Multiple choice Questions and Answers on Heat exchanger
Multiple choice Questions and Answers on Heat exchanger
1. Water (specific heat = 4 k J/kg K) enters a cross flow exchanger (both fluids unmixed) at 15 degree Celsius and flows at the rate of 7.5 kg/s. It cools air (C P = 1 k J/kg K) flowing at the rate of 10 kg/s from an inlet temperature of 120 degree Celsius. For an overall heat transfer coefficient of 780 k J/m2 hr degree and the surface area is 240 m2, determine the NTU
a) 4.2
b) 5.2
c) 6.2
d) 7.2
Answer: 5.2
2. Consider the above problem, find the capacity ratio of the heat exchanger
a) 0.555
b) 0.444
c) 0.333
d) 0.222
Answer: 0.333
3. The engine oil at 150 degree Celsius is cooled to 80 degree Celsius in a parallel flow heat exchanger by water entering at 25 degree Celsius and leaving at 60 degree Celsius. Estimate the exchanger effectiveness
a) 0.56
b) 0.66
c) 0.76
d) 0.86
Answer: 0.56
4. In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the effectiveness of the heat exchanger. At the condensing pressure, stream has a saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to the water. Take specific heat of water as 4 k J/kg K
a) 0.224
b) 0.706
c) 2.224
d) 3.224
Answer: 0.706
5. In how many categories heat exchangers are classified on the basis of mechanical design of heat exchanger surface?
a) 2
b) 4
c) 1
d) 3
Answer: 3
6. In how many categories heat exchangers are classified on the basis of physical state of heat exchanging fluids?
a) 1
b) 2
c) 3
d) 4
Answer: 2
7. Heat exchangers are classified into how many categories?
a) 1
b) 2
c) 3
d) 4
Answer: 4
8. Based upon the nature of heat exchange process, the heat exchangers are classified into how many categories
a) 1
b) 2
c) 3
d) 4
Answer: 3
9. Consider the above problem, if the fluid flow rates and the inlet conditions remain unchanged, workout the lowest temperature to which the oil may be cooled by increasing length of the exchanger
a) 46.62 degree Celsius
b) 56.62 degree Celsius
c) 66.62 degree Celsius
d) 76.62 degree Celsius
Answer: 66.62 degree Celsius
10. Consider the above problem, find the tube length. Let the diameter of tube is 25 mm
a) 14.5 m
b) 15.5 m
c) 16.5 m
d) 17.5 m
Answer: 14.5 m
11. In how many categories heat exchangers are classified on the basis of direction of flow of fluids?
a) 4 categories
b) 3 categories
c) 2 categories
d) 1 categories
Answer: 3 categories
12. A single pass shell and tube heat exchanger, consisting of a bundle of 100 tubes (inner diameter 25 mm and thickness 2 mm) is used for heating 28 kg/s of water from 25 degree Celsius to 75 degree Celsius with the help of a steam condensing at atmospheric pressure on the shell side with condensing heat transfer coefficient 5000 W/m2 degree. Make calculation for overall heat transfer coefficient based on the inner area. Take fouling factor on the water side to be 0.002 m2 degree/W per tube and neglect effect of fouling factor on the shell side and thermal resistance of the tube wall
Find overall heat transfer coefficient on inner area if fouling factor is on water side
a) 647.46 W/m2 degree
b) 747.46 W/m2 degree
c) 847.46 W/m2 degree
d) 947.46 W/m2 degree
Answer: 847.46 W/m2 degree
13. 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: both a) and b)
14. 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: The mechanical design
15. Which of the following is NOT a type of heat exchanger?
a) Recuperator
b) Regenerator
c) Mixer
d) none of the above
Answer: none of the above
16. 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: Transfer type heat exchanger or recuperator
17. 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: all of the above
18. What are the compact heat exchangers?
a) the heat exchangers having small surface area per unit volume
b) the heat exchangers having large surface area per unit volume
c) the heat exchangers having small surface area per unit weight
d) the heat exchangers having large surface area per unit weight
Answer: the heat exchangers having large surface area per unit volume
19. The heat exchanger is said to be compact when its area density is
a) equal to 700 m2/ m3
b) less than 700 m2/ m3
c) more than 700 m2/ m3
d) unpredictable
Answer: more than 700 m2/ m3
20. Which of the following can be considered as more compact efficient heat exchanger?
a) Car radiators
b) Stirling engine regenerator
c) Ceramic regenerator in gas turbine
d) none of the above
Answer: Stirling engine regenerator
21. The compact heat exchangers are commonly used in
a) gas to gas heat transfer
b) gas to liquid heat transfer
c) both a. and b.
d) none of the above
Answer: both a. and b.
22. Usually, the flow arrangement of two fluids in compact heat exchangers is
a) parallel flow
b) counter flow
c) cross flow
d) none of the above
Answer: cross flow
23. What is the purpose of using baffles in shell-and-tube heat exchangers?
a) to maintain uniform spacing between tubes
b) to enhance heat transfer
c) both a. and b.
d) none of the above
Answer: both a. and b.
