Fluids

• 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.