2. Energy Fundamentals
What is Work?
WORK is done when a force causes an object to move in
the direction of the force. For work to be done, two things must occur.
First, you must apply a force to an object. Second, the object must move
in the same direction as the force you apply. If there is no motion, there is
no work. Work can be calculated with this formula:
Work = Force X Distance
W = FXd
standard metric unit of force is the Newton and the standard meteric unit
of displacement is the meter, then the standard metric unit of work is a
Newton•meter, defined as a Joule and abbreviated with a J.
eg.eurem.net
4. Energy Fundamentals
What is Power?
is the rate of doing work or the rate of using energy, which are numerically the
same.
- or Power is defined as the rate at which work is done upon an object. Like all
rate quantities, power is a time-based quantity. Power is related to how fast a
job is done.
- the standard metric unit for power is a Joule / second
Power = Work / time
P=W/t
eg.eurem.net
6. Energy Fundamentals
What is Energy?
The capacity or power to do work, such as the capacity to move an object (of a
given mass) by the application of force. Energy can exist in a variety of forms,
such as electrical, mechanical, chemical, thermal, or nuclear, and can be
transformed from one form to another. It is measured by the amount of work
done, usually in joules or watts
eg.eurem.net
8. Energy Fundamentals
Mechanical, Kinetic and Potential Energies
There are two forms of mechanical energy - potential energy and kinetic energy.
Potential energy is the stored energy of position. In this set of problems, we
will be most concerned with the stored energy due to the vertical position of an
object within Earth's gravitational field. Such energy is known as the
gravitational potential energy (PEgrav) and is calculated using the equation
PEgrav = m•g•h
where
m is the mass of the object (with standard units of kilograms),
g is the acceleration of gravity (9.8 m/s/s)
h is the height of the object (with standard units of meters) above some
arbitraily defined zero level (such as the ground or the top of a lab table in a
physics room).
eg.eurem.net 8
9. Energy Fundamentals
Kinetic energy is defined as the energy possessed by an object due to its
motion. An object must be moving to possess kinetic energy. The amount of
kinetic energy (KE) possessed by a moving object is dependent upon mass
and speed. The equation for kinetic energy is
KE = 0.5 • m • v2
Where
m is the mass of the object (with standard units of kilograms) and
v is the speed of the object (with standard units of m/s).
The total mechanical energy possessed by an object is the sum of its kinetic
and potential energies
eg.eurem.net 9
10. Energy Fundamentals
Types of POTENTIAL Energy
Stored energy and the energy of position (gravitational).
CHEMICAL ENERGY is the energy stored in the bonds of atoms and
molecules. Biomass, petroleum, natural gas, propane and coal are
examples.
NUCLEAR ENERGY is the energy stored in the nucleus of an atom –
the energy that holds the nucleus together. The nucleus of a uranium
atom is an example.
STORED MECHANICAL ENERGY is energy stored in objects by the
application of force. Compressed springs and stretched rubber bands
are examples.
GRAVITATIONAL ENERGY is the energy of place or position. Water in a
reservoir behind a hydropower dam is an example.
eg.eurem.net
11. Energy Fundamentals
Types of KINETIC Energy
Motion: the motion of waves, electrons, atoms, molecules and substances.
RADIANT ENERGY is electromagnetic energy that travels in transverse
waves. Solar energy is an example.
THERMAL ENERGY or heat is the internal energy in substances – the
vibration or movement of atoms and molecules in substances.
Geothermal is an example.
MOTION is the movement of a substance from one placed to another.
Wind and hydropower are examples.
SOUND is the movement of energy through substances in longitudinal
waves.
ELECTRICAL ENERGY is the movement of electrons. Lightning and
electricity are examples.
eg.eurem.net
12. Energy Fundamentals
Forms of Energy
Energy is found in different forms, such as light, heat, sound, and motion.
There are many forms of energy, but they can all be put into two categories:
kinetic and potential.
eg.eurem.net
13. Energy Fundamentals
Energy types
Kinetic Energy E = 1/2 × m × v2
Potential Energy E=m×g×h
Electrical Energy E=I×U×t
Magnetic Energy E = 1/2 × B × H × V
Thermal Energy Ei = cv × m × T
with Ei = Internal Energy;
cv= Specific Thermal
Constant
Chemical Energy (the binding energy of molecules)
Nuclear (Atomic) Energy (E = m × c2)
Light Energy (Solar Energy) E = hv
eg.eurem.net
14. Energy Fundamentals
Important information
conservation of energy : The law of conservation of energy says that
energy is neither created nor destroyed. When we use energy, it doesn’t
disappear. We change it from one form of energy into another.
