1. BASICS OF ENERGY AND ITS VARIOUS FORMS
2.1
Definition
Energy is the ability to do work and work is the transfer of energy from one form to another.
In practical terms, energy
is what we use to manipulate the world around us, whether by exciting our muscles, by using electricity, or by
using mechanical devices such as automobiles. Energy comes in different forms - heat (thermal), light (radiant),
mechanical, electrical, chemical, and nuclear energy.
2.2
Various Forms of Energy
There are two types of energy - stored
(potential) energy and working (kinetic) energy. For example, the food
we eat contains chemical energy, and our body stores this energy until we release
it when we work or play.
2.2.1
Potential Energy
Potential energy is stored energy and the
energy of position (gravitational). It exists in various forms.
Chemical Energy
Chemical energy is the energy stored in the
bonds of atoms and molecules. Biomass, petrole- um, natural gas, propane and coal are examples of stored chemical
energy.
Nuclear Energy
Nuclear energy is the energy stored in the
nucleus of an atom - the energy that holds the nucle- us together. The nucleus of a uranium
atom is an example of nuclear energy.
Stored Mechanical
Energy
Stored mechanical energy is energy stored in
objects by the application of a force. Compressed springs and stretched
rubber bands are examples of stored mechanical energy.
Gravitational Energy
Gravitational energy is the energy of place or position. Water in a reservoir behind a hydropow-
er dam is an example
of gravitational energy.
When the water
is released to spin the turbines, it becomes motion energy.
2.2.2 Kinetic Energy
Kinetic energy is energy in motion- the
motion of waves, electrons, atoms, molecules and sub- stances. It exists in various forms.
Radiant Energy
Radiant energy is electromagnetic energy that
travels in transverse waves. Radiant energy includes
visible light, x-rays, gamma rays and radio waves. Solar energy is an example
of radi- ant energy.
Thermal Energy
Thermal energy (or heat) is the internal
energy in substances- the vibration and movement of atoms and molecules within substances. Geothermal
energy is an example of thermal energy.
Motion
The movement of objects or substances from one place to another
is motion. Wind and hydropower are examples of motion.
Sound
Sound is the movement of energy through
substances in longitudinal (compression/rarefaction) waves.
Electrical Energy
Electrical energy is the movement of electrons. Lightning
and electricity are examples of elec- trical energy.
2.2.3 Energy Conversion
Energy is defined as "the ability to do
work." In this sense, examples of work include moving something, lifting something, warming
something, or lighting something. The following is an example of the transformation of different types of energy into heat and power.
Oil burns to generate heat --> Heat boils water -->
Water turns to steam -->
Steam
pressure turns a turbine --> Turbine turns an electric
generator -->
Generator
produces electricity --> Electricity powers
light bulbs -->
Light bulbs give off light and heat
It is
difficult to imagine
spending an entire
day without using energy. We use energy to light our cities and homes, to power machinery in
factories, cook our food, play music, and operate our TV.
2.2.4 Grades of Energy High-Grade Energy
Electrical and chemical energy are high-grade
energy, because the energy is concentrated in a small space. Even a small amount of electrical and chemical
energy can do a great amount of work.
The molecules or particles that store these forms of energy are highly ordered
and com- pact and thus considered as
high grade energy. High-grade energy like electricity is better used for high grade applications like melting of metals rather than simply heating of water.
Low-Grade Energy
Heat is low-grade
energy. Heat can still be used to do work (example of a heater boiling water),
but it rapidly dissipates. The molecules, in which this kind of energy
is stored (air and water molecules),
are more randomly distributed than the molecules of carbon in a coal. This
disor- dered state of the molecules and the dissipated energy are classified as low-grade energy.
2.3
Electrical Energy Basics
Electric current is divided into two types:
Directional Current (DC) and Alternating Current (AC).
Directional (Direct)
Current
A non-varying, unidirectional electric current
(Example: Current produced
by batteries)
Characteristics:
•
Direction of
the flow of positive and negative charges
does not change with time
•
Direction of current (direction of flow for positive charges) is constant
with time
•
Potential difference (voltage) between
two points of the circuit does not change polarity
with time
Alternating Current
A current which reverses in regularly
recurring intervals of time and which has alternately pos- itive and negative values, and occurring
a specified number of times per second. (Example: Household electricity produced
by generators, Electricity supplied by utilities.)
