1. Chapter 6: Fluids Engineering
An Introduction to Mechanical Engineering, 3rd Edition Wickert & Lewis
Fluids Engineering
Chapter 6:

2. Chapter 6 Lesson Objectives
Understand key aspects of fluid power
Manipulate key equations for fluid mechanics
Ideal gas equations
Pressure relationships
Practical Applications

3. © 2013 Cengage Learning Engineering. All Rights Reserved.
An Introduction to Mechanical Engineering, 3rd Edition Wickert & Lewis
© 2013 Cengage Learning Engineering. All Rights Reserved.

4. Pneumatic Power Pneumatics
The use of a gas flowing under pressure to transmit power from one location to another
Gas in a pneumatic system behaves like a spring since it is compressible.
Air is most commonly used in pneumatic systems, although some systems use nitrogen. Pure nitrogen may be used if there is a danger of combustion in a work environment.

5. Pneumatics vs. Hydraulics
Pneumatic Systems . . .
Use a compressible gas
Possess a quicker, jumpier motion
Are not as precise
Require a lubricant
Are generally cleaner
Often operate at pressures around 100 psi
Generally produce less power

6. Early Pneumatic Uses Otto von Guericke
Showed that a vacuum can be created
Created hemispheres held together by atmospheric pressure
Von Guericke held public demonstrations in Germany during the 1660s where teams of horses tried to pull apart hemispheres held together by atmospheric pressure created using a pump.

7. Early Pneumatic Uses America’s First Subway Designed by Alfred Beach
Built in New York City
Completed in 1870
312 feet long, 8 feet in diameter
Closed in 1873

8. Properties of Gases Gases are affected by 3 variables Temperature (T)
Pressure (p)
Volume (V)
Gases have no definite volume
Gases are highly compressible
Gases are lighter than liquids

9. Pascal’s Law
Pressure exerted by a confined fluid acts undiminished equally in all directions.
Pressure: The force per unit area exerted by a fluid against a surface
Symbol
Definition
Example Unit p
Pressure
lb/in.2 F
Force lb A
Area
in.2
The area of a cylinder will be the surface area of the piston.

10. Pascal’s Law Example
How much pressure can be produced with a 3 in. diameter (d) cylinder and 50 lb of force?
d = 3 in. p = ?
F = 50 lb A = ?

11. Ideal Gas Law Manipulation
The perfect gas laws describe the behavior of pneumatic systems
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law

12. Boyle’s Law
The volume of a gas at constant temperature varies inversely with the pressure exerted on it.
NASA
p1 (V1) = p2 (V2)
Symbol
Definition
Example Unit V
Volume
in.3

13. Boyle’s Law Example
A cylinder is filled with 40. in.3 of air at a pressure of 60. psi. The cylinder is compressed to 10. in.3. What is the resulting absolute pressure?
p1 = 60. lb/in.2 V1 = 40. in.3
p2 = ? V2 = 10. in.3
Convert p1 to absolute pressure.
p1 = 60. lb/in lb/in.2 = 74.7 lb/in.2

14. Charles’ Law
Volume of gas increases or decreases as the temperature increases or decreases, provided the amount of gas and pressure remain constant.
NASA
Note: T1 and T2 refer to absolute temperature.

15. Charles' Law Example
An expandable container is filled with 28 in.3 of air and is sitting in ice water that is 32°F. The container is removed from the icy water and is heated to 200.°F. What is the resulting volume?
V1 = 28in.3
V2 = ?
T1 = 32°F
T2 = 200.°F
Convert T to absolute temperature.
T1 = 32°F °F =492°R
T2 = 200.°F °F =660°R
The temperature readings must be converted to absolute temperature in order for the equation to work.

16. Charles' Law Example
An expandable container is filled with 28 in.3 of air and is sitting in ice water that is 32°F. The container is removed from the icy water and is heated to 200°F. What is the resulting volume?
V1 = 28in.3
V2 = ?
T1 = 32°F
T2 = 200.°F

17. Gay-Lussac’s Law
Absolute pressure of a gas increases or decreases as the temperature increases or decreases, provided the amount of gas and the volume remain constant.
Note: T1 and T2 refer to absolute temperature.
p1 and p2 refer to absolute pressure.