Energy Efficiency Energy efficiency is the amount of useful energy you get
from a system. A perfect energy-efficient machine would change all the
energy put in it into useful work
nonrenewable energy sources. Coal, petroleum, natural gas, propane, and
uranium are nonrenewable energy sources. They are used to make electricity,
heat our homes, move our cars, and manufacture all kinds of products. These
energy sources are called nonrenewable because their supplies are limited.
Petroleum, for example, was formed millions of years ago from the remains of
ancient sea plants and animals. We can’t make more crude oil deposits in a
short time.
eg.eurem.net
15. Energy Fundamentals
Sources of Energy
nonrenewable energy sources. Coal, petroleum, natural gas, propane, and
uranium are nonrenewable energy sources. They are used to make electricity,
heat our homes, move our cars, and manufacture all kinds of products. These
energy sources are called nonrenewable because their supplies are limited.
Petroleum, for example, was formed millions of years ago from the remains of
ancient sea plants and animals. We can’t make more crude oil deposits in a
short time.
Renewable energy sources include biomass, geothermal energy,
hydropower, solar energy, and wind energy. They are called renewable
because they are replenished in a short time. Day after day, the sun shines,
the wind blows, and the rivers flow. We use renewable energy sources mainly
to make electricity
eg.eurem.net
17. Energy Fundamentals
Origin of the Concept of Energy
The concept of energy was developed in the middle of the 19th
century.
Scientists and philosophers looked for
– the comprehensive reason behind many phenomena
– a never changing characteristic in the world which would
constitute a hidden common background for constant changes
Around 1840 they discovered the characteristic within the overall
global system that never changes. They called this characteristic
Energy
eg.eurem.net
18. Energy Fundamentals
The Conservation of Energy Principle
Energy can neither be created nor destroyed,
but only transformed from one form of energy
into another.
eg.eurem.net
19. Energy Fundamentals
System
A system is a region in space that contains an amount
of matter and is separated from the environment even
if only in an abstract or spiritual sense. This borderline is
called system boundary.
A system is in a state that can be defined and
reproduced if all characteristics have been identified.
Systems can be closed:
Only heat and work can pass through the system boundary,
Or open:
Also matter can pass beyond the system boundary.
eg.eurem.net
20. Energy Fundamentals
Heat
Heat: A type of a system’s internal energy,
which changes according to temperature
differences.
Units:
Calorie ( The amount of heat needed to warm up 1g
of water by 1°K.
Joule: SI unit (the mechanical energy used to
increase the temperature of 2 kg of water by 1°K).
eg.eurem.net
21. Energy Fundamentals
Basic Units
Power 1 N = 1 kgm/s²
Power =
Energy, Work 1 J = 1 Ws = 1 Nm
Mass *
Performance 1 W = 1 J/s = 1 Nm/s
Acceleration
Pressure 1 Pa = 1 N/m²
…
1 bar = 105 Pa
Specific Thermal J/(kgK) bzw. J/(m³K)
Capacity
Specific Weight N/m³
Density kg/m³
Thermal Conductivity W/(mK)
Coefficient
Thermal Transfer W/(m²K)
Coefficient
eg.eurem.net
23. Energy Fundamentals
Thermodynamics
Thermodynamics is the science of the interrelationship between work and
heat on the one hand and the internal energy of a system.
eg.eurem.net
24. Energy Fundamentals
The Main Theorems of Thermodynamics
1st Main Theorem of Thermodynamics:
The energy of an isolated system remains constant, i.e.
energy can neither be created out of nothing, nor can it
be destroyed, it can only be converted from one form
into another.
2nd Main Theorem of Thermodynamics:
If no energy is introduced into a system nor removed
from it, in all energy conversions the potential energy of
the resulting state is lower than that of the initial state.
eg.eurem.net
25. Energy Fundamentals
First Law of Thermodynamics
The first law of thermodynamics is the application of the conservation of energy
principle to heat and thermodynamic processes:
The first law makes use of the key concepts of internal energy, heat, and
system work. It is used extensively in the discussion of heat engines. The
standard unit for all these quantities would be the joule, although they are
sometimes expressed in calories or BTU.
eg.eurem.net 25
26. Energy Fundamentals
It is typical for chemistry texts to write the first law as ΔU=Q+W. It is the same
law, of course - the thermodynamic expression of the conservation of energy
principle. It is just that W is defined as the work done on the system instead of
work done by the system.
eg.eurem.net 26
27. Energy Fundamentals
Enthalpy
Four quantities called "thermodynamic potentials" are useful in the chemical
thermodynamics of reactions and non-cyclic processes.