24. Large sized and heavy shell-and-tube heat exchangers are suitable for
a) automotive applications
b) aircraft applications
c) marine applications
d) none of the above
Answer: none of the above
25. Some examples of heat exchanger are
(i) Condensers and evaporators in refrigeration units
(ii) Evaporator of an ice plant and milk chiller of a pasteurizing plant
(iii) Automobile radiators and oil coolers of heat engines
Identify the correct answer
a) i only
b) ii and iii
c) i, ii and iii
d) i and ii
Answer: i, ii and iii
26. The energy transfer between the hot fluid and cold fluids is brought about by their complete physical mixing in
a) Direct contact heat exchanger
b) Regenerators
c) Recuperators
d) Boilers
Answer: Direct contact heat exchanger
27. Which of the following is not an example of recuperators type heat exchanger?
a) Automobile radiators
b) Condensers
c) Chemical factories
d) Oil heaters for an aero plane
Answer: Chemical factories
28. Many types of heat exchangers have been developed to meet the widely varying applications. Based upon their
(i) Operating principle
(ii) Arrangement of flow path
(iii) Design
Identify the correct statements
a) i, ii and iii
b) i and ii
c) ii and iii
d) i and iii
Answer: i, ii and iii
29. Capacity ratio is defined as the product of
a) Mass and temperature
b) Mass and specific heat
c) Specific heat and temperature
d) Time and temperature
Answer: Mass and specific heat
30. Which of the following is not associated with a heat exchanger?
a) Fouling
b) NTU
c) Capacity ratio
d) Mc Adam’s correction factor
Answer: Mc Adam’s correction factor
31. For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference for parallel flow is
a) Does not depend on counter flow
b) Smaller than counter flow
c) Greater than counter flow
d) Equal to counter flow
Answer: Equal to counter flow
32. Conduction heat flux is
a) -k A dt/dx
b) -k dt/dx
c) +k A dt/dx
d) None of the mentioned
Answer: -k dt/dx
33. The correction factor ‘F’ for multi-pass heat exchangers depends on
a) P+Z
b) P/Z
c) P & Z
d) None of the mentioned
Answer: P+Z
34. The expression for overall heat transfer coefficient for a single wall construction is
a) 1/U = 1/hi + x/k + 1/ho
b) 1/UA = 1/hi Ai + x/kA + 1/ho Ao
c) 1/UA = 1/hi Ao + x/kA + 1/ho Ai
d) None of the mentioned
Answer: 1/U = 1/hi + x/k + 1/ho
35. The regenerator heat exchanger operate under
a) Transient conditions
b) Steady state conditions
c) Transient/steady state conditions
d) None of the mentioned
Answer: Transient conditions
36. When one of the fluids flowing in heat exchanger is of low thermal conductivity, the overall heat transfer coefficient
a) Decreases
b) Increases
c) Remains constant
d) None of the mentioned
Answer: Decreases
37. The overall heat transfer coefficient in condensers and boilers is
a) High
b) Low
c) High & low
d) None of the mentioned
Answer: High
38. Do we consider the conduction heat transfer in the tube in between the two fluids?
a) No
b) Yes
c) Yes/No
d) None of the mentioned
Answer: No
39. The specific heat of hot fluid in a heat exchanger is
a) Increasing
b) Decreasing
c) No change
d) None of the mentioned
Answer: No change
40. The specific heat of cold fluid in a heat exchanger is
a) Increasing
b) Decreasing
c) No change
d) None of the mentioned
Answer: No change
41. The overall heat transfer coefficient in a heat exchanger is
a) Increasing
b) Decreasing
c) No change
d) None of the mentioned
Answer: No change
42. The parameter ‘P’ in a multi-pass heat exchanger is the ratio of
a) Rise in temperature of cold fluid and fall of temperature of hot fluid
b) Fall of temperature of hot fluid to rise of temperature of cold fluid
c) Rise of temperature of cold fluid to difference between inlet temperatures of hot and cold fluids
d) None of the mentioned
Answer: Rise of temperature of cold fluid to difference between inlet temperatures of hot and cold fluids
43. Factor ‘Z’ in multi-pass heat exchanger is the ratio of
a) Rise in temperature of cold fluid and fall of temperature of hot fluid
b) Fall of temperature of hot fluid to rise of temperature of cold fluid
c) Rise of temperature of cold fluid to difference between inlet temperatures of hot and cold fluids
d) None of the mentioned
Answer: Fall of temperature of hot fluid to rise of temperature of cold fluid
44. The change in correction factor ‘F’ with the increasing value of parameter ’Z’ at a fixed value of parameter ‘P’
a) Constant
b) Increases
c) Decreases
d) None of the mentioned
Answer: Increases
45. The change in correction factor ‘F’ with the increasing value of parameter ’P’ at a fixed value of parameter ‘Z’
a) Constant
b) Increases
c) Decreases
d) None of the mentioned
Answer: Decreases
46. Overall heat transfer coefficient is associated with
a) Conduction
b) Convection
c) Radiation
d) None of the mentioned
Answer: None of the mentioned
47. Overall heat transfer coefficient is associated with
a) Conduction and radiation
b) Convection and radiation
c) Radiation, convection and conduction
d) None of the mentioned
Answer: None of the mentioned
48. all heat transfer coefficient is associated with
a) Conduction and radiation
b) Convection and conduction
c) Radiation and convection
d) None of the mentioned
Answer: Convection and conduction
49. 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 of the mentioned
Answer: Rough surfaces in contact
50. Thermal contact resistance decreases the temperature
a) Linearly
b) Parabolic
c) Instantaneously
d) None of the mentioned
Answer: Instantaneously
51. Temperature variation in a pipe is
a) linear
b) Parabolic
c) logarithmic
d) None of the mentioned
Answer: logarithmic
52. Temperature variation in a plain wall is
a) linear
b) Parabolic
c) logarithmic
d) None of the mentioned
Answer: linear
53. 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 of the mentioned
Answer: In a Condenser
Comments
Post a Comment