2. Thermodynamics is the study of how heat can be transformed
into useful energy in the form of work, hence the
name thermo + dynamics.
LAWS OF THERMODYNAMICS:
1) Zeroth law of thermodynamics
Its states that if two systems A and B are in thermal equilibrium
with the third system C are also in thermal equilibrium with each
other
3. For example: Consider two glasses of water, one having hot
water and other having cold water. Now if you leave them in
table for few hours they will attain thermal equilibrium with
the temperature of room.
2) 1ST law of thermodynamics
Its states that energy can neither be created nor
Be destroyed but it can only change from one form to other.
Mathematically
ΔQ=ΔU+ΔW
4. ΔQ= Heat energy
ΔU= Internal energy
ΔW= work done (all measured in joules)
Joule= Its is the amount of work done when a force of 1 Newton
displaces a mass through a distance of 1 meter in the direction of
force applied.
1J= 1Nm
3) 2nd law of thermodynamics
This law states that entropy(S) of an isolated system is always
increasing.
For example= if we look at the piston in an engine, gas is heated to
increase its pressure and drive a piston. However even as the piston
moves, there is some leftover heat in the gas that cannot be used for
carrying out any other work and has to be discarded.
Mathematically
ΔS > 0
Note= Entropy is the measure of energy in an isolated system
5. 4) 3rd law of thermodynamics
Its states that as the temperature of system approaches absolute
zero(temperature at which thermodynamic system has lowest
energy) its entropy approaches a constant.
Numericals:
The sign conventions
Q is positive if the heat added to the system
W is positive if work is done by the system
Q is negative if heat leaves the system
W is negative if work is done on the system
1. 3000 J of heat is added to a system and 2500 J of work is
done by the system. What is the change in internal energy of the
system? Known Heat (Q) = +3000 Joule Work (W) = +2500 Joule
Wanted: the change in internal energy of the system
6. Solution:
The equation of the first law of thermodynamics ΔQ=ΔU+ΔW
The change in internal energy of the system ΔU=3000-2500
ΔU = 500 Joule
Internal energy increases by 500 Joule.
2. 2000 J of heat is added to a system and 2500 J of work is
done on the system. What is the change in internal energy of the
system. Known: Heat (Q) = +2000 Joule Work (W) =-2500 Joule
Wanted: The change in internal energy of the system
Solution:
ΔQ=ΔU+ΔW
ΔU=2000-(-2500)
=4500J
7. 3. 2000 J of heat leaves the system and 3000 J of work is done
on the system. What is the change in internal energy of the
system? Known Heat (Q) =-2000 Joule Work (W) = -3000 Joule
Wanted: The change in internal energy of the system
Solution:
ΔQ=ΔU+ΔW
ΔU=-2000-(-3000)
=1000J
MODE OF HEAT TRANSFER:
The heat transfer is defined as the transmission of heat energy
from one region to another region as a result of temperature
gradient.
The transfer of heat energy from one region to another region
takes place by the following three modes −
Conduction= When the heat transfers from one part of the
substance to another part by direct contact, it is called the
conduction mode of heat transfer. For example touching hot cup
of tea.
8. Convection= When the transfer of heat takes place from one part
to another part of the substance or fluid due to the actual motion
of the molecules, it is called the convection mode of heat
transfer. For example boiling water.
Radiation= When the heat transfer takes place from the source of
heat to the substance to be heated without direct contact
between them, it is called the radiation mode of heat transfer.
For example heat released from a stove burner
9. THERMODYNAMIC SYSTEM AND ITS PROPERTIES:
A thermodynamic system is defined as a quantity of matter or a
region in space that is of interest. The mass or region outside
the system is called the surroundings, and the surface that
separates the system and the surroundings is called the
boundary.
A property of a system is any characteristic of the system which
can be measured directly or indirectly, while the system remains
at equilibrium. The properties of a system may be classified into
two groups as:
(a) Intensive or Intrinsic properties
(b) Extensive or Extrinsic properties
(a) Intrinsic properties are those properties which are
independent of the mass of system. These properties are
inherent and do not depend on mass of the system e.g.
temperature, pressure, specific volume, density, viscosity etc.
(b) Extrinsic properties are those which are dependent on mass
of the system. Values of these properties depend directly on
mass of the system. Value of extrinsic properties increases with
increase in mass of system e.g. total or net volume, energy,
weight.
10. LAWS AND PROPERTIES OF PERFECT GAS:
A perfect gas (or an ideal gas) may be defined as a state of a
substance, whose evaporation from its liquid state is complete.
