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SAIL Model questions of Chemical Engineering Heat Transfer for learn and practice,SAIL multiple choice objective questions with answers and detailed explanations
1. Loss of heat from unlagged steam pipe to the ambient air is by
(a) conduction
(b) convection
(c) radiation
(d) all (a),(b) & (c) (Ans)
2. Fourier's law applies to the heat transfer by
(a) convection
(b) radiation
(c) conduction (Ans)
(d) all (a),(b) & (c)
3. Fourier's law of heat conduction applies to .......... surfaces.
(a) isothermal
(b) non-isothermal
(c) both (a) and (b) (Ans)
(d) neither (a) and (b)
4. Unsteady state heat conduction occurs, when
(a) temperature distribution is independent of time
(b) temperature distribution is dependent on time (Ans)
(c) heat flows in one direction only
(d) three dimensional heat flow is concerned
5. What is the unit of thermal conductivity ?
(a) Kcal/hr.m20C
(b) Kcal/hr.m. 0C (Ans)
(c) Kcal/hr.m
(d) Kcal/hr.0C
6. The unit of heat transfer co-efficient is
(a) BTU/hr.ft20F (Ans)
(b) BTU/hr.0F.ft.
(c) BTU/hr.0F
(d) BTU/hr.ft
7. Which of the following is correct ?
(a) Rate = Driving force * Resistance
(b) Driving force = Rate * Resistance (Ans)
(c) Resistance = Driving force * Rate
(d) Rate = Resistance/Driving force
8. An insulator should have
(a) low thermal conductivity (Ans)
(b) high thermal conductivity
(c) less resistance to heat flow
(d) a porous structure
9. Heat flux through several resistance in series in analogous to the current flowing through several
(a) resistances in parallel
(b) capacitors in series
(c) resistances in series (Ans)
(d) none of these
10. The overall resistance for heat transfer through a series of flat resistance, is the ..... of the resistances.
(a) average
(b) geometric mean
(c) product
(d) sum (Ans)
11. Which of the following has the highest thermal conductivity ?
(a) Brick
(b) Air
(c) Water
(d) Silver (Ans)
12. Which area is used in case of heat flow by conduction through a cylinder ?
(a) Logarithmic mean area (Ans)
(b) Arithmetic mean area
(c) Geometric mean area
(d) None of these
13. For heat flow through very thick walled cylinder, use ............ mean radius.
(a) arithmetic
(b) logarithmic (Ans)
(c) geometric
(d) either (a) or (c)
14. What is the logarithmic mean of r1 and r2 ?
(a) r1 - r2/ln r1/r2 (Ans)
(b) r1 - r2/ln r2/r1
(c) r2 - r1/ln r1/r2
(d) r1 - r2/ - ln r1/r2
15. What is Nusselt number ?
(a) Cp.μ/k
(b) hD/k (Ans)
(c) h.Cp/μ
(d) Cp.μ/h
16. Prandtl number is given by
(a) Cp.μ/a
(b) hD/k
(c) Cp.μ/k (Ans)
(d) μ/h.Cp
17. Thermal diffusivity is given by
(a) k/r.Cp (Ans)
(b) r.Cp/k
(c) Cp.μ/a
(d) μ/hCp
18. Grashhoff number is given by
(a) g D3. β .â tr2/μ2 (Ans)
(b) g D2βâtr/μ2
(c) g D2βâtr2μ
(d) g D3βâtr2/μ
19. If h1 = inner film co-efficient and h2 = outer film co-efficient, then the overall heat transfer co-efficient is
(a) always less than h1
(b) always between h1 and h2 (Ans)
(c) always higher than h2
(d) dependent on metal resistance
20. Gratez number is give by
(a) mCp/kL (Ans)
(b) kL/mCp
(c) mCp/kμ
(d) kL/mCp
21. In the equation Q= UA ât ; ât is
(a) geometric mean temperature difference.
(b) arithmetic mean temperature difference.
(c) logarithmic mean temperature difference. (Ans)
(d) the difference of average bulk temperatures of hot and cold fluids.
22. Peclet number (Pe) is given by
(a) Pe = Re.Pr (Ans)
(b) Pe = Re/Pr
(c) Pe = Pr/Re
(d) Pe = Nu.Re
23. Prandtl number is the reciprocal of
(a) Thermal diffusivity/ Momentum diffusivity (Ans)
(b) thermal diffusivity x Momentum
(c) Thermal diffusivity x Mass diffusivity
(d) Mass diffusivity x Momentum diffusivity
24. Maximum heat transfer rate is obtained in .......... flow.
(a) laminar
(b) turbulent (Ans)
(c) creeping
(d) transition region
25. Heat flux is the time rate of heat transfer per unit
(a) length
(b) area (Ans)
(c) volume
(d) none of these
26. Nusselt number is the ratio of the
(a) temperature gradient of the wall to that across the entire pipe. (Ans)
(b) temperature difference to the temperature gradient at the wall.
