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On this topic, we (wiktec Team) have tried to explore the complete analysis of the thermal engineering portion or, you may say, thermodynamics with all of its applied formulas with basic concepts in competitive or semester-wise examinations. Dear aspirant, please take a moment to read the full articles, which will be your appreciation and trust in us as we help you achieve your goals.
Table of ContentsThermodynamics:Definition:Basic Concepts:System
Vs Surrounding Vs Boundary:
|
Thermodynamics:
Definition:
It deals with the study of energy and its transformations, how energy is transferred between systems, and how it changes subsequently.
Not only does it deal with
energy, but it also has an extensive relation to heat, work, temperature, and
all physical properties of substances, governed by fundamental laws.
Basic Concepts:
System Vs Surrounding Vs Boundary:
A
System, where a quantity or a region within a space is enclosed. But exclude
the system, rest of the whole part left is Surrounding. If we consider both the
system and surrounding, we see the whole Universe. Both System and Surrounding
are detached via medium is Boundary, where the boundary may be fixed or
motionable. These parameters are very interesting and exclusive to study and
its application in various fields efficiently.
 |
| [System, Surrounding and Boundary] |
Now take a look on some basics more detailed:
Here, we can categorize the System into three following segments, such like Closed System, Open System & Isolated System.
|
Types |
Mass Transfer |
Energy Transfer |
Applications |
|
Closed |
No |
Yes |
Piston cylinder alignment |
|
Open |
Yes |
Yes |
Compressor, Turbine, Pump & Nozzle |
|
Isolated |
No |
No |
Universe, Thermoflask |
Control Volume and Control Surface:
If we go for analysis of open
system in thermodynamic, such like Air Compressor, where there is a certain
region or volume within a space surround the compressor called as Control
Volume, and the surface bounded by it called as Control Surface.
Here, we take a pictorial example
for this.
 | |
|
Basic Properties of Thermodynamics:
let's have a look
The points to be noted, the system properties are point
functions and exact or perfect differentials, for example internal energy,
enthalpy, entropy etc. We will discuss more detailed later.
Here, we have differentiated the properties into two categories. Such as Intensive Properties and Extensive Properties. You may follow such like, it's easy to understand.
|
System
Properties with e.g. |
Mass
Dependent |
Mass
Independent |
|
Intensive e.g. Pressure, Temperature etc |
No |
Yes |
|
Extensive e.g. Volume,
Energy etc |
Yes |
No |
|
Specific
Extensive e.g. Sp. Volume
Sp. Energy, Density |
Extensive
Properties per unit Mass |
|
Thermodynamic Equilibrium:
Any system that should be satisfied all the conditions under mechanical, chemical and thermal equilibrium.
Now look at this
|
Types of Equilibrium |
Equality State |
|
Thermal |
Temperature |
|
Mechanical |
Forces
and Couples |
|
Chemical |
Chemical
Substances |
Processes and Cycles:
Let's take a graphical representation:
 |
| Cycle vs Process |
Above the P-V diagram, what we
see, the change of state or phase is considered as Process of a system. But the
series of states, where a system goes through a process is considered to be a
path of process.
A Process means the system changes from one equilibrium state or position to other equilibrium state or position.
But if, we consider a Cycle, then all the processes within a system have a capability to restore its original state or position at the end of the process, which we have already figured out above under P-V diagram.
Here, we have discussed about
Process one by one.
Reversible Process Vs Irreversible Process:
Without any changes under whole
universe, both system and surrounding restore to their initial states at the
end of the reverse process. That's mean, restoration will possible.
Where in case of irreversible
process, both system and surrounding do not restore its original or initial
state, once the process begins. That's mean, the surroundings usually do some
work on the system, for such case restoration never possible.
Points to be remembered: -
When the initial and final points
are identical, the system possess a Cycle
During a Cyclic Period, the
change in property is Zero
Now, we have discussed another process
Quasistatic Process Vs Non-Quasistatic
Process:
See the above figures of both Quasistatic and Non-quasistatic Equilibrium: -
for Quasistatic-equilibrium slow
process, when we move the piston slowly, then the molecules have much time to
redistribute or escape without any overlap over piston head inside the
cylinder, which will result uniform pressure execute at all locations. This
kind of process is called as quasistatic-equilibrium.
where for non-quasistatic
equilibrium fast process, when we move the piston rapidly, then the molecules
don't have much time to escape, otherwise the molecules rise in a small region
in front of piston head.