Characteristics:
·
Direction of
the current reverses periodically with time
·
Voltage (tension) between
two points of the circuit
changes polarity with time.
·
In 50 cycle AC, current
reverses direction 100 times a second (two times during onecycle)
Ampere (A)
Current is the rate of flow of charge. The
ampere is the basic unit of electric current. It is that current which produces a specified
force between two parallel wires, which are 1 metre apart in a vacuum.
Voltage (V)
The volt is the International System of Units (SI) measure of electric
potential or electromo-
tive force. A potential
of one volt appears across a
resistance of one ohm when a current
of one ampere flows through that resistance.
 |
Resistance
Resistance =
Voltage Current
The unit of resistance is ohm (W)
Ohm' Law
Ohm's law states that the current through a conductor
is directly proportional to the potential
difference across it, provided the temperature
and other external conditions remain
constant.
Frequency
The supply frequency
tells us the cycles at which alternating current changes. The unit of fre- quency is hertz (Hz :cycles per second).
Kilovolt Ampere (kVA)
It is the
product of kilovolts and amperes. This measures the electrical load on a circuit or sys- tem. It is also called the apparent power.
For
a single phase electrical circuit , Apparent
power (kVA) = Voltage x Amperes
1000
For a three phase electrical circuit , Apparent
power (kVA) =
kVAr (Reactive Power)
3 x Voltage x Amperes
1000
kVAr is the reactive power. Reactive power is the portion of apparent power that does no work. This
type of power must be supplied to all types of magnetic equipment, such as
motors, trans- formers etc. Larger the magnetizing requirement, larger the kVAr.
Kilowatt (kW) (Active Power)
kW is the active power or the work-producing part of apparent
power.
For sin gle phase, Power (kW )
= Voltage
x Amperes x Power factor
1000
For Three phase, Power (kW )
= 1.732 xVoltage
x Amperes x Power factor
1000
Power Factor
Power Factor (PF) is the ratio between the active power (kW) and apparent power (kVA).
 |
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When current lags the voltage
like in inductive
loads, it is called lagging
power factor and when current leads the voltage like in capacitive loads, it is called leading
power factor.
Inductive loads such as
induction motors, transformers, discharge lamp, etc. absorb com- paratively more lagging reactive
power (kVAr) and hence, their
power factor is poor. Lower
the power factor; electrical
network is loaded with more current. It would be advisable to have highest power factor (close to 1) so that
network carries only active power which does real work. PF improvement is done by installing capacitors near the
load centers, which improve power factor from the point of installation back to the generating station.
Kilowatt-hour
(kWh)
Kilowatt-hour is the energy consumed
by 1000 Watts in one hour. If 1kW (1000 watts) of a elec- trical
equipment is operated for 1 hour, it would consume 1 kWh of energy (1 unit of
electrici- ty).
For a company, it is the amount of electrical
units in kWh recorded in the plant over a month for billing purpose.
The company is charged / billed based on kWh consumption.
Electricity Tariff
Calculation of electric bill for a company
Electrical utility or power supplying
companies charge industrial customers not only based on the amount of energy used (kWh) but also on the peak demand (kVA) for each month.
Contract Demand
Contract demand is the amount
of electric power that a customer demands
from utility in a spec- ified
interval. Unit used is kVA or kW. It is the amount of electric power that the
consumer agreed upon with the utility. This would mean that utility
has to plan for the specified capacity.
Maximum demand
Maximum demand is the highest average kVA
recorded during any one-demand interval with-
in the month. The demand interval is normally 30 minutes, but may vary
from utility to utility from 15
minutes to 60 minutes. The demand is measured using a tri-vector meter /
digital ener- gy meter.
Prediction of Load
While considering the methods of load prediction, some of the terms used in connection with power supply must be appreciated.
Connected Load - is the nameplate
rating (in kW or kVA) of the apparatus installed
on a con- sumer's premises.
Demand Factor - is the ratio of maximum demand to the connected
load. Load Factor - The ratio of average load to maximum load.
Load
Factor =
Average Load
Maximum Load
The load factor can also be defined as the
ratio of the energy consumed during a given period to the energy,
which would have been used if the maximum load had been maintained through-
out that period. For example, load factor for a day (24 hours) will be given by:
Load Factor =
Energy consumed during
24 hours
PF Measurement
Maximum load recorded x 24 Hours
A power analyzer can measure PF directly, or
alternately kWh, kVAh or kVArh readings are recorded
from the billing meter installed at the incoming point of supply. The relation
kWh / kVAh gives the power factor.
