Practice Test: Question Set - 18
1. In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell)
- (A) D/5 and D
- (B) D/2 and 2 D
- (C) D/4 and 2 D
- (D) D and 2 D
2. Pick out the wrong statement.
- (A) The controlling resistance in case of heating of air by condensing
steam is in the air film
- (B) The log mean temperature difference (LMTD) for counter flow and
parallel flow can be theoretically same when any one of the fluids (hot or cold
fluid) passes through the heat exchanger at constant temperature
- (C) In case of a 1 - 2 shell and tube heat exchanger, the LMTD
correction factor value increases sharply, when a temperature cross occurs
- (D) Phase change in case of a pure fluid at a given
pressure from liquid to vapor or vice-versa occurs at saturation temperature
3. Double pipe heat exchangers are used
- (A) When heat transfer area required is very high
- (B) When heat transfer area required is very low, i.e. (100-200 ft2).
- (C) Because it occupies less floor area
- (D) Because it is less costly
4. Sensible heat of hot industrial flue gases cannot be recovered by a/an
- (A) Economizer
- (B) Regenerator
- (C) Ceramic recuperator
- (D) None of these
5. A body is called grey if the monochromatic emissivity of the body is
- (A) Zero
- (B) Unity
- (C) Same for all wavelengths
- (D) Different for all wavelengths
6. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
- (A) Greater than that for un-insulated steam pipe
- (B) Less than that of the un-insulated steam pipe
- (C) Equal to that of the un-insulated steam pipe
- (D) Less than the steam pipe with 5 cms insulation
7. While the total emissivity of a perfect black body is unity, the same for a real body is
- (A) 0
- (B) 1
- (C) > 1
- (D) Between 0 and 1
8. In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
- (A) Concentrations
- (B) Chemical potentials
- (C) Activity co-efficient
- (D) Mass transfer co-efficient
9. Crystal size in a continuous crystallizer depends upon the
- (A) Rate of heat transfer
- (B) Degree of turbulence
- (C) Degree of super-saturation
- (D) All (a), (b) and (c)
10. The critical radius 'r' of insulation on a pipe is given by
- (A) r = 2k/h
- (B) r = k/h
- (C) r = k/2h
- (D) r = h/k
11. Boiling of milk in an open vessel is an example of __________ boiling.
- (A) Film
- (B) Sub-cooled
- (C) Saturated nucleate
- (D) None of these
12. In an extended surface heat exchanger, fluid having lower co-efficient
- (A) Flows through the tube
- (B) Flows outside the tubes
- (C) Can flow either inside or outside the tubes
- (D) Should not be used as it gives very high pressure drop
13. Black liquor generated during paper manufacture is concentrated in a
- (A) Single effect evaporator
- (B) Single effect evaporator followed by a crystallizer
- (C) Multiple effect evaporator
- (D) Multiple effect evaporators followed by a crystallizer
14. What is Nusselt number?
- (A) CP. µ/k
- (B) hD/k
- (C) h. CP/µ
- (D) CP. µ/h
15. 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
- (C) Always higher than h2
- (D) Dependent on metal resistance
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