thermodynamicsthermodynamics. mechanical equivalent of heat heat produced by other forms of energy...
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Mechanical Equivalent of HeatMechanical Equivalent of HeatMechanical Equivalent of HeatMechanical Equivalent of Heat
Heat produced by other forms of energyHeat produced by other forms of energy Internal EnergyInternal Energy: total available potential & : total available potential &
kinetic energy of particleskinetic energy of particlesAdding heat increases internal energyAdding heat increases internal energyJoule’s experiment with the paddles Joule’s experiment with the paddles
stirring the water proved heat is form of stirring the water proved heat is form of energyenergy
Expansion and WorkExpansion and WorkExpansion and WorkExpansion and Work
Many thermodynamic processes involve Many thermodynamic processes involve expansion or compression of gasesexpansion or compression of gases
Expanding gases exert pressure Expanding gases exert pressure (force/area) and can do work (car engine)(force/area) and can do work (car engine)
Work done equals pressure times volume Work done equals pressure times volume change for constant pressurechange for constant pressure
For expansion with pressure change, work For expansion with pressure change, work equals area under curve of pressure vs. equals area under curve of pressure vs. volume graphvolume graph
First Law of ThermodynamicsFirst Law of ThermodynamicsFirst Law of ThermodynamicsFirst Law of Thermodynamics
Heat energy supplied to closed system Heat energy supplied to closed system equals work done by system plus change equals work done by system plus change in internal energy of system.in internal energy of system.
Q = Q = U + WU + W1st Law is actually conservation of energy 1st Law is actually conservation of energy
restated to include heat energyrestated to include heat energy If no work is done by system, heat added If no work is done by system, heat added
equals change in internal energyequals change in internal energy
Adiabatic ProcessesAdiabatic ProcessesAdiabatic ProcessesAdiabatic Processes
A process where no heat is added or A process where no heat is added or allowed to escapeallowed to escape
Process must happen very quickly or be Process must happen very quickly or be well insulatedwell insulated
Adiabatic compression of gas causes Adiabatic compression of gas causes temp. increasetemp. increase
Adiabatic expansion of gas causes coolingAdiabatic expansion of gas causes cooling
Isothermal ProcessesIsothermal ProcessesIsothermal ProcessesIsothermal Processes
No temperature change occursNo temperature change occurs Isothermal expansion requires heat input Isothermal expansion requires heat input
from surroundingsfrom surroundings Isothermal compression requires heat Isothermal compression requires heat
emission to surroundingsemission to surroundings
Specific Heats of GasesSpecific Heats of GasesSpecific Heats of GasesSpecific Heats of Gases
Gases have two specific heats, one for Gases have two specific heats, one for constant volume (constant volume (ccv v )) , and one for , and one for
constant pressure (constant pressure (ccp p ))
((ccv v )) < < ((ccp p )) becausebecause work must be done work must be done
against pressure to change volumeagainst pressure to change volume
Second Law of Second Law of ThermodynamicsThermodynamicsSecond Law of Second Law of
ThermodynamicsThermodynamics It is impossible to convert all heat energy It is impossible to convert all heat energy
into useful workinto useful work Device that uses heat to do work can never Device that uses heat to do work can never
be 100% efficientbe 100% efficient Some heat will remain and must be expelled Some heat will remain and must be expelled
into low temp. sinkinto low temp. sink Heat will never flow from a cold object to a Heat will never flow from a cold object to a
hot object by itself without work inputhot object by itself without work input Absolute zero is unattainableAbsolute zero is unattainable
Heat EnginesHeat EnginesHeat EnginesHeat EnginesAny device that turns heat into mechanical Any device that turns heat into mechanical
energyenergyAnything that burns fuel or uses steam to Anything that burns fuel or uses steam to
move or do workmove or do work Ideal heat engine cycle: Ideal heat engine cycle:
takes heat from high temp. source, takes heat from high temp. source, does work using part of the energy, does work using part of the energy, expels remaining heat energy into low temp. expels remaining heat energy into low temp.
heat sink.heat sink.
