3. What is Thermodynamics?
• The word thermodynamics stems from the Greek
words therme (heat) and dynamis (force).
• The capacity of hot bodies to produce work.
• Thermodynamics is study about energy and
properties of a system
3Taught by Meng Chamnan
5. Definition
• A property is a macroscopic characteristic of a system such
as mass, volume, energy, pressure, and temperature to
which a numerical value can be assigned at a given time
without knowledge of the previous behavior (history) of the
system.
• The word state refers to the condition of a system as
described by its properties.
• A process is a transformation from one state to another.
• A system is said to be at steady state if none of its properties
changes with time.
• A thermodynamic cycle is a sequence of processes that
begins and ends at the same state.
5Taught by Meng Chamnan
6. • Extensive property if its value for an overall system is the sum
of its values for the parts into which the system is divided (ex:
mass, volume, energy, and several other properties..)
• Intensive properties are not additive in the sense and may be
functions of both position and time, whereas extensive
properties vary at most with time. (ex: specific volume,
pressure, and temperature)
• The term phase refers to a quantity of matter that is
homogeneous throughout in both chemical composition and
physical structure.
• A pure substance is one that is uniform and invariable in
chemical composition.
• Thermodynamics equilibrium is a balance condition among
force (mechanical equilibrium), temperature (thermal
equilibrium), phase equilibrium (no phase change), and
chemical equilibrium (no chemical reaction) 6
7. Example 1: As illustrated in this figure, water circulates
between a storage tank and a solar collector. Heated water
from the tank is used for domestic purposes. Considering the
solar collector as a system, identify locations on the system
boundary where the system interacts with its surroundings
and describe events that occur within the system. Repeat for
an enlarged system that includes the storage tank and the
interconnecting piping.
Taught by Meng Chamnan
7
9. Example 2: A dish of liquid water is placed on a
table in a room. After a while, all of the water
evaporates. Taking the water and the air in the room
to be a closed system, can the system be regarded
as a pure substance during the process? After the
process is completed? Discuss.
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11. Units and Dimensions
11Taught by Meng Chamnan
SI is the abbreviation for Système International d’Unités (International System of Units)
1 0.453592lb kg 1 0.3048ft m
2 2
1 1 32.174 / 32.174 /lbf lb ft s lb ft s
12. 12Taught by Meng Chamnan
Newton’s second law is
expressed as the equality
F ma
2 2
1 1 1 / 1 /N kg m s kg m s
13. Example 3:
An object has a mass of 20 kg. Determine its
weight, in N, at a location where the acceleration of
gravity is 9.78 m/s2.
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15. Pressure and Pressure Units
Taught by Meng Chamnan 15
The pressure, p, at the specified point is defined as the limit
'
lim normal
A A
F
p
A
2
1 1 /pascal N m
3 2
5 2
6 2
1 10 /
1 10 /
1 10 /
kPa N m
bar N m
MPa N m
5 2
2
1.01325 10 /
14.696 / .
N m
lbf in
1 standard atmosphere (atm)
16. Specific Volume
Taught by Meng Chamnan 16
1/v
m
n
M
molar basis in terms of the kilomole (kmol) or the pound mole
(lbmol)
The number of kilomoles of a substance, n, is obtained by dividing
the mass, m, in kilograms by the molecular weight, M, in kg/kmol
specific volume v is defined as the reciprocal of the density
SI units for density
and specific volume
are kg/m3 and m3/kg
17. Example 4:
Atomic and molecular weights of some common
substances are listed in Appendix Tables T-1 and T-
1E. Using data from the appropriate table,
determine:
(a) the mass, in kg, of 20 kmol of each of the
following: air, H2O, CO2.
(b) the number of lbmol in 50 lb of each of the
following: N2, NH3, C4H10.
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18. Example 5:
A spherical balloon has a diameter of 10 ft. The
average specific volume of the air inside is 15.1
ft3/lb. Determine the weight of the air, in lbf, at a
location where g = 31 ft/s2.
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19. Temperature Scale
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Taught by Meng Chamnan
273.15o
T C T K
1.8o
T R T K
459.67o o
T F T R
1.8 32o o
T F T C
A process occurring at
constant temperature is
an isothermal process.
20. Example 6:
Convert the following temperatures from oC to oF:
(a) 21 oC,
(b) 17.78 oC,
(c) 100 oC,
(d) 273.15oC.
Convert each temperature to oR.
Taught by Meng Chamnan
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