# Heat Transfer Test Questions - Set - 4

1)   Consider the heat is transferred through a wall of surface area A and thickness t at the rate of q, what is the thermal resistance of the system? The thermal conductivity of the wall is k and the heat is transferred normal to the surface area A.

a. kA
b. 1 / kA
c. kAt
d. t / kA
 Answer  Explanation  Related Ques ANSWER: t / kA Explanation: No explanation is available for this question!

2)   The potential difference in an electrical system, is analogously considered as

a. a temperature difference in the heat transfer system
b. a current flow in the heat transfer system
c. a resistance in the heat transfer system
d. none of the above
 Answer  Explanation  Related Ques ANSWER: a temperature difference in the heat transfer system Explanation: No explanation is available for this question!

3)   What is the correct formula for the rate of heat transfer (q) through a plane wall of thickness l and surface are A, when  temperature difference between two surfaces is ΔT ? The thermal conductivity is k.

a. q = (k A ΔT) / l
b. q = k A l ΔT
c. q = (ΔT) / (k A l)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: q = (k A ΔT) / l Explanation: No explanation is available for this question!

4)   Thermal conductivity of the same material varies with

a. the thickness of the material
b. the temperature of the material
c. both a. and b.
d. thermal conductivity of the same martial does not vary at all
 Answer  Explanation  Related Ques ANSWER: the temperature of the material Explanation: No explanation is available for this question!

5)   The surface temperatures of a plate with thickness of 0.06 m are 100°C and 40°C. The thermal conductivity (k) of wall is 350 W/mK. What is the rate of heat transfer through the plate in kW/m2?

a. 350000
b. 350
c. 35
d. 0.35
 Answer  Explanation  Related Ques ANSWER: 350 Explanation: No explanation is available for this question!

6)   How does the thermal conductivity of a material change with respect to change in temperature of the same material?

a. thermal conductivity of a material increases with increase in its temperature
b. thermal conductivity of a material decreases with increase in its temperature
c. thermal conductivity of a material remains same with change in its temperature
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: thermal conductivity of a material increases with increase in its temperature Explanation: No explanation is available for this question!

7)   What does a composite wall mean?

a. two walls of different materials are connected in series without any gap between them
b. three walls of different materials are connected in series without any gap between them
c. more than three walls of different materials are connected in series without any gap between them
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

8)   When a composite wall of three layers in series having thermal resistances R1, R2 and R3 respectively, the heat transfer takes place normal to the surface of the layers. How is the total thermal resistance of the composite system calculated?

a. 1 / (R1 + R2 + R3)
b. ( (1 / R1) + (1 / R2) + (1 / R3) )
c. (R1 + R2 + R3)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: (R1 + R2 + R3) Explanation: No explanation is available for this question!

9)   Calculate the rate of heat flow through a composite wall of having three layers. The thicknesses of three layers are 0.5m, 1m and 0.2m respectively.
Thermal conductivity of these layers are 2.5 W/mK, 2 W/mK and 2.2 W/mK respectively. The temperature T1 and T4 are maintained at 1000 K and 200 K respectively. Take surface area of heat transfer 1 m2. a. 1011.5 W/m2
b. 911.5 W/m2
c. 501.5 W/m2
d. 1211.5 W/m2
 Answer  Explanation  Related Ques ANSWER: 1011.5 W/m2 Explanation: No explanation is available for this question!

10)   Consider a composite wall with two layers combined in parallel and heat is transferred through wall as shown in figure. The thermal resistances of two layers are R1 and R2 respectively. How is the total thermal resistance (R) of the wall calculated? a. R = (R1 + R2) / R1R2
b. R = R1R2 / (R1 + R2)
c. R = R1 / (R1 + R2)
d. R = R2 / (R1 + R2)
 Answer  Explanation  Related Ques ANSWER: R = R1R2 / (R1 + R2) Explanation: No explanation is available for this question!

11)   Why is the Buckingham π–Theorem used?

a. to determine number of dependent dimensionless groups which are necessary to represent the phenomenon in a mathematical expression
b. to determine number of independent dimensionless groups which are necessary to represent the phenomenon in a mathematical expression
c. to determine number of dependent groups with their dimensions which are necessary to represent the phenomenon in a mathematical expression
d. to determine number of independent groups with their dimensions which are necessary to represent the phenomenon in a mathematical expression
 Answer  Explanation  Related Ques ANSWER: to determine number of independent dimensionless groups which are necessary to represent the phenomenon in a mathematical expression Explanation: No explanation is available for this question!

