# Chapter 6: Fluids Engineering

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

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

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.

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

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.

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

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

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.

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 = ?

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

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

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

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.

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.

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

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.

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?

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

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

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

HYDRAULIC POWER

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.

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

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.

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.

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.

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

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

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=?

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=?