Some More Processes about:
Isothermal Process Vs Isobaric Process Vs Isochoric Process:
For Isothermal Process:
During such process, the
temperature(T) remains constant.
For Isobaric Process:
During such process, the pressure(P) remains constant.
For Isochoric Process:
During such
process, the specific volume(V) remains constant.
For Steady-Flow Process:
During such
process, the volume(v), the mass(m), and the total energy (E) of the control
volume remain constant.
N.B: - No changes occur
within the control volume with time.
For Unsteady-Flow Process:
During such
process, the mass and energy factors of the control volume as well as energy
interactions occur across the boundary.
N.B: - Changes occur within
the control volume with respect to time.
Thermostatics:
The word 'Thermostatics' signifies that all properties
with the systems under in equilibrium conditions in thermodynamics. That's mean
the properties like temperature, pressure and volume remain constant over
time. However, most of the real processes are non-quasi-static and dynamic
in nature.
Units and Dimensions:
In all engineering fields,
basically we use SI (System International) units.
Here, we have discussed all
quantities under both fundamental units and derived units of the system
with respect to their symbols and SI units.
|
Fundamental Units |
||
|
Physical Quantity |
SI Units |
Symbol |
|
Mass |
Kilogram |
kg |
|
Length |
Meter |
m |
|
Time |
Second |
sec |
|
Temperature |
Kelvin |
K |
|
Electric
Current |
Ampere |
Amp |
|
Luminous
Intensity |
Candela |
cd |
|
Substance
Amount |
Mole |
mole |
|
Plane
Angle |
Radian |
rad |
|
Solid
Angle |
Steradian |
sr |
|
Derived
Units |
||
|
Physical
Quantity |
SI
Units |
Symbol |
|
Force |
Newton |
N |
|
Area |
m^2 |
length
square |
|
Volume |
m^3 |
length
cube |
|
Density |
kgm^-3 |
mass/volume |
|
Energy |
Joule |
J |
|
Power |
Watt |
W |
|
Velocity |
ms^-1 |
displacement/time |
|
Pressure |
Pascal |
pa |
|
Frequency |
Hertz |
hz |
|
Linear
momentum |
Kgms^-1 |
Mass
X velocity |
|
Electric
charge |
Coulomb |
C |
|
Electric
potential |
Volt |
V |
|
Capacitance |
Farad |
F |
|
Resistance |
Ohm |
R
(ohm) |
|
Magnetic
flux |
Weber |
Wb |
|
Flus
Density |
Tesla |
T |
|
inductance |
Henry |
H |
Gibb's Phase Rule:
 |
| T:100 degreeC T:150 degreeC T:200 degreeC |
Here, we have marked that, as per the
Gibb's Phase rule, a single-component, two phase-system should have only one
independent variable.
The points to be noted that a single
component two phase system should exist in equilibrium state at different
temperatures or pressures. Once the temperature is fixed, the entire system
will fall into equilibrium state.
Hence, P + F = C + 2
(Valid at Equilibrium
Condition)
Where, P is expressed as no. of phases
(Solid, liquid and gas)
F is expressed as minimum no. of independent intensive properties
(Degree of Freedom)
C is expressed as no. of components in equilibrium state.
or it may also be expressed as
IV = C - PH + 2
Where, IV is expressed as no. of
independent variables
C is expressed as no. of Components
PH is expressed as no. of phases exist in equilibrium state.
For single component C=1, where
two-phase PH=2
Force:
Any external agent applying on a particular body or
object, then it tends to move or change its position in a certain direction of
applying force.
Where F = m X a
F=Force, m=Mass & a=Acceleration
SI unit of Force is Newton(N), hence 1N= 1kilogram
per Second Square
Or you may say it like this, the product of its mass of
the body or object and the gravitational acceleration. You may also express as
it is in Weight of the body.
W= m X g
Where, we can be expressed as W= weight of the body, m=
Mass of the body & g=Acceleration due to gravity, where the value of
g=9.807 m/Sec Square
Note: The define weight per unit volume of a substance is
called Specific Weight(γ)
Specific Weight(γ)= Density(ρ) X Gravitational
acceleration(g)
Pressure:
A normal force acted by a fluid per unit area of the
specified region, it may be gas or liquid.
