# Fluid Mechanics Questions and Answers – Flow through Nozzles

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This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Flow through Nozzles”.

1. When a gas is pushed through a pipe, the gaseous molecules are _________ by the pipe’s walls
a) Attracted
b) Absorbed
c) Deflected
d) Dissipated

Explanation: This is because there is no attractive force present in the tube for the process of attraction to occur. Also, the surface of pipes is not an absorbing one, hence absorption is also ruled out. A pipe is not capable of dissipation of the molecules. Hence, the right option is deflected.

2. If the speed of sound is much ________ than that of the gas, the gas density will stay constant.
a) Smaller
b) Larger
c) Equal to
d) Non-existent

Explanation: This is because only with speed of sound Is larger, it’ll be able to compensate for the speed of gas. Under such situations, the gas density will be able to stay constant. If they are equal, density will get compressed.

3. Isentropic nozzle flow states about the movement of a gas or fluid through a narrow orifice without an increase or decrease in ___________
a) Pressure
b) Energy
c) Displacement
d) Entropy

Explanation: Entropy is defined as the measure of degree of randomness. It is a thermodynamics quantity. As this nozzle flow deals with thermodynamics, entropy is the right choice. The other options are not parameters of entropy.
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4. In fluid dynamics, the velocity of the fluid in the stagnation point is
a) Zero
b) Infinite
c) Non-existent
d) Negative

Explanation: Stagnant point is a point where there is no movement of the fluid. When there is no movement, the velocity will be 0. Hence the answer is 0.

5. The stagnation state is obtained after a _____________ to zero velocity.
a) Accelerating
b) Decelerating
c) Equilibrium
d) Exponential increase

Explanation: Initially the flow has a velocity. In the stagnant state, the velocity is 0. For this to happen, there should be a deceleration of the velocity. Hence, deceleration is the answer.

6. To refrain from separation in subsonic nozzles, the expansion angle must not be more than _____
a) 10 degrees
b) 20 degrees
c) 30 degrees
d) 40 degrees

Explanation: If the angle is more than 10 degrees, there will be a drift amidst the nozzle. At any angle more than 10 degrees, this separation will occur. But the minimum value is 10 degrees. So, the answer is 10 degrees.

7. Gas flows through the nozzle from an area of _____ pressure (called the chamber) to one of _____ pressure
a) High, low
b) Low, high
c) Same, same
d) Constant, Infinite

Explanation: Anything that flows or runs moves from a region of higher value to lower value. We can take the example of any physical parameter like pressure, altitude etc. Hence, here the gas will flow from high to low pressure regions.

8. Converging-diverging nozzle is also known as __________
a) Pascal nozzle
b) Bernouille’s nozzle
c) Toricelli’s nozzle
d) de Laval’ nozzle

Explanation: This is because this nozzle was invented by Carl de Laval. So, it is also named after him. Hence De-Laval nozzle is the option.

9. When the pressure chamber is big, the flow velocities are _________
a) Large
b) Negligible
c) Constant
d) Increasing

Explanation: When the chamber is large, the area is high. Velocity is inversely proportional to area. So in a large chamber, the flow velocity will be less. It will be negligible.

10. For a compressible, ideal gas, mass flow rate depends on parameters such as flow area, pressure, temperature, properties of the gas, and _________
a) Avogardo’s Number
b) Mach Number
c) Reynold’s Number
d) Le-Grange’ Number

Explanation: Mass flow rate should depend on the velocity. Here Mach number denotes the velocity. So, the Mach number gives the right answer.

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