The behavior of a perfect gas, undergoing any change in these
three variables, is governed by the following laws :
1. Boyles law. This law was formulated by Robert Boyle in 1662.
It states, "The absolute pressure of a given mass of a perfect gas
varies inversely as its volume, when the temperature remains
constant." Mathematically,
p ∝ 1/v
P= constant/v
Pv= constant
2. Charles law. The volume of a given mass of a perfect gas
varies directly as its absolute temperature, when the absolute
pressure remains constant.
v ∝ T
V=constant T
11. 3. Gay Lussac law. This law states, "The absolute pressure of a
given mass of a perfect gas varies directly as its absolute
temperature, when the volume remains constant."
Mathematically
p ∝ T
P=constant T
P/T= constant
PROPERTIES OF PERFECT GAS:
For a gas to be “perfect” there are four governing assumptions:
The gas particles have negligible volume.
The gas particles are equally sized and do not have
intermolecular forces (attraction or repulsion) with other gas
particles.
The gas particles move randomly in agreement with Newton’s
Laws of Motion.
The gas particles have perfect elastic collisions with no energy
loss.
12. ENTHALPY:
Enthalpy, a property of a thermodynamic system, is the sum of the
system's internal energy and the product of its pressure and volume.
So, enthalpy can be shown as:
H = U + PV
where:
U is Internal Energy,
P is pressure and
V is volume.
Problem 1: For a reaction, 5 kJ of heat is released from the system
and 10 kJ of work was done on the system. What are the changes in
the Internal energy and Enthalpy of the system?
Solution:
According to first law of thermodynamics,
ΔU = Q - W
Q = -5 kJ, W = -10 kJ
ΔU = -5 kJ –(-10 kJ) = +5 kJ
13. and Q = ΔH
∴ ΔH = -5 kJ
Thus, the Internal energy increases by 5 kJ and Enthalpy decreases
by -5 kJ.
Problem 2: An Ideal gas expands from a volume of 5 dm3 to 15
dm3 against a constant external pressure of 3.036 x 105Nm-2. Find
ΔH if ΔU is 400 J.
Solution:
ΔH = ΔU + PΔV
ΔH = ΔU + P(V2 – V1)
Assume that Pex = P, P =3.036 *105 N m-2
ΔU = 400 J
Substituting the values in the equation
ΔH = 400 J + 3.036 × 105 Nm-2 * (15-5) × 10-3 m3
ΔH = 400 J + 3.036 ×105 Nm-2 * (15 – 5) × 10-3 m3
ΔH = 400 J + 3.036 × 103 J
ΔH = 3436 J.
14. Thermodynamic cycle refers to any closed system that undergoes
various changes due to temperature, pressure, and volume,
however, its final and initial state are equal.
Otto cycle
An Otto cycle is an idealized
thermodynamic cycle that describes
the functioning of a typical spark
ignition piston engine
15. The diagram of the Otto cycle is based on four phases which
correspond to the four processes it carries out to generate the
power. They are as follows:
Induction
In this phase, the downward movement of the piston within the
cylinder allows the mixture of fuel and oxygen to go in. The intake
valve is open and the exhaust valve, closed.
Compression
Once the piston reaches the lowest part of the cylinder, both valves
close, and it starts its upward stroke
16. Expansion
When the top of the cylinder is reached, the maximum pressure
is also reached. In this phase, both valves are closed; it is the
only phase in which work is produced.
In Otto Cycle engines, the spark is generated by the spark plug
Once the mixture has combusted, the piston starts its downward
stroke at high speed.
17. Escape
It is the final process of the Otto cycle. The cylinder travels
upwards again and, this time, the exhaust valve is
open, expelling the gases generated during combustion.
Diesel cycle:
The Diesel cycle is a combustion process of a reciprocating
internal combustion engine. In it, fuel is ignited by heat
generated during the compression of air in the combustion
chamber, into which fuel is then injected.
There is no fuel in the cylinder at the beginning of the
compression stroke. Therefore auto ignition does not occur in
Diesel engines.
Because of the high temperature developed during the adiabatic
compression, the fuel spontaneously ignites as it is injected.
Therefore no spark plugs are needed.
18. APPLICATION OF THERMODYNAMICS
1) Heat engines are based on the second law of thermodynamics.
Engines are a device used to convert heat energy into mechanical
energy.
2) An air conditioner also works like this: hot air in a room
evaporates, and this evaporation flows through a fan that is at
the backside, and this fan pump heats outside the room. The
back of an air conditioner is hot as heat moves from the area to
be cooled.
3)Ice cubes present in a drink absorb heat from the drink and
starts melting making the drink cooler.
4)Heat energy is used to change water into steam in he boiler.
5) Our heaters are usually installed with a heating coil, which
requires electrical energy to function. When the heater is turned
on, the electrical energy travels through the heating coil and is
converted into heat energy. Coldwater is brought in through a
separate dip tube where it is heated by the heat energy
generated, producing the warm water for your cosy bath.
