# Thermo by paohugnan

VIEWS: 55 PAGES: 15

• pg 1
```									1. Some Introductory Comments

Examples of the processes that involve
in Thermodynamic

• power plants: steam or gas turbine

• refrigerators and air-conditioning
units

• internal combustion engines

• jet or rocket engines
2. Some Concepts and Definitions

Thermodynamics:
the science that deals with

• energy

• entropy

• related properties of a substance

The basis of thermodynamics is based
on an experimental observation.
Mainly, there are four basic laws in
Thermodynamics, i.e., the zeroth, first,
second, and third laws.
2.1 The Thermodynamics System and
Control Volume

A control mass (closed system):

• fixed mass

• movable or fixed boundary
A control volume (open system):

• involves flows

• allows mass, momentum and energy
flowing across the control surface

Note: It is very important to recognize
the type of the system before
starting the analysis !
2.2 Macroscopic Versus Microscopic
Points of View

1) Classical Thermodynamics
• macroscopic or “gross average”
quantities
• continuum concept

2) Statistical (or Microscopic) Thermo-
dynamics
• “statistical” values of the molecules
• effects of microscopic behavior on
macroscopic quantities
2.3 Properties and State of a Substance

Phase: a quantity of a matter that is
homogeneous throughout

Property: any characteristic of a system
• Intensive Properties: independent of
mass
• Extensive Properties: varies directly
with mass

State: a set of properties that
completely describe the condition

Thermodynamics Equilibrium:
• Mechanical Eq.: no change in P
• Thermal Eq.: no change in T
• Phase Eq.: no change in mass of each
phase
• Chemical Eq.: no change in chemical
composition
2.4 Process and Cycle

Process: a path of the succession of
states through which the system passes.

Quasi-equilibrium Process:
a sufficiently low process, in which the
deviation from the thermodynamics
equilibrium is infinitesimal.
isothermal process: constant T
isobaric process: constant P
isochoric process: constant V
Cycle: a system that returns to the
initial state at the end of
processes
Quantities                SI               U.S Custom
2.5 Units

Unit         Symbol    Unit     Symbol
Mass          Kilogram         kg      Slug      Slug
Length          Meter           m       foot       ft
Time          Second           s      Second      s
Temperature       Kelvin          K      Rankine     R
Number of matter    Mole           mol      Mole      mol
2.6 Energy

Energy can be
• defined as the capability to produce
an effect
• stored within a system
• transferred from one system to
another

Three general forms of energy
• intermolecular potential energy:
forces between molecules
• molecular kinetic energy:
translational velocity of molecules
• intramolecular energy:
forces related to molecular and
atomic structure
2.7 Specific Volume and Density
Specific volume (v or v ) [m3/kg or
m3/mol]:
the volume per unit mass (or mole)
Density (ρ or ρ ) [kg/m3 or mol/m3]:
the mass (or mole) per unit volume
2.8 Pressure

Pressure (P) [N/m2 or Pa]:
the normal component of forces per
unit area
Other commonly used units: bar, atm
absolute and gauge pressure:
Manometer

The pressure P can be measured as
follows:

∆P = P − P o = ρ g H
2.9 Equality of Temperature

Temperature (T) [oC or K]:
a sense of hotness and coldness (but
this definition is not reliable)

Equality of temperature:

For an iron block and a copper block at
different temperature, if they are
brought into thermal communication,
after a long period of time, both objects
have equality of temperature.
2.10 The Zeroth Law of
Thermodynamics

If an object A has an equality of
temperature with a thermometer M,
if an object B has an equality of
temperature with a thermometer M, and
if both thermometers reads the same
scale, we conclude that both objects (A
and B) are in an equality of temperature
as well.

2.11 Temperature Scale

Most commonly used scale:
Celsius (oC) and Fahrenheit (F)
Both scales are based on the freezing
and boiling points of water at 1 atm.

Absolute scale:
Kelvin (K) and Rankine (R)
T(K) = T(oC) + 273.15
T(R) = T(F) + 459.67

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