Practice Test: Question Set - 10
1. Finned tube heat exchangers
- (A) Give larger area per tube
- (B) Use metal fins of low thermal conductivity
- (C) Facilitate very large temperature drop through tube wall
- (D) Are used for smaller heat load
2. Tube expansion allowances exist in __________ heat exchanger.
- (A) Multipass fixed tube sheet
- (B) U-tube
- (C) Single pass fixed tube sheet
- (D) None of these
3. Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator.
- (A) Long tube
- (B) Falling film
- (C) High pressure
- (D) None of these
4. Pick out the wrong statement.
- (A) In process heat exchangers, saturated steam is preferred over the
superheated steam
- (B) The maximum is the emissive power of a surface at a temperature T1 occurs
at a wavelength of λ1. If the surface temperature is halved, the
maximum in the emissive power would occur at a wavelength of 0.5 λ1
- (C) When a vertical plate is heated in infinite air environmental under
natural convection conditions, the velocity profile in air, normal to the
plate, exhibits a maximum
- (D) A body at 925 K emits an energy of 1.42 x 1011σW/m2 (σ
is the Stefan-Boltzmann constant) in the wavelength band between 3 μm to 4 μm.
The fraction of this energy in the total energy emitted over the entire
wavelength range is equal to emissivity
5. The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as
- (A) D-1.8
- (B) D-0.2
- (C) D0.2
- (D) D1.8
6. Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter).
- (A) 0.2 D
- (B) 0.5 D
- (C) 0.66 D
- (D) 0.80 D
7. For heat flow through very thick walled cylinder, use _________mean radius.
- (A) Arithmetic
- (B) Logarithmic
- (C) Geometric
- (D) Either (a) or (c)
8. Corrosiveness of steam condensate is due to the presence of
- (A) CO2
- (B) Dissolved O2
- (C) Both (a) & (b)
- (D) Neither (a) nor (b)
9. In a shell and tube heat exchanger, the shell side fluid velocity can’t be changed by changing the
- (A) Tube layout
- (B) Tube diameter
- (C) Tube pitch
- (D) Number of baffles
10. Solid angle subtended by the finite surface at the radiating element is
- (A) Called the view factor
- (B) Called the angle of vision
- (C) Proportional to the square of the distance between surfaces
- (D) Expressed in terms of radians
11. LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counter-flow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow.
- (A) Parallel
- (B) Mixed
- (C) Counter flow
- (D) Same in either 'a', b' or 'c'
12. A sphere of radius 'R1' is enclosed in a sphere of radius 'R2'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is
- (A) 0
- (B) R2/(R1+R2)
- (C) 1
- (D) (R1/R2)2
13. The maximum heat transfer co-efficient from steam heating will be attained when the steam is:
- (A) Supersaturated
- (B) Saturated
- (C) Wet
- (D) None of these
14. One kilogram of water at 0°C is changed to superheated steam of one atm pressure and 300° C. The major heat consumption in the process will be to
- (A) Heat the water from 0°C to 100°C
- (B) Evaporate the water
- (C) To superheat the steam
- (D) Data insufficient, can't be predicted
15. The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is
- (A) More
- (B) Less
- (C) Some
- (D) Either more or less; depends on the nature of vapor
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