1.741 h 1

Question 2

If h₁ = inner film co-efficient and /h₂ = outer film co-efficient, then the overall heat transfer co-efficient is

Accepted Answer

Always between h₁ and h₂

Answer

Always less than h₁

Answer

Always higher than h₂

Answer

Dependent on metal resistance

Question 3

The unit of heat transfer co-efficient is

Accepted Answer

BTU/hr.ft 2 °F

Answer

BTU/hr.°F.ft

Answer

BTU/hr.°F

Answer

BTU/hr.ft

Question 4

Heat transfer co-efficient equation for forced convection, Nu = 0.023 R e 0.8 . P r n , is not valid, if the value of

Accepted Answer

Reynolds number for the flow involved is <2100

Answer

N = 0.4 is used for heating

Answer

N = 0.3 is used for cooling

Answer

Reynolds number for the flow involved is >10000

Question 5

Heat transfer by radiation between two bodies at T 1 & T 2 and in an ambient temperature of T a °C depends on

Accepted Answer

None of these

Answer

T 1 - T 2

Answer

T 1 - T a

Answer

T 2 - T a

Question 6

Double pipe heat exchangers are used

Accepted Answer

When heat transfer area required is very low, i.e (100 - 200 ft 2 )

Answer

When heat transfer area required is very high

Answer

Because it occupies less floor area

Answer

Because it is less costly

Question 7

Pick out the wrong statement.

Accepted Answer

S.I. unit of fouling factor is Watt/m 2 .°K

Answer

Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient

Answer

In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles

Answer

Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube

Question 8

Overall heat transfer co-efficient of a particular tube is U 1 . If the same tube with some dirt deposited on either side has coefficient U 2 , then

Accepted Answer

U 1 > U 2

Answer

U 1 = U 2

Answer

U 2 > U 1

Answer

U 1 = dirt factor - U 2

Question 9

It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is

Accepted Answer

<0.75

Answer

>0.75

Answer

<0.5

Answer

<0.25