# Heat Transfer Test Questions - Set - 5

1)   When the layers of a composite wall are in series and the thermal resistance of every individual layer is given then the total thermal resistance of the composite wall is given by

a. substantiating lower value thermal resistance from higher value thermal resistance
b. adding both the thermal resistances
c. multiplying both the thermal resistances
d. none of the above
 Answer  Explanation  Related Ques ANSWER: adding both the thermal resistances Explanation: No explanation is available for this question!

2)   A composite wall of two layers in parallel as shown in figure has the rate of heat transfer 2 kW/m2. The thermal resistance R1 = 0.6 K/W and R2 = 0.4 K/W. The initial temperature T1 is at 1000 K. What is the temperature T2 of the other surface?

a. 320 K
b. 520 K
c. 220 K
d. insufficient data
 Answer  Explanation  Related Ques ANSWER: 520 K Explanation: No explanation is available for this question!

3)   What is the formula for the thermal resistance (R) of a hollow cylinder of internal radius Ri, outer radius Ro and the length l ? Thermal conductivity of the cylinder material is k. The heat flows from inner side to outer side.

a. R = ln (Ro / Ri) / 2πkl
b. R = ln (Ri / Ro) / 2πkl
c. R = (Ro + Ri) / 2πkl
d. R = (RoRi) / 2πkl
 Answer  Explanation  Related Ques ANSWER: R = ln (Ro / Ri) / 2πkl Explanation: No explanation is available for this question!

4)   A hollow cylinder of length of 1m, inner radius (Ri) 0.01m and outer radius (Ro) 0.05m has a thermal conductivity (k) 20 W/mK. The inside surface temperature is at 500K. What is the outside surface temperature of the cylinder when the rate of radial heat transfer is 3.13 kW?

a. 400 K
b. 360 K
c. 460 K
d. insufficient data
 Answer  Explanation  Related Ques ANSWER: 460 K Explanation: No explanation is available for this question!

5)   As the radius increases in hollow cylinder the temperature

a. also increases
b. decreases
c. it depends upon the direction of heat flow
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: it depends upon the direction of heat flow Explanation: No explanation is available for this question!

6)   For the composite cylinder as shown in figure, the thermal resistances of every layer from inside to outside of the cylinder are given as follows,
R1 =  ln (r1 / ri) / 2πk1l
R1 =  ln (ro / r1) / 2πk2l
What will be the total thermal resistance of the composite cylinder?

a. R = R1 + R2
b. R = R1R2 / (R1 + R2)
c. R = R1 / (R1 + R2)
d. R = R2 / (R1 + R2)
 Answer  Explanation  Related Ques ANSWER: R = R1 + R2 Explanation: No explanation is available for this question!

7)   What is the effect of change in outer radius of the hollow cylinder on the thermal resistance of conduction?

a. the thermal resistance of conduction increases with increase in outer radius of the hollow cylinder
b. the thermal resistance of conduction decreases with increase in outer radius of the hollow cylinder
c. the thermal resistance of conduction remains same with change in outer radius of the hollow cylinder
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: the thermal resistance of conduction increases with increase in outer radius of the hollow cylinder Explanation: No explanation is available for this question!

8)   What is the effect of change in outer radius of the hollow cylinder on the thermal resistance of convection?

a. the thermal resistance of convection increases with increase in outer radius of the hollow cylinder
b. the thermal resistance of convection decreases with increase in outer radius of the hollow cylinder
c. the thermal resistance of convection remains same with change in outer radius of the hollow cylinder
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: the thermal resistance of convection decreases with increase in outer radius of the hollow cylinder Explanation: No explanation is available for this question!

9)   What is the formula for thermal resistance for convection at the outer surface of hollow cylinder?
Where,
h = convection heat transfer coefficient
l = length of hollow cylinder
r = outer radius of the cylinder

a. Rc = 1 / h r l
b. Rc = 2 π h r l
c. Rc = 1 / 2 π h r l
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Rc = 1 / 2 π h r l Explanation: No explanation is available for this question!

