Introduction
(Lecture 1)
2021
년1
학기열역학
(M2794.001100.002)
송한호1.1 Thermodynamic system & control volume
è Thermodynamic system: a device or combination of devices containing a quantity of matter that is being studied
è Control volume: contains the matter and devices inside a control surface (or System)
l The control surface may be open or closed to mass flows, and may have flows of energy in terms of heat and work across it
l The boundaries may be movable or stationary
è Surroundings: everything external to control volume
è Control mass: Control volume that contains the same amount of matter at all times
Introduction
Mass
Mass
Energy Closed system(↔Control Mass)
- Mass transfer NO (fixed mass) - Energy transfer allowed
Open system (↔Control Volume) - Mass transfer YES
- Energy transfer allowed
Energy Introduction
An isolated system is a closed system that is not influenced in any way by the surroundings. This means that no mass, heat or work cross the system boundary.
Thermodynamic System
Closed System Open System
Isolated System
No mass flow Energy flow
Mass flow Energy flow No mass flow
No energy flow Introduction
Macroscopic Microscopic
25 mm
Atmospheric P, T
1020 atoms
6*1020 equations!
Classical Thermodynamics
-Average effect of many molecules à This is our approach!
Continuum
Statistical Thermodynamics
- Statistical and probabilistic approach
1.2 Macroscopic vs. Microscopic points of view
Introduction
1.3 Properties and State of a substance
è Phase: gas, liquid, solid (e.g. steam, water, ice)
è State: conditions at which a substance exists (e.g. 25°C, 1 bar)
è Thermodynamic property: Observables
l Extensive property: mass, volume, etc. (proportional to mass)
l Intensive property: pressure, temperature, density, etc. (independent of mass) (*) Specific property: (extensive property / mass) à Intensive property
è Thermodynamic equilibrium
l Thermal equilibrium: T
l Mechanical equilibrium: P
l Chemical equilibrium: μ (chemical potential) Introduction
1.4 Processes and Cycles
è Process: path of state change
è States during a process?
l Quasi-equilibrium process: at any instant, the system is very close to an equilibrium state
l Non-equilibrium process
State 1
State 2 Quasi-equilibrium
process
Non-equilibrium process
P
Gas expands à P drops Introduction
è Iso-(property) process: constant (property)
l Isothermal: T=const.
l Isobaric: P=const.
l Isochoric: V=const.
è Cycle: a combination of processes where final state is equal to initial state.
P
Process A
Process B 1
2
Thermodynamic Cycle
1 (initial state) à 2 à 1 (final state) 2 (initial state) à 1 à 2 (final state) Introduction
è SI units: Metric International System
l Time: second [s]
l Length: meter [m]
l Mass: kilogram [kg]
cf) mole [mol]: 12 g of carbon-12
l Force: newton [N] (=mass*acceleration [kg∙m/s2])
1.5 Units for Mass, Length, Time, and Force
k Kilo 10^3 m mili 10^-3
M Mega 10^6 μ micro 10^-6
G Giga 10^9 n nano 10^-9
T Tera 10^12 p pico 10^-12
(Unit Prefixes)
Introduction
1.6 Specific Volume and Density (intensive properties)
è v , Specific volume = volume / mass [m3/kg]
è r , Density = mass / volume [kg/m3]
è Continuum concept
è Molal property: v [m3/kmol]
1
, v
m
v = V r =
v
Continuum limit Classical world
To give you some sense, 1 kmol of molecules
à 22.4 m3 and 6.02x1026 molecules à2.69x1025 molecules/m3
à2.69x1016 molecules/mm3 à2.69x107 molecules/um3 à??? molecules/nm3
Introduction
1.7 Pressure
è Force / Area
è Applied to liquids and gases à for solids, use “stress”
è Continuum concept
A
P F
nA
A
d
d
d d ® ¢
= lim
Unit: 1 Pa (pascal) = 1 N/m2 1 bar = 105 Pa = 0.1 MPa 1 atm = 101325 Pa ~ 1 bar
piston stationary
a for
ext
Piston
GasA F
P =
Introduction
è Absolute vs. Gauge pressure
0 0
P P gH P
gH P
P
B A
B
+
=
=
®
= -
r r
Barometer
-measurement of atmospheric pressure
Manometer
-measurement of pressure difference
H
gH Patm = r
(source: barometerplanet.com)
Introduction
1.8 Energy
è Macroscopic view
l Energy transferred as heat
l Energy stored in H2O
l Change in states (e.g. phases)
è Microscopic view
l Intermolecular (potential) energy
l Molecular kinetic energy
l Intra-molecular energy Macroscopic View (phases, states, etc.)
Introduction
1.9 Equality of temperature
è Temperature: Sense of hotness or coldness, however, difficult to be rigorously defined
è Two objects in thermal contact for a long time à No change à thermal equilibrium
1.10 The Zeroth Law of Thermodynamics
è Basis of temperature measurement
è The zeroth law precedes 1st and 2nd law of thermodynamics.
if TA = Tthermometer
TB = Tthermometer
Introduction
1.11 Temperature Scales
è SI system of units: Celsius(°C) (cf.) Fahrenheit(°F)
Fixed point of the
temperature Fahrenheit Celsius
Ice point 32 0
Boiling point 212 100
Temperature scale 1/180 1/100
Absolute temperatures R = °F + 459.67 K = °C + 273.15
Introduction