Time of Day
(TOD) Tariff
Many electrical utilities like to have flat demand curve to achieve
high plant effi- ciency. They encourage user to draw more power during off-peak hours (say during night time)
and less power during
peak hours. As per their plan, they offer TOD Tariff, which may be incen- tives or disincentives. Energy meter will record peak and non- peak
consumption sep- arately by timer con- trol. TOD tariff gives
opportunity for the user to reduce their
billing, as off peak hour tariff charged are quite low in comparison to peak hour tariff.
Three phase AC power measurement
Most of the motive drives such as pumps,
compressors, machines etc. operate with 3 phase AC Induction motor. Power consumption can be determined by using the relation.
Power = Ö3 x V x I x Cosq
Portable power analysers /instruments are available for measuring all electrical parameters.
Example:
A 3-phase AC
induction motor (20 kW capacity) is used for pumping operation. Electrical parameter such as current, volt and power factor were measured
with power analyzer. Find energy consumption of motor in one hour?
(line volts. = 440 V, line current
= 25 amps and PF
= 0.90).
Energy consumption = Ö 3 x 0.440 (kV) x 25(A) x 0.90(PF) x 1(hour) = 17.15 kWh
Motor loading calculation
The nameplate details of motor, kW or HP
indicate the output parameters of the motor at full load. The voltage, amps and PF refer to the rated input parameters at full load.
Example:
A three phase,10 kW
motor has the name plate details as 415 V, 18.2 amps and 0.9 PF. Actual input measurement shows 415 V, 12 amps
and 0.7 PF which was measured with power analyz- er during motor running.
Rated output at full load = 10 kW
Rated input at full load = 1.732 x 0.415 x 18.2 x 0.9 = 11.8 kW The rated efficiency
of motor at full load = (10 x 100) / 11.8 = 85%
Measured (Actual) input power = 1.732x 0.415 x 12x 0.7 = 6.0 kW
Motor
loading % =
Measured kW
x 100 =
6.0
x 100 = 51.2 %
Rated kW 11.8
Which applications use single-phase power in an industry?
Single-phase power is mostly used for lighting,
fractional HP motors and electric
heater appli- cations.
Example :
A 400 Watt mercury vapor lamp was switched on for 10 hours per day. The supply volt is 230
V. Find the power consumption per day? (Volt = 230 V, Current
= 2 amps, PF = 0.8)
Electricity consumption (kWh) = V x I x Cos x No of Hours
= 0.230 x 2 x 0.8 x 10 = 3.7 kWh or Units
Example :
An electric heater of
230 V, 5 kW rating is used for hot water generation in an industry. Find electricity consumption per hour (a) at the rated voltage (b) at 200 V
(a) Electricity consumption (kWh) at rated voltage = 5 kW x 1 hour = 5 kWh.
(b)
Electricity consumption at 200
V (kWh) = (200 / 230)2 x 5 kW x 1 hour = 3.78 kWh.
2.4
Thermal Energy Basics
Temperature and Pressure
Temperature and pressure are measures of the
physical state of a substance. They
are closely related to the energy
contained in the substance. As a result, measurements of temperature and pressure
provide a means of determining energy content.
Temperature
It is the degree of hotness or coldness
measured on a definite scale. Heat is a form of energy; temperature is a measure of its thermal
effects. In other
words, temperature is a means
of deter- mining sensible heat content of the substance
In the Celsius scale the freezing point of water is 0°C and the boiling point of water is 100°C at atmospheric pressure.
To change
temperature given in Fahrenheit (°F) to Celsius
(°C)
Start with (°F); subtract
32; multiply by 5; divide by 9; the answer is (°C)
To change
temperature given in Celsius (°C) to Fahrenheit (°F)
Start with (°C); multiply
by 9; divide by 5; add on 32; the answer is (°F)
 |
Pressure
It is the force per unit area applied to outside of a body. When we heat a gas in a confined
space, we create more force; a
pressure increase. For example, heating the air inside a balloon will cause the balloon to stretch as the pressure increases.
Pressure, therefore, is
also indicative of stored energy. Steam at high pressures contains much more energy than at low pressures.
Heat
Heat is a form of energy,
a distinct and measurable property of all matter. The quantity of heat depends on the quantity and type of substance
involved.
