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Energy Fundamentals
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Energy Fundamentals
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.
What is Work?
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Energy Fundamentals
What is Work?
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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
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Energy Fundamentals
What is Power?
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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
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Energy Fundamentals
What is Energy?
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Energy Fundamentals
8
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).
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Energy Fundamentals
9
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
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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.
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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.
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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.
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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
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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.
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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
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Energy Fundamentals
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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
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Energy Fundamentals
The Conservation of Energy Principle
Energy can neither be created nor destroyed,
but only transformed from one form of energy
into another.
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Energy Fundamentals
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.
System
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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).
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Energy Fundamentals
Power 1 N = 1 kgm/s²
Energy, Work 1 J = 1 Ws = 1 Nm
Performance 1 W = 1 J/s = 1 Nm/s
Pressure 1 Pa = 1 N/m²
1 bar = 105 Pa
Specific Thermal
Capacity
J/(kgK) bzw. J/(m³K)
Specific Weight N/m³
Density kg/m³
Thermal Conductivity
Coefficient
W/(mK)
Thermal Transfer
Coefficient
W/(m²K)
Basic Units
Power =
Mass *
Acceleration
…
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Energy Fundamentals
Conversion Factors
Work kJ kWh kcal kpm
kJ 1 0.0002778 0.2388 101.97
kWh 3600 1 860 367000
kcal 4.1868 0.001163 1 427
kpm 0.00981 0.00000272 0.0000037 1
Performance kW Kcal/h kpm/s PS
1 kW 1 860 102 1
1 kcal/h 0.0011628 1 0.119 0.00158
1 kpm/s 0.0098067 8.43 1 0.01333
1 PS 0.7365498 632 75 1
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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.
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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.
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Energy Fundamentals
25
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.
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Energy Fundamentals
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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.
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Energy Fundamentals
27
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
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Energy Fundamentals
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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
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Energy Fundamentals
Internal energy consists of - thermal energy
- chemical binding energy
- potential energy of atomic nuclei
- interactions with electric and magnetic dipoles
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Energy Fundamentals
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
Gas Laws
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Energy Fundamentals
Gas Laws
Compressing results in higher pressure Heat supply -> Volume expansion
What happens when a piston gets locked?
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Energy Fundamentals
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Gas Law
Calculations
Boyle’s Law
PV = k
Charles’ Law
V
T
Combined
Gas Law
PV
T
Ideal
Gas Law
PV = nRT
= k
= k
T and V
change
P, n, R are
constant
P, V, and T change
n and R are constant
P and V
change
n, R, T are
constant
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Energy Fundamentals
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P = pressure
V = volume
T = temperature (Kelvin)
n = number of moles
R = gas constant
Standard Temperature and Pressure (STP)
T = 0 oC or 273 K
P = 1 atm = 101.3 kPa = 760 mm Hg
Solve for constant (R)
PV
nT
= R
Substitute values:
(1 atm) (22.4 L)
(1 mole)(273 K)
R = 0.0821 atm L / mol K or R = 8.31 kPa L / mol K
R = 0.0821 atm L
mol K
Recall: 1 atm = 101.3 kPa
(101.3 kPa)
( 1 atm) = 8.31 kPa L
mol K
1 mol = 22.4 L @ STP
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Energy Fundamentals
34
Gas Law #1 – Boyles’ Law
(complete TREE MAP)
“The pressure of a gas is
inverse related to the
volume”
Moles and Temperature
are constant PVVP
kPV
kVP
k
V
kP
VP
oo
oo
alityproportion ofconstant
1
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Energy Fundamentals
35
Gas Law #2 – Charles’ Law
“The volume of a gas is
directly related to the
temperature”
Pressure and Moles are
constant
T
V
T
V
T
Vk
T
Vk
kTVTV
o
o
o
o
oooo
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Energy Fundamentals
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Gas Law #3 – Gay-Lussac’s Law
“The pressure of a gas is
directly related to the
temperature”
Moles and Volume are
constant
T
P
T
P
T
Pk
T
Pk
kTPTP
o
o
o
o
oooo
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Energy Fundamentals
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Gas Law #4 – Avogadro’s Law
“The volume of a gas is
directly related to the #
of moles of a gas”
Pressure and
Temperature are
constant
n
V
n
V
n
Vk
n
Vk
knVnV
o
o
o
o
oooo
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Energy Fundamentals
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Gas Law #5 – The Combined Gas
Law
You basically take Boyle’s
Charles’ and Gay-
Lussac’s Law and
combine them together.
Moles are constant
T
PV
T
VP
T
PVk
T
VPk
kTVPTVP
o
oo
o
oo
oooooo
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Energy Fundamentals
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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.
)2)(15(
)300)(5.3)(12(T
VP
PVTT
T
PV
T
VP
oo
o
o
oo
420 K
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Energy Fundamentals
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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.
nRTPV
R
nTPV
Kmol
J8.31 Constant Gas UniversalR
alityproportion ofconstant
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Energy Fundamentals
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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.
RT
PVnnRTPV
atmP
T
rVsphere
05.1
27320
)18.0(3
4
3
4 33
)293)(31.8(
)0244.0)(1005.1( 5xn
0.0244 m3
293 K
1.05x105 Pa
1.052 moles
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Energy Fundamentals
Machine Energy Work
Losses
Heat
Noise
Vibration
Efficiency η
η = Work / Energy < 100%
Efficiency
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Energy Fundamentals
Energy Flow, Heat Transfer
Heat transfer occurs in three ways, convection, conduction and
radiation, tell the system reach to Equilibrium
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Energy Fundamentals
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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
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Energy Fundamentals
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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.
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Energy Fundamentals
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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
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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)
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Energy Fundamentals
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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.
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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:
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Energy Fundamentals
0
50
100
150
200
250
300
350
Kelv
in
0°C
-20°C
+20°C
Tension
40K
Heat Flow
Wall
Thermal Transfer through a Wall
q = D T / R [W/m²] ,
Q´= A x q [W] Transfer, performance
Q = Q´ x t [kWh/a] Work
Insulation Losses
Energy Flow = Tension / Resistance
Wall Thermal Resistance R [m²K/W] = S d [m] / l [W/mK]
Thermal Transfer towards Air Wall Resistance Thermal Transfer of Air
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Energy Fundamentals
Energy Optimisation - Boiler
Quality of
Combustion,
Exhaust Gas Losses
Distribution Losses
Burner
Boiler Efficiency
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Energy Fundamentals
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