19. PROPERTIES OF STEAM
Steam is the vapor or gaseous phase of water.
It is produced by heating of water and carries large
quantities of heat within itself.
Hence, it could be used as a working substance for heat
engines and steam turbines.
Steam exists in following states or types or conditions.
(i) Wet steam- Obtained at boiling point of water and
contains water droplets.
(ii) Dry steam (dry saturated steam) - Obtained at boiling
point of water but does not contain water droplets.
(iii) Superheated steam- Obtained at higher temperature
than boiling point of water and does not contain water
droplets.
20. STEAM BOILER AND ITS TYPES:
A boiler (also known as a steam boiler)
is a closed vessel in which fluid
(typically water) is heated.
Working Principle of Boiler
The basic working principle of boiler is
very simple and easy to understand.
The boiler is essentially a closed vessel
inside which water is stored. Fuel
(generally coal) is burnt in a furnace
and hot gasses are produced.
These hot gasses come in contact with
water vessel where the heat of these
hot gases transfer to the water and
consequently steam is produced in the
boiler.
21. Types of Boiler
There are mainly two types of boiler – water tube
boiler and fire tube boiler.
fire tube boiler consists of numbers of tubes through
which hot gasses are passed. These hot gas tubes are
immersed into water, in a closed vessel.
Actually in fire tube boiler one closed vessel or shell
contains water, through which hot tubes are passed.
These fire tubes or hot gas tubes heated up the water
and convert the water into steam and the steam
remains in same vessel.
Water tube boiler is reverse of the fire tube boiler. In
water tube boiler the water is heated inside tubes and
hot gasses surround these tubes.
22.
23. STEAM AND GAS TURBINE:
A mechanical device which converts the kinetic energy of some fluid like
steam, water, gas, etc. into rotational energy to perform work is called a
turbine.
TYPES OF TURBINE:
1. Steam turbine
2. Gas turbine
WORKING OF GAS TURBINE
The gas turbine operates on the principle of drawing the fresh atmospheric
air at ambient conditions into the compressor where the air is compressed.
The compressor will raise the temperature and pressure of the atmospheric
air. The compressed air at the higher pressure is fed into a combustion
chamber, where the fuel will be burned. The high-pressure hot gases drive
the turbine producing work
24. WORKING OF STEAM TURBINE:
A boiler is used to convert water into steam. This steam is then
passed through a nozzle to create a fast speed steam jet. The
kinetic energy of this jet moves the turbine creating work. The
steam then moves to the condenser chamber which converts the
steam back into water and water then goes back to the boiler.
25. Size
The steam
turbines are
bigger in size,
hence requires
larger installation
area.
The size of a gas
turbine is
comparatively
small. Therefore,
it needs less
installation
space.
26. Efficiency
The steam
turbine has high
efficiency.
The efficiency of
a gas turbine is
relatively less.
Internal
combustion
Steam turbine
does not involve
internal
combustion of
fuel.
There is internal
combustion of
fuel in case of
gas turbine.
Applications
Steam turbines
are used in
thermal power
plants, nuclear
power plants, etc.
Gas turbines are
widely used in
gas turbine
power stations,
aircraft engines,
etc.
27. INTERNAL COMBUSTION ENGINE (IC ENGINE):
Combustion, also known as burning, is the basic chemical
process of releasing energy from a fuel and air mixture. In an
internal combustion engine (ICE), the ignition and combustion of
the fuel occurs within the engine itself. The engine then partially
converts the energy from the combustion to work.
28. PETROL AND DIESEL ENGINE:
Both represent internal combustion engines (ICEs),
The major difference between these two is how energy is
created. In diesel engines, the air is compressed before
the fuel is injected. In petrol engines, gas and air are
mixed, and then compressed and ignited.
TWO STROKE VS FOUR STROKE:
A stroke is when a piston moves from TDC to BDC or vice
versa.
A two-stroke engine is a type of internal combustion engine
that completes a power cycle with two strokes of the piston
this is in contrast to a four-stroke engine that requires four
strokes of the piston to complete a power cycle .
29. Four-stroke engines are fuel-efficient and environmentally-
friendly. They operate in four steps:
Intake: The intake valve is open, and fuel is drawn in with a
downward stroke.
Compression: As the piston moves upward, the fuel is
compressed.
Power: After the fuel is compressed, it is ignited to produce the
engine’s power.
Exhaust: The exhaust valve opens, and the exhaust gases exit
the cylinder.
A two-stroke engine combines the compression and ignition
steps on the upstroke and the power and exhaust steps on the
down stroke.
1. Upstroke (ignition/compression): The piston goes up, air and fuel
enter the crankcase. The fuel-air mixture is compressed and ignited.
2. Down stroke (power/exhaust): Once the fuel is ignited, the piston is
pushed down, and the exhaust is expelled.