They are internal energy, the enthalpy, the Helmholtz free energy and the Gibbs
free energy. Enthalpy is defined by
H = U + PV
where P and V are the pressure and volume, and U is internal energy. Enthalpy is
then a measurable state variable, since it is defined in terms of three other
precisely definable state variables. It is somewhat parallel to the first law of
thermodynamics for a constant pressure system
eg.eurem.net 27
28. Energy Fundamentals
Internal Energy
Internal energy is defined as the energy associated with the random, disordered
motion of molecules.
- For example, a room temperature glass of water sitting on a table has no
apparent energy, either potential or kinetic . But on the microscopic scale it is a
seething mass of high speed molecules traveling at hundreds of meters per
second. If the water were tossed across the room, this microscopic energy would
not necessarily be changed when we superimpose an ordered large scale motion
on the water as a whole.
U is the most common symbol used for internal energy
eg.eurem.net 28
29. Energy Fundamentals
Internal energy consists of
- thermal energy
- chemical binding energy
- potential energy of atomic nuclei
- interactions with electric and magnetic dipoles
eg.eurem.net
30. Energy Fundamentals
Gas Laws
P*V = Rn*T
P – Pressure (bar) V – Volume (m3)
T – Absolute temperature (ºK) n – Number of moles
R – Gas constant for ideal gases
Rn – Specific gas constant
eg.eurem.net
31. Energy Fundamentals
Gas Laws
Compressing results in higher pressure Heat supply -> Volume expansion
What happens when a piston gets locked?
eg.eurem.net
32. Energy Fundamentals
Charles’ Law
Boyle’s Law
V = k
PV = k
T
P and V T and V
Ideal
change change
Gas Law
n, R, T are P, n, R are
constant constant
PV = nRT
P, V, and T change
Gas Law n and R are constant
Calculations Combined
Gas Law
PV
= k
T
eg.eurem.net 32
33. Energy Fundamentals
Standard Temperature and Pressure (STP)
P = pressure
V = volume
T = temperature (Kelvin)
T = 0 oC or 273 K
n = number of moles
R = gas constant P = 1 atm = 101.3 kPa = 760 mm Hg
Solve for constant (R) 1 mol = 22.4 L @ STP
PV
nT Recall: 1 atm = 101.3 kPa
Substitute values:
(1 atm) (22.4 L) = R R = 0.0821 atm L (101.3 kPa) = 8.31 kPa L
(1 mole)(273 K) mol K ( 1 atm) mol K
R = 0.0821 atm L / mol K or R = 8.31 kPa L / mol K
eg.eurem.net 33
34. Energy Fundamentals
Gas Law #1 – Boyles’ Law
(complete TREE MAP)
1 k
P P
“The pressure of a gas is V V
inverse related to the k constant of proportionality
volume” PoVo k
Moles and Temperature PV k
are constant PoVo PV
eg.eurem.net 34
35. Energy Fundamentals
Gas Law #2 – Charles’ Law
“The volume of a gas is Vo To Vo kTo
directly related to the Vo
temperature” k
Pressure and Moles are To
constant V
k
T
Vo V
To T
eg.eurem.net 35
36. Energy Fundamentals
Gas Law #3 – Gay-Lussac’s Law
Po To Po kTo
“The pressure of a gas is
directly related to the Po
temperature” k
To
Moles and Volume are
P
constant k
T
Po P
To T
eg.eurem.net 36
37. Energy Fundamentals
Gas Law #4 – Avogadro’s Law
“The volume of a gas is Vo no Vo kno
directly related to the #
Vo
of moles of a gas” k
Pressure and no
Temperature are
V
constant k
n
Vo V
no n
eg.eurem.net 37
38. Energy Fundamentals
Gas Law #5 – The Combined Gas
Law P V T P V kT
o o o o o o
You basically take Boyle’s
PoVo
Charles’ and Gay- k
Lussac’s Law and To
combine them together.
PV
Moles are constant k
T
PoVo PV
To T
eg.eurem.net 38
39. Energy Fundamentals
Example
Pure helium gas is admitted into a leak proof cylinder containing a
movable piston. The initial volume, pressure, and temperature
of the gas are 15 L, 2.0 atm, and 300 K. If the volume is
decreased to 12 L and the pressure increased to 3.5 atm, find
the final temperature of the gas.
PoVo PV To PV
T
To T PoVo
(12)(3.5)(300)
T 420 K
(15)(2)
eg.eurem.net 39
40. Energy Fundamentals
Gas Law #6 – The IDEAL Gas Law
All factors contribute! In the previous examples, the constant, k,
represented a specific factor(s) that were constant. That is
NOT the case here, so we need a NEW constant. This is
called, R, the universal gas constant.
