Formula Sheet: Zeroth Law | Thermodynamics - Mechanical Engineering PDF Download

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Basic Concepts and Zeroth La w of Thermo dynamics
F orm ula Sheet
Basic Concepts
• Thermo dynamic System : Defined as a sp ecific quan tit y of matter or a region in
space c hosen for study .
– T yp es : Op en (mass and energy transfer), Closed (energy transfer only), Isolated
(no mass or energy transfe r).
• Thermo dynamic Prop erties :
– Intensive : Indep enden t of mass (e.g., pressureP (Pa ), temp eratureT (K ), densit y
? (kgm
-3
)).
– Extensive : Dep end on mass (e.g., v olumeV (m
3
), in ternal energyU (J ), en thalp y
H (J )).
– Sp e cific Pr op erties : Extensiv e prop ert y p er unit mass (e.g., sp ecific v olume v =
V
m
(m
3
kg
-1
), sp ecific in ternal energy u=
U
m
(Jkg
-1
)).
• State : Condition of a system defined b y its prop erties.
• Pro cess : Change of a system from one state to another.
– T yp es : Isothermal (T = constan t), Isobaric (P = constan t), Iso c horic (V =
constan t), A diabatic (no heat tra nsfer).
• Equilibrium : State where no sp on taneous c hanges o ccur.
– T yp es : Thermal (uniform T ), Mec hanical (uniform P ), Chemical (uniform com-
p osition).
• State P ostulate : The state of a simple compressible system is completely sp ecified
b y t w o indep enden t in tensiv e prop erties.
Zeroth La w of Thermo dynamics
• Statemen t : If t w o systems are eac h in thermal equilibrium with a third system, they
are in thermal equilibrium with eac h other.
• Implication : Defines temp erature as a measurable prop ert y that go v erns thermal
equilibrium.
• T emp erature Scales :
– Celsius (
?
C ): T
C
=T
K
-273.15
– Kelvin (K ): Absolute temp erature scale, T
K
=T
C
+273.15
• T emp erature Measuremen t : No direct form ula; relies on thermometric prop erties
(e.g., expansion of mercury , resistance of a thermo couple).
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Basic Concepts and Zeroth La w of Thermo dynamics
F orm ula Sheet
Basic Concepts
• Thermo dynamic System : Defined as a sp ecific quan tit y of matter or a region in
space c hosen for study .
– T yp es : Op en (mass and energy transfer), Closed (energy transfer only), Isolated
(no mass or energy transfe r).
• Thermo dynamic Prop erties :
– Intensive : Indep enden t of mass (e.g., pressureP (Pa ), temp eratureT (K ), densit y
? (kgm
-3
)).
– Extensive : Dep end on mass (e.g., v olumeV (m
3
), in ternal energyU (J ), en thalp y
H (J )).
– Sp e cific Pr op erties : Extensiv e prop ert y p er unit mass (e.g., sp ecific v olume v =
V
m
(m
3
kg
-1
), sp ecific in ternal energy u=
U
m
(Jkg
-1
)).
• State : Condition of a system defined b y its prop erties.
• Pro cess : Change of a system from one state to another.
– T yp es : Isothermal (T = constan t), Isobaric (P = constan t), Iso c horic (V =
constan t), A diabatic (no heat tra nsfer).
• Equilibrium : State where no sp on taneous c hanges o ccur.
– T yp es : Thermal (uniform T ), Mec hanical (uniform P ), Chemical (uniform com-
p osition).
• State P ostulate : The state of a simple compressible system is completely sp ecified
b y t w o indep enden t in tensiv e prop erties.
Zeroth La w of Thermo dynamics
• Statemen t : If t w o systems are eac h in thermal equilibrium with a third system, they
are in thermal equilibrium with eac h other.
• Implication : Defines temp erature as a measurable prop ert y that go v erns thermal
equilibrium.
• T emp erature Scales :
– Celsius (
?
C ): T
C
=T
K
-273.15
– Kelvin (K ): Absolute temp erature scale, T
K
=T
C
+273.15
• T emp erature Measuremen t : No direct form ula; relies on thermometric prop erties
(e.g., expansion of mercury , resistance of a thermo couple).
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Pressure and Its Measuremen t
• Pressure (P ) : F orce p er unit area.
P =
F
A
(Units: Pa or Nm
-2
)
where F is force (N ), A is area (m
2
).
• Absolute, Gauge, and V acuum Pressure :
P
absolute
=P
gauge
+P
atm
, P
v acuum
=P
atm
-P
absolute
where P
atm
˜101.3kPa .
• Pressure Measuremen t Devices :
– Manometer: ?P = ?gh , where ? is fluid densit y ( kgm
-3
), g is 981m/s
2
, h is
heigh t difference ( m ).
– Bourdon Gauge: Measures gauge pressure.
W ork and Heat (Basic Definitions)
• W ork (W ) : Energy transfer due to mec hanical in teraction.
W =
?
P dV (Units: J )
where P is pressure, V is v olume.
• Heat (Q ) : Energy transfer due to temp erature difference (no direct form ula for basic
concepts).
• Sign Con v en tion :
– W ork done by system: P ositiv e.
– Heat added to system: P ositiv e.
Key Notes
• Standard v alues: P
atm
=101.3kPa , g =9.81ms
-2
, ?
w ater
=1000kgm
-3
.
• Use SI units for GA TE calculations.
• T emp erature con v ersions: T
K
= T
C
+ 273.15 , T
C
= (T
F
- 32)×
5
9
, where T
F
is
F ahrenheit.
• F or pro cesses, iden tify if the system is op en, closed, or isolated b efore analysis.
• Zeroth La w ensures temp erature is a v alid prop ert y for comparing thermal equilibrium.
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