Thermodynamics-I
Pakistan Institute of Engineering and Applied Sciences,
Islamabad
MUJEEB UR REHMAN ATIF
1
Course Content
Basic concepts; dimensions and units; system and control volume; properties of system; state and equilibrium; process and
cycles; temperature and zeroth law; pressure and pressure measurement devices; energy and energy transfer; first law of
thermodynamics; energy conversion efficiencies; pure substance, phases of pure substance, phase change process of pure
substance; property diagrams for phase change process; evaluating the properties of vapors using property tables; ideal gas
equation; compressibility factor and using generalized compressibility charts; other equation of states; energy analysis of closed
systems (understanding p-v diagrams with application of 1st law of thermodynamics on constant pressure, constant volume,
isothermal, reversible adiabatic and polytropic process’ for vapors and ideal gases); internal energy, enthalpy and specific heats
for ideal gases, solids and liquids; mass and energy analysis of control volumes; introduction to 2nd law of thermodynamics and
its perspectives, Kelvin and Clausius statements; reversible and irreversible process; Carnot cycles (forward and reversed);
Carnot principle; thermodynamic temperature scale; introduction to entropy; increase of entropy principle; understanding T-s
diagrams for reversible processes (for vapors and ideal gases); determination of heat, work and change in entropy for reversible
processes in closed systems; entropy change for liquids and solids; isentropic efficiencies of steady flow devices; entropy balance
for closed and open systems.
Recommended Texts
❑Y A Cengel, M A Boles, Thermodynamics, An Engineering Approach, 8th Ed, McGraw Hill, 2014.
❑C Borgnakke, R E Sonntag, Fundamentals of Thermodynamics, 8 th Ed, Wiley, 2012.
❑M J Moran, H N Shapiro, Fundamentals of Engineering Thermodynamics, 8th Ed, Wiley, 2014.
❑T D Eastop, A Mcckonkey, Applied Thermodynamics for Engineering Technologists, 5th Ed, Pearson, 1996.
2
Course Learning Outcomes
Taxonomy level
PLO #
1
DESCRIBE the basic concepts and scope of fundamental
Cognitive
laws of thermodynamics.
2
1
2
DETERMINE state characteristics for working
substances (gas and vapor) undergoing various Cognitive
thermodynamic processes.
3
2
3
ANALYZE closed and open systems using 1st and 2nd
Cognitive
Law of Thermodynamics.
4
2
Sr. No. Specific Course Learning Outcomes:
Knowledge
Domains
Upon completion of this course, the students will be able to:
3
Chapter 1
4
What is thermodynamics?
Two Greek words
“Therme”
(Heat)
“Dynamics”
(Power)
Other energy forms
Electrical energy
Mechanical energy
Chemical energy
Potential energy
Mechanical energy
Internal energy
Branch of science that deals with the heat and work and
properties of substance that have relation with heat and
work.
Energy flows in the form of heat when two systems with difference in
Temperature interact with each other.
Temperature is a property of a system
5
What is thermodynamics?
Examples of Energy conversion;
Electric heater : converts electrical energy into heat energy.
Falling stone: Potential energy is converted into kinetic energy of
stone.
Heat Engines: converts heat energy into mechanical work.
Combustion engines: are type of heat engines that convert chemical energy of fuel (petrol, diesel etc.) into
heat and then convert into work (shaft work).
All the phenomena and devices are governed by three Laws of thermodynamics;
First law, Second law and Third law of thermodynamics.
Details of these laws will be studied later.
6
Dimensions and Units
❖To measure any physical quantity in a thermodynamics phenomena is we need Dimensions.
Primary dimensions:
❖Length L
❖Mass m
❖Time t
❖Temperature T
❖Intensity of Light
❖Amount of Matter N
❖Electric Current I
Secondary/derived Dimensions:
Combination of above primary dimensions. e.g.
