HEAT AND MASS TRANSFER QUIZ

Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of

0.043055555555556

0.084027777777778

0.16736111111111

0.042361111111111

TRUE ANSWER : ?
YOUR ANSWER : ?

When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by

Conduction

Radiation

Conduction and convection

Convection

TRUE ANSWER : ?
YOUR ANSWER : ?

In counter flow heat exchangers

Both the fluids at inlet are in their hottest state

One fluid is in hottest state and other in coldest state at inlet

Both the fluids at exit are in their hottest state

Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state

TRUE ANSWER : ?
YOUR ANSWER : ?

LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is

Depends on the area of heat exchanger

Lower

Same

Higher

TRUE ANSWER : ?
YOUR ANSWER : ?

According of Kirchhoff's law

Emissive power and absorptivity are constant for all bodies

Emissive power depends on temperature

Radiant heat is proportional to fourth power of absolute temperature

Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

TRUE ANSWER : ?
YOUR ANSWER : ?

The heat transfer by conduction through a thick sphere is given by

Q = 8πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 2πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 4πkr1 r2 (T1 - T2)/ (r2 - r1)

Q = 6πkr1 r2 (T1 - T2)/ (r2 - r1)

TRUE ANSWER : ?
YOUR ANSWER : ?

If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of

81

270

9

3

TRUE ANSWER : ?
YOUR ANSWER : ?

Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

One

Three

Two

Four

TRUE ANSWER : ?
YOUR ANSWER : ?

Fouling factor is used

None of these

When a liquid exchanges heat with a gas

In heat exchanger design as a safety factor

In case of Newtonian fluids

TRUE ANSWER : ?
YOUR ANSWER : ?

Which of the following has maximum value of thermal conductivity?

Steel

Brass

Copper

Aluminium

TRUE ANSWER : ?
YOUR ANSWER : ?