1 Dept. of Agricultural & Biological Engineering University of Illinois ABE223: ABE Principles – Machine Systems ABE223: ABE Principles – Machine Systems Air cannon as a pneumatic safety testing device Tony Grift

2 Agenda Introduction to cannon function Adiabatic expansion theory: What happens inside the cannon when you fire it? Build an Excel spreadsheet to deal with ANY air cannon Derivation of dynamics in equation form: What happens to a flying projectile in air? Solving non-linear equations in MatLab® Linking MatLab and Excel

3 The piston design allows for very fast air release Drawings in SolidWorks®

4 Air cannon used for high speed cutting of Miscanthus Giganteus

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7 Charging the reservoir takes place while the piston seals the barrel Open main valve Piston is pushed against barrel with great force sealing the barrel (pressure inside barrel is atmospheric) Pressure rises until the main chamber pressure equals the feed line pressure Close main valve

8 The cannon is fired by dropping the pressure behind the piston instantaneously Disconnect feed line Quickly open main valve Pressure drops behind piston Piston slams back REALLY fast Projectile is accelerated and released from the barrel

9 The air while expanding has no time to transfer energy to the environment: Adiabatic expansion

10 Thermodynamics 101 Ideal gas law: First law of thermodynamics: Internal energy is composed of heat and work performed on or by the gas Processes: Isochoric (constant volume) Isothermal (constant temperature) Adiabatic (no heat exchange with environment) Internal energy = Heat + Work Enthalpy

11 Three possible processes: Isochoric (const. volume) Isothermal (const. temperature) Adiabatic (no heat exchange with environment: fast processes!)

12 Isochoric (constant volume) process

13 Isothermal (constant Temperature) process

14 Adiabatic process: No heat exchange with the environment

15 Adiabatic equation Adiabatic process: No heat exchange with the environment

16 How much work do we get from the gas that is expanding adiabatically? Work is Force through a distance change or Pressure through a Volume change

17 This work is (at least partially) used to accelerate our projectile Assuming that all energy from the gas is converted into kinetic energy of the projectile (this is a major assumption) we get: The exit velocity of the projectile would now be:

18 In the computer lab we will develop a spread sheet for the complete cannon

19 Keep things safe during the lab! Your assignment Think of everything that could go wrong Make a safety procedure sheet for the test cannon before and after we fire it

20 Lab Outdoor part Fire the cannon with various pressure settings and various projectile Indoor part Build complete Excel spreadsheet from a template to model the cannon assuming adiabatic expansion Use MatLab to simulate a ballistic model Connect MatLab and Excel using a Dynamic Data Exchange (DDE) link and make them work together

21 Air cannon as a safety testing device: The End