❖Volume
❖Force
❖Energy
7
Unit system
Absolute system
❖Force is defined in terms of length, mass,
time
❖Force is derived quantity
Gravitational System
❖mass is defined in terms of length, force,
time
❖Mass is derived quantity
Example: SI system
Example: English System
Dimension
Unit
Dimension
Unit
Length
m
Length
ft
Mass
kg
Mass
Slug* (32.174 lbm)
Time
S
Time
S
Temperature
K
Temperature
oF
Force
N* (kg .m /s2)
Force
lbf (32.174 lbm. ft/s2)
Energy
Joule
Energy
Btu
pressure
Pa (N/m2)
pressure
Psi (lbf/ in2)
8
Unit System
SI System
W = mg
1 N = 1kg . m / s2
British System
W = mg
1 lbf = 1 slug . ft / s2
1 slug = 32.174
1 lbf = 32.174 lbm. ft / s2
9
Unit Conversions
1kg
1m
1N
1Btu
1oC
1calorie
1 hp
1 kgf
1 lbf
1 bar
1 atm
1 hp
2.2 lbm
3.48 ft
0.224 lbf
1.9551 J
273K
4.186 J
746 W
9.81 N
32.174 lbm.ft/s2
105 N
101325 Pa
550 lbf. ft/sec
10
Problem # 1
A 150-lbm astronaut took his bathroom scale (a spring scale) and a beam scale (compares
masses) to the moon, where the local gravity is g = 5.48 ft/s2. Determine how much he will
weigh (a) on the spring scale and (b) on the beam scale.
Ans: a:) 25.55 lbf b:) 150 lbf
11
12
System, Surrounding and Boundary
System: it is amount of matter, region in space under consideration/study.
Surrounding: Matter and space around the system is called surrounding.
Boundary: The real or imaginary surface that separate system from surrounding.
Boundary can be stationary or moving.
Whole universe other than
selected for system can be
considered as surrounding.
13
System Classification
The system classification based on its type of interaction (mass and energy) with surrounding.
System
Open System
(Control
volume)
Closed System
(Control mass)
Isolated
System
14
Open System
Open System:
✓ Mass can enter and leave the system.
✓ Energy can enter and leave the system in the form of
work and heat.
✓ It is also called control volume.
The boundaries of a control volume are called control surface
and
can be real or imaginary.
And
can be moving or stationary.
❖ It usually encloses a device that involves mass flow such as a compressor, turbine, or nozzle.
❖ Flow through these devices is best studied by selecting the region within the device as the control volume.
15
Closed System
Closed System:
✓ System has fixed mass, No mass can cross the boundary.
✓ Energy can enter and leave the boundary in the form of heat and
work.
✓ It is also called Control mass system.
The boundaries of a control can be
real or imaginary.
And
can be moving or stationary.
16
Isolated System
Isolated System:
✓ System has fixed mass, No mass can cross the boundary.
✓ System has fixed energy, No energy can cross the boundary in the form of heat and work.
✓ It is also called Control mass system
No system in this universe is practically isolated.
But in theory, for mathematical simplifications, a system can be considered as an isolated system.
Surrounding
Heat/work
mass
System
Boundary
17
Identify the System Type
Closed System
Open System
Open System
18
Properties of a System
Whenever you buy a product. e.g. a mobile
you check its specifications.
Whenever you have a system.
You check its characteristics.
Screen Size, Weight,
Mass, Volume, density
Any characteristic of a system is called property.
List of Properties of a system
Pressure “P”
Temperature “T”
Viscosity “ν”
Thermal conductivity “K”
Modulus of elasticity “E”
Coefficient of thermal conductivity “α”
Velocity “v”
Elevation “h”
Electrical Resistivity “ρ”
19
Properties(Types)
Intensive Properties
Properties that are independent of size (mass) of a system.
e.g. Pressure, Temperature, thermal conductivity
Extensive Properties
Properties that are dependent of size (mass) of a system.
e.g. Volume, momentum
Properties
Extensive properties are symbolized by uppercase letter (with major exception of mass “m”.)
Intensive properties are symbolized by lowercase letter (with major exception of pressure “P” and temperature “T”.
Extensive property divided by mass are called Specific properties.
𝐸
e.g. 𝑇𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦: 𝐸
= 𝑒 = 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑡𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦
𝑚
20
Extensive v/s Intensive
Divide the system into two equal parts;
If value of property is halved; it is an extensive property e.g. volume
If value of property is remain same; it is an intensive property e.g. pressure
21
Specific Properties
Specific volume; Ratio of volume “V” to the mass of system “m”.