Where P (Pressure) = F (Force) per unit Square Area
SI unit of Pressure is Pascal (Pa), hence 1Pa= 1N/Square
Meter
The points to be noted, the Pressure is measured as pascal,
which is very small in unit.
Also, there are another two units of pressure, we can use
often bar and atm. (atmospheric)
1bar =10^5 Pascal
1atm=101.325
More about Pressure Gauges:
Pressure Gauge:
The basic principle of pressure gauge is to convert the
fluid pressure into measurable or needful output as per our requirement.
Here, we have discussed about Zero Pressure or Vacuum
Pressure, Absolute Pressure & Gauge Pressure.
Zero Pressure or Vacuum Pressure:
The pressure below the atmospheric pressure is called as
Vacuum Pressure, or you may say it as expression term as the difference between
the atmospheric pressure and absolute pressure.
Absolute Pressure:
The pressure exists and measures from relative to absolute
vacuum (zero pressure) or you can express as it as the difference between
atmospheric pressure and vacuum pressure.
Gauge Pressure:
The Pressure exists correspond to the atmospheric or you may
consider as it is the difference between absolute pressure and the local
atmospheric pressure.
Here, we have symbolized by a diagram presentation for your
better understanding.
Here, we have analysed from above from both diagram that
Pabs = Patm - Pvac
Pgauge = Pabs - Patm
Where, Pabs =Absolute Pressure, Patm = Atmospheric
Pressure, Pvac=Vacuum Pressure & Pgauge = Gauge Pressure
Specific Volume(v):
The volume(v) of a substance per unit mass and it’s
measured in cubic meter per kg(m^3/kg).
Density(ρ):
The mass (m) per unit volume of a substance and it’s
measured in kg per cubic meter(kg/m^3).
That's mean, you may say it as like the reciprocal of
density(ρ) is also considered as the specific volume of a substance.
Molar Specific Volume (vm):
The mole of a substance having
mass, which is equal to the molecular weight of the substance. The measurement
of the molar specific volume (vm) is m^3/kmol.
N.B. One gm mole of
Oxygen (O2) having a mass 32gm and 1kg mole of Nitrogen having mass of 28kg.
Energy:
The ability of doing some work to
execute an external agent like force a distance. There are two circumstances,
where body is able to do work.
When the body is in motion
condition or the body is strained or stored position.
The unit of Energy in SI unit is
Nm (joule).
Here, if we consider the energy
per unit mass is called as the specific energy and its unit is J/kg.
Power:
How much the
rate of energy, we can transfer or storage is called power. The unit of power
is Watt(W).
1W=1J/s=1Nm/s or you may express it as P=Work Done/Time(W/t).
1kW=1000 Watt
Work:
When we apply a constant force on a particular body, then
the body moves in a straight line in the direction of force apply. Also, we can
express as the product of force (F) and the distance(s) through which body
moves.
Hence, we can also write as W=F.s
Here, its SI unit is Nm (Joule).
|
N.B. The points to be noted
that if Work is done by the system, then the system is Positive(+ve).
Similarly, if Work is done on the system, then the system is Negative(-ve).
More about Work:
The points to be noted that Work is a path function and
inexact or imperfect differential. Work is not considered as a property.
For quasi-static process (reversible) process, work
done(W) from 1 to 2 position is considered as ∫pdV.
Some assumptions should be taken from above expression:
1.The system should be Closed System.
2.The process should be reversible.
3.The work done should cross the boundary.
Some important points:
If the
process should be Irreversible, then the irreversibility should be satisfied as
following conditions:
It must be
Quasi-static equilibrium with friction and non-equilibrium process.
That's
mean ∫dW = ∫Pexternal dv
But case of
reversible process Pexternal =Pinternal
Now,we can
analyse the various processes by P-V diagram.
 |
|
|
|
|
Process |
k |
|
P=constant |
If, k=0 |
|
V=constant |
If, k= ∞ |
|
T=constant |
If, k=1 |
|
Adiabatic |
If, k= γ |
|
Polytropic |
If, k=n |
Here, we have discussed about Closed System vs Open System Work:
Closed System Work under various processes:
We have already discussed earlier about the various
processes like isothermal, isochoric & isobaric etc.
