ME111

THERMODYNAMICS 1
Weeks 1.1 BASIC CONCEPTS ON THERMODYNAMICS

Prepared by: Engr. Estelito V. Mamuyac

26 JULY 2018
INTRODUCTION TO THERMODYNAMICS

Thermodynamics is the branch of science

which deals with the study of energy, its
transformation or conversion from one form to
another and its movement from one location
to another.
therme – means heat
dynamis – means force (strength)
Applications of Thermodynamics
Application Areas
 Heating, Ventilating, & Air-
 Automobile engines
conditioning systems
 Turbines
 Cooling of Electronic
 Compressors, Pumps Equipment
 Fossil- & Nuclear-fueled  Alternative Energy Systems
Power Stations  Fuel cells, thermoelectric
 Propulsion systems for devices, geothermal systems,
wind power, solar, etc.
aircraft & rockets
 Biomedical Applications
 Combustion systems
 Life-support systems; artificial
 Cryogenic systems, Gas organs
separation & Liquefaction
THERMODYNAMIC SYSTEM
Thermodynamic System
-any collection of matter or region in space that occupies a
given volume, has specific boundary, with a thermodynamic
substance and surroundings in which it may interact

Volume – amount of space occupied by matter

Boundary – imaginary surface separating the
system and surroundings
Thermodynamic substance – medium in which
energy can be stored & extracted
Surroundings – anything outside the
boundary in which the system may interact
TYPES OF THERMODYNAMIC SYSTEMS

1. Closed System – mass does not cross boundary

2. Open System – mass does cross
3. Isolated System – there is no interaction with the
surroundings
4. Steady System – state does not change w/ time
5. Unsteady – state changes with respect to time boundary
CLOSED SYSTEM (Control Mass)
Energy, not mass, crosses closed-system boundaries
A closed system consists of a
fixed amount of mass and no
mass may cross the system
boundary. The closed system
boundary may move.

Examples of closed systems

are sealed tanks and piston
cylinder devices (note the
volume does not have to be
fixed). However, energy in
the form of heat and work
may cross the boundaries of
a closed system.
OPEN SYSTEM (Control Volume)
Mass and Energy Cross Control Volume Boundaries

An open system, or
control volume, has mass
as well as energy crossing
the boundary, called a
control surface.

Examples of open systems

are pumps, compressors,
turbines, valves, and heat
exchangers.
 ISOLATED SYSTEM
Isolated System Boundary

Heat = 0 Work

Work = 0 Surr 4
Mass
Mass = 0 System
Surr 3
Across
Surr 1 Mass
Isolated
Heat Surr 2
Boundary

An isolated system is a general system of fixed mass where no

heat or work may cross the boundaries. An isolated system is a
closed system with no energy crossing the boundaries and is
normally a collection of a main system and its surroundings that
are exchanging mass and energy among themselves and no
other system.
 PROPERTY

 Anycharacteristic of a system in
equilibrium is called a property.
 The
property is independent of the path
used to arrive at the system condition.
 Some thermodynamic properties are
pressure P, temperature T, volume V, and
mass m.
 PROPERTY
 Properties may be intensive or extensive.
 Extensive properties are those that vary directly with size---or
extent---of the system.
 Some Extensive Properties
a. mass
b. volume
c. total energy
d. mass dependent property
 Extensive properties per unit mass are called specific properties, ex:
specific volume  = V/m; specific weight  = g
PROPERTY
 Intensive properties are those that do not depend on
the mass of the system
Some Intensive Properties
a. temperature
b. pressure
c. density
d. color
e. any mass independent property
 DIMENSIONS AND UNITS

 Units
Used to characterize any physical quantity
 Dimensions
Magnitudes assigned to dimensions

*The system of units selected for this course is the SI System that is
also known as the International System (sometimes called the metric
system).
*In SI, the units of mass, length, and time are the kilogram (kg),
meter (m), and second (s), respectively.
 Dimensions and Units in Engineering
Thermodynamics
I. Fundamental dimensions → length, mass and time
 Metric unit
MKS: meter (m), kilogram (kg) and second (s)
CGS: centimeter (cm), gram (g) and second (s)
 English unit
foot (ft), pound-mass (lbm) and second (sec)
 Conversions
1 m = 100 cm = 3.28 ft = 39.37 in
1 kg = 1000 g = 2.204 lbm
1 s = 1 sec
 Dimensions and Units in Engineering
Thermodynamics

II. Derived dimensions → based on primitive units

(a) Force
derived unit from Newton's second law, i.e.,
F = mass x acceleration = ma
Metric unit MKS: Newton (N)
English unit: pounds (lbf)
cgs: dyne
Conversions
1 N = 1 kg m s-2 = 105 dynes = 0.2248 lbf
 Dimensions and Units in Engineering
Thermodynamics

 The term weight is often misused to express mass. Unlike

mass, weight is a force. Weight is the gravitational force
applied to a body, and its magnitude is determined
from Newton's second law.
W = mg (for English units: divide by gc to convert lbm to lbf)
where m is the mass of the body and g is the local gravitational acceleration
(g is 9.807 m/s2 at sea level and 45o latitude).
 Dimensions and Units in Engineering
Thermodynamics