Unit of Heat
Calorie is the unit for
measuring the quantity of heat. It is the quantity
of heat, which can raise the temperature of 1 g of water by 1°C.
Calorie is too small a
unit for many purposes. Therefore, a
bigger unit Kilocalorie (1 Kilocalorie
= 1000 calories)
is used to measure heat. 1 kilocalorie can raise the temperature of 1000g (i.e. 1kg) of water by 1°C.
However, nowadays generally
joule as the unit of heat energy is used. It is the internation- ally accepted unit. Its relationship with calorie is as follows:
 |
Specific
Heat
If the same amount of heat energy is supplied
to equal quantities of water and milk, their tem- perature goes up by different amounts. This property is called
the specific heat of a substance and
is defined as the quantity of heat required to raise the temperature of 1kg of
a substance through 1°C.
The specific heat of water
is very high as compared to other common substances; it takes a lot of heat to raise the temperature of
water. Also, when water is cooled, it gives out a large quantity of heat.
|
TABLE 2.1 SPECIFIC HEAT OF SOME COMMON SUBSTANCES |
|
|
Substance |
Specific Heat (Joules / kg °C) |
|
Lead |
130 |
|
Mercury |
140 |
|
Brass |
380 |
|
Copper |
390 |
|
Iron |
470 |
|
Glass |
670 |
|
Aluminium |
910 |
|
Rubber |
1890 |
|
Ice |
2100 |
|
Alcohol |
2400 |
|
Water |
4200 |
Sensible heat
It is that heat which when added or subtracted results in a change of temperature.
Quantity of Heat
The quantity
of heat, Q, supplied to a substance
to increase its temperature by t°C depends on
–
mass of the substance (m)
–
increase in temperature
(Dt)
–
specific heat of the substance
(Cp)
The quantity of heat is given by:
Q = mass x specific
heat x increase in temperature Q = m x Cp x Dt
Phase Change
The change of state from the solid state to a liquid
state is called fusion. The fixed temperature
at which a solid changes into a liquid is called its melting point.
The change of a state from a liquid state to a gas is called vaporization.
Latent heat of fusion
The latent heat of fusion of a substance is
the quantity of heat required to convert 1kg solid to liquid state without change of temperature. It is represented by
the symbol L. Its unit is Joule per kilogram (J/Kg)
Thus, L (ice) = 336000 J/kg,
Latent Heat of Vaporization
The latent heat of vaporization of a substance
is the quantity of heat required to change 1kg of the substance from liquid to vapour state without change of temperature. It is also denoted by the symbol
L and its unit is also J/kg.
The latent heat of vaporization of water is 22,60,000 J/kg.
When 1 kg of steam at 100°C condenses to form water at 100°C, it gives out 2260 kJ (540 kCals) of heat. Steam gives out more heat than an equal amount
of boiling water
because of its
latent heat.
Latent heat
It is the change in heat content of a
substance, when its physical state is changed without a change in temperature.
Super Heat
The heating of vapour, particularly saturated
steam to a temperature much higher than the boil- ing point at the existing pressure. This is done in power
plants to improve efficiency and to avoid condensation in the turbine.
Humidity
The moisture content of air is referred
to as humidity and may be expressed
in two ways: spe- cific humidity and relative humidity.
Specific Humidity
It is the actual weight of water vapour mixed in a kg of dry air.
Humidity Factor
Humidity factor = kg of water per kg of dry air (kg/kg).
Relative Humidity (RH)
It is the measure of degree of saturation of
the air at any dry-bulb (DB) temperature. Relative humidity given as a percentage is the actual water content of
the air divided by the moisture content of fully saturated
air at the existing temperature.
Dew Point
It is the temperature at which condensation
of water vapour from the air begins as the temper- ature of the air-water vapour mixture falls.
Dry bulb Temperature
It
is an indication of the sensible heat content of air-water vapour mixtures.
Wet bulb Temperature
It is a measure of total heat content or enthalpy. It is the temperature approached by the dry bulb and the dew point as saturation occurs.
Dew Point Temperature
It is a measure of the latent heat content of
air-water vapour mixtures and since latent heat is a function of moisture
content, the dew point temperature is determined by the moisture
content.
Fuel Density
Density is the ratio of the mass of the fuel to the volume of the fuel at a stated temperature.