12)   According to the Buckingham π–Theorem, the number of independent dimensionless groups, formed by combining the physical variables of a problem, is equal to

a. [total number of physical quantities (n)] – [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities]
b. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] – [total number of physical quantities (n)]
c. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] + [total number of physical quantities (n)]
d. [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] x [total number of physical quantities (n)]
 Answer  Explanation  Related Ques ANSWER: [total number of physical quantities (n)] – [the number of primary dimensions (m) needed to express the dimensional formulae of n physical quantities] Explanation: No explanation is available for this question!

13)   Which of the following dimensions is/are primary dimension/s?

a. length (L)
b. time (t)
c. temperature (T)
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

14)   What is the dimensional formula for work?

a. [M L t– 3 ]
b. [M L2 t– 2 ]
c. [M L2 t– 3 ]
d. [M L2 T– 3 ]
 Answer  Explanation  Related Ques ANSWER: [M L2 t– 2 ] Explanation: No explanation is available for this question!

15)   [M L– 1 T–2 ] is the dimensional formula for

a. power
b. force
c. pressure
d. heat
 Answer  Explanation  Related Ques ANSWER: pressure Explanation: No explanation is available for this question!

16)   What is the formula for Reynolds number (Re)?
Where,
ρ = density of the fluid
μ = viscosity of the fluid
D = tube diameter through which fluid is flowing
v = velocity of the fluid

a. (Re) = (D v ρ) / μ
b. (Re) = (D ρ μ) / v
c. (Re) = (D v μ) / ρ
d. none of the above
 Answer  Explanation  Related Ques ANSWER: (Re) = (D v ρ) / μ Explanation: No explanation is available for this question!

17)   The principle of similarity or model law states that

a. if the ratios of linear dimensions, forces, velocities, etc. of two systems are the same, then their behavior will be different as per the dimensions
b. if the ratios of linear dimensions, forces, velocities, etc. of two systems are the same, then their behavior will be similar
c. if the ratios of linear dimensions, forces, velocities, etc. of two systems are the different, then only their behavior will be similar
d. none of the above
 Answer  Explanation  Related Ques ANSWER: if the ratios of linear dimensions, forces, velocities, etc. of two systems are the same, then their behavior will be similar Explanation: No explanation is available for this question!

18)   Prandtl number is the ratio of

a. thermal diffusivity (α) to absolute viscosity (μ)
b. absolute viscosity (μ) to thermal diffusivity (α)
c. kinematic viscosity (ν) to thermal diffusivity (α)
d. thermal diffusivity (α) to kinematic viscosity (ν)
 Answer  Explanation  Related Ques ANSWER: kinematic viscosity (ν) to thermal diffusivity (α) Explanation: No explanation is available for this question!

19)   Wien's displacement law gives the relationship between

a. the wavelength of radiation at which total emissive power is maximum and the temperature
b. the wavelength of radiation at which total emissive power is minimum and the temperature
c. the wavelength of radiation at which total emissive power does not change and the temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the wavelength of radiation at which total emissive power is maximum and the temperature Explanation: No explanation is available for this question!

20)   What is a gray body?

a. a body of which the monochromatic emissivity (ε) is different wavelengths
b. a body of which the monochromatic emissivity (ε) is constant for the entire wavelength spectrum
c. a body of which the monochromatic emissivity (ε) is maximum for longest wavelength
d. none of the above
 Answer  Explanation  Related Ques ANSWER: a body of which the monochromatic emissivity (ε) is constant for the entire wavelength spectrum Explanation: No explanation is available for this question!

21)   The emissive power of gray body is

a. less than the emissive power of the black body
b. greater than the emissive power of the black body
c. equal to the emissive power of the black body
d. cannot say
 Answer  Explanation  Related Ques ANSWER: less than the emissive power of the black body Explanation: No explanation is available for this question!