10)   Consider a plane wall of area A, having a layer of insulation on it. What will happen to the thermal resistance for convection of wall if the thickness of the insulation is increased?

a. the thermal resistance for convection increases with increase in thickness of insulation
b. the thermal resistance for convection decreases with increase in thickness of insulation
c. the thermal resistance for convection remains same with increase in thickness of insulation
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: the thermal resistance for convection remains same with increase in thickness of insulation Explanation: No explanation is available for this question!

11)   Which of the following assumptions is/are correct to obtain an analytical solution for the problem on laminar boundary layer of fluid on flat plate?

a. The fluid is incompressible
b. The fluid is in steady-state
c. The is not affected by fluid flow
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

12)   Consider the flow of fluid in a boundary layer. Take a control volume which has a shape of a parallelopiped with dimensions (dx x dy x 1)
u = velocity of the fluid entering the control volume
v = velocity of the fluid leaving the control volume

Considering above condition, the equation

(∂u / ∂x) + (∂v / ∂y) = 0

is known as

a. continuity equation for incompressible, steady, two dimensional flow
b. continuity equation for compressible, steady, two dimensional flow
c. continuity equation for incompressible, unsteady, two dimensional flow
d. continuity equation for incompressible, steady, three dimensional flow
 Answer  Explanation  Related Ques ANSWER: continuity equation for incompressible, steady, two dimensional flow Explanation: No explanation is available for this question!

13)   Change in momentum is

a. the result of powers acting on the surface of the control volume
b. the result of works acting on the surface of the control volume
c. the result of forces acting on the surface of the control volume
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the result of forces acting on the surface of the control volume Explanation: No explanation is available for this question!

14)   When the hydrodynamic boundary layer thickness (δ), which is the distance from the surface at which the local velocity (u) reaches 99% of the free-stream velocity, then

a. (δ / x) = 5 / (Rex)(1/2)
b. (δ / x) = 5 / (Rex)(2)
c. (δ / x) = 10 / (Rex)(1/2)
d. (δ / x) = 10 / (Rex)(2)
 Answer  Explanation  Related Ques ANSWER: (δ / x) = 5 / (Rex)(1/2) Explanation: No explanation is available for this question!

15)   Assume a turbulent flow of a fluid on a flat plate. A very thin region near the plate surface is called as

a. laminar buffer layer
b. laminar sublayer
c. laminar turbulent layer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: laminar sublayer Explanation: No explanation is available for this question!

16)   The layer above the laminar sublayer with some turbulence and still having importance of viscous action is called as

a. sub-sublayer
b. turbulent layer
c. buffer layer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: buffer layer Explanation: No explanation is available for this question!

17)   The layer through which the momentum and energy transfer take place via the movement of macroscopic lumps of matter from one region to another is called as

a. the laminar sublayer
b. the buffer layer
c. the turbulent layer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the turbulent layer Explanation: No explanation is available for this question!

18)   What is used instead of ν, in turbulent boundary layer condition?

a. eddy diffusivity for momentum
b. eddy diffusivity for force
c. eddy diffusivity for heat
d. none of the above
 Answer  Explanation  Related Ques ANSWER: eddy diffusivity for momentum Explanation: No explanation is available for this question!

19)   The eddy properties are used in turbulent boundary layer condition because

a. the eddy properties may be small compared to molecular properties
b. the eddy properties may be large compared to molecular properties
c. the eddy properties may be small or may be large compared to molecular properties, but never equals to molecular properties
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the eddy properties may be large compared to molecular properties Explanation: No explanation is available for this question!

20)   Generally, natural convection occurs due to

a. change in velocity of a fluid
b. change in density of a fluid
c. change in molecular structure of a fluid
d. none of the above
 Answer  Explanation  Related Ques ANSWER: change in density of a fluid Explanation: No explanation is available for this question!

