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# Fluid Mechanics MCQ – Area Velocity Relationship for Compressible Flow

The exit velocity in the nozzle increases as per __________

a) Stagnation point

b) Continuity equation

c) Prandtl Number

d) Newton’s law

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Answer: b

Explanation: In the nozzle, the exit velocity of the fluid increases as per the continuity equation. Continuity equation is given as Av= constant as per the Bernoulli’s equation. It is essential for an incompressible flow.

With the increase in pressure, the exit velocity _________

a) Decreases

b) Increases

c) Same

d) Independent

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Answer: a

Explanation: Pressure is inversely proportional to the velocity. So, with the increase in pressure, the exit velocity decreases. We know that the pressure is equal to force per unit area, this contradicts the above statement.

The Prandtl Number approximates ___________

a) Momentum diffusivity to thermal diffusivity

b) Thermal diffusivity to momentum diffusivity

c) Shear stress to thermal diffusivity

d) Thermal diffusivity to kinematic viscosity

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Answer: a

Explanation: The Prandtl number is a dimensionless number. It approximates the ratio of momentum diffusivity to thermal diffusivity. It can be expressed as Pr = v/ α(1). Where α= thermal diffusivity and v= momentum diffusivity.

Pumps increase __________

a) Pressure

b) Velocity

c) Momentum

d) Heat

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Answer: a

Explanation: Pumps increase pressure rather than velocity. During the pumping process, a housing is provided for the pumping elements. These parts can change the speed. Pumps create a passage way that will squirt the fluid passing through it. Thus, pumping increases pressure.

Which among the following is the formula for volumetric flow rate?

a) Q = v/A

b) Q = Av

c) Q = A+v

d) Q = A-v

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Answer: b

Explanation: Volumetric flow rate is given by Q= A.v. Where v is the flow velocity of the fluid, and A is the area of cross section of the surface. Area of a surface is also called as the vector area. Thus, the right answer is Q = Av.

Which among the following is the formula for mass flow rate?

a) Q = m/p

b) Q = mp

c) Q = m + p

d) Q = m – p

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Answer: b

Explanation: Mass flow rate is given by Q=m/p. This is a relation expressed for mass flow rate. When ‘m’ is the mass flow rate. And, p is the density of the fluid flow. They are expressed in their standard units.

Compressible flow is a flow that deals with ______

a) Fluid temperature

b) Fluid pressure

c) Fluid density

d) Fluid geometry

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Answer: c

Explanation: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies in the change in fluid density. Thus, the correct option is Fluid density .

Answer: c

Explanation: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies in the change in fluid density. Thus, the correct option is Fluid density .

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Answer: c

Explanation: Compressible flow is a branch of fluid mechanics that deals with different types of flow. Its main significance lies in the change in fluid density. It deals with gas dynamics.

Which among the following is an assumption of the compressible flow?

a) Resistance to flow of object

b) No-slip condition

c) Known mass flow rate

d) Resistance to flow of heat

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Answer: b

Explanation: The related assumption of a compressible fluid flow is No-slip condition. It is assumed that the flow velocity at the solid surface is equal to the velocity of the surface itself. It is in direct consequence with the continuum flow.

What is Mach number?

a) Speed of object * speed of sound

b) Speed of object /speed of sound

c) Speed of object + speed of sound

d) Speed of object- speed of sound

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Answer: b

Explanation: Mach number is defined as the ratio of the speed of an object to the speed of sound. Mach number is denoted by ‘M’. Mach number ranges from zero to infinity. It falls into several flow regimes.