 The weight of a unit volume of a substance is called the

specific weight  and is determined from  =  gc where 
is density.
gc = dimensional constant

Weight changes w/ a change in gravitational

acceleration
* A body weighs less on top of a mountain; on the
surface of the moon, an astronaut weighs 1/6 of his
weight on earth.
 Examples
Example 1
An object at sea level has a mass of 400 kg.
a) Find the weight of this object on earth.
b) Find the weight of this object on the moon where the local gravitational
acceleration is one-sixth that of earth.
Example 2
An object has a mass of 180 lbm. Find the weight of this object at a
location acceleration is 30 ft/s2.
Example 3
An astronaut weighs 730N in Houston, Texas where the local acceleration
of gravity is 9.792 m/s2. What is the mass of the astronaut, and what does
he weigh on the moon, where g = 1.67 m/s2?
 THERMODYNAMIC PROPERTIES
Density of a substance is defined as the ratio of its mass to its volume.
ρ = m/V where: m - mass, in kgs., lbs.
V - volume, in cu.m., cu.in.

Specific Volume is the reciprocal of density, ratio of its volume to its

mass.
ν = V/m

Specific Gravity (or Relative Density) is defined as the ratio of the density
of the substance to the density of an equal volume of water.
S.G. = ρs / ρw
Weight is the force acting on a body due to the earth’s gravity.
W = mg/gc where gc = 1 kgm– m / N - s2 = 32.2 lbm – ft / lbf –s2
Specific Weight (or Weight Density) is the force exerted by gravity per
unit volume.
‫ = צּ‬W/V = mg/gcV = ρ g/gc
Pressure is defined as the normal force per unit area.
Also defined as force exerted by the fluid per unit area of surface.
P = F/A
Temperature is an indicator of energy, measure of hotness or coldness
of a body.
 PROBLEMS
1. What is the weight of a 1 kg mass at an altitude where the local
acceleration of gravity is 9.75 m/s2 ?
2. A 1 m3 container is filled with 0.12 m3 granite (SG=2.75), 0.15 m3 sand
(SG = 1.5), 0.2 m3 of liquid 25◦C water (density = 997 kg/m3); the rest
of the volume, 0.53m3, is air with a density of 1.15kg/m3. Find the
overall (average) specific volume and density.
3. Two liquids of different densities (ρ1=1500 kg/m3 , ρ2=500 kg/m3) are
poured together into a 100 L tank, filling it. If the resulting density of the
mixture is 800 kg/m3. Find the respective amounts of liquids used.
4. The mass of a fluid system is 0.311 slug (1slug=32.174lbm); its density
is 30 lb/ft3 & g= 31.90fps2. Find (a) the specific volume, (b) the specific
weight, (c) the total volume.
 Dimensions and Units in Engineering
Thermodynamics
(b) Pressure
P = force/area = F/A
Metric unit MKS: Bar (bar)
English unit: atmosphere (atm)
cgs: pascal (Pa)
Conversions
1 bar = 100 N m-2
= 100 kPa
= 100 dyne cm-2
= 0.986 atm = 14.504 psia = 750 torr
1 atm = pressure exerted by the air at sea level
1 atm = 760 mm Hg = 14.7 psia = 101.325 kPaA
1 psia = 1 pound per square inch
Dimensions and Units in Engineering
Thermodynamics
Atmospheric Pressure
Pressure Measurement
 Barometers – pressure of the atmosphere
 Manometers – fluid pressure
P = gh where h= height of the fluid in the
column
Pressure Measurement

• Small to moderate pressure differences are measured by a

manometer, and a differential fluid column of height h
corresponds to a pressure difference of

where  is the fluid density and g is the local gravitational

acceleration.
 Practice Problems
1. The height of water from the base of a rectangular tank is 1.5 m.
The base measures 100cm. by 80cm. Compute
a.) the weight of the water in the tank.
b.) the pressure exerted by the water at the base of the tank.
2. A pressure gauge connected to a pressure vessel reads 110
kPa. Compute for the absolute pressure. Assume that the
standard atmospheric pressure is 101.325 kPaA.
3. The gauge on a closed container indicates 90 kPaA. What is the
absolute pressure?
4. You dive 5 m. down the ocean. What is the absolute pressure
there?
5. A weatherman carried an aneroid barometer from the
ground floor to his office atop the Sears Tower in Chicago. On
the level ground, the barometer reads 30.15in.Hg.A; topside
read 28.607in.Hg.A. The average atmospheric air density was
0.075 lb/cu.ft. Estimate the height of the building.
 Textbooks & References

• Textbook
 Fundamentals of Engineering Thermodynamics, by Moran
and Shapiro, 2010, John Wiley and Sons
• References
 Fundamentals of Thermodynamics, 7th Edition, Claus
Borgnakke & Richard E. Sonntag, John Wiley and Sons 2009
 Thermodynamics: An Engineering Approach, by Yunus A.
Cengel, 2006
 Thermodynamics, by Jose Francisco, 2006 Edition
 Thermodynamics: Concepts and Applications, by Stephen
Turns, 2006 Cambridge University Press
 Thermodynamics Demystified, by Merle Potter, McGraw-Hill
Companies, 2009