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• Flow• Take shape of container• Liquids or gases• Exert pressure • Pressure = force / area
Fluids
http://i.ehow.com/images/GlobalPhoto/Articles/5122397/246186-main_Full.jpg
Fluids• Move from high
pressure low pressure• If no pressure difference,
no motion (equilibrium)
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
http://rt492.org/dl/img/jetcar.gif
Calculating fluid pressure• Pressure = force / area• Force measured in lbs or N• Area measured in cm2 or
inch2.• Area = Pr2 or length *
width• Radius = 1/2 diameter
http://www.sweethaven02.com/Aviation/AvEngines01/fig0101.gif
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
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
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
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)
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
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
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
Fluid Power PhysicsWork
Force multiplied by distanceMeasured in foot-poundsor Newton-meters
Example:How much work is completed by moving a 1000 lb force 2 ft?2000 foot-pounds of work
Fluid Power PhysicsPowerThe rate of doing workWork 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
Fluid Power Principles -- UnitsWatt – measure of power in SI system
Pressure x volume flow rateHorsepower –measure of power in English
systemHydraulic horsepower is expressed as:
flow( gpm) pressure( psi)Horsepower=
1714( constant)
Fluid Power PrinciplesCalculate the horsepower needed in the system below to lift a 10,000 lb force in 2 s.