18. Gay-Lussac’s Law Example
A 300. in.3 sealed air tank is sitting outside. In the morning the temperature inside the tank is 62°F, and the pressure gauge reads 120. lb/in.2. By afternoon the temperature inside the tank is expected to be close to 90.°F. What will the absolute pressure be at that point?

19. Gay-Lussac’s Law Example
A 300 in.3 sealed air tank is sitting outside. In the morning the temperature inside the tank is 62°F, and the pressure gauge reads 120 lb/in2. By afternoon the temperature inside the tank is expected to be closer to 90°F. What will the absolute pressure be at that point?
If the absolute pressure is lb/in.2, what is the pressure reading at the gauge?
141.9 lb/in.2 – 14.7 lb/in.2 = lb/in.2
= 130 lb/in.2

20. Pneumatic Power Pneumatic power Pneumatics vs. hydraulics
Early pneumatic uses
Properties of gases
Pascal’s Law
Perfect gas laws
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
Common pneumatic system components
Compressor types
Future pneumatic possibilities

21. Future Pneumatic Possibilities
What possibilities may be on the horizon for pneumatic power?
Could it be human transport?
zapatopi.net

22. HYDRAULIC POWER

23. Hydraulic Power Hydraulics
The use of a liquid flowing under pressure to transmit power from one location to another
Liquid in a hydraulic system behaves like a solid since it compresses very little
Oil is most often used in hydraulic systems, although other systems also may use synthetic oils or water.

24. Hydraulic Power
At least two examples of hydraulic power are visible on the fire truck.

25. Early Hydraulic Uses Water Wheels Create rotational motion
Descriptions exist as early as 1st century BC
Several examples in ancient China
Grist mill is pictured
Modern turbines in hydro-powered dams are a sophisticated version of the water wheel used to create electricity.

26. Most common in industrial settings
Hydrostatic Systems
Fluid is at rest
Fluid is pressurized
Pressure creates force and energy
Most common in industrial settings
National Fluid Power Association & Fluid Power Distributors Association
Pneumatic systems can also be referred to as hydrostatic since such systems are often pressurized.

27. Hydrostatic Systems
Pascal’s Law Pressure exerted by a confined fluid acts undiminished equally in all directions
Click the arrows to activate the hydraulic press.

28. Mechanical Advantage Example
A force of 100. lb is applied to the input cylinder of the hydraulic press seen below. What is the pressure in the system? How much force can the output cylinder lift? What is the mechanical advantage of the system?
din = 4.0 in.
Fin = 100. lb
Fin = 100. lb Fout = ?
din = 4.0 in dout = 12.0 in.
Ain = ? Aout = ?
p = ? MA = ?
dout = 12.0 in

29. Mechanical Advantage Example
Find the area of each cylinder.
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=? Aout=? p=? MA=?

30. Mechanical Advantage Example
Find the pressure in the system.
Fin=100. lb Fout=? Rin=2.0 in. Rout=6.00 in.
Ain=12.57 in Aout= in p=? MA=?

31. Mechanical Advantage Example
Find the force that the output cylinder can lift.
Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout= in p=7.955 lb/in MA=?

32. Mechanical Advantage Example
Find the mechanical advantage of the system.
Fin=100. lb Fout= lb Rin=2.0 in. Rout =6.00 in.
Ain=12.57 in.2 Aout= in p=7.955 lb/in MA=?

33. Emerging Hydraulic Application Example
Hydraulic Hybrid Vehicles
Braking provides stored energy that is used to propel the vehicle forward.
UPS™ expects 60-70% better fuel economy and 40% reduction in CO2 emissions.
Although this technology is being explored for other purposes, delivery trucks can benefit from such technology because of frequent stops and starts.
This hybrid allows for a smaller engine, resulting in better gas mileage and lower emissions. During braking a hydraulic hybrid converts the potential energy of the vehicle in motion to hydraulic pressure stored in the fluid power equivalent of a battery, which is called an accumulator. This stored energy can then be reused during the acceleration process.
For more information visit
UPS