# Natural Convection and Forced Convection - 2 - MCQs with Answers

## Natural Convection and Forced Convection – 2 – MCQs with Answers

1. 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: d. hydrodynamic entry region

2. What is hydrodynamically 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: b. a region where velocity profile of the fluid is fully developed

3. 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: d. Grashof number (Gr)

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: c. Gr and Pr

5. 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: c. (Gr / Re2) >> 1

6. 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: b. Reynolds number (Re)

7. 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