introduction chapter Eme or thermodynamics

Prepare by:-Shivkumar PanjabiPrepare by:-Shivkumar Panjabi

 Prime movers is a device which uses natural
resources to convert their energy into mechanical
energy or useful work.
Prepare by:-Shivkumar Panjabi 2

 Fuel
 Flow of river water
 Atoms
 Renewable energy sources

1. mechanical energy
2. Thermal (heat) energy
3. electromagnetic energy
4. electrical energy
5. nuclear energy
6. chemical energy

 “the ability to do work”
 The combination of energy and matter
make up the universe:
◦ Matter is substance, and energy is the mover of
substance.

Potential
Energy
Kinetic
Energy
All Energy
Gravitation
Potential
Energy
Elastic
Potential
Energy
Chemical
Potential
Energy

 energy of position
or energy in
storage.
◦ Water behind a dam
◦ Hammer over head
◦ Food on the plate
 energy of motion,
the form capable
of doing work
◦ Flowing water
◦ A falling hammer
◦ Electrons regenerating
ATP in a bio’l cell

Mass- the amount of matter an object has.
Matter- something that has mass and takes up
space.
Weight- is the amount of mass of an object, it is
dependent upon gravity.

 Force is an action that can change motion.
◦ A force is what we call a push or a pull, or
any action that has the ability to change an
object’s motion.
◦ Forces can be used to increase the speed
of an object, decrease the speed of an
object, or change the direction in which an
object is moving.

 is equal to the force that is exerted times the
distance over which it is exerted.
 W = F x d
 The unit of work combines the unit of
force (N) with the unit of distance (m)
 Newton-meter (N-m) aka Joule.

 measures the rate of work done.
 or the rate at which energy is expended.
 Power is the amount of work done, divided
by the time it takes to do it.
 Power (watts) = work (joules) / time (sec)
 P = W/t

The normal stress (or “pressure”) on the
feet of a chubby person is much greater
than on the feet of a slim person.
Some basic
pressure
gages.
Pressure: A normal force exerted
by a fluid per unit area

 Absolute pressure: The actual pressure at a given position. It is
measured relative to absolute vacuum (i.e., absolute zero pressure).
 Gage pressure: The difference between the absolute pressure and
the local atmospheric pressure. Most pressure-measuring devices are
calibrated to read zero in the atmosphere, and so they indicate gage
pressure.
 Vacuum pressures: Pressures below atmospheric pressure.
Throughout
this text, the
pressure P
will denote
absolute
pressure
unless
specified
otherwise.

 Temperature is a measure of hotness or coldness
 Ice point: A mixture of ice and water that is in equilibrium
with air saturated with vapor at 1 atm pressure (0°C or
32°F).
 Steam point: A mixture of liquid water and water vapor
(with no air) in equilibrium at 1 atm pressure (100°C or
212°F).
 Triple point of water- A mixture of ice,liquid water and
water vapor (with no air) in equilibrium(0.01°C)
 Celsius scale: in SI unit system
 Fahrenheit scale: in English unit system
 Thermodynamic temperature scale: A temperature scale
that is independent of the properties of any substance.
 Kelvin scale (SI) Rankine scale (E)
A constant-volume gas thermometer would read -273.15°C at
absolute zero pressure. Known as absolute zero temperature

Energy as Heat
• Heat is the energy transferred between
objects that are at different temperatures
• Though energy has many different forms, all
energy is measured in units called joules (J).

0>Q
Signs for heat, Q and work, W
Sign convention for heat, Q :
Q = positivepositive value
Q = negativenegative value
Heat flow into the
system
Heat flow out of the
system
17
Surrounding
s
(environmen
t)
System
0=W
(a
)
Surrounding
s
(environme
nt)
System
0=W
(b
)

0=Q
Sign convention for work,
W:
W = positive value
W = negative value
Work done by the
system
Work done on the
system
Surrounding
s
(environmen
t)
System
0>W
Surrounding
s
(environmen
t)
System
0<W

The two most commonly used are-
1.Specific heat at constant volume (CV)
It is the amount of heat required to raise the
temperature of unit mass of a gas through 1°C,
when volume is kept constant. t
2.Specific heat at constant pressure (CP)
It is the amount of heat required to raise the
temperature of unit mass of a gas through 1°C,
when the pressure of the gas is kept constant
However, CP > CV and CP / CV = γ. γ is called
the ratio of specific heats.
At constant volume, ΔQ = m CV θ
At constant pressure, ΔQ = m CP θPrepare by:-Shivkumar Panjabi 19

Internal energy -
The internal energy of a gas is the kinetic energy of thermal
motion of its molecules.
Enthalpy is the sum of the internal energy of a system
plus the product of the system’s volume multiplied by the
pressure that the system exerts on its surroundings
Enthalpy: H = U + PV
Entropy definition:
- A measure of disorder of the system.
- ΔS is equal to the heat Q it absorbs, divided by T.
T
dQ
dS rev
=

input
output
efficiency =
Brake power –brake power of engine is the power
available at engine output shaft.
Indicated power –indicated power is a power
developed inside engine cylinder by burning fuel.
Friction power –
F.P.= I.P.-B.P.

 Energy cannot be created or destroyed; it may be
transformed from one form into another, but the
total amount of energy never changes.

1. Zeroth law of thermodynamics
If two systems are at the same time in equilibrium
with a third system, they are in equilibrium with each
other.
Practically, this means that all three systems are at the
same temperature.
A
B
C
Since A and B are at
equilibrium and B and
C are at equilibrium, A
and C are also at
equilibrium according
to the zeroth law

 Statement:
- Energy can not be created or destroyed and the total
energy of a system is always constant.
 Mathematical formula for a closed system:
 Where;
∆U: change in internal energy
Q: heat transferred to the system.
W: work done by the system.
WUQ +∆=

 This is sometimes called the "first form" of the
second law, and is referred to as the Kelvin-
Planck statement of the second law.
 It is impossible to extract an amount of heat QH
from a hot reservoir and use it all to do work W .
Some amount of heat QC must be exhausted to a
cold reservoir.

3. Second law of thermodynamics:
Clausius statement-it is impossible to have a device
that operating in a cycle produce no effect other than
transfer heat from a body at lower temperature to a
body at higher temperature.
I.Second law in terms of heat flow:
Heat flows spontaneously from hotter to colder
objects but not vice versa.
II.Second law in terms of heat engines:
It is impossible to construct an engine which has
100% efficiency or a system in which the heat added
to the system is solely used to perform work.

a. Open; mass & heat can transfer
b. Closed; no mass transfer
c. Isolated; no mass or heat transfer
System: A quantity of matter or a region in space chosen
for study.
Surroundings: The mass or region outside the system
Boundary: The real or imaginary surface that separates
the system from its surroundings
Universe = System + Boundary

Example: Piston and cylinder - a closed system
m
Gas at pressure, p
Piston

Example: The gas turbine engine - an open system
Shaft Work Output
Combustor
Fuel Flow In
Air Flow In
Exhaust Gases Out
Compressor Work Out

 Property: Any characteristic of a
system.
 Some familiar properties are
pressure P, temperature T, volume
V, and mass m.
 Properties are considered to be
either intensive or extensive.
 Intensive properties: Those that
are independent of the mass of a
system, such as temperature,
pressure, and density.
 Extensive properties: Those
whose values depend on the size—
or extent—of the system.
 Specific properties: Extensive
properties per unit mass.
Criterion to differentiate intensive
and extensive properties.

introduction chapter Eme or thermodynamics

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