Two Marks questions and answers

TWO MARKS QUESTIONS AND ANSWERS

1. Distinguish between gauge and absolute pressures. Give the relationship between them.

If the pressure is measured with reference to the atmospheric pressure, then it is called gauge pressure. The pressure measured with respect to vacuum is called an absolute pressure.

Relationship: Absolute pressure = Gauge pressure + Atmospheric pressure

2. State Pascal's law (or) State the basic law that is important in applying fluid power. 

Pascal's law states that the pressure generated at any point in a confined fluid acts equally in all directions.

3. Name any two applications of Pascal's law.

1. Bramah's hydraulic press.

2. Air-to-hydraulic pressure booster.

4. What is the purpose of a hydraulic press ?

The hydraulic press amplifies the hydraulic force in the hydraulic systems. That is, in a hydraulic press a small input force is applied to generate a large output force.

5. What is the use of air-to-hydraulic pressure booster?

The air-to-hydraulic pressure booster is a device used for converting compressed air into the higher hydraulic pressure, which is required for operating hydraulic cylinders.

6. Differentiate between laminar and turbulent flow.

• A laminar flow is one in which paths taken by the individual particles do not cross one another and move along well-defined paths. The laminar flow is characterised by the fluid flowing in smooth layers of laminae.

• A turbulent flow is that flow in which fluid particles move in a zig-zag way. The turbulent flow is characterised by continuous small fluctuations in the magnitude and direction of the velocity of the fluid particles.

7. What is Reynold's number? Write its significance with reference to fluid power systems. 

where

ρ = Density of the liquid,

V = Velocity of flow,

D = Diameter of the pipe,

μ = Absolute viscosity of the fluid, and

v = Kinematic viscosity of the fluid.

Reynold's number is the basis for determining the laminar and turbulent flow. If Re < 2000, then the flow is laminar; and if Re > 4000, then the flow is turbulent.

8. Name two causes of turbulence in fluid flow.

(i) More resistance to flow.

(ii) Greater energy loss.

9. If the temperature increases so that the fluid viscosity decreases, would the Reynolds number increase, decrease, or remain the same?

Since Re = ρVD / μ = VD/ v, any decrease in fluid viscosity would increase the Reynolds number.

10. What is meant by flow rate?

Flow rate (or discharge) is the volume of the liquid flowing through a pipe in a specific period of time. Mathematically, Q = V/t = A × V

11. State the continuity equation.

Continuity equation states as: "If no fluid is added or removed from the pipe in any length then the mass passing across different sections shall be same". Mathematically, 

A1V1 = A2V2 = A3V3

12. State Bernoulli's equation.

Bernoulli's equation states as follows: "In an ideal, incompressible fluid when the flow is steady and continuous, the sum of potential energy, kinetic energy and pressure energy is constant across all cross sections of the pipe." Mathematically,

13. List out the various energy losses when liquid flows through a pipe.

1. Major energy losses

This loss is due to friction.

2. Minor energy losses

These losses are due to:

(i) Losses in valves and pipe fittings.

(ii) Sudden enlargement/Contraction of pipe.

(iii) Bend in pipe, etc.

14. Explain the term friction factor. 

Friction factor is a dimensionless number required to calculate the energy losses due to friction in the pipe. For laminar flow, the friction factor 'f' is function of Reynolds number only whereas for turbulent flow 'f' is a function of Reynolds number as well as the relative roughness of the pipe.

15. Give the Darcy's equation. What is the use of it?

The Darcy's equation for the head losses in pipes is as follows:

The Darcy's equation is used to calculate the energy losses due to friction in the pipe. 

16. Write down the Hagen-Poiseuille equation.

The Hagen-Poiseuille, to find frictional losses in laminar flow, is as follows:

17. Give the expression used to determine friction factor for laminar flow through pipes. 

For laminar flow, the friction factor (ƒ) is function of Reynolds number only and is given by f = 84/Re.

18. Define the term relative roughness.

The relative roughness is defined as the pipe inside surface roughness (ɛ) divided by the inside diameter of the pipe (D).

⸫ Relative roughness = ɛ/D

19. What is a Moody diagram? Write its use.

• The Moody diagram contains many curves. The curves indicate the value of friction factor as a function of Reynolds number and relative roughness.

• The Moody diagram can be used to determine the friction factor for use in Darcy's equation.

20. Give the expression to calculate the loss of head in the valves and fittings of a pipe.

The loss of head in the various valves and fittings is given by :

21. Write the procedure to calculate the pressure drop in hydraulic circuits.

If the loss of head H1 is known, it can be expressed into equivalent pressure drop by using the relation,

where

woil = Weight density of oil flowing through valves and fittings.

22. Name any three flow-measuring devices.

1. Rotometer,

2. Turbine flowmeter, and

3. Orifice flowmeter.

23. Name any two pressure-measuring devices.

1. Bourdam gauge, and, 2. Schrader gauge.

REVIEW QUESTIONS

1. Write Pascal's law. Explain any one applications of Pascal's law with neat diagram. 

 [Ans. Refer Section 3.5]

2. Explain the working principle of hydraulic press with neat sketch.

 [Ans. Refer Section 3.5.1]

3. Differentiate between laminar and turbulent fluid flow with examples.

 [Ans. Refer Section 3.6]

4. What is Reynolds number? How is Reynolds number determined?

 [Ans. Refer Section 3.7]

 [Ans. Refer Section 3.15]

5. Explain how Bernoulli's equation can be used to determine the pressure drop between two stations in a hydraulic system. Assume that there are some number of bends, tees, elbows, globe and gate valves in between these two stations separated by a long distance. 

[Ans. Refer Sections 3.11 to 3.15]

6. Write short notes on Darcy's equation.

 [Ans. Refer Section 3.14]

7. What is Moody diagram? Explain the important characteristics of it.

 [Ans. Refer Section 3.14.2]

8. Write short notes on frictional losses in laminar and turbulent flow. (or) How can you measure the frictional losses in laminar flow and turbulent flow?

 [Ans. Refer Sections 3.14.1 & 3.14.2]

9. List the various valves and fittings used in hydraulic systems. How to calculate frictional losses in common valves and fittings.

10. How losses take place in valves and fittings? Explain the significance of 'K' factor. 

 [Ans. Refer Section 3.15]