22)   What is the correct formula for the total emissive power of the gray body (Eg)?

a. (Eg) = ε σ T4
b. (Eg) = ε T4
c. (Eg) = (1/ε) σ T4
d. none of the above
 Answer  Explanation  Related Ques ANSWER: (Eg) = ε σ T4 Explanation: No explanation is available for this question!

23)   What is the intensity of radiation (I)?

a. rate of heat radiation from a surface per unit area
b. rate of heat radiation from a surface per unit solid angle
c. rate of heat radiation from a surface per unit area per unit solid angle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: rate of heat radiation from a surface per unit area per unit solid angle Explanation: No explanation is available for this question!

24)   What is solid angle?

a. the ratio of spherical surface enclosed by a cone, with its vertex at the centre of sphere, to the radius of the sphere
b. the ratio of spherical surface enclosed by a cone, with its vertex at the centre of sphere, to the square of the radius of the sphere
c. the ratio of spherical surface enclosed by a cone, with its vertex at the centre of sphere, to the cube of the radius of the sphere
d. the ratio of spherical surface enclosed by a cone, with its vertex at the centre of sphere, to the fourth power of the radius of the sphere
 Answer  Explanation  Related Ques ANSWER: the ratio of spherical surface enclosed by a cone, with its vertex at the centre of sphere, to the square of the radius of the sphere Explanation: No explanation is available for this question!

25)   What is the correct formula for the intensity of the emitted radiation of a black body (I) in terms of its emissive power (Eb)?

a. I = (Eb)
b. I = π (Eb)
c. I = 2 π (Eb)
d. I = (1/π) (Eb)
 Answer  Explanation  Related Ques ANSWER: I = (1/π) (Eb) Explanation: No explanation is available for this question!

26)   The radiation heat exchange between two bodies depends upon

a. the views of two surfaces with each other
b. the medium between the two bodies
c. emitting and absorbing characteristics of the bodies
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

27)   Assume that two black bodies of areas A1 and A2 are placed as shown in figure. dA1 and dA2 are the small area elements of the black bodies. The distance between them is r and the angles made by the normals of the surfaces with the joining line are Φ1 and Φ2 respectively. What is the formula for net heat exchange (Q12)net between A1and A2? Given that
A1F12 = A2 F21
for the shape factors F12 and F21 a. (Q12)net = A1F12 σ (T14 – T24)
b. (Q12)net = A1F12 A2 F21 σ (T14 – T24)
c. (Q12)net = F12 F21 σ (T14 – T24)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: (Q12)net = A1F12 σ (T14 – T24) Explanation: No explanation is available for this question!

28)   Shape factor is also called as

a. view factor
b. geometry factor
c. configuration factor
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

29)   How does heat flux change with increasing excess temperature in transition boiling regime of boiling heat transfer process?

a. heat flux increases with increasing excess temperature
b. heat flux decreases with increasing excess temperature
c. heat flux becomes constant with increasing excess temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: heat flux decreases with increasing excess temperature Explanation: No explanation is available for this question!

30)   Which regime in boiling heat transfer process can represent a transition from nucleate boiling to film boiling?

a. pure convection regime
b. nucleate boiling regime
c. transition boiling regime
d. stable film boiling regime
 Answer  Explanation  Related Ques ANSWER: transition boiling regime Explanation: No explanation is available for this question!

31)   The nuclei of bubbles form in nucleate boiling, when there is presence of

a. superheated vapour
b. superheated liquid
c. dissolved gases
d. un-dissolved gases
 Answer  Explanation  Related Ques ANSWER: dissolved gases Explanation: No explanation is available for this question!

32)    When is the condensate flow almost always laminar?

a. when condensation occurs on a horizontal tube
b. when condensation occurs on a vertical bank of horizontal tubes
c. when condensation occurs on a vertical tube
d. when condensation occurs on a bunch of vertical tubes
 Answer  Explanation  Related Ques ANSWER: when condensation occurs on a horizontal tube Explanation: No explanation is available for this question!

33)   In forced convection boiling process, a liquid flows through a tube with

a. superheated or unsaturated boiling
b. subcooled or saturated boiling
c. subcooled to superheated boiling
d. vapour in boiling
 Answer  Explanation  Related Ques ANSWER: subcooled or saturated boiling Explanation: No explanation is available for this question!