A form of energy - LEAM

flinkexistenceΜηχανική

27 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

59 εμφανίσεις

UP466

Energy Basics

Donald Fournier

Adjunct Professor

University of Illinois

Lecture
Overview


Introduction


What is Energy?


The Language of
Energy


Basic Laws of
Energy


Efficiency and
conversions

What is energy?


Energy, for all its
complexity, has a
simple and concise
definition:

Energy
is a
substance (or
property) which
can be converted
into work.

Types of Energy


Mechanical


Elastic


Gravitational


Kinetic


Chemical


Thermal


Potential
(stored)


Sound


Luminous


Radiant


Nuclear


Magnetic


Electrical

Sources of Energy


The
Sun:


Fossil
Fuels
-


Coal, Oil, Natural
Gas, Propane


Renewable
Fuels
-


Wind, Solar,
Hydrokinetic,
Biomass


Nuclear Reactions


Nuclear Fission


Nuclear
Decay


Nuclear
Fusion (someday?)


International
Thermonuclear
Experimental
Reactor

Hoover Dam

The British Thermal Unit (
Btu)


A Btu is the amount
of energy required to
raise the temperature
of one pound of
water 1 degree
Fahrenheit at ~39ºF.

How much energy is in….

Energy Source

Energy Content (Btu)

Units

Sunlight

200 Btu

per hour per square foot

Wind

75 Btu

per hour per square foot
of wind turbine swept
area in 22 mile per
hour wind.

Biomass

7,000 Btu

per pound (value is for
switchgrass
)

Wood

8,000 to 10,000 Btu

per pound

Coal (Anthracite)

14,000 to 15,000 Btu

per pound

Coal (Bituminous)

10,500 to 15,500 Btu

per pound

Oil (#2 Fuel)

137,000
-
141,800 Btu

per gallon

Natural Gas

950 to 1,150 Btu

per cubic foot

Gasoline

109,000
-

125,000 Btu

per gallon

Kerosene

130,000 to 140,000 Btu

per gallon

Nuclear Fuel (Uranium)

35,000,000,000 Btu

per pound Uranium
-
235

Zero
th

Law of Thermodynamics


Thermal Equilibrium
among bodies


If
A

and
C

are each in thermal equilibrium with
B
,
A

is also in equilibrium with
C.


A

C

B

First Law of Thermodynamics


Conservation of Energy


Energy cannot
be created or destroyed


it can be
transferred from one object to another or
transformed from one form to
another.


We use various conversions processes to
convert energy from one form to
another.


During conversion, it is common to lose (not
be able to put to use) some of the energy


it
is lost to us but not lost in physical
sense.


Most often, what we lose (or fail to use) is
heat.


Second Law of Thermodynamics


Entropy



when converting heat into work
the conversion cannot be complete.


Implications:


Heat
flows
from
hotter to colder
places.


Entropy
tends to
increase
or at the least stay the
same.


No
heat engine (an engine which produces work
while moving heat between two separate places)
can be more efficient than a Carnot heat engine.


Carnot Efficiency

(absolute
temperatures)

Electrical Energy


A form of energy
characterized by the
presence and motion of elementary charged
particles generated by friction, induction, or
chemical
change.


A
secondary energy source
, made from the
conversion of other sources of energy, like
coal, natural gas, and other natural sources,
which are primary energy
sources.


Sources
of electricity
can be renewable or
non
-
renewable, but electricity itself is neither
renewable or
non
-
renewable.


Energy and Power


Energy is not the
same as power.


Power is Energy
per unit time.


Energy is related
to power as
gallons are
related to gallons
per minute
.

Energy and Power terms


Therm


100,000 Btu
, heat energy sources
such as natural gas and steam may be sold in
therms
.


A cubic foot
of natural gas is 1,028 Btu.


Kilowatt (kW)


a measure of electrical power
equal to 1,000 watts, it is also equal to
3,412
Btu/
hr


Kilowatt
-
hour (kWh)

-

A kilowatt
-
hour is the
quantity of energy delivered when power flows
at the rate of one kilowatt for one hour. It is
equal to

3,412

Btu
.


Ton

of Air Conditioning


12,000
Btu/
hr

(cooling
provided by one ton of ice melting in a 24 hour
period).



Energy for
the Built Environment


In buildings, we are interested
in two
forms of
energy:


Electricity Heat

Energy Flexibility


Heat is easy to produce and essential
for a comfortable
life.


Electricity
is harder to produce, but
can be transferred over long
distances and easily transformed into
many other kinds of
energy.


Electricity
is a very flexible energy
form (it is an energy carrier).


Using Heat Energy


Primarily made from combustion of
various fuels like wood, waste, coal, peat,
natural gas,
and petroleum.


Heat
can be transformed into mechanical
work in different types of heat
engines (IC
engine, steam engines, turbines, etc.)


Most
famous is Watts steam engine that
led
to the industrial
revolution.


Combustion


Fuel is oxidized, thus rearranging the
molecular bonds and releasing
energy.


We use hydrocarbon
-
based fuels
due to
the high energy release from the strongly
bound final
products.


Heat Engines


Convert
thermal
energy to
mechanic
al energy.

Heat Engines


The first law and second
law of thermodynamics
constrain the operation of
a heat engine.


The
first law is the
application of conservation
of energy to the system,
and the second sets limits
on the possible efficiency
of the machine and
determines the direction of
energy flow.

Source:
hyperphysics.phy
-
astr.gsu

Types of Heat Engines


Phase change cycles:


Rankine

engines
(steam
engines &
steam turbines
)


Gas only cycles:


Carnot, Diesel, Otto
(gasoline motors), Miller


Brayton

(
gas turbines)


Other
cycles:


Stirling motors


Ericsson engines

Source: mpoweruk.com

Heat Transmission


Heat
is hard to transfer over long distances
due to
expense of the transport system (hot
water and steam piping).


Although quite efficient, heat
is
used
near the
place where it was
produced.


For
instance in district heating systems and
domestic oil
boilers/furnaces.


Electrical Generation


Mostly generated by
a prime mover (steam
turbine, gas turbine, diesel engine, water
turbine) connected to a generator.


The generator transforms
mechanical energy
into electric energy by electromagnetic
induction.


It
is also possible to generate electricity
directly from light in photovoltaic cells or
thermoelectric devices
--

their
efficiency is
low and their costs high compared
to turbines
and
generators. Also, the scale is smaller.


Steam/Electrical Generation


Physical
layout of
the four
main
devices
used in
the
Rankine

cycle.

Source: Wikimedia Commons

US Electricity Flow Diagram 2011

Source: EIA, 2013

Heat Pumps


Heat pumps are the opposite of heat
engines


we put in mechanical energy
and can pump heat from a cool source to
a higher temperature one.


Air conditioning and refrigeration are
examples of a heat pump processes. We
pump heat from a cooler space to a hotter
outside environment.


Generally an “up
-
hill” process.

Efficiency of a System


Efficiency is the ratio of useful work out to
the total amount of work input, as a
percentage.

Terms You’ll See


Definitions:


AFUE


annual fuel use efficiency


HSPF


heating season performance factor


EER


energy efficiency ratio (Btu / hr / W)


IEER


integrated energy efficiency ratio


SEER


seasonal energy efficiency ratio


COP


coefficient of performance (Btu/Btu)


Horse Power


0.746 kW or 550 foot


pounds/second


Questions
&
Discussion