Heat Transfer MCQs

Question 1

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?

Accepted Answer

Sphere

Answer

Cube

Answer

Plate

Answer

All of the above

Question 2

Choose the correct equation.

Accepted Answer

Nu = (Re) (Pr) (St)

Answer

Nu = (Re) (Pr) (Gz)

Answer

Nu = (Re)(Pr)

Answer

Nu = (Pr)(St)

Question 3

Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface)

Accepted Answer

$$\frac{1}{{{{	ext{U}}_1}}} - \frac{1}{{{{	ext{U}}_2}}}$$

Answer

U1 - U2

Answer

$$\frac{1}{{{{	ext{U}}_2}}} - \frac{1}{{{{	ext{U}}_1}}}$$

Answer

U2 - U1

Question 4

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

Accepted Answer

Higher economy

Answer

Lower capacity

Answer

Both A & B

Answer

Lower economy

Question 5

Pick out the wrong statement.

Accepted Answer

The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x

Answer

In case of heat transfer by purely forced convection, GR/Re2 $$ \leqslant $$ 1

Answer

Distillation process is not the same as evaporation

Answer

The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface

Question 6

Film boiling is usually not desired in commercial equipments, because

Accepted Answer

The heat transfer rate is low in view of the large temperature drop

Answer

It is difficult to maintain

Answer

It is not economic

Answer

None of these

Question 7

Natural convection is characterised by

Accepted Answer

Grashhoff number

Answer

Peclet number

Answer

Reynolds number

Answer

Prandtl number

Question 8

Absorptivity and refletivity of a perfect black body are respectively

Accepted Answer

1 and 0

Answer

0 and 1

Answer

1 and $$\infty $$

Answer

0 and 0.5

Question 9

Economy of a multiple effect evaporator depends upon the

Accepted Answer

Heat balance consideration

Answer

Rate of heat transfer

Answer

Both A and B

Answer

Neither A nor B