# Heat Transfer Test Questions Set - 3

1)   What should be the temperature of black body to emit radiant energy which is independent of the conditions in the surroundings?

a. temperature of black body should be less than zero
b. temperature of black body should be more than zero
c. temperature of black body should be equal to zero
d. all of the above
 Answer  Explanation  Related Ques ANSWER: temperature of black body should be more than zero Explanation: No explanation is available for this question!

2)   Consider two black bodies at temperatures T1 and T2 (T1 > T2) having same surface area A, are placed in vacuum. What will be the correct formula for net rate of radiant heat transfer between these surfaces?

Where σ is a Stefan-Boltzmann constant

a. q = σ A (T1 – T2)4
b. q = σ A (T14 – T24)
c. q = σ A (T1 – T2)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: q = σ A (T14 – T24) Explanation: No explanation is available for this question!

3)   Gray body can emits radiation

a. at higher rate than the black body
b. at lower rate than the black body
c. at equal rate than the black body
d. cannot predict
 Answer  Explanation  Related Ques ANSWER: at lower rate than the black body Explanation: No explanation is available for this question!

4)   What is the correct formula for the rate of heat transfer by convection form a surface of area A at temperature T to the surrounding fluid at temperature T0?
Where h is convection heat transfer coefficient

a. qc = h A (T – T0)4
b. qc = h A (T4 – T04)
c. qc = h A (T – T0)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: qc = h A (T – T0) Explanation: No explanation is available for this question!

5)   What is the mode of heat transfer from the hot surface to the adjacent layer of fluid which surrounds the surface?

a. conduction mode of heat transfer
b. radiation mode of heat transfer
c. convection mode of heat transfer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: conduction mode of heat transfer Explanation: No explanation is available for this question!

6)   Convective heat transfer coefficient is also known as

a. film convection factor
b. film coefficient
c. film conductance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: film conductance Explanation: No explanation is available for this question!

7)   Suppose a hot water is placed inside a closed metal vessel of thickness 5 mm. There is atmospheric air outside the vessel at temperature lower than the temperature of hot water. The heat is transferred from the hot water to atmospheric air. What is the mode of heat transfer in this condition?

a. conduction then convection
b. convection then conduction
c. convection then conduction then convection
d. conduction then convection then conduction
 Answer  Explanation  Related Ques ANSWER: convection then conduction then convection Explanation: No explanation is available for this question!

8)   The current in the electrical system is analogous to

a. the temperature in the heat transfer system
b. the heat flow in the heat transfer system
c. the thermal conductance in the heat transfer system
d. the thermal resistance in the heat transfer system
 Answer  Explanation  Related Ques ANSWER: the heat flow in the heat transfer system Explanation: No explanation is available for this question!

9)   The term in the heat transfer system which is analogous to the electrical resistance is called as

a. thermal resistance
b. conductive resistance
c. potential resistance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: thermal resistance Explanation: No explanation is available for this question!

10)   What will be the simple correct formula for the rate of heat flow (q) through a wall of surface area A and thickness of t ?
The two surfaces of the wall are at temperatures T1 and T2 (T1>T2). Consider thermal resistance for the heat transfer system as Rh.

a. q = Rh (T1 – T2)
b. q = Rh A (T1 – T2)
c. q = (T1 – T2) / Rh
d. q = Rh A ((T1 – T2) / t)
 Answer  Explanation  Related Ques ANSWER: q = (T1 – T2) / Rh Explanation: No explanation is available for this question!

11)   In turbulent flow of the fluid,

a. conduction becomes more important
b. conduction becomes less important
c. doesn't matter
d. none of the above
 Answer  Explanation  Related Ques ANSWER: conduction becomes less important Explanation: No explanation is available for this question!

12)   Mixing of fluid from regions of high temperature with the fluid from region of low temperature

a. increases the rate of heat transfer
b. decreases the rate of heat transfer
c. rate of heat transfer is not affected
d. none of the above
 Answer  Explanation  Related Ques ANSWER: increases the rate of heat transfer Explanation: No explanation is available for this question!

