Gas Laws in Pneumatics: Calculations and Applications

1. MECH1300 Basic Principles of Pneumatics Topics Absolute Pressure and Temperature Gas Laws Gas Flow Vacuum Pneumatic Systems Chapter 10

2. MECH1300 Basic Principles of Pneumatics Pneumatics – The use of gas to transmit power from one point to another. Comparison

3. MECH1300 Absolute Pressure and Temperature Gauge Pressure – Pressure that is above atmospheric pressure. Atmospheric pressure is due to the weight of the air above us. Absolute Pressure – The total pressure exerted on a system, including atmospheric pressure.

4. MECH1300 Absolute Pressure and Temperature Temperature: Absolute Zero - Standard Units Absolute Temperature: Rankine = Metric Units Absolute Temperature: kelvin (K)

5. MECH1300 Gas Laws Isothermal process – A process in which temperature remains constant. Boyle’s Law – the absolute pressure of a confined gas is inversely proportional to its volume, as long as its temperature remains constant. Absolute pressure must be used!

6. MECH1300 Gas Laws EX: A cylinder is initially filled with of air at a pressure of . The air is compressed to a volume of . What is the pressure in psig after compression? Convert to psia: Calculate the new pressure: Convert back to psig:

7. MECH1300 Gas Laws EX: A cylinder is initially filled with of air at a pressure of . The air is compressed to a volume of . What is the pressure in kPa after compression? Convert kPa to abs: Calculate the new pressure: Convert back to kPa gauge:

8. MECH1300 Gas Laws Gay-Lussac’s Law – The absolute pressure of a confined gas is proportional to its temperature, provided its volume remains constant. Used when heating or cooling gases. = absolute pressure of the gas at state 1 = absolute temperature of the gas at state 1 = absolute pressure of the gas at state 2 = absolute temperature of the gas at state 2

9. MECH1300 Gas Laws EX: Air in a fixed volume container is initially at atmospheric pressure (0 psig) and . Its temperature is then raised to . What is the gauge pressure at the final temperature. Convert to absolute temperature : Convert to psia: Calculate the final pressure: Convert back to psig:

10. MECH1300 Gas Laws EX: Air in a fixed volume container is initially at atmospheric pressure (0 kPa gauge) and . Its temperature is then raised to . What is the gauge pressure at the final temperature. Convert to absolute temperature : Convert kPa abs: Calculate the final pressure: Convert back to kPa:

11. MECH1300 Gas Laws Charles law – The volume of a confined gas is proportional to its temperature, provided its pressure remains constant. = volume of the gas at state 1 = absolute temperature of the gas at state 1 = volume of the gas at state 2 = absolute temperature of the gas at state 2

12. MECH1300 Gas Laws EX: Air is held in a container with a free sliding piston. It is initially at a temperature of and a volume of . Its temperature is then raised to . What is the volume of the air after being heated? Convert to absolute temperatures (: Calculate the final volume:

13. MECH1300 Gas Laws General Gas Law – relates temperature, pressure and volume. (nothing remains constant)

14. MECH1300 Gas Laws EX: Air initially at and 800kPa occupies a volume of . If the air is heated to while its volume is reduced to , what is the resulting final pressure? Convert to absolute temperature: Convert to absolute pressure: Calculate the final pressure: Convert back to kPa gauge:

15. MECH1300 Gas Laws Adiabatic Process – none of the heat is transferred to the atmosphere, so the temperature of the gas will increase to a maximum when compressed or expanded. The temperature changes without heat being added. k is a constant that measures the heat absorption properties of the gas, for Air k =1.4

16. MECH1300 Gas Laws EX: Air that is initially at and atmospheric pressure is compressed from to . Assuming the process is adiabatic, what is the final pressure and temperature of the gas? Convert to absolute temperature: Calculate the final pressure: Calculate the final temperature:

17. MECH1300 Gas Flow Units – scfm(standard cubic feet per minute) metric Standard conditions: 14.7 psia and relative humidity 36% Equivalent flow of atmospheric air, not necessarily pressurized air

18. MECH1300 Vacuum Use pressures that are below atmospheric pressure to create suction. Used for pick and place to lift and manipulate parts. Measured in inches of mercury (Hg), using a mercury barometer. mmHg in metric

19. MECH1300 Vacuum Mercury is used because it is a heavy liquid. At sea level the air pressure will push mercury to a height of 30 inches. 30 in Hg represents a perfect vacuum. At higher elevations, it will be less than 30 in Hg because atmospheric pressure is lower. A vacuum generates less force at higher elevations.

20. MECH1300 Vacuum Vacuum pumps never generate a perfect vacuum because they cannot evacuate all the air. Industry pumps operate around 20in Hg at sea level at sea level As air is removed, pressure decrease

21. MECH1300 Vacuum EX: A suction cup with an inside diameter of 3 in is used in a vacuum system that pulls 20 in Hg. What is the maximum lifting force? Convert to psig: Calculate the area: Calculate the Force: The negative indicates that the object is being drawn toward the suction cup

22. MECH1300 Vacuum EX: A suction cup with an inside diameter of 40mm is used in a vacuum system that pulls 200mmHg. What is the maximum lifting force? Convert to kPaguage: Calculate the area: Calculate the Force:

23. MECH1300 Pneumatic Systems • 3 segments – • Power Supply – Power supply segment (compressor, receiver tank). • Prime mover is still usually an electric motor. • Compressor pumps air into the receiver tank, storing air. • System draws air from the tank as needed. • Control Valves – directional, pressure and flow • Output – actuator (motor, cylinder) and load