HEAT EXCHANGERS

MULTIPLE CHOICE QUESTIONS

(MCQ) WITH ANSWERS

MCQ are very helpful in complete understanding

and clarity. Fundamentals are easily applied in

practically used heat exchangers.

Fig. Line Diagram of a Parallel Flow Heat Exchanger

Fig. Temperature Variations of Hot & Cold Fluid

in a Parallel Flow Heat Exchanger

Fig. Line Diagram Of a Counter Flow Heat Exchanger

Fig. Temperature Variations of Hot & Cold

Fluids in a Counter Flow Heat Exchanger

 

1. A heat exchanger transfers heat from one fluid to another

   1. Solid

   2. Fluid

   3. Solid & fluid

   4. None

ANS: (b)

2. Latent heat is transferred in a heat exchanger during

   1. Heating

   2. Cooling

   3. Phase change

   4. None

ANS: (c )

3. Sensible heat is transferred in a heat exchanger like

   1. Cooler

   2. Boiler

   3. Condenser

   4. None

(ANS: (a)

4. In a direct contact heat exchanger, there is

   1. Mass transfer

   2. Heat transfer

   3. Heat & mass transfer

   4. None

ANS: (c )

5. The direct contact heat exchanger is

   1. Boiler

   2. Condenser

   3. Desert cooler

   4. None

ANS: (c )

6. In a regenerator heat exchanger

   1. Both hot and cold fluids are passed simultaneously

   2. First hot fluid & then cold fluid is passed

   3. Can’t say

   4. None

ANS: (b)

7. The operation of a regenerator heat exchanger is

   1. Continuous

   2. Intermittent

   3. Both continuous & intermittent

   4. None

ANS: (b)

8. In a recuperator heat exchanger, the hot & cold fluids

   1. Mix physically

   2. Do not mix physically

   3. Mix chemically

   4. None

ANS: (b)

9. Which of the following is the recuperator heat exchanger

   1. Automobile radiator

   2. Desert cooler

   3. Cooling tower

   4. None

ANS: (a)

10. In a parallel flow heat exchanger, the angle between hot and cold fluids is

(a) 90⁰

(b) 180⁰

(c ) 0⁰

(d)None

ANS: (c )

11. In a counter flow heat exchanger, the angle between hot and cold fluids is

1. (a) 90⁰

2. (b) 180⁰

3. (c ) 0⁰

4. (d)None

ANS: (b )

12. In a cross flow heat exchanger, the angle between hot and cold fluids is

(a) 90⁰

(b) 180⁰

(c ) 0⁰

(d)None

ANS: (a)

13. In a condenser, the temperature of the hot fluid is

         (a) Decreasing

(b)  Increasing

(c ) Remains constant

(d) None

ANS: (c )

     14. In a condenser, the temperature of the cold fluid is

         (a) Decreasing

• (b) Increasing

• (c )Remains constant

• (d)None

ANS: (b)

      15. In a boiler, the temperature of the hot fluid is

1. 1. Decreasing

   2. Increasing

   3. Remains constant

   4. None

ANS: (a)

         16. In a boiler, the temperature of the boiling fluid is

1. 1. Decreasing

   2. Increasing

   3. Remains constant

   4. None

ANS: (c )

       17. Rate of heat transfer by condensing fluid is

1. m^.c_p Δt

2. m^. LH

3. m^.Δt

4. None

ANS (b)

         18. The sequence of the modes of heat transfer in case of a heat exchanger are

1.  Cond + Conv + rad

2.  Conv+ Rad +Conv

3.  Conv +Cond +Conv

4.  None

      ANS:(c)

        19. The effectiveness of a parallel and counter flow heat exchanger is of same value in a

1.   Radiator

2.  Condenser

3.   Pre-heater

4.  None

      ANS: (b)

          20. Use a correction factor ‘F’ to calculate the rate of heat transfer in case of a

1.  Parallel flow heat exchanger

2.  Counter flow heat exchanger

3.  Cross flow heat exchanger

4.  None

      ANS:  (c)

        21. NTU in a heat exchanger is

1.  UA/C

2.  C _min/UA

3. UA/C _max

4.  None

      ANS:  (d)

        22. Temperature variation in a heat exchanger is

1.  Linear

2.  Parabolic

3.  Exponential

4.  None

      ANS: (b)

        23. The heat capacity ratio ‘C’ in a heat exchanger is zero in case of a

1.  Radiator

2.  Pre-heater

3.  Condenser

4. None

        ANS: (c)

          24. In case of a 1:1 heat exchanger, use

1.  LMTD

2.  NTU

3.   LMTD or NTU

4.  None

      ANS:  (c)

        25.The equation of LMTD is

1.  Firstly     (θ₁ + θ₂)/ ln(θ₁/θ₂)

2.  Secondly     (θ₁ θ₂)/ ln(θ₁/θ₂)

3.  Thirdly     (θ₁ –θ₂)/ ln(θ₁/θ₂)

4.  None

        ANS: (c)

         26. ‘C’ heat capacity ratio in a heat exchanger be

1.  =1

2.  > 1

3.  >4

4.  None

      ANS:  (d)

        27. Heat exchanger effectiveness is

1.  <1

2.  =1

3.  >1

4.  None

      ANS: (a)

