Questions and answers for exam Preparation

MCQs

Total Questions : 63 | Page 6 of 7 pages

Question 51. Identify the wrong statement with respect to boiling heat transfer?

The steam boilers employing natural convection have steam raised through pool boiling
Boiling occurs when a heated surface is exposed to a liquid and maintained at a temperature lower than the saturation temperature of the liquid
Leiden-frost effect refers to the phenomenon of stable film boiling
The nucleation boiling is characterized by the formation of bubbles at the nucleation sites and the resulting liquid agitation

Discuss Question

Answer: Option B. -> Boiling occurs when a heated surface is exposed to a liquid and maintained at a temperature lower than the saturation temperature of the liquid
Answer: (b).Boiling occurs when a heated surface is exposed to a liquid and maintained at a temperature lower than the saturation temperature of the liquid

Question 52. A 1.0 mm diameter and 300 mm long nickel wire is submerged horizontal in water at atmospheric pressure. At burnout, the wire has a current of 195 A. Calculate the voltage at burnout. The relevant thermos-physical properties are
p f (fluid) = 959.52 kg/m³
p g (vapor) = 0.597 kg/m³
h f g = 2257000 J/kg
σ = 0.0533 N/m

6.15 V
7.15 V
8.15 V
9.15 V

Discuss Question

Answer: Option B. -> 7.15 V
Answer: (b).7.15 V

Question 53. Condensation refers to a change from the

Solid to a liquid phase
Vapor to a liquid phase
Liquid to a solid phase
Liquid to a vapor phase

Discuss Question

Answer: Option B. -> Vapor to a liquid phase
Answer: (b).Vapor to a liquid phase

Question 54. What is the value of surface fluid constant for water-brass combination?

0.004
0.005
0.006
0.007

Discuss Question

Answer: Option C. -> 0.006
Answer: (c).0.006

Question 55. Spherical bubbles of 3 mm diameter are observed in the bulk fluid boiling of water at standard atmospheric pressure. Assuming pure water vapor in the bubble and vapor pressure equal to 101.325 k N/m², calculate the temperature of the vapor

100.217 degree Celsius
200.217 degree Celsius
300.217 degree Celsius
400.217 degree Celsius

Discuss Question

Answer: Option A. -> 100.217 degree Celsius
Answer: (a).100.217 degree Celsius

Question 56. An electric wire of 1.25 mm diameter and 250 mm long is laid horizontally and submerged in water at 7 bar. The wire has an applied voltage of 2.2 V and carries a current of 130 amperes. If the surface of the wire is maintained at 200 degree Celsius, make calculations for the heat flux

0.0915 * 10⁶ W/m²
0.1915 * 10⁶ W/m²
0.2915 * 10⁶ W/m²
0.3915 * 10⁶ W/m²

Discuss Question

Answer: Option C. -> 0.2915 * 10⁶ W/m²
Answer: (c).0.2915 * 10⁶ W/m²

Question 57. Which of the following parameters affect burnout heat flux in the nucleate boiling region
(i) Heat of evaporation
(ii) Temperature difference
(iii) Density of vapor
(iv) Density of liquid
(v) Surface tension at the vapor-liquid interface
Mark the correct answer from the codes indicated below

i, ii, iii and v
i, iii, iv and v
i, ii, iii and iv
i, iii and v

Discuss Question

Answer: Option B. -> i, iii, iv and v
Answer: (b).i, iii, iv and v

Question 58. All the following statements are correct, except

Nucleate boiling gets promoted on a smooth surface
In subcooled heating, the temperature of the heating surface is more than the boiling point of the liquid
Film boiling region is usually avoided in commercial equipment
There occurs transition from nucleate to film boiling burn-out point on the boiling curve

Discuss Question

Answer: Option A. -> Nucleate boiling gets promoted on a smooth surface
Answer: (a).Nucleate boiling gets promoted on a smooth surface

Question 59. Milk spills over when it is boiled in an open vessel. The boiling of milk at this instant is referred to as

Interface evaporation
Sub-cooled boiling
Film boiling
Saturated nucleate boiling

Discuss Question

Answer: Option B. -> Sub-cooled boiling
Answer: (b).Sub-cooled boiling

Question 60. For laminar film condensation on a vertical plate, the mass flow rate of the condensate per unit depth of the film at any position x is given by