Specific gravity of fuel
The density of fuel, relative to water, is
called specific gravity. The specific gravity of water is defined as 1. As it is a ratio there are
no units. Higher the specific gravity, higher will be the heating values.
Viscosity
The viscosity of a fluid is a measure of its internal resistance to flow. All liquid fuels decrease in viscosity with increasing temperature
Calorific Value
Energy content in an organic matter
(Calorific Value) can be measured by burning it and mea- suring the heat released. This is done by placing a sample of
known mass in a bomb calorime- ter, a
device that is completely sealed and insulated to prevent heat loss. A
thermometer is placed inside
(but it can be read from the outside) and the increase
in temperature after the sam- ple is burnt completely is measured. From this data,
energy content in the organic
matter can be found out.
The heating value of fuel
is the measure of the heat released during the complete combus- tion of unit weight of fuel.
It is expressed as Gross
Calorific Value (GCV)
or Net Calorific Value (NCV). The difference between GCV and NCV
is the heat of vaporization of the moisture and atomic hydrogen (conversion to water vapour)
in the fuel. Typical GCV and NCV for heavy fuel oil are 10,500 kcal/kg and 9,800 kcal/kg.
Heat Transfer
Heat will always be transferred from higher
temperature to lower temperature independent of the mode. The energy transferred is measured in Joules (kcal or
Btu). The rate of energy trans- fer, more commonly called heat transfer,
is measured in Joules/second (kcal/hr or Btu/hr).
Heat is transferred by three primary
modes:
o Conduction (Energy transfer in a solid)
o Convection (Energy transfer in a fluid)
o Radiation
(Does not need a material
to travel through)
Conduction
The conduction of heat takes place, when two
bodies are in contact with one another. If one
body is at a higher temperature than the other, the motion of the
molecules in the hotter body will
vibrate the molecules at the point of contact in the cooler body and
consequently result in increase in temperature.
The amount of heat transferred by conduction depends
upon the temperature difference, the properties of the material involved, the
thickness of the material, the surface contact area, and the duration of the transfer.
Good conductors of heat are
typically substances that are dense as they have molecules close together. This allows the molecular agitation process to permeate
the substance easily.
So, metals are good conductors
of heat, while gaseous substance, having low densities or widely spaced molecules, are poor conductors of
heat. Poor conductors of heat are usually called insu- lators.
The measure of the ability
of a substance to insulate is its thermal resistance. This is com- monly referred to as the R-value (RSI in
metric). The R-value is generally the
inverse of the thermal conductivity, the ability to conduct heat.
Typical units of measure for conductive heat transfer are:
Per unit area (for a given thickness)
Metric
(SI) : Watt per square meter (W/m2 )
Overall
Metric (SI) : Watt (W) or kilowatts (kW)
Convection
The transfer of heat by convection involves
the movement of a fluid such as a gas or liquid
from the hot to the cold portion.
There are two types of convection: natural and forced.
In case of natural
convection, the fluid in contact with or adjacent to a high temperature body is heated by conduction. As it is
heated, it expands, becomes less dense and consequent- ly rises. This begins a fluid motion process in which a
circulating current of fluid moves past the heated body, continuously transferring heat away from it.
In the case of forced convection, the movement of the fluid is forced
by a fan, pump or other external
means. A centralized hot air heating
system is a good example of forced convection.
Convection depends on the
thermal properties of the fluid as well as surface conditions at the body and other factors that affect the
ability of the fluid to flow. With a low conductivity fluid such as air, a rough surface can trap air against the surface reducing the conductive heat
transfer and consequently reducing the
convective currents. Units of measure
for rate of convective heat transfer are:
Metric (SI) : Watt (W) or kilowatts
(kW)
Thermal Radiation
Thermal radiation is a process in which
energy is transferred by electromagnetic waves similar to light waves. These
waves may be both visible (light) and invisible. A very common example
of thermal radiation is a heating element on a heater. When the heater
element is first switched on, the
radiation is invisible, but you can feel the warmth it radiates. As the element heats, it will glow orange and some of the radiation
is now visible. The hotter the
element, the brighter it glows and the more radiant energy it emits.
The key processes in the interaction of a substance
with thermal radiation
are:
Absorption the process by which radiation
enters a body and
becomes heat
Transmission the process by which radiation
passes through a body
Reflection the process by which
radiation is neither absorbed or transmitted
through the body; rather it bounces off
Objects receive thermal
radiation when they are struck by electromagnetic waves, