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chemical engineering heat transfer chemical engineering MCQs

Practise multiple-choice questions from chemical engineering heat transfer chemical engineering for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

chemical engineering heat transfer chemical engineering Mcqs
1. The unit of heat transfer co-efficient is_________________?
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A. BTU/hr. F. ft

B. BTU/hr. ft2F

C. BTU/hr. ft

D. BTU/hr. F

2. In a forward feed multiple effect evaporator unit__________________?
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A. None of these

B. Transfer from effect to effect is done by pumps

C. No pump is required to withdraw the product from the last effect

D. Viscosity of liquid is highest in first effect

3. For heat flow through very thick walled cylinder, use ___________mean radius?
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A. Either A. or C.

B. Logarithmic

C. Arithmetic

D. Geometric

4. An ejector is used to__________________?
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A. Increase temperature

B. None of these

C. Remove condensate

D. Increase pressure

5. Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is__________________?
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A. 0.5

B. 10

C. 2

D. 100

6. Multiple effect evaporation accounts for___________________?
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A. None of these

B. Lower operating costs

C. Steam economy

D. Investment economy

7. Nucleate boiling is promoted ___________________?
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A. On rough surfaces

B. None of these

C. On polished surfaces

D. In the absence of agitation

8. During crystallisation, formation of crystal can occur in ______________ solution only?
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A. Saturated

B. All A., B. and C.

C. Supersaturated

D. Under-saturated

9. The range of electromagnetic spectrum important in heat transfer by radiation is ______________ microns?
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A. 0.38-0.78

B. May-50

C. 100-1000

D. 0.5-50
10. In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is _____________ the outlet temperature of the cold fluid?
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A. Either more or less than (depending upon the fluid)

B. Equal to

C. More than

D. Less than

11. In a single evaporator system, the steam economy ________________ by creating vacuum in the evaporator?
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A. Remain constant

B. Increases

C. May increase or decrease, depends on the vacuum

D. Decreases

12. A multiple effect evaporator as compared to a single effect evaporator of the same capacity has _________________?
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A. Higher solute concentration in the product

B. Lower steam economy

C. Higher steam economy

D. Lower heat transfer area

13. Prandtl number is given by__________________?
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A. ?/h CP

B. CP ?/k

C. hD/k

D. CP ?/a

14. In pipe flow, heat is transferred from hot wall to the liquid by__________________?
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A. Forced convection only

B. Conduction only

C. Forced convection and conduction

D. Free and forced convection

15. In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid___________________?
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A. Varies as square of the area

B. Directly proportional to LMTD and inversely proportional to the area

C. Varies directly as the area and the LMTD

D. None of these

16. The absorptivity of a body is equal to its emissivity _________________?
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A. At a particular temperature

B. Under thermal equilibrium

C. None of these

D. For circular bodies

17. Viscosity of gases ______________ with increase in temperature?
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A. Increase very rapidly

B. Decrease slowly

C. Increase slowly

D. Remain unaffected

18. Use of transverse baffles in a shell and tube heat exchanger is done to increase the___________________?
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A. Flow velocity

B. All A., B. and C.

C. Rate of heat transfer

D. Turbulence of shell side fluid

19. For a multipass shell and tube heat exchanger, the LMTD correction factor is always________________?
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A. < 1

B. Between 1 & 2

C. > 1

D. 1

20. Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m2.C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the_________________?
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A. Lower pressure drop through the exchanger is desired

B. Higher condensing film co-efficient is desired

C. Condensate is corrosive in nature

D. Temperature of the incoming vapor is very high

21. In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will___________________?
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A. Either increase or decrease; depends on the coolant flow rate

B. Remain unchanged

C. Increase

D. Decrease

22. What is the emissivity of a black body ?
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A. 0.9

B. 0

C. 1

D. 0.5

23. Which area is used in case of heat flow by conduction through a cylinder ?
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A. Arithmetic mean area

B. Logarithmic mean area

C. Geometric mean area

D. None of these

24. Prandtl number is the reciprocal of____________________?
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A. Mass diffusivity Momentum diffusivity

B. Thermal diffusivity Mass diffusivity

C. Thermal diffusivity/Momentum diffusivity

D. Thermal diffusivity Momentum

25. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the_________________?
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A. Existence of thermal boundary layer

B. Buoyancy of the bubbles produced at active nucleation site

C. Temperature gradient produced due to density difference

D. None of these
26. Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because___________________?
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A. Conduction becomes important

B. Sub-cooled boiling occurs

C. Radiation becomes important

D. Convection becomes important

27. Overall heat transfer co-efficient of a particular tube is U1. If the same tube with some dirt deposited on either side has coefficient U2, then_________________?
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A. U2 > U1

B. U1 > U2

C. U1 = U2

D. U1 = dirt factor U2

28. For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it________________?
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A. All A., B. and C.

