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# Practice Test: Question Set - 25

1. 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 = 2hl
(C) ha = 0.5 hl
(D) ha = 0.75 hl

2. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is
(A) Minimum
(B) Maximum
(C) Zero
(D) Infinity

3. Harmonic mean temperature difference is given by
(A) √(ΔT1 . ΔT2)
(B) 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)
(C) 2 (ΔT1 . ΔT2)/(ΔT1 - ΔT2)
(D) T1 - ΔT2)/(ΔT1 . ΔT2)

4. Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is
(A) In the central core of the fluid
(B) Uniformly distributed throughout the fluid
(C) Mainly confined to a thin film of fluid near the surface
(D) None of these

5. 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid).
(A) 0.5
(B) 0.05
(C) 0.1
(D) 0.15

6. If Prandtl number is greater than the Schmidt number, then the
(A) Thermal boundary layer lies inside the concentration boundary layer
(B) Concentration boundary layer lies inside the thermal boundary layer
(C) Thermal & concentration boundary layers are of equal thickness
(D) Hydrodynamic (i.e., momentum) boundary layer is thicker than the other two

7. Fourier's law of heat conduction applies to __________ surfaces.
(A) Isothermal
(B) Non-isothermal
(C) Both (a) and (b)
(D) Neither (a) and (b)

8. Thermal diffusivity is the most important in heat transfer by
(A) Conduction
(C) Condensation
(D) Natural convection

9. Which of the following is generally considered as opaque surface towards radiations?
(A) Gases
(B) Solids
(C) Liquids
(D) Both (b) and (c)

10. LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is
(A) 0
(B) 1
(C) > 1
(D) < 1

11. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is
(A) Vertical heat exchanger with steam on tube side
(B) Vertical heat exchanger with steam on shell side
(C) Horizontal heat exchanger with steam on tube side
(D) Horizontal heat exchanger with steam on shell side

12. The statement that "maximum wavelength of radiation is inversely proportional to the temperature" is __________ law.
(A) Stefan-Boltzmann’s
(B) Planck's
(C) Wien's displacement
(D) None of these

13. The steam ejector is used to
(A) Remove condensate from the steam pipelines
(B) Create vacuum
(C) Superheat the steam
(D) None of these

14. Among liquids, water has a comparatively high value of thermal conductivity, due to its
(A) Low density
(B) High viscosity
(C) Partial ionization
(D) Dense structure

15. Heat flux is the time rate of heat transfer per unit
(A) Length
(B) Area
(C) Volume
(D) None of these

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