Now, we can analyse work done under such various process.
|
Process |
Work done |
|
Constant Volume
(Isochoric) |
W1-2=0 |
|
Constant Pressure
(Isobaric) |
W1-2 =p(V2-V1) |
|
Constant Temperature
(Isothermal) |
W1-2 =p1V1ln(p1/p2) |
|
Adiabatic (Isentropic) |
W1-2 = p1V1- p2V2/ γ-1 |
|
Polytropic (pV^n constant) |
W1-2 = p1V1- p2V2/n-1 |
Under Closed System work,
there are some conditions to satisfy the reversible as well as irreversible
process.
For reversible closed system,
the work done(W) is W= ∫pdV ; P=Pexternal =Pinternal
Where for irreversible closed
system, the work done(W) is W= ∫PexternaldV
That's mean Pexternal ≠ Pinternal
Open System Work:
Under Open System Work, it should
satisfy the following criteria in P-V diagram.
 |
| Open System Work in P-V diagram |
∫dW = ∫vdp from the pressure(P1) to
pressure(P2).
Form these above two systems of work, we got to know that
in Closed System work can obtain under Volume axis of P-V diagram and Open
System work can obtain under Pressure axis of P-V diagram.
Specific Heat Vs Latent Heat Vs
Specific Heat Ratio:
Here, we have discussed about Specific Heat and Latent
Heat of the substance.
Where, the specific heat(c) of a substance is the
amount of heat necessary to raise a unit mass in (kg/gm) of a substance by unit
temperature in (degree Celsius/kelvin) raise.
The specific
Heat(c) can be expressed as c=[Q/mcΔT]
Here, we have converted its unit as J/kgK;
Where Q is expressed as Joule, the amount or mass(m) of a substance expressed
as kg and unit temperature(ΔT) raise expressed as Kelvin(K).
The Specific heat ratio (γ) is the ratio between
constant pressure (Cp) and constant volume (Cv). The specific heat
ratio (γ)= Cp/Cv
Some Consideration for Air at time of problem solving,
the sp.heat ratio(γ)=1.4; Cp=1.005 kJ/kgK ; Cv=0.718 kJ/kgK ; R=0.287
kJ/kgK
N.B. Here, if we consider the
mass and specific heat and their products, then we get Heat Capacity of a
substance. That's mean the product of mass(m) and specific heat(c) is expressed
as mc=Cp. Where Cp is called as Heat Capacity.
Similarly, for the Latent Heat(l), the amount of
heat necessary to change the phase in a unit mass of a substance through a
constant pressure and temperature.
Basically, we have three phases like Solid, Liquid and
Gas or you may say vapour.
Under these phases, there are some changes, which occur
at specific amount of heat supply in the system.
We have discussed one by one.
Latent heat of fusion (Ifu):
The required amount of heat is necessary to melt the unit
mass of solid into liquid or you may freeze the unit mass of liquid into solid
condition.
Latent heat of vaporization (Ivap):
Similarly, the amount of heat necessary to make vapour
the unit mass of liquid into vapour state.
Latent heat of sublimation (Isub):
The amount of heat necessary to change the unit mass of
solid into vapour or Vapour into solid.
Applications:
Apart from all of this above discussion, now we have
signified some points of applicable field of Thermodynamics. Today's technology
is very fast and next gen scenario, always we have been seeing it.
Thermodynamics is preferable used or you may say applicable in many engineering
sectors, which is very essential part of our daily life.
Let's take an example of our daily life
When we pour some hot water into a cup, we see that the
temperature of water contaminates with wall of cup as well as atmosphere, after
some couple of periods, it becomes neutralise with atmospheric
temperature. That's mean the extraction of temperature flows from higher medium
to lower medium always. So, it implies that the Law of Second in
Thermodynamics, which we discuss next post.
Thermodynamics principle has large scale of application
area, no doubt, it plays significant role in engineering systems. We design
many engineering parts like solar hot water system, refrigerator, pressure
cooker, water heater, the computer and TV also. There are also many applicable
areas of our household parts.
Conclusion:
In this post-discussion, we are emphasizing the
point-to-point bullet lines, or, concisely, the topic of the basic principles
of thermodynamics, or you may say fundamental ideas, only with most relevant
and important explanations, as well as its formulas to help our readers with
their revision and enable them to move confidently towards success. We wish you
to ace your path significantly.
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