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

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

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

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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.

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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

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Early Pneumatic Uses Otto von Guericke Showed that a vacuum can be created Created hemispheres held together by atmospheric pressure

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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

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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

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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 SymbolDefinitionExample Unit p Pressurelb/in. 2 F Forcelb A Areain. 2

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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 lbA = ?

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

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Boyle’s Law The volume of a gas at constant temperature varies inversely with the pressure exerted on it. p 1 (V 1 ) = p 2 (V 2 ) NASA SymbolDefinitionExample Unit V Volumein. 3

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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? p 1 = 60. lb/in. 2 V 1 = 40. in. 3 p 2 = ?V 2 = 10. in. 3 Convert p 1 to absolute pressure. p 1 = 60. lb/in. 2 + 14.7 lb/in. 2 = 74.7 lb/in. 2

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Charles’ Law Volume of gas increases or decreases as the temperature increases or decreases, provided the amount of gas and pressure remain constant. Note: T 1 and T 2 refer to absolute temperature. NASA

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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? V 1 = 28in. 3 V 2 = ? T 1 = 32°F T 2 = 200.°F Convert T to absolute temperature. T 1 = 32°F + 460.°F =492°R T 2 = 200.°F + 460.°F =660°R

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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? V 1 = 28in. 3 V 2 = ? T 1 = 32°F T 2 = 200.°F

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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: T 1 and T 2 refer to absolute temperature. p 1 and p 2 refer to absolute pressure.

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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?

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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 closer to 90°F. What will the absolute pressure be at that point? If the absolute pressure is 141.9 lb/in. 2, what is the pressure reading at the gauge? 141.9 lb/in. 2 – 14.7 lb/in. 2 = 127.2 lb/in. 2 = 130 lb/in. 2

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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

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

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HYDRAULIC POWER

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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

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Hydraulic Power

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Early Hydraulic Uses Water Wheels Create rotational motion Descriptions exist as early as 1 st century BC Several examples in ancient China Grist mill is pictured

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National Fluid Power Association & Fluid Power Distributors Association Hydrostatic Systems Fluid is at rest Fluid is pressurized Pressure creates force and energy Most common in industrial settings

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

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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? d in = 4.0 in. F in = 100. lb F in = 100. lb F out = ? d in = 4.0 in. d out = 12.0 in. A in = ? A out = ? p = ? MA = ? d out = 12.0 in

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Mechanical Advantage Example F in =100. lb F out =? R in =2.0 in. R out =6.00 in. A in =? A out =? p=? MA=? Find the area of each cylinder.

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Mechanical Advantage Example F in =100. lb F out =? R in =2.0 in. R out =6.00 in. A in =12.57 in. 2 A out =113.10 in. 2 p=? MA=? Find the pressure in the system.

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Mechanical Advantage Example F in =100. lb F out =? R in =2.0 in. R out =6.00 in. A in =12.57 in. 2 A out =113.10 in. 2 p=7.955 lb/in. 2 MA=? Find the force that the output cylinder can lift.

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Mechanical Advantage Example F in =100. lb F out =900.28 lb R in =2.0 in. R out =6.00 in. A in =12.57 in. 2 A out =113.10 in. 2 p=7.955 lb/in. 2 MA=? Find the mechanical advantage of the system.

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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 CO 2 emissions. UPS

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