Fundamentals of Thermodynamics
Chapter 1
Introduction
Prof. Siyoung Jeong
Thermodynamics I
MEE2022-01
Chapter 1. Introduction
• Thermodynamics : Science of energy and
entropy
- Science of heat and work and properties related
to heat and work
• Basis for diverse scientific disciplines
- Physics, chemistry, biology, etc.
• Applied to various fields
- Mechanical engineering, chemical engineering,
aerospace engineering, etc.
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Chapter 1. Introduction
1.1 A Thermodynamic system and the control volume
• Schematic diagram of a steam power plant
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Chapter 1. Introduction
• Schematic diagram of a refrigerator
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Chapter 1. Introduction
• Thermodynamic system
-
System / Surroundings
Control mass (no mass flow)
Control volume (more general)
Open / closed systems
System boundary / Control surface
Isolated system : No influence from surroundings
Control mass
Control volume
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Chapter 1. Introduction
1.2 Macroscopic versus microscopic points of view
• Macroscopic
vs.
Microscopic
10^20 atoms
25 mm
Atmospheric P, T
Continuum
6*10^20 equations!
Classical Thermodynamics
Statistical Thermodynamics
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Chapter 1. Introduction
1.3 Properties and state of a substance
• Phase : gas, liquid, solid
• A substance may exist in in various states (T, p, etc.).
• Thermodynamic property : observable & macroscopic
- Intensive : pressure, temperature, density, etc.
- Extensive : mass, volume, etc.
- Specific property : property/mass,
intensive property, ex) specific volume
• Thermodynamic equilibrium
- Thermal equilibrium : T
- Mechanical equilibrium : P
- Chemical equilibrium : μ (chemical potential)
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Chapter 1. Introduction
1.4 Processes and cycles
• Process : Path of state change
• States during a process?
- Quasi-equilibrium process : Defined ideally but
applied to many practical cases
- Non-equilibrium process
• Iso-X process : Constant X
- Isothermal : T=const.
- Isobaric (isopiestic) : P=const.
- Isochoric : V=const.
• Cycle : Initial state = Final state
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Chapter 1. Introduction
1.5 Units for mass, length, time, and force
• SI units : Metric International System
- Time : second [s]
- Length : meter [m]
- Mass : kilogram [kg]
cf) mole [mol] : 12 g of carbon-12
- Force : Newton [N]
• English Engineering Units
- ft, in, lbm, lbf, …
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Chapter 1. Introduction
Ex. 1.1
What is the weight of a 1 kg mass at an altitude where the local acceleration of gravity is 9.75 m/s 2?
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Chapter 1. Introduction
1.6 Specific volume and density
• v , Specific volume = volume / mass [m3/kg]
r , Density = mass / volume
[kg/m3]
}Both intensive properties
V
• Continuum concept : v  Vlim
V  m
• Molal property : v [m3/kmol] , r [kmol/m3]
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Chapter 1. Introduction
Ex. 1.2
A 1 m3 container, shown in Fig. 1.9, is filled with
0.12 m3 of granite, 0.15 m3 of sand, and 0.2m3 of
liquid 25℃ water; the rest of the volume, 0.53 m3,
is air with a density of 1.15 kg/m3. Find the
overall (average) specific volume and density.
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Chapter 1. Introduction
1.7 Pressure
• Continuum concept
Fn
P  lim
AA A
• Unit :
1 Pa = 1 N/m2
1 bar = 105 Pa = 0.1 MPa
1 atm = 101325 Pa ~ 1 bar
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Chapter 1. Introduction
• Absolute vs. gauge pressure
PB A  P0 A  mg  P0 A  rAgH
PB  P0  rgH
P  PB  P0  rgH
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Chapter 1. Introduction
Fluid with a constant density: P  PB  P0  r gH
H
Fluid with a varying density: P  PB  P0   dP   r ( z ) gdz
0
z0
P  P0
z
z  dz
P
zH
P  PB
P  dP
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Chapter 1. Introduction
Ex. 1.3
The hydraulic piston/cylinder system shown in
Fig. 1.11 has a cylinder diameter of D = 0.1 m
with a piston and rod mass of 25 kg. The rod has
a diameter of 0.01 m with an outside atmospheric
pressure of 101 kPa. The inside hydraulic fluid
pressure is 250 kPa. How large a force can the
rod push with in the upward direction?
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Chapter 1. Introduction
Ex. 1.4
A mercury barometer located in a room at 25 ℃ has a height of 750 mm. What is the atmospheric
pressure in kPa?
Ex. 1.5
A mercury (Hg) manometer is used to measure the pressure in a vessel as shown in Fig. 1.13. The
mercury has a density of 13,590 kg/m3, and the height difference between the two columns is
measured to be 24 cm. We want to determine the pressure inside the vessel.
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Chapter 1. Introduction
Ex. 1.6
What is the pressure at the bottom of the 7.5 m tall storage tank of fluid at 25 ℃ , shown in Fig.
1.15? Assume that the fluid is gasoline with atmospheric pressure 101 kPa on the top surface.
Repeat the question for the liquid refrigerant R-134a when the top surface pressure is 1 MPa.
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Chapter 1. Introduction
Ex. 1.7
A piston/cylinder with a cross-sectional area of 0.01 m2 is connected with a hydraulic line to another
piston/cylinder with a cross-sectional area of 0.05 m2. Assume that both chambers and the line are
filled with hydraulic fluid of density 900 kg/m 3 and the larger second piston/cylinder is 6 m higher
up in elevation. The telescope arm and the buckets have hydraulic piston/cylinders moving them, as
seen in Fig. 1.16. With an outside atmospheric pressure of 100 kPa and a net force of 25 kN on the
smallest piston, what is the balancing force on the second larger piston?
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Chapter 1. Introduction
1.8 Energy
• Microscopic view
- Intermolecular (potential) energy
- Molecular kinetic energy
- Intramolecular energy
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Chapter 1. Introduction
1.9 Equality of temperature
• “Sense of hotness or coldness”
However, difficult to rigorously define temperature
• Two objects in thermal contact for a long time
→ No change → thermal equilibrium
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Chapter 1. Introduction
1.10 The zeroth law of thermodynamics
• Zeroth law
TA = Tthermometer
TB = Tthermometer
∴ TA = TB
Basis of temperature measurement
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Chapter 1. Introduction
1.11 Temperature scales
• Fahrenheit, Celsius
- Celsius: formerly know as centigrade
Fahrenheit
Celsius
Ice pt
32
0
Steam pt
212
100
• Absolute temperatures
K = °C + 273.15
R = F + 459.67
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Chapter 1. Introduction
1.12 Engineering applications
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Chapter 1. Introduction
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Chapter 1. Introduction
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Chapter 1. Introduction
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Chapter 1. Introduction
Home Work - 2017
•
•
•
•
1.42
1.60
1.78
1.81
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