30. INDICATED POWER, BRAKE POWER, FRICTION POWER:
Indicated Power( ip), is the power that is produced in the cylinder
of an engine as a result of the combustion of fuel
Brake power is the power developed by an engine at the output
shaft and is given by
Power = 2piNT/60
N=speed in rpm, T=torque in Nm
Frictional power:
The difference between the Indicated power and Brake power is
called as frictional power. It is the power lost in overcoming the
friction between the moving parts.
FP=IP-BP
31.
32. Problem 1:
Calculate the brake power and mechanical efficiency of a 4
stroke 4 cylinder internal combustion engine, having following
dimensions: Cylinder bore, D = 125 mm, Stroke length, L =
150mm, Crankshaft speed, N = 1000 mm rev/min, Friction
power = 20 kW, Mean effective pressure, P = 700 kPa, No. of
cylinder, n = 4.
Solution:
Where,
Pressure P = Pascal = N/m2
L = Length of stroke, mm
A = Cross sectional area, mm2
N = Speed, rpm.
n = Number of cylinder
33. Indicated power (ip) = 42.95 kW
Brake power = Indicated power - friction power
42.95-20
Brake power 22. 95 kW
=
Mechanical efficiency=BP/IP= 22.55 x
100/42.55=52.99%
Mechanical efficiency= 52.99%
34. Problem 2 :
Calculate the brake power of a 2 cylinder 4 stroke cycle I.C. engine
12 X 15 cm. The mean effective pressure is 700 k Pa and speed of
crankshaft is 1200 revolutions per minute. The mechanical efficiency
is 75%.
Solution: Bore diameter, D = 120 mm, Stroke length, L = 150 mm
Mep, P = 700 k Pa
Speed, N = 1200 rpm.
No. of cylinder, n = 2
We know that,
Where,
Pressure P = Pascal = N/m2
L = Length of stroke, mm
A = Cross sectional area, mm2
N = Speed, rpm.
n = Number of cylinder
35. Indicated power (ip) = 23.75 kW
Brake power = Indicated x mechanical efficiency
Brake power = 23.75 X 75/100
Brake power = 17.81 kW
AIR COMPRESSOR AND PERFORMANCE:
An air compressor is a pneumatic device that converts
power into potential energy stored in pressurized air. By one of
several methods, an air compressor forces more and more air
into a storage tank, increasing the pressure.
36. Factors That Affect Operational Efficiency of an Air Compressor
The Intake Conditions
The intake conditions in which the air compressor is operating in
are known to affect its performance. These conditions are usually
dependent on the weather and location of the air compressor &
they include:
Ambient temperature
Relative humidity
Absolute pressure
Power Supply
Power supply affects the performance of an air compressor. You
have to measure the following aspects:
Voltage
Frequency
Power factor
37. Motor Efficiency
The condition of the air compressor significantly affects its
performance. It’s important to ensure your air compressor is
continuously serviced to ensure optimum performance over time.
Operating Pressure
You need to determine the operating pressure and ensure that
it’s in accordance with the FAD specifications stated by the
manufacturer.
SINGLE STAGE RECIPROCATING COMPRESSOR:
A single-stage reciprocating compressor is a type of
compressor in which the gas or air is compressed in a single
stage. This compressor uses a single cylinder and a piston for
the compression of air. And also, the air is compressed only
one time.
38. The major difference between a single-stage compressor and
a multistage compressor is that a multistage compressor
completes the compression process in more than one stage,
while a single stage compressor completes the compression
process in just one stage. A multi-stage compressor has two or
more cylinders connected in series. Single stage compressor is
less efficient than a multistage compressor.
39. REFRIGERATION TERMINOLOGIES:
BTU - British thermal unit. A unit of heat energy - approximately
the amount of energy needed to heat one pound of water by one
degree Fahrenheit.
Capacity – the ability of a heating or cooling system to heat or
cool a given amount of space. For heating, this is usually
expressed in BTU’s. For cooling, it is usually given in tons.
HVAC – heating, ventilation and air conditioning.
Refrigerant-Substance used in a heat cycle to transfer heat from
one area, and remove it to another.
Condenser- Condenser removes heat from the refrigerant and
condenses it to liquid.
Evaporator- The refrigerant absorbs heat from the air and begins
to boil hence changes to low pressure vapour.
41. Stage1: Low temperature, low pressure
refrigerant enters the compressor and leaves it as
high temperature and high pressure gas.
Stage 2: It then enters condensor which removes
heat from the refrigerant and condenses it to
liquid.
Stage 3: The refrigerant expands due to
expansion valve, reducing temperature and
pressure.
Stage 4: The low temperature low pressure
refrigerant when enters the evaporator absorbs
heat and changes to low pressure vapour.