21)   When two bodies of areas A1and A2 are exchanging radiant heat energy, F12 is the shape factor of A1with respect to A2 and F21 is the shape factor of A2 with respect to A1, then what is the correct relation for reciprocating theorem? Assuming A1> A2

a. A1F12 > A2 F21
b. A1F12 < A2 F21
c. A1F12 = A2 F21
d. none of the above
 Answer  Explanation  Related Ques ANSWER: A1F12 = A2 F21 Explanation: No explanation is available for this question!

22)   When F12 is the shape factor of A1with respect to A2 and F21 is the shape factor of A2 with respect to A1and A1= A2, then what is the relation between F12 and  F21?

a. F12 > F21
b. F12 < F21
c. F12 = F21
d. none of the above
 Answer  Explanation  Related Ques ANSWER: F12 = F21 Explanation: No explanation is available for this question!

23)   Which parameter in the radiant heat exchange between two black bodies is analogous to the voltage in electrical system?

a. Difference in areas of the two black bodies (A1– A2)
b. Difference in two shape factors (F12 – F21)
c. Difference in emissive powers of the two black bodies (Eb1 – Eb2)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Difference in emissive powers of the two black bodies (Eb1 – Eb2) Explanation: No explanation is available for this question!

24)   What is the formula for the analogous resistance for radiant heat exchange between two black bodies?

a. 1 / (A1F21)
b. 1 / (A1F12)
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!

25)   The rate of radiant flux between two black bodies is analogous to

a. resistance in electrical system
b. voltage in electrical system
c. current in electrical system
d. none of the above
 Answer  Explanation  Related Ques ANSWER: current in electrical system Explanation: No explanation is available for this question!

26)   How does the gray body differ from the black body?

a. all the incident radiation is not absorbed completely by gray body
b. the emissivity of the gray body is less than unity
c. the absorptivity of the gray body is less than unity
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

27)   How are the real bodies in terms of diffuseness?

a. real bodies are perfectly diffuse
b. real bodies are not perfectly diffuse

 Answer  Explanation  Related Ques ANSWER: real bodies are not perfectly diffuse Explanation: No explanation is available for this question!

28)   For the diffuse surfaces

a. the intensity of emitted radiation is constant and depends upon the direction
b. the intensity of emitted radiation is not constant and depends upon the direction
c. the intensity of emitted radiation is constant and does not depend upon the direction
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the intensity of emitted radiation is constant and does not depend upon the direction Explanation: No explanation is available for this question!

29)   What is the relation between absorptivity (α), reflectivity (ρ) and transmissivity (τ) for gray body?

a. ρ + α + τ =1
b. α + τ =1
c. ρ + τ =1
d. ρ + α =1
 Answer  Explanation  Related Ques ANSWER: ρ + α =1 Explanation: No explanation is available for this question!

a. the total radiation incident upon a surface per unit time per unit surface area
b. the total radiation leaving a surface per unit time per unit surface area
c. the net radiation exchanging between two surfaces per unit time per unit surface area
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the total radiation incident upon a surface per unit time per unit surface area Explanation: No explanation is available for this question!

31)   Which of the following is/are example/s of heat exchanger?

a. Feed water heater in which a stream of steam is directly mixed with cold water and the mixture leaves at uniform temperature
b. Feed water heater in which a stream of steam and cold water are not mixed and separated by partition through which heat flows
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)   Which of the following phases of designing of heat exchangers does designer consider corrosive nature of the fluid in?

a. The thermal analysis
b. The mechanical design
c. The design for manufacture
d. none of the above
 Answer  Explanation  Related Ques ANSWER: The mechanical design Explanation: No explanation is available for this question!

33)   Which of the following is NOT a type of heat exchanger?

a. Recuperator
b. Regenerator
c. Mixer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: none of the above Explanation: No explanation is available for this question!

34)   The two fluids are not mixed and kept separated as they both flow through heat exchanger in

a. Transfer type heat exchanger or recuperator
b. Storage type heat exchanger or regenerator
c. Direct contact type heat exchanger or mixer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Transfer type heat exchanger or recuperator Explanation: No explanation is available for this question!

35)   Which of the following is/are example/s of direct contact type heat exchanger?

a. jet condenser
b. desuperheater
c. cooling tower
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!