Heat Transfer MCQ for GATE - Set 21 - ObjectiveBooks

# Practice Test: Question Set - 21

1. Economy of a multiple effect evaporator is not influenced much by the

(A) Boiling point elevations
(B) Temperature of the feed
(C) Rate of heat transfer
(D) Ratio of the weight of the thin liquor to thick liquor

2. For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is

(A) Forward
(B) Backward
(C) Parallel
(D) None of these

3. What is the absorptivity of a black body?

(A) 1
(B) 0
(C) 0.78
(D) 0.95

4. Multiple effect evaporators are used to

(A) Increase the steam economy & decrease the capacity
(B) Increase the steam economy & the capacity
(C) Decrease the steam economy & the capacity
(D) Decrease the steam economy & increase the capacity

5. The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, Î”T = Temperature drop across condensate film)

(A) (Î”T)2
(B) √(Î”T)
(C) (Î”T)1/4
(D) (Î”T)3/2

6. Heat transfer co-efficient (h1) for liquids increases with

(A) Increasing temperature
(B) Decreasing temperature
(C) Decreasing Reynolds number
(D) None of these

7. Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger?

(A) Corrosiveness
(B) Fouling characteristic
(C) Viscosity
(D) None of these

8. Steady state one dimensional heat flow by conduction as given by Fourier's low does not assume that

(A) There is no internal heat generation
(B) Boundary surfaces are isothermal
(C) Material is anisotropic

9. An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is

(A) 4000
(B) 9000
(C) 4600
(D) 3000

10. A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

(A) Higher economy
(B) Lower capacity
(C) Both (a) & (b)
(D) Lower economy

11. Analogy between mass and heat transfer is not applicable in case of

(A) Same velocity profile or equal eddy diffusivities
(B) Thermal or pressure mass diffusion
(C) Viscous heating or chemical reaction
(D) Both (b) and (c)

12. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be

(A) 15 min
(B) 22 min
(C) 44 min
(D) 51 min

13. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)

(A) K/h0
(B) 2K/h0
(C) h0/K
(D) h0/2K

14. Heat waves

(A) Cannot pass through vacuum
(B) Travel in straight line
(C) Can be reflected by a mirror
(D) Both (b) and (c)

15. Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be

(A) 0.35
(B) 0.45
(C) 0.55
(D) 0.85

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