𝑉
𝑚
1
𝜈=
As, 𝜌 =
𝜌=
𝑚
𝑉
𝜈
Specific Gravity; The ratio of the density of a substance to the density
of some standard substance at a specified temperature (usually water
at 4°C, for which ρH2O = 1000 kg/m3)
𝜌
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝐺𝑟𝑎𝑣𝑖𝑡𝑦 =
𝜌𝐻2𝑂
Specific weight; Ratio of weight “W” to the mass of system “m”.
𝑊
𝛾=𝑚
𝛾 = 𝜌𝑔
Exericse-1:
A cube 50×50×50 cm3 is filled with water @4oC, if water is replaced
with mercury, what will be the weight of cube?
22
Macroscopic vs Microscopic Approach
System
Continuum
Macroscopic Approach
Classical Thermodynamics
Microscopic Approach
Statistical thermodynamics
Rarified gas theory
• Size of a system is so large as compared to space between atoms.
• Spaces can be neglected.
• Properties are continuous on whole system
•
•
•
•
Method used by human to perceive the characteristics of a system e.g. Tea is hot.
Properties are measured using a measuring instrument e.g. Pressure gauge
Measured property is average of effect of all atoms in system.
Properties are considered to be same for all atoms of system
•
•
•
•
Define properties at molecular level.
Human can not perceive properties at this level.
Properties vary from molecule to molecule.
Statistical approach is used to determine the distribution.
23
Continuum
Rarified Gas
Gaps between molecules can not be neglected
Continuum
Gaps between molecules can be neglected
24
State
The condition of a system is called state.
State of a system is defined by determining/measuring the properties of
system when no changes are occurring in system.
If a single property of a system changes, state of the system changes.
Thermodynamics always deals with system in equilibrium.
Change in volume
State Postulate
The state of a system, in equilibrium, can be completely determined
by the two independent, intensive properties.
State of Nitrogen by two independent intensive properties
25
Equilibrium
❖The word equilibrium implies a state of balance.
❖In an equilibrium state there are no unbalanced potentials (or driving forces) within the
system.
❖A system in equilibrium experiences no changes when it is isolated.
Thermal equilibrium if the temperature is the same throughout the entire system.
Mechanical equilibrium is related to pressure, and a system is in mechanical equilibrium if there is no change in pressure
at any point of the system.
If a system involves two phases, it is in phase equilibrium when the mass of each phase reaches an equilibrium level.
Chemical equilibrium if its chemical composition does not change with time, that is, no chemical reactions occur.
26
Process
The succession of changes through which system passes is called a process.
The series of states through which system passes from initial to final equilibrium
state is called Path.
If a process proceeds in such a manner that the system remains infinitesimally
close to an equilibrium state at all times, it is called a quasi-static, or quasiequilibrium, process.
Quasi-equilibrium process is an idealized process and is not a true representation
of an actual process.
Engineers are interested in quasi-equilibrium processes for two reasons.
• They are easy to analyze
• Work-producing devices deliver the most work when they operate on quasiequilibrium
27
Types of Processes
Isothermal Process: Temperature during the process remains constant.
P
Isobaric Process: Pressure during the process remains constant.
3
Isochoric Process: Volume during the process remains constant.
Isentropic Process: Entropy (will study later) during the process remains
constant.
1
Adiabatic Process: system is isolated from surrounding (No heat and
work flow.)
Cycle:
The series of process that lead the system to its initial
position.
2
v
1-2: Isobaric Process
2-3: Isothermal process
3-1: Isochoric Process
1-2-3-1: Complete cycle
28
Type of processes
Unsteady
The flow properties change with time
Time
Steady
The flow properties do not change with time
Constant
Uniform
The flow properties do not change with location
Non-uniform
The flow properties do not change with location
Location
After 2 hrs
The process is
steady.
29
Temperature
Definition: “It is the measure of hotness or coldness of a body.”
It can be felt by human body through sense of touch.
It is an intensive property.
Two bodies reaching thermal
equilibrium after being brought into
contact in an isolated enclosure.