13)   What does the Nusselt modulus or Nusselt number physically signify?

a. the ratio of the temperature gradient at the surface [(∂T / ∂y)y=0] to the reference temperature gradient [(Tw – T) / l]
b. the ratio of the reference temperature gradient [(Tw – T) / l] to the temperature gradient at the surface [(∂T / ∂y)y=0]
c. the sum of the temperature gradient at the surface [(∂T / ∂y)y=0] and the reference temperature gradient [(Tw – T) / l]
d. the sum of the reference temperature gradient [(Tw – T) / l] and the temperature gradient at the surface [(∂T / ∂y)y=0]
 Answer  Explanation  Related Ques ANSWER: the ratio of the temperature gradient at the surface [(∂T / ∂y)y=0] to the reference temperature gradient [(Tw – T∞) / l] Explanation: No explanation is available for this question!

14)   The Nusselt modulus or Nusselt number is a convenient measure of

a. rate of heat transfer
b. convective heat transfer coefficient
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: convective heat transfer coefficient Explanation: No explanation is available for this question!

15)   What is the correct formula for the Nusselt modulus or Nusselt number (Nu)?

a. Nu = h k l
b. Nu = (h k) / l
c. Nu = (k l) / h
d. Nu = (h l) / k
 Answer  Explanation  Related Ques ANSWER: Nu = (h l) / k Explanation: No explanation is available for this question!

16)   Which among the following are the methods for estimation of convective heat transfer coefficient?

(1) Analogy between heat, mass and momentum transfer
(2) Dimensional analysis coupled with experimental data
(3) Approximate analysis of the boundary layer equation
(4) Exact mathematical analysis of the boundary layer equation

a. (1), (2) and (3)
b. (2), (3) and (4)
c. (1), (2) and (4)
d. all of the given (1), (2), (3) and (4)
 Answer  Explanation  Related Ques ANSWER: all of the given (1), (2), (3) and (4) Explanation: No explanation is available for this question!

17)   Which among the following methods for estimation of convective heat transfer coefficient are having some limitations?

(1) Analogy between heat, mass and momentum transfer
(2) Dimensional analysis coupled with experimental data
(3) Approximate analysis of the boundary layer equation
(4) Exact mathematical analysis of the boundary layer equation

a. (1), (2) and (3)
b. (2), (3) and (4)
c. (1), (2) and (4)
d. all of the given (1), (2), (3) and (4)
 Answer  Explanation  Related Ques ANSWER: all of the given (1), (2), (3) and (4) Explanation: No explanation is available for this question!

18)   Which method for estimation of convective heat transfer coefficient is mathematically simple and finds wide range of applications?

a. Analogy between heat, mass and momentum transfer
b. Dimensional analysis coupled with experimental data
c. Approximate analysis of the boundary layer equation
d. Exact mathematical analysis of the boundary layer equation
 Answer  Explanation  Related Ques ANSWER: Dimensional analysis coupled with experimental data Explanation: No explanation is available for this question!

19)   A thorough knowledge of the mechanism is necessary for the estimate of convective heat transfer coefficient so that the process can be adequately represented by mathematical equation. This is a limitation of the method of

a. analogy between heat, mass and momentum transfer
b. approximate analysis of the boundary layer equation
c. dimensional analysis coupled with experimental data
d. exact mathematical analysis of the boundary layer equation
 Answer  Explanation  Related Ques ANSWER: exact mathematical analysis of the boundary layer equation Explanation: No explanation is available for this question!

20)   What is/are the limitation/s of dimensional analysis for estimation of convection heat transfer coefficient?

a. it does not provide any knowledge of the mechanism
b. it is necessary to know theoretically the variables which influence the phenomena
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

21)   What is the black body or an ideal radiator?

a. the body which transmits all the radiations incident upon it
b. the body which absorbs all the radiations incident upon it
c. the body which reflects all the radiations incident upon it
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the body which absorbs all the radiations incident upon it Explanation: No explanation is available for this question!

22)   As a radiator, the black body emits the maximum possible thermal radiation

a. at a constant single wavelength
b. at the maximum wavelength
c. at all wavelengths
d. none of the above
 Answer  Explanation  Related Ques ANSWER: at all wavelengths Explanation: No explanation is available for this question!

23)   Which of the following sentences are correct for black body

(1) The black body is a hypothetical body
(2) The black body is a real body
(3) The black body is used as a standard of perfection against which the radiation characteristics of other bodies are compared

a. sentences (1) and (2)
b. sentences (1) and (3)
c. sentences (2) and (3)
d. all the sentences (1), (2) and (3)
 Answer  Explanation  Related Ques ANSWER: sentences (1) and (3) Explanation: No explanation is available for this question!

