Practice Core Heat Transfer Question & Answers for GATE - Set 24 - ObjectiveBooks
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# Practice Test: Question Set - 24

1. The film thickness for laminar film condensation on vertical surface __________ from top to bottom.
(A) Cumulatively increases
(B) Cumulatively decreases
(C) Remain constant
(D) And the surface conductance increase

2. A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is
(A) 5.6
(B) 0.025
(C) 3.5
(D) 0.0035

3. __________ paint has the minimum absorption co-efficient.
(A) Black
(C) Grey
(D) Light cream

4. The value of Stefan-Boltzmann constant in SI unit is
(A) 5.6697 × 10-8W/m2.°K4
(B) 0.1714 × 10-8W/m2.°K4
(C) 5.6697 × 10-8kcal/m2. °K4
(D) 0.1714 × 10-8kcal/m2. °K4

5. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area
(A) Increases
(B) Decreases
(C) Remain constant
(D) Passes through a maxima

6. What is the thermal conductivity of a perfect heat insulator?
(A) Zero
(B) One
(C)
(D) Between 0 and ∞

7. Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called
(B) Natural convection
(C) Forced convection
(D) Conduction

8. The ratio of momentum diffusivity to thermal diffusivity is the __________ number.
(A) Prandtl
(B) Nusselt
(C) Stanton
(D) Grashoff

9. Steam traps are provided in steam carrying pipelines to
(A) Condense steam
(B) Release excess steam pressure by bleeding steam
(C) Remove condensate and inert gases
(D) None of these

10. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
(A) 555
(B) 55.5
(C) 0.55
(D) 0.15

11. Kirchoff’s law applies to __________ radiation.
(A) Total
(B) Monochromatic
(C) Both (a) & (b)
(D) Neither (a) nor (b)

12. Heat transfer occurs by natural convection because change in temperature causes difference in
(A) Viscosity
(B) Density
(C) Thermal conductivity
(D) Heat capacity

13. Log mean temperature difference (LMTD) cannot be used, if
(A) Heat transfer co-efficient over the entire heat exchanger is not constant
(B) There exists an unsteady state
(C) The heat capacity is not constant and there is a phase change
(D) None of these

14. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as
(A) (ΔT)1/4
(B) (ΔT)1/2
(C) (ΔT)5/4
(D) (ΔT)3/4

15. Pick out the wrong statement.
(A) In case of heat transfer by purely forced convection, GR/Re2 ≤ 1
(B) The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x
(C) Distillation process is not the same as evaporation
(D) The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface

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