Convection - Mechanical Engineering (MCQ) questions and answers

1)   The Grashof number in natural convection plays same role as

a. Prandtl number (Pr) in forced convection
b. Reynolds number (Re) in forced convection
c. Nusselt number (Nu) in forced convection
d. none of the above
Answer  Explanation 

ANSWER: Reynolds number (Re) in forced convection

Explanation:
No explanation is available for this question!


2)   If there are no externally induced flow velocities, then the Nusselt number (Nu) does not depend upon

a. Prandtl number (Pr)
b. Reynolds number (Re)
c. Grashof number (Gr)
d. none of the above
Answer  Explanation 

ANSWER: Reynolds number (Re)

Explanation:
No explanation is available for this question!


3)   Which of the following condition is correct for natural convection?

a. (Gr / Re2) = 1
b. (Gr / Re2) << 1
c. (Gr / Re2) >> 1
d. none of the above
Answer  Explanation 

ANSWER: (Gr / Re2) >> 1

Explanation:
No explanation is available for this question!


4)   In natural convection, the Nusselt number (Nu) depends on

a. Pr and Re
b. Gr and Re
c. Gr and Pr
d. none of the above
Answer  Explanation 

ANSWER: Gr and Pr

Explanation:
No explanation is available for this question!


5)   What is the ratio of the buoyancy force to the viscous force acting on a fluid called?

a. Prandtl number (Pr)
b. Reynolds number (Re)
c. Nusselt number (Nu)
d. Grashof number (Gr)
Answer  Explanation 

ANSWER: Grashof number (Gr)

Explanation:
No explanation is available for this question!


6)   What is hydro-dynamically developed region in fluid flowing inside a pipe?

a. a region where velocity profile of the fluid is partially developed
b. a region where velocity profile of the fluid is fully developed
c. a region where velocity profile of the fluid changes according to the distance
d. none of the above
Answer  Explanation 

ANSWER: a region where velocity profile of the fluid is fully developed

Explanation:
No explanation is available for this question!


7)   Assume fluid flowing in a tube forcefully. The velocity boundary layer develops along the tube. Thickness of this boundary layer increases in the flow direction until the boundary layer reaches the tube centre. This region from the tube inlet to the point at which the boundary layers merge at the centerline is called as

a. laminar entry region
b. hydraulic entry region
c. hydrostatic entry region
d. hydrodynamic entry region
Answer  Explanation 

ANSWER: hydrodynamic entry region

Explanation:
No explanation is available for this question!


8)   Below figure shows a natural convection heat transfer on a horizontal flat plate and fluid is above it. Which condition satisfies the figure below?

a. Plate temperature is lower than the fluid temperature
b. Plate temperature is higher than the fluid temperature
c. Plate temperature is equal to the fluid temperature
d. unpredictable
Answer  Explanation 

ANSWER: Plate temperature is higher than the fluid temperature

Explanation:
No explanation is available for this question!


9)   Assume a natural convection heat transfer on a vertical flat plate surrounded by a fluid. Where will be the fully developed turbulent layer of fluid established, if the plate is hotter than the fluid?

a. At the bottom of the plate
b. At the middle of the plate
c. At the top of the plate
d. Nowhere
Answer  Explanation 

ANSWER: At the top of the plate

Explanation:
No explanation is available for this question!


10)   Below figure shows a natural convection heat transfer on a vertical flat plate surrounded by a fluid.
What is the relation between the upward velocity of the fluid and the distance from the bottom of the plate, when plate is hotter that fluid?


a. as the distance from the bottom of the plate increases, the upward velocity of the fluid near the plate surface decreases
b. as the distance from the bottom of the plate increases, the upward velocity of the fluid near the plate surface increases
c. the upward velocity of the fluid near the plate surface is same all over the plate
d. unpredictable
Answer  Explanation 

ANSWER: as the distance from the bottom of the plate increases, the upward velocity of the fluid near the plate surface increases

Explanation:
No explanation is available for this question!


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