     28. The effectiveness of a parallel flow heat exchanger with increasing value of heat capacity ratio & for a fixed value of NTU

1. Remains constant

2. Decreases

3. Increases

4. None

      ANS: (b)

        29. The effectiveness of a parallel flow heat exchanger with increasing value of heat capacity ratio & for a fixed value of NTU

1. Remains constant

2. Decreases

3. Increases

4. None

5. ANS: (b)

         30. In condensers/boilers, heat capacity ratio is

1. Infinity

2. Zero

3. 1

4. None

      ANS: (b)

 

      31. The direct contact heat exchanger operate under

1. Transient conditions

2. Steady state conditions

3. Transient/steady state conditions

4. None

       ANS: (b)

       32. The recuperator heat exchangers operate under

1. Transient conditions

2. Steady state conditions

3. Transient/steady state conditions

4. None

      ANS: (b)

       33. The regenerator heat exchanger operate under

1. Transient conditions

2. Steady state conditions

3. Transient/steady state conditions

4. None

       ANS: (a)

      34. When one of the fluids flowing in heat exchanger is of low thermal conductivity, the overall heat transfer coefficient

1. Decreases

2. Increases

3. Remains constant

4. None

     ANS: (a)

       35. The overall heat transfer coefficient in condensers and boilers is

1. High

2. Low

3. High & low

4. None

       ANS: (a)

       36. Do we consider the conduction heat transfer in the tube in between the two fluids?

1. No

2. Yes

3. Yes/No

4. None

       ANS: (a)

        37. The specific heat of hot fluid in a heat exchanger is

1. Increasing

2. Decreasing

3. No change

4. None

        ANS: (c )

        38. The specific heat of cold fluid in a heat exchanger is

• (a) Increasing

  (b) Decreasing

  (c )No change

• (d) None

          ANS; (c )

          39. The overall heat transfer coefficient in a heat exchanger is

1.  Increasing

2. Decreasing

3. No change

4. None

       ANS: (c )

        40. The correction factor ‘F’ for multi-pass heat exchangers depends on

1. P +Z

2. P/Z

3. P & Z

4. None

       ANS: (c )

        41. The parameter ‘P’ in a multi-pass heat exchanger is the ratio of 

1. Rise in temperature of cold fluid and fall of temperature of hot fluid

2. Fall of temperature of hot fluid to rise of temperature of cold fluid

3. Rise of temperature of cold fluid to difference between inlet temperatures of hot and cold fluids

4. None

        ANS: (c )

        42. Factor ‘Z’ in multi-pass heat exchanger is the ratio of

1. Rise in temperature of cold fluid and fall of temperature of hot fluid

2. Fall of temperature of hot fluid to rise of temperature of cold fluid

3. Rise of temperature of cold fluid to difference between inlet temperatures of hot and cold fluids

4. None

       ANS: (b )

          43. The change in correction factor ‘F’ with the increasing value of parameter ’Z’ at a fixed value of parameter ‘P’

1. Constant

2. Increases

3. Decreases

4. None

       ANS: (b)

        44. The change in correction factor ‘F’ with the increasing value of parameter ’P’ at a fixed value of parameter ‘Z’

1. Constant

2. Increases

3. Decreases

4. None

        ANS: (c). 

     45. Overall heat transfer coefficient is associated with
(a) Conduction
(b) Convection
(c) Radiation
(d) None
(Ans: d)

     46. Overall heat transfer coefficient is associated with
(a) Conduction and radiation
(b) Convection and radiation
(c) Radiation, convection and conduction
(d) None
(Ans: d)

       47. Overall heat transfer coefficient is associated with
(a) Conduction and radiation
(b) Convection and conduction
(c) Radiation and convection
(d) None
(Ans: b)

       48. Thermal contact resistance in conduction heat transfer is due to
(a) Polished surfaces in contact
(b) Rough surfaces in contact
(c) Smooth surfaces in contact
(d) None
(Ans: b)

    49. Thermal contact resistance decreases the temperature
(a) Linearly
(b) Parabolic
(c) Instantaneously
(d) None
(Ans: c)

      50. Conduction heat flux is
(a) -k A dt/dx
(b) -k dt/dx
(c) +k A dt/dx
(d) None
(Ans: b)

      51. Convective heat flux is
(a) h A dt
(b) h A
(c) h dt
(d) None
(Ans: c)

      52. Radiation heat flux is
(a) σ A T⁴
(b) σ A dT
(c) σ T⁴
(d) None
(Ans: c)

   53. The expression for overall heat transfer coefficient for a single wall construction is

(a) 1/U = 1/h_i + x/k + 1/h_o

(b) 1/UA = 1/h_i A_i + x/kA + 1/h_o A_o

(c) 1/UA = 1/h_i Ao + x/kA + 1/h_o Ai

(d) None

(Ans: a)

    54. Temperature variation in a pipe is

(a) linear

(b) Parabolic

(c) logarithmic

(d) None

(Ans: c)

55. Temperature variation in a plain wall is

(a) linear

(b) Parabolic

(c) logarithmic

(d) None

(Ans: a)

56. The effectiveness of a parallel and counter flow heat exchanger is of same value

(a) in a radiator

(b) In a Condenser

(c) in a Pre-heater

(d) None

ANS: (b)

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