Summary HD AMME2262 –COMPLETE NOTES

AMME2262&–!SEMESTER&2"
Engineering'thermodynamics'is'the'science'of'energy'that'applies'to'the'design'and'analysis'of'
energy'conversion'systems'
Energy"can"be:"

• Thermal"or"internal"energy"(stored"in" • Potential"energy"(elevation)"
molecular"forces)"
• Nuclear,"magnetic"and"electric"energy""
• Chemical"energy"in"molecular"bonds"
• Sum"of"all"energies"="total"energy"E"of"the"
(combustion)"
system"
• Kinetic"energy"(motion)"

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Important!Terms:!

Pressure!(Pa,! • Absolute'pressure:"measured"relative"to"absolute"zero"pressure"(used!mostly)"
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Nm )!
• Gage/Vacuum'pressure:"measured"relative"to"atmospheric"pressure"


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Temperature! • Use"Kelvin"Scale"for"units"
(K)!
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• Engineering"thermodynamics"deals"with"temperatures"in"the"range"of"200KH3000K"

Force!(N)! • F=ma,"or"where"a=g"(gravity)"F=mg"
• kgf,"relative"to"local"gravity"

Pascal’s!law:! • The"pressure"applied"to"a"confined"fluid"increases"the"pressure"throughout"by"the"same"
amount"




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Density!and!specific!gravity!
33 3 31
Density!(kgm )! Specific!Volume!(m kg )"




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Specific!Weight!(Nm )! Specific!Gravity"


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, Determining!Type!of!System!

Closed!System! Open!System!

• no"mass"transfer"across"boundaries" • mass"transfer"across"boundaries"
• Energy"transfer"across"boundaries"




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Assumption:'Substances'are!treated'as'a'continuum'because'of'the'very'large'number'of'molecules'even'in'
an'extremely'small'volume'(no'need'to'consider'on'atomic'level)'

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Properties!of!Systems:!

Intensive! Independent"of"System"Size"
Property! 3
• TemperatureHT"(K),"PressureHP"(Pa),"DensityH'ρ'(kg/m )"

Extensive! Dependent"of"System"Size"
Property! 3
• Mass"H"m"(kg),"Volume"H"V"(m ),"Energy"H"E"(J)"

Specific! Extensive"Properties"per"unit"mass"that"become"intensive"properties"
Properties!
• massHm"(kg)"
• V/m=,"specific"volume"(m3/kg)""
• U/m=u,"specific"internal"energy"(kJ/kg)"
• "E/m=e,"specific"energy"(kJ/kg)"

Units!(metric!system)!
All"equations"must"be"dimensionally"homogeneous"
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Equilibrium!
• System"in"thermodynamic"equilibrium"if"it"is"in"thermal,"mechanical,"phase"and"chemical"equilibrium.""
• Properties"of"system"do"not"change"over"entire"system"

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Temperature!and!the!Zeroth!law!of!thermodynamics!
• Zeroth"law"states"that"two"bodies"are"in"thermal"equilibrium"if"both"have"the"same"temperature"reading"
even"without"being"in"contact"
• Heat"moves"from"hot"to"cold"objects"

Equations!Of!State!(The!Ideal!Gas!Equation)!
Ideal"Gas"Equation"relates"pressure,"temperature"and"specific"volume"of"a"substance."The"assumptions"made"
for"it"to"hold"true"include:"
• The"gas"is"composed"of"a"large"amount"of"small"molecules""
• The"gas"molecules"are"elastic"(KE"is"conserved)"
• The"size"and"total"volume"of"the"molecules"is"small"relative"to"the"volume""
• Thermal"motions"of"the"gas"are"random""
Note:"real"gases"can"be"approximated"by"an"ideal"gas"at"“low”"densities:"“low”"pressures"and"“high”"
temperatures"




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, State!Postulate!
State!postulate:!The"number"of"properties"required"to"fix"the"state"of"a"system""

• The"state"of"a"simple*!compressible!system"(i.e.'A'system'that'involves'no' !
electrical,'magnetic,'gravitational,'motion,'and'surface'tension'effects)"is"
completely"specified"by"2!independent,!intensive!properties""
• The"state"of"the"nitrogen"here"is"fixed"by"two"independent,"intensive"
properties""

Pure!Substances!
• A"substance"that"has"a"fixed"chemical"composition"throughout.""
• Air"is"a"pure"substance"at"atmospheric"pressure"and"temperature,"despite"being"a"mixture"of"several"
gases"




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Phase!Change! Description!

1. Compressed!liquid!(subcooled! A"substance"that"it"is"not,about'to'vaporize'(i.e."liquid"phase)"
liquid):""

2. Saturated!liquid:"" Exists"as"liquid"that"is"about,to'vaporize."

3. Saturated!liquid–vapor! The"state"at"which"the"liquid'and'vapor'phases'coexist'in"
mixture:"" equilibrium"

4. Saturated!vapor:"" A"vapor"that"is"about,to'condense"

5. Superheated!Vapour! A"vapor"that"is"not,about'to'condense'(i.e.,"not"a"saturated"
vapor)""

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