Gas And Fluid Mechanics

• Heat - In the English system the unit of measurement for heat is the BTU. 1 BTU is equal to 778 foot pounds of work
  • • • Latent heat - When a substance changes from a liquid to a gas the heat used to make the change is called heat of vaporization or latent heat.
      • Dimensional Changes- When heat energy is added to an object, the molecular movement increases and the object expands in physical dimension.
        • • • • • • • • • Coefficient of Linear Expansion - is used to find the amount of expansion in solids and liquids.
    • Specific Heat - Is the heat required to raise the temperature of one gram of a material by one degree Celsius.
    • Transfer of Heat
      • • • • • • Convection - Process by which heat is transferred by movement of a heated fluid.
                • Conduction- Requires physical contact between a body having a high level of heat energy and a body having a lower level of heat energy. When a cold object touches a hot object, the violent action of the molecules in the hot material speed up and molecules in the cold material until temperature is equalized.
                • Radiation - Refers to the continual emission of energy from the surface of all bodies and is the only way of heat transfer that doesn't require the presence of matter.
                • Insulators - Materials that prevent the transfer of heat.

• Temperature - Is the measurement of the amount of molecular agitation in a substance due to heat.
  • • • • • • Scales for measuring temperature
              • • • • • • Fahrenheit - Water freezes at 32 and boils at 212.
                          • • • • • • • Rankine - Used when working with variables of absolute zero. Water freezes at 492 and boils at 672.
    • Celsius - Water freezes at 0 and boils at 100.
      • • • • • • • • • • • • • • • • Kelvin - Used when working with variables of absolute zero. Water freezes at 273 and boils at 373.
  • Absolute Zero - is a term used when all molecular activity is stopped in a substance ( Louis Gay Lussac)

• Pressure - Is the measurement of a force exerted on a given area and is expressed in pounds per square inch.
  • • Standard Pressures - 29.92 inches of mercury, 14.7 pounds per square inch, 1013.2 milibars (atmospheric pressure at sea level.)
    • Gauge Pressure - Gauge is the pressure read directly from a gauge and represents the pressure in excess of barometric pressure. PSIG
    • Absolute Pressure - Is used when pressure is referenced from zero rather than from atmospheric pressure. PSIA
    • Differential Pressure - Is the difference between any two pressures. PSID

• Gas Laws - gasses differ from liquids in that they are compressible.
  • • Boyle's Law - When you change the volume of a confined gas that is held at a constant temperature, the gas pressure also changes.
    • Charle's Law - all gasses expand an contract in direct proportion to any change in absolute temperature.
    • General Gas Law - Combines Boyle's law and Charle's law which allows you to calculate pressure, volume, or temperature when one or more of the variables change.
    • Dalton's Law - States that when two gasses which do not combine chemically are placed in a container each gas expands to fill the canister and create partial pressures. The total pressure exerted on the container is the sum of the partial pressures.

• Fluid Mechanics - Fluids are any substance that flows or conforms to the outline of a container. (Liquids and Gasses)
  • • Fluid Pressure - is the measurement of pressure exerted by a column of liquid and is determined by it's height and not by the volume of the liquid.
    • Archimedes' Principle - states that when an object is submerged in a liquid, the object displaces a volume of liquid equal to its volume and is supported by a force equal to the weight of the liquid displaced. The force that supports the object is known as the liquids Buoyant Force.
    • Pascal's Law - When pressure is applied to a confined liquid, the liquid exerts an equal pressure at right angles to the container that encloses it. The shape of the container has no effect on pressure.
    • Differential Areas - A piston is flat on one side and is 4 sq in. When 1000psi is added to the flat side it exerts 4000 lbs of force, but since the piston rod is on the other side it takes away 1 sq in of area and the same 1000psi only exerts 3000 lbs of force.
    • Bernoullie's Principal - Explains the relationship between potential and kinetic energy in a fluid.
      • • • • • Venturi Tube - A specially shaped tube that is narrower in the middle than at the ends. As fluid enters the tube it is traveling at a known velocity and pressure. When the fluid enters the restriction, it must speed up, or increase its kinetic energy. However, when the kinetic energy increases, the potential energy decreases.

• Sound - Is any vibration of an elastic medium in the frequency range that affects our auditory senses.
  • • Sound Intensity - Is determined by the amplitude of the sound wave. The higher the amplitude the louder the sound.
      • • • Decibels - is the measurement of sound intensity and is the ratio of one sound to another.
            • • • One DB is the smallest change in sound intensity the human ear can detect. And 60 db is a comfortable level for conversation and back round music
  • Frequency - Is the number of vibrations completed per second and is expressed in cycles per second or Hertz. It determines the pitch of a sound.
  • Sound Propagation - There are three things required for the transmission of sound; A source, a Medium for carrying the sound, and a detector.
    • • Sound Waves - Are made of a series of compressions and expansions or Rarefactions
  • Doppler Effect - Is when a source of sound moves and the frequency ahead of the source is higher than the frequency behind it.
  • Speed of Sound - In any uniform medium, under given physical conditions, sound travels at a definite speed.
    • • • Sound travels faster the denser the medium. Sound travels faster in water than in air.
        • The Speed of sound varies directly with the temperature of the air.
  • Mach Number - Is used to represent the ratio of speed of the airplane to the speed of sound in the same atmospheric conditions.
  • Resonance - Is when two objects have the same natural frequency and are set to one another and when one vibrates it transfers its wave energy to the other object making it vibrate.

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