Fluid Mechanics and Machinery MCQs | Page - 1

Dear candidates you will find MCQ questions of Fluid Mechanics and Machinery here. Learn these questions and prepare yourself for coming examinations and interviews. You can check the right answer of any question by clicking on any option or by clicking view answer button.

πŸ“Š Fluid Mechanics and Machinery
Q. The Reynolds number is found out for a flow in a circular pipe. This circular pipe is moulded into a square pipe, keeping length of the pipe same. Ignore the thickness of the pipe. The Reynolds number changes by
  • (A) 57% decrease
  • (B) 57% increase
  • (C) 43% decrease
  • (D) 43% increase
πŸ’¬ Discuss
βœ… Correct Answer: (B) 57% increase

Explanation: the reynolds number directly depends upon the hydraulic diameter of the pipe. suppose the diameter of the pipe is d, the hydraulic diameter of square pipe is 1.57d. hence, 57% increase.

πŸ“Š Fluid Mechanics and Machinery
Q. The flow through a circular pipe is laminar. Now, the fluid through the pipe is replaced with a more viscous fluid and passed through the pipe again with the same velocity. What can we say about the nature of this flow?
  • (A) the flow will become turbulent
  • (B) the flow will be a transition flow
  • (C) the flow will remain laminar
  • (D) the reynolds number of the earlier flow is required to answer this question
πŸ’¬ Discuss
βœ… Correct Answer: (C) the flow will remain laminar

Explanation: a flow through a circular pipe is said to be laminar when the reynolds

πŸ“Š Fluid Mechanics and Machinery
Q. What can be the maximum diameter of the pipe for the water flow of velocity 1 m/s (ν = 10-6) to be laminar in nature? Assume Lower critical Reynolds number to be 2100.
  • (A) 2.1 mm
  • (B) 21 mm
  • (C) 21 cm
  • (D) 0.21 mm
πŸ’¬ Discuss
βœ… Correct Answer: (A) 2.1 mm

Explanation: if the reynolds number of the flow is below its lower critical reynolds number, the flow is clearly laminar. the maximum diameter can be found for re = 2100. the diameter comes out to be 2.1 mm.

πŸ“Š Fluid Mechanics and Machinery
Q. Which of the following flows have the highest critical Reynolds number (lower)?
  • (A) flow in a pipe
  • (B) flow between parallel plates
  • (C) flow in an open channel
  • (D) flow around spherical body
πŸ’¬ Discuss
βœ… Correct Answer: (A) flow in a pipe

Explanation: the approximate lower critical reynolds number for flow in a pipe, flow between parallel plates, flow in an open channel and flow around the spherical body are 2000, 1000, 500 and 1 respectively.

πŸ“Š Fluid Mechanics and Machinery
Q. The flow separation occurs when the fluid travels away from the
  • (A) surface
  • (B) fluid body
  • (C) adverse pressure gradient
  • (D) inter-molecular spaces
πŸ’¬ Discuss
βœ… Correct Answer: (C) adverse pressure gradient

Explanation: adverse pressure gradient takes place when the static pressure increases. it increases the direction of the flow. adverse pressure gradient plays an important role in flow separation. thus, option c is correct.

πŸ“Š Fluid Mechanics and Machinery
Q. The swirl caused due to eddies are called as
  • (A) vortices
  • (B) vertices
  • (C) volume
  • (D) velocity
πŸ’¬ Discuss
βœ… Correct Answer: (A) vortices

Explanation: vortices are a region in a fluid. it takes place when the flow revolves around an axis line. vortices can be straight or curved. they form shapes like smoke rings and whirlpools.

πŸ“Š Fluid Mechanics and Machinery
Q. Eddy viscosity is a turbulent transfer of
  • (A) fluid
  • (B) heat
  • (C) momentum
  • (D) pressure
πŸ’¬ Discuss
βœ… Correct Answer: (C) momentum

Explanation: eddy viscosity is a turbulent transfer of momentum by eddies. it gives rise to an internal fluid friction. it is in analogous to the action of molecular viscosity in laminar fluid flow. eddy viscosity takes place on a large scale.

πŸ“Š Fluid Mechanics and Machinery
Q. Which among the following is a device that converts a laminar flow into a turbulent flow?
  • (A) dead weight gauge
  • (B) vacuum gauge
  • (C) turbulator
  • (D) ionization gauge
πŸ’¬ Discuss
βœ… Correct Answer: (C) turbulator

Explanation: turbulator is a device that converts a laminar flow into a turbulent flow. the turbulent flow can be desired parts of an aircraft or also in industrial applications.

πŸ“Š Fluid Mechanics and Machinery
Q. Boundary layer separation does not undergo detachment.
  • (A) true
  • (B) false
  • (C) ---
  • (D) ---
πŸ’¬ Discuss
βœ… Correct Answer: (B) false

Explanation: boundary layer separation undergoes detachment from the surface into a broader wake. it occurs mainly when the portion of the boundary layer is closest to the wall. it leads to reverse in the flow direction.

πŸ“Š Fluid Mechanics and Machinery
Q. With the boundary layer separation, displacement thickness
  • (A) increases
  • (B) decreases
  • (C) remains same
  • (D) independent
πŸ’¬ Discuss
βœ… Correct Answer: (A) increases

Explanation: with the boundary layer separation, displacement thickness increases sharply. this helps to modify the outside potential flow and its pressure field. thus, option ‘a’ is the correct choice.

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