Efficiency of Heat EnginesEfficiency of Heat EnginesEfficiency of Heat EnginesEfficiency of Heat Engines
Efficiency = work done/heat input Efficiency = work done/heat input Work done = heat energy usedWork done = heat energy used Sadi Carnot (1796 – 1832) showed max. Sadi Carnot (1796 – 1832) showed max.
efficiency for any heat engine = temp. efficiency for any heat engine = temp. difference between hot source and cold difference between hot source and cold sink divided by temp. of source sink divided by temp. of source
eeidealideal = (T = (Thothot - T - Tcold cold )/ T)/ Thothot
For max. efficiency, industry uses high For max. efficiency, industry uses high temp. source, large body of water for sink.temp. source, large body of water for sink.
Types of Heat EnginesTypes of Heat EnginesTypes of Heat EnginesTypes of Heat Engines
Steam Engines: first heat engines; Watt, Steam Engines: first heat engines; Watt, Fulton, Newcomen; external combustionFulton, Newcomen; external combustion
Steam Turbine: uses high pressure steam Steam Turbine: uses high pressure steam to turn wheel with many cupped fan-like to turn wheel with many cupped fan-like bladesblades
Gasoline Engines: internal combustion Gasoline Engines: internal combustion engine; heat from expanding combustion engine; heat from expanding combustion gases drive pistongases drive piston
Types of Heat EnginesTypes of Heat EnginesTypes of Heat EnginesTypes of Heat Engines
Diesel Engines: heat from compression Diesel Engines: heat from compression ignites fuel; efficient, powerful, but heavyignites fuel; efficient, powerful, but heavy
Gas Turbines: air compressed by turbine Gas Turbines: air compressed by turbine forced through combustion chamber; used forced through combustion chamber; used on airplaneson airplanes
Types of Heat EnginesTypes of Heat EnginesTypes of Heat EnginesTypes of Heat Engines
Jet Engines: expanding combustion gases Jet Engines: expanding combustion gases forced out rear of engine; action-reaction & forced out rear of engine; action-reaction & conservation of momentum create forward conservation of momentum create forward thrustthrust
Rockets: like jets, but carries own oxidizer Rockets: like jets, but carries own oxidizer to work outside atmosphere. Thrust to work outside atmosphere. Thrust depends on velocity of exhaust gasesdepends on velocity of exhaust gases
Heat PumpsHeat PumpsHeat PumpsHeat Pumps
Reverse cycle of heat engine; work from Reverse cycle of heat engine; work from electric motor causes heat to flow from electric motor causes heat to flow from cool area to warm areacool area to warm area
Uses easily condensed vapor (freon); Uses easily condensed vapor (freon); motor condenses vapor in compressor; motor condenses vapor in compressor; When allowed to vaporize, it extracts its When allowed to vaporize, it extracts its heat of vaporizationheat of vaporization
Basis for refrigerators, air conditioners Basis for refrigerators, air conditioners
EntropyEntropyEntropyEntropy
A measure of the disorder of a systemA measure of the disorder of a system Is related to the amount of energy that Is related to the amount of energy that
cannot be converted into mechanical workcannot be converted into mechanical workNatural systems tend toward greater Natural systems tend toward greater
disorder (greater entropy)disorder (greater entropy)Controls the direction of timeControls the direction of time
EntropyEntropyEntropyEntropy
Work must be done to decrease entropy of Work must be done to decrease entropy of systemsystem
Heat is disordered energy, increased Heat is disordered energy, increased entropyentropy
Change in entropy of system equals heat Change in entropy of system equals heat added divided by absolute temperatureadded divided by absolute temperature
S = S = Q/T Q/T (J/K)(J/K)
EntropyEntropyEntropyEntropy
Entropy increased in melting, evaporation, Entropy increased in melting, evaporation, organic decayorganic decay
Total energy of universe is constant, but Total energy of universe is constant, but usable energy decreases due to increased usable energy decreases due to increased entropyentropy