Questions and answers for exam Preparation

MCQs

Total Questions : 63 | Page 3 of 7 pages

Question 21. Saturated steam is allowed to condense over a vertical flat surface and the condensate film flows down the surface. The local coefficient of heat transfer for condensation

Remains constant at all heights of the surface
Decreases with increasing distance from the top of the surface
Increases with increasing thickness of film
Increases with increasing temperature differential between the surface and vapour

Discuss Question

Answer: Option B. -> Decreases with increasing distance from the top of the surface
Answer: (b).Decreases with increasing distance from the top of the surface

Question 22. A plate condenser was designed to be kept vertical. How would the condensation coefficient be effected if due to site constraints, it has to be kept at 60 degree to the horizontal?

1.53% reduction in condensation coefficient
2.53% reduction in condensation coefficient
3.53% reduction in condensation coefficient
4.53% reduction in condensation coefficient

Discuss Question

Answer: Option C. -> 3.53% reduction in condensation coefficient
Answer: (c).3.53% reduction in condensation coefficient

Question 23. For film wise condensation on a vertical plane, the film thickness δ and heat transfer coefficient h vary with distance x from the leading edge as

δ decreases, h increases
Both δ and h increases
δ increases, h decreases
Both δ and h decreases

Discuss Question

Answer: Option C. -> δ increases, h decreases
Answer: (c).δ increases, h decreases

Question 24. In condensation over a vertical surface, the value of convection coefficient varies as

k^0.25
k^0.33
k^0.75
k^-0.5

Discuss Question

Answer: Option A. -> k^0.25
Answer: (a).k^0.25

Question 25. What is the value of surface fluid constant for water-copper combination?

0.010
0.011
0.012
0.013

Discuss Question

Answer: Option D. -> 0.013
Answer: (d).0.013

Question 26. A plate condenser of dimensions l * b has been designed to be kept with side l in the vertical position. However due to oversight during erection and installation, it was fixed with side b vertical. How would this affect the heat transfer? Assume laminar conditions and same thermos-physical properties and take b = l/2

The condenser should be installed with shorter side horizontal
The condenser should be installed with longer side horizontal
The condenser should be installed with longer side vertical
The condenser should be installed with shorter side vertical

Discuss Question

Answer: Option D. -> The condenser should be installed with shorter side vertical
Answer: (d).The condenser should be installed with shorter side vertical

Question 27. Determine the length of a 25 cm outer diameter tube if the condensate formed on the surface of the tube is to be same whether it is kept vertical or horizontal

61.5 cm
71.5 cm
81.5 cm
91.5 cm

Discuss Question

Answer: Option B. -> 71.5 cm
Answer: (b).71.5 cm

Question 28. Which of the following is a wrong statement in the context of a convective heat transfer coefficient in laminar film condensation?
The heat transfer coefficient varies as