B. Occupies smaller space

C. Is more economical

D. Is easy to operate and maintain

29. In a forward feed multiple effect evaporator, the pressure is ____________________?
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A. Dependent on the number of effects

B. Same in all effects

C. Lowest in last effect

D. Highest in last effect

30. Presence of a non-condensing gas in a condensing vapour___________________?
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A. Increases the rate of condensation

B. Decreases thermal resistance

C. None of these

D. Is desirable to increase the film co-efficient

31. Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling ?
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A. Square pitch

B. Triangular pitch

C. None of these

D. Diagonal square pitch

32. Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger ?
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A. Convective heat transfer co-efficient

B. Effective tube surface area for convective heat transfer

C. All A. B. and C.

D. Tube side pressure drop and the heat transfer rate

33. Tube pitch is the _______________ of tube diameters and the clearances?
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A. Sum

B. None of these

C. Difference

D. Ratio

34. The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the________________ ?
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A. None of these

B. Evaporators operate at atmospheric pressure

C. Solution has an elevation of boiling point

D. Evaporators operate under vacuum

35. Which has the lowest Prandtl number ?
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A. Water

B. Aqueous solution

C. Liquid metal

D. Lube oil

36. Thermal conductivity of a gas at low density, ___________ with increase in temperature ?
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A. May increase or decrease; depends on the gas

B. Remains unchanged

C. Increases

D. Decreases

37. Which one gives the monochromatic emissive power for black body radiation ?
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A. Plancks law

B. Kirchhoffs law

C. Wiens law

D. Stefan-Boltzmann law

38. The absorptivity of a grey body at a given temperature _____________ with increasing wavelength of radiation?
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A. May increase or decrease; depends on the material

B. Remain constant

C. Decreases

D. Increases

39. What is the geometric mean of two heat transfer areas A1 and A2 ?
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A. ?(A1 . A2)

B. ?(A1 + A2)

C. ?(A1 . A2)

D. 2 ?(A1 . A2)

40. Heat sensitive materials can be concentrated in an evaporator employing_______________?
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A. High pressure

B. Vacuum

C. High residence time

D. None of these

41. Which of the following situations can be approximated to a steady state heat transfer system ?
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A. ntained constant at 180C

B. Boiling brine kept in open vessel when the bottom surface temperature of the vessel is

C. osed to atmospheric air at 35C</strong>

D. e exposed to atmospheric air at 35C

E. A red hot steel slab (having outside surface temperature as 1300C) exposed to the

F. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe
42. In case of a super-cooled solution, which is on the verge of crystallisation, the free energy of the solution as compared to that of the solid is ________________?
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A. Same

B. More or less; depends on the nature of solution

C. Less

D. More
43. The inner wall of a furnace is at a temperature of 700C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.C- 1 respectively. The ambient air is at 30C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.C-1. The rate of heat loss from the outer surface in W.m-2is__________________?
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A. 172.5

B. 165.4

C. 167.5

D. 175

44. Peclet number (Pe) is given by____________________?
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A. Pe = Nu.Re

B. Pe = Re.Pr

C. Pe = Re/Pr

D. Pe = Pr/Re

45. The purpose of providing expansion bellows in the shell of tubular exchanger is to _____________________?
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A. Facilitate increase of shell length, if needed

B. Account for the uneven expansion of shell and tube bundles

C. Increase the heating load

D. Impart structural strength

46. The advantage of using a 1 2 shell and tube heat exchanger over a 1 1 shell and tube heat exchanger is_________________?
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A. Higher shell side heat transfer co-efficient

B. Higher tube side heat transfer co-efficient

C. Lower tube side pressure drop

D. Lower shell side pressure drop

47. Prandtl number is the ratio of________________?
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A. Thermal diffusivity to momentum diffusivity

B. Momentum diffusivity to thermal diffusivity

C. Thermal diffusivity to mass diffusivity

D. Momentum diffusivity to mass diffusivity

48. A graph between _____________ is called Wilson plot?
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A. (1/U) Vs. (1/V)

B. v0.8 Vs . U

C. (1/U) Vs. (1/v0.8)

D. (1/v0.8) Vs. U

49. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m2.K. The overall heat transfer co-efficient at this time is _____________________?
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A. 287 W/m2.K

B. 333 W/m2.K

C. 894 W/m2.K

D. 1200 W/m2.K

50. Evaporator tubes are generally_____________________?
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A. Horizontal

B. Vertical

C. Inclined

D. Random