Heat Transfer Questions and Solutions - Set 17 - ObjectiveBooks

# Practice Test: Question Set - 17

1. Natural convection is characterized by
(A) Grashoff number
(B) Peclet number
(C) Reynolds number
(D) Prandtl number

2. Colburn analogy is applicable for the value of Prandtl number from
(A) 0.001 to 1
(B) 0.6 to 120
(C) 0.5 to 5
(D) 120 to 400

3. A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1. A 1 - 1 shell and tube heat exchanger is available. The best arrangement is
(A) Counter flow with process stream on shell side
(B) Counter flow with process stream on tube side
(C) Parallel flow with process stream on shell side
(D) Parallel flow with process stream on tube side

4. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be
(A) W/m.k
(B) W/m
(C) W/m.k2
(D) None, 'a' is just a number

5. Heat exchanger tubes are never made of
(A) Plain carbon steel
(B) Stainless steel
(D) Copper

6. Presence of a non-condensing gas in a condensing vapor
(A) Increases the rate of condensation
(B) Decreases thermal resistance
(C) Is desirable to increase the film co-efficient
(D) None of these

7. The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe)
(A) K/h0
(B) 2K/h0
(C) hi/K
(D) 2hi/K

8. Multiple effect evaporators are commonly used in the manufacture of
P. Paper
Q. Superphosphate
R. Sugar
S. Fats
(A) P and Q
(B) P and R
(C) P and S
(D) R and S

9. In natural convection heat transfer, the correlating parameter is the
(A) Graetz number
(B) Eckert number
(C) Grashoff number
(D) Bond number

10. Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is
(A) Finned tube heat exchanger with air inside and steam outside
(B) Finned tube heat exchanger with air outside and steam inside
(C) Shell and tube heat exchanger with air inside tubes and steam on shell side
(D) Shell and tube heat exchanger with air on shell side and steam inside tubes

11. In a multiple effect evaporator, the effect of boiling point elevation is to
(A) Reduce the capacity
(B) Reduce the economy
(C) Increase the economy
(D) None of these

12. Correction is applied to LMTD for __________ flow.
(A) Parallel
(B) Counter
(C) Cross
(D) None of these

13. The heat flux in the nucleate boiling regimes is proportional to (where, Î”T = excess temperature)
(A) (Î”T)2
(B) (Î”T)4
(C) (Î”T)3
(D) √(Î”T)

14. Increasing the liquor level in the evaporator results in the
(A) Decreased capacity
(B) Increase in liquor film co-efficient
(C) Decreased effect of hydrostatic head
(D) Increased true temperature drop

15. In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased.
(A) Velocity of circulation
(B) Liquor-film co-efficient
(C) Both (a) and (b)
(D) Neither (a) and (b)

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