PV nT
R constant of proportionality
J
R Universal Gas Constant 8.31
mol K
PV nRT
eg.eurem.net 40
41. Energy Fundamentals
Example
A helium party balloon, assumed to be a perfect sphere, has a
radius of 18.0 cm. At room temperature, (20 C), its internal
pressure is 1.05 atm. Find the number of moles of helium in
the balloon and the mass of helium needed to inflate the
balloon to these values.
4 3 4
Vsphere r (0.18)3 0.0244 m3
3 3
T 20 273 293 K
P 1.05atm 1.05x105 Pa
PV (1.05 x105 )(0.0244)
PV nRT n n 1.052 moles
RT (8.31)(293)
eg.eurem.net 41
42. Energy Fundamentals
Efficiency
Efficiency η
η = Work / Energy < 100%
Heat
Noise
Vibration
Machine
Losses
Energy
Work
eg.eurem.net
43. Energy Fundamentals
Energy Flow, Heat Transfer
Heat transfer occurs in three ways, convection, conduction and
radiation, tell the system reach to Equilibrium
eg.eurem.net
44. Energy Fundamentals
Conduction:
When you give heat to an object the kinetic energy of the atoms at that point
increases and they move more rapidly. Molecules or atoms collide to each other
randomly and during this collision they transfer some part of their energy. With the
same way, all energy transferred to the end of the object until it reaches thermal
balance.
As you can see from the picture, atoms at the bottom of the object first gain
energy, their kinetic energies increase, they start to move and vibrate rapidly and
collide other atoms and transfer heat.
Conduction is commonly seen in solids and a
little bit in liquids. In conduction, energy transfer
is slow with respect to convection and radiation.
Metals are good conductors of heat
and electricity
eg.eurem.net 44
45. Energy Fundamentals
Formula to calculate the conductivity gradient for a given system:
q = - kA (Δ T/Δ n)
Where Δ T/Δ n is the temperature gradient in the direction of area A, and k
is the thermal conductivity constant obtained by experimentation in
W/m.K.
eg.eurem.net 45
46. Energy Fundamentals
Convection:
n liquids and gases, molecular bonds are weak with respect to solids. When
you heat liquids or gases, atoms or molecules which gain energy move
upward, since their densities decrease with the increasing temperature. All
heated atoms and molecules move upward and cooler ones sink to the
bottom. This circulation continues until the system reaches thermal
balance. This type of heat transfer does not
work in solids because molecular bonds
are not weak as in the case of fluids.
Heat transfer is quick with respect to conduction
eg.eurem.net 46
47. Energy Fundamentals
Convection
Convection occurs when a solid state body exchanges
heat with an adjacent liquid or gas (air). The movement of
liquids or gases supports the convection.
Newton:
Q = h A (TSurface-TEnvironment)
eg.eurem.net
48. Energy Fundamentals
Radiation:
It is the final method of heat transfer. Different from conduction and convection,
radiation does not need medium or particles to transfer heat. As it can be
understood from the name, it is a type of electromagnetic wave and
shows the properties of waves like having speed of light and traveling in a
straight line.
In addition to, it can travel also in vacuum just like sun lights.
Radiation is a good method of transferring heat, in microwave
ovens or some warming apparatus radiation is
used as a method of heat transfer.
eg.eurem.net 48
49. Energy Fundamentals
Radiation
Thermal radiation does not need a thermal
transfer medium. Radiation energy when
meeting a surface will:
reflect
absorb
transfer
(semi-transparent materials)
Stefan Boltzman Law:
eg.eurem.net
50. Energy Fundamentals
Insulation Losses
Energy Flow = Tension / Resistance
350
+20°C
Thermal Transfer through a Wall
q = D T / R [W/m²] ,
300
Tension
0°C
40K
-20°C
250
200
Q´= A x q [W] Transfer, performance
Kelvin
Heat Flow
150 Q = Q´ x t [kWh/a] Work
100
50
0
Wall
Wall Thermal Resistance R [m²K/W] = S d [m] / l [W/mK]
Thermal Transfer towards Air Wall Resistance Thermal Transfer of Air
eg.eurem.net
51. Energy Fundamentals
Energy Optimisation - Boiler
Distribution Losses
Boiler Efficiency
Quality of
Combustion,
Exhaust Gas Losses
Burner
eg.eurem.net
52. Energy Fundamentals
Your trainer: Mohamed Mahmoud Mahmoud Ali
Phone: +20 10 0525 4496
Email: Encpc_mm@yahoo.com
Your material: http://eg.eurem.net/display/EUREMEG/Training+Materials
Partners:
Supported by:
eg.eurem.net 5252