Temperature is a relative term.
It is necessary and sufficient condition for thermal equilibrium between bodies.
“It is measure of kinetic energy of the molecules of the matter”
As the real zero temperature is unknown, we need a reference against which temperature can be measured.
30
Zeroth Law of Thermodynamics
❖Zeroth law was first formulated and labeled by R. H. Fowler in 1931.
“If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium
with each other.”
TA
TB
TC
❖This law provides basis to validity of temperature measurements.
❑Replace third body with thermometer in above statement.
❑it means if two bodies have same temperature measured using thermometer. They will be in thermal equilibrium, even if
they are not in contact with each other.
31
Temperature Scales
❖Temperature scales are based on some reproducible states.
❑Freezing and boiling temperatures of water at pressure of 1 atm.
❑ Freezing point is also called Ice-point.
❑ Boiling point is also called steam point.
❖Ice-point: the temperature at which ice, water and air saturated with vapors are in
equilibrium with each other at 1-atm.
❖Boiling point: the temperature at which liquid water and water vapors are in equilibrium at 1atm.
❖Temperature is measured in
❑Celsius Scale oC,
❑Fahrenheit Scale oF,
❑Kelvin Scale K
❑Rankine scale R
32
Celsius Scale
❖Used in SI system.
❖Formerly known as centigrade scale.
❖Renamed after A. Celsius who devised this scale.
❖It is a two-point scale.
❖Ice point is given zero value on scale.
❖Steam point is given 100 value on scale.
❖100 equal divisions are made between the ice-point 0oC and steam point 100oC.
❖That’s why it was called “centigrade scale” (centi means hundredth part).
❖Conversion of Celsius and Fahrenheit is given as;
5
𝐶 = [𝐹 − 32]
9
33
Fahrenheit Scale
❖Used in English system.
❖Named after G. Fahrenheit who devised this scale.
❖It is a two point scale.
❖Ice point is given 32o value on scale.
❖Steam point is given 212o value on scale.
❖180 equal divisions are made between the ice-point 0oC and steam point 100oC.
❖Conversion of Celsius and Fahrenheit is given as;
𝐹=
9
𝐶 + 32
5
34
Thermodynamic Temperature Scale
❖A temperature scale that is independent of the properties of any substance or substances.
❖Developed in conjunction with the Second Law of thermodynamics.
❖Kelvin Scale:
❑Thermodynamic temperature scale in the SI is the Kelvin scale, named after Lord Kelvin.
❑Represented by K (Not oK)
❑The lowest temperature on Kelvin scale is absolute zero or 0K.
❑Using nonconventional refrigeration techniques, scientists have approached absolute zero kelvin (they achieved
0.000000002 K in 1989).
❖Rankine Scale:
❑The thermodynamic temperature scale in the English system is the Rankine scale, named after William Rankine.
❑Represented by R (Not oR).
𝑇ℎ𝑒𝑠𝑒 𝑠𝑐𝑎𝑙𝑒𝑠 𝑎𝑟𝑒 𝑢𝑠𝑒𝑑 𝑖𝑛 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛𝑠 𝑜𝑓 𝑡ℎ𝑒𝑟𝑚𝑜𝑑𝑦𝑛𝑎𝑚𝑖𝑐𝑠 𝑙𝑎𝑤𝑠 𝑜𝑓 𝑖𝑑𝑒𝑎𝑙 𝑔𝑎𝑠𝑒𝑠.
35
Thermodynamic Temperature Scale
❖A temperature scale that is independent of the properties of any substance or substances.
❖Developed in conjunction with the Second Law of thermodynamics.
❖Kelvin Scale:
❑Thermodynamic temperature scale in the SI is the Kelvin scale, named after Lord Kelvin.
❑Represented by K (Not oK)
❑The lowest temperature on Kelvin scale is absolute zero or 0K.
❑Using nonconventional refrigeration techniques, scientists have approached absolute zero kelvin (they achieved
0.000000002 K in 1989).
❖Rankine Scale:
❑The thermodynamic temperature scale in the English system is the Rankine scale, named after William Rankine.
❑Represented by R (Not oR).
