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Fluids

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  1. Fluids

  2. Fluids • Flow • Take shape of container • Liquids or gases • Exert pressure • Pressure = force / area http://i.ehow.com/images/GlobalPhoto/Articles/5122397/246186-main_Full.jpg

  3. Fluids • Move from high pressure  low pressure • If no pressure difference, no motion (equilibrium) http://rt492.org/dl/img/jetcar.gif http://images.google.com/imgres?imgurl=http://hyperphysics.phy-astr.gsu.edu/Hbase/fluids/flupic/bernlev.jpg&imgrefurl=http://hyperphysics.phy-astr.gsu.edu/Hbase/pman.html&usg=__zR0eA8X2YfzjNx1oK3YEqTgA9fg=&h=411&w=359&sz=33&hl=en&start=65&um=1&itbs=1&tbnid=ZKd7dOr6DEn4YM:&tbnh=125&tbnw=109&prev=/images%3Fq%3Dfluid%2Bpressure%2Bdifference%26ndsp%3D21%26hl%3Den%26safe%3Dactive%26rlz%3D1T4GGIH_enUS266US269%26sa%3DN%26start%3D63%26um%3D1 http://i.telegraph.co.uk/telegraph/multimedia/archive/01485/eyedrops_1485563c.jpg

  4. Calculating fluid pressure • Pressure = force / area • Force measured in lbs or N • Area measured in cm2 or inch2. • Area = Pr2or length * width • Radius =1/2 diameter http://www.sweethaven02.com/Aviation/AvEngines01/fig0101.gif

  5. Liquids • Not compressible; pressure difference supplied by pump • Basis for hydraulic systems (usually water or oil) • More dense than gases; molecules close together http://www.chemprofessor.com/liquids_files/image005.jpg

  6. Gases • Compressible; pressure difference supplied by compressor • Basis for pneumatic systems (usually utilize compressed air) • Less dense and therefore more buoyant http://www.grc.nasa.gov/WWW/K-12/airplane/Images/state.gif

  7. Basic components of fluid system • Tank, reservoir or accumulator – holds fluid • Pump (liquid) or compressor (gas) – creates pressure difference • Valve or regulator – control flow • Actuator – device that changes fluid pressure to linear or rotational mechanical movement. Often an arm, piston, etc. • Conductor – pipe, tubing, hose

  8. Pascal’s Principle • Pressure exerted on confined fluid is transmitted equally to all parts of the fluid within the closed container • P = F1 / A1 = F2 / A2 • Results: • Pressurized gas, when released, allows for propulsion (rockets, balloons) • Pressure in hydraulic systems allows movement of very heavy loads (hydraulic lift)

  9. Boyle’s Law • Volume increases when pressure decreases (temp stays constant) P1V1 = P2V2 • When P goes up, V goes down (inverse relationship) • Applies to astronauts walking in space, and to scuba divers

  10. Charles’ and Gay-Lussac’s Law • Volume increases when temp increases (pressure stays constant). V1 / T1 = V2 / T2 • Hot air balloons use this concept http://www.google.com/search?hl=en&safe=active&rlz=1T4GGIH_enUS266US269&q=Charles%27++law&start=10&sa=N

  11. Bernoulli’s Principle • Pressure of a moving fluid decreases as velocity increases • Basis for airplane wing design http://www.sweethaven02.com/Aviation/AvEngines01/fig0101.gif

  12. Fluid Power Physics Work Force multiplied by distance Measured in foot-pounds or Newton-meters Example: How much work is completed by moving a 1000 lb force 2 ft? 2000 foot-pounds of work

  13. Fluid Power Physics Power The rate of doing work Work over time in seconds Example: How many units of power are needed to lift a 1000 pound force 2 feet in 2 seconds? 1000 units of power (1000lb x 2ft) / 2 s

  14. Fluid Power Principles -- Units Watt – measure of power in SI system Pressure x volume flow rate Horsepower –measure of power in English system Hydraulic horsepower is expressed as:

  15. Fluid Power Principles Calculate the horsepower needed in the system below to lift a 10,000 lb force in 2 s.