24)   What is the relation between emissive power of a real body (E) and emissive power of black body (Eb) when both are at same temperature?
Where,
α =absorptivity

a. Eb / E = 1
b. Eb / E = α
c. E / Eb = 1
d. E / Eb = α
 Answer  Explanation  Related Ques ANSWER: E / Eb = α Explanation: No explanation is available for this question!

25)   The emissivity (ε) can be defined as the ratio of

a. emissive power of real body to the emissive power of black body
b. emissive power of black body to the emissive power of real body
c. reflectivity of real body to emissive power of black body
d. reflectivity of black body to emissive power of real body
 Answer  Explanation  Related Ques ANSWER: emissive power of real body to the emissive power of black body Explanation: No explanation is available for this question!

26)   What does the Kirchoff's identity state?

a. the emissivity and the absorptivity of the black body are same and always less than 1
b. the emissivity and the absorptivity of the black body are same and always more than 1
c. the emissivity and the absorptivity of the black body are same and always equal to 1
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the emissivity and the absorptivity of the black body are same and always equal to 1 Explanation: No explanation is available for this question!

27)   Stefan-Boltzmann law states that the energy radiated per unit area per unit time by the black body is

a. directly proportional to the square of the temperature of the black body
b. inversely proportional to the square of the temperature of the black body
c. directly proportional to the forth power of the temperature of the black body
d. inversely proportional to the fourth power of the temperature of the black body
 Answer  Explanation  Related Ques ANSWER: directly proportional to the forth power of the temperature of the black body Explanation: No explanation is available for this question!

28)   What is the SI unit for Stefan-Boltzmann constant (σ)?

a. W / m K4
b. W / m2 K4
c. W / K4
d. W K4 / m2
 Answer  Explanation  Related Ques ANSWER: W / m2 K4 Explanation: No explanation is available for this question!

29)   Which among the following sentences are correct for Stefan-Boltzmann law?

(1) The Stefan-Boltzmann law gives the total emissive power of a black body.
(2) The Stefan-Boltzmann law is based on quantum theory
(3) The Stefan-Boltzmann law does not provide distribution of energy among different wavelengths

a. sentences (1) and (2) are correct
b. sentences (2) and (3) are correct
c. sentences (1) and (3) are correct
d. all of the sentences (1), (2) and (3) are correct
 Answer  Explanation  Related Ques ANSWER: sentences (1) and (3) are correct Explanation: No explanation is available for this question!

30)   The relation derived for the total emissive power of the black body as a function of wavelength and based of quantum theory is known as

a. Kirchoff's law
b. Stefan-Boltzmann law
c. Planck's law
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Planck's law Explanation: No explanation is available for this question!

31)   Which of the following is/are example/s of pool boiling?

a. completely submerged electrically heated coil in pool of liquid
b. boiling of liquid in a kettle placed on stove
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

32)   In pool boiling, as soon as the temperature of heating surface reaches the boiling point of the liquid, heat transfer takes place

a. by conduction
b. by natural convection
c. by forced convection
d. cannot say
 Answer  Explanation  Related Ques ANSWER: by natural convection Explanation: No explanation is available for this question!

33)   In pool boiling process, the region after the natural convection in which the vapour bubbles form with increase in heat flux, is called as

a. impure boiling regime
b. pure boiling regime
c. nucleate boiling regime
d. non-nucleate boiling regime
 Answer  Explanation  Related Ques ANSWER: nucleate boiling regime Explanation: No explanation is available for this question!

34)   When the formation of bubbles becomes very high in pool boiling, then the heat flux

a. rises
b. reduces
c. remains constant
d. becomes unpredictable
 Answer  Explanation  Related Ques ANSWER: reduces Explanation: No explanation is available for this question!

35)   What is critical heat flux in boiling heat transfer process?

a. the heat flux which reaches at a certain constant value at a particular excess temperature
b. the heat flux which reaches at the minimum value at a particular excess temperature
c. the heat flux which reaches at the maximum value at a particular excess temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the heat flux which reaches at the maximum value at a particular excess temperature Explanation: No explanation is available for this question!