𝑇ℎ𝑒𝑠𝑒 𝑠𝑐𝑎𝑙𝑒𝑠 𝑎𝑟𝑒 𝑢𝑠𝑒𝑑 𝑖𝑛 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛𝑠 𝑜𝑓 𝑡ℎ𝑒𝑟𝑚𝑜𝑑𝑦𝑛𝑎𝑚𝑖𝑐𝑠 𝑙𝑎𝑤𝑠 𝑜𝑓 𝑖𝑑𝑒𝑎𝑙 𝑔𝑎𝑠𝑒𝑠.
36
Ideal Gas Temperature Scale
❖It turns out to be nearly identical to the Kelvin scale is the
ideal-gas temperature scale.
❖ The temperatures on this scale are measured using a
constant-volume gas thermometer,
❖These thermometers are vessel filled with a gas, usually
hydrogen or helium, at low pressure.
❖At sufficiently low pressure the temperature and pressure of
filled gas follow the relation
𝑇 = 𝑎 + 𝑏𝑃
❖The values of the constants a and b for a gas thermometer
are determined experimentally.
❖The value of “a” comes out to be 273.15oC. and is
unchanged for all gases. If assigned 0K value.
𝑇 = 𝑏𝑃 (in Kelvin Scale)
37
Thermodynamic Temperature Scale
❖Following are the interconversions of temperature scales.
𝐾 = 𝐶 + 273.15
R= 𝐹 + 459.67
𝑅 = 1.8𝐾
The reference temperature chosen in the original Kelvin scale was 273.15
K (or 0°C), which is the temperature at which water freezes (or ice
melts)and water exists as a solid–liquid mixture in equilibrium under
standard atmospheric pressure (the ice point).
Which was later changed to
much more precisely reproducible point, the triple point of water (the
state at which all three phases of water coexist in equilibrium), which is
assigned the value 273.16 K
𝐶
𝐹 − 32
𝑅
𝐾 − 273
=
=
=
100
32
80
100
38
Pressure
Definition:
It is the normal force exerted by the fluid per unit area.
It is a scalar quantity.
Units:
SI System: Pa (N/m2)
British System: Psi (lbf/in2)
1 bar = 105 bars
1 atm = 101325 pa =1.01325 bars
39
Pressure
Absolute pressure:
the actual pressure at a given position is called absolute pressure.
Gauge Pressure:
The pressure measured using a measuring device.
𝑃𝑔𝑎𝑔𝑒 = 𝑃𝑎𝑏𝑠 − 𝑃𝑎𝑡𝑚
Vacuum Pressure:
The pressure of gas below atmospheric pressure.
𝑃𝑔𝑎𝑔𝑒 = 𝑃𝑎𝑡𝑚 − 𝑃𝑎𝑏𝑠
40
Pressure variation with depth
The pressure variation with depth is given by
𝑑𝑃
𝑑𝑧
= −𝜌𝑔
So,
Δ𝑃 = 𝜌𝑔Δ𝑧
OR,
𝑃 = 𝜌𝑔𝑧
In given figure;
𝑃𝑏𝑒𝑙𝑜𝑤 = 𝑃𝑎𝑏𝑜𝑣𝑒 + 𝜌𝑔ℎ
𝑃𝑏𝑒𝑙𝑜𝑤 = 𝑃𝑎𝑡𝑚 + 𝜌𝑔ℎ
Pressure does not vary in horizontal direction.
41
Pascal’ Law
If the pressure is applied to a confined fluid, it increases the pressure throughout by the same
amount. This is called Pascal’s law.
𝑃1 = 𝑃2
𝐹1 𝐹2
=
𝐴1 𝐴2
𝐹1 𝐴1
=
𝐹2 𝐴2
Pascal Law is used in hydraulics too lift heavy objects
42
Pressure Measuring Devices
Barometer:
Manometer:
43
Pressure Measuring Devices
Bourdon gage:
Piezoelectric transducers:
Solid-state pressure transducers, work on the principle that
an electric potential is generated in a crystalline substance
when it is subjected to mechanical pressure.
Deadweight tester (Calibration Device)
44
45
Example
46
Example
Whether the above calculated pressure is absolute or gauge?
47