(c) heat flux at the wall to that across the entire pipe.
(d) none of these
27. Fouling factor
(a) is a dimensionless quantity.
(b) does not provide a safety factor for design.
(c) accounts for additional resistances to heat flow. (Ans)
(d) none of these.
28. Viscosity of gases ....... with increase in temperature.
(a) increase very rapidly
(b) increase slowly (Ans)
(c) decrease slowly
(d) remain unaffected
29. Heat transfer co-efficient (h1) for liquids increases with
(a) increasing temperature (Ans)
(b) decreasing temperature
(c) decreasing Reynolds number
(d) none of these
30. At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe ?
(a) 0.5
(b) < 0.5
(c) > 0.6 (Ans)
(d) < 0.1
31. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the
(a) buffer zone
(b) turbulent core (Ans)
(c) both (a) and (b)
(d) viscous sub-layer
32. Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is
(a) 0.1
(b) > 1
(c) < 1 (Ans)
(d) 1
33. Natural convection is characterized by
(a) Grashhoff number (Ans)
(b) Peclet number
(c) Reynolds number
(d) Prandtl number
34. Which of the following is unimportant in forced convection ?
(a) Reynolds number
(b) Prandtl number
(c) Grashhoff number (Ans)
(d) none of these
35. In fored convection, the heat transfer depends on
(a) Re, Pr (Ans)
(b) Re, Gr
(c) mainly Gr
(d) Re only
36. The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
(a) Re. Gz
(b) Nu, Pr
(c) Nu, Pr, Re
(d) Nu, Gz (Ans)
37. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical ?
(a) 1 (Ans)
(b) < 1
(c) > 1
(d) none of these
38. Reynold's analogy states that
(a) St = f/2 (Ans)
(b) St = f/4
(c) St = 4f
(d) St = f1/2
39. For what value of Prandtl number, St = f/2 ?
(a) 1.5
(b) 1 (Ans)
(c) > 1
(d) < 1
40. Which has the lowest Prandtl number ?
(a) Liquid metal (Ans)
(b) Aqueous solution
(c) Water
(d) Lube oil
41. Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid
(a) for fluids in laminar flow
(b) for fluids in tubulent flow (Ans)
(c) when Grashhoff number is very important
(d) for liquid metals
42. For what value of Prandtl number, the Colburn analogy is valid ?
(a) 0.06 to 120
(b) 0.6 to 120 (Ans)
(c) 1 to 103
(d) 1 to 50
43. Pick out the correct equation.
(a) jH = (St) (Pr)2/3 = f/2 (Ans)
(b) jH = (St) (Pr)1/3 = f/2
(c) jH = (St)2/3 (Pr)= f/2
(d) jH = (St)1/3 (Pr)= f/2
44. Choose the correct equation.
(a) Nu = (Re) (Pr) (Gz)
(b) Nu = (Re) (Pr) (St) (Ans)
(c) Nu = (Re) (Pr)
(d) Nu = (Pr) (St)
45. For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
(a) Nu = 0.023 Re0.8 . Pr0.4
(b) Nu = p/2 Gz
(c) Nu = 2/p Gz (Ans)
(d) Nu = 2Gz0.5
46. If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length
(a) ha = hl
(b) ha = 2 hl (Ans)
(c) ha = 0.5 hl
(d) ha = 0.75 hl
47. When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids ?
(a) At high fluid velocity (Ans)
(b) At low velocity
(c) When fluid flows past a smooth surface
(d) None of these
48. The heat transfer co-efficient in film type condensation is ....... that for dropwise condensation.
(a) greater than
(b) lower than (Ans)
(c) is same as
(d) half
49. Prandtl number is the ratio of
(a) momentum diffusivity to mass diffusivity
(b) momentum diffusivity to thermal diffusivity (Ans)
(c) thermal diffusivity to mass diffusivity
(d) thermal diffusivity to momentum diffusivity
50. All analogy equations connecting friction factor and heat transfer co-efficient apply only to
(a) wall or skin friction (Ans)
(b) form friction
(c) both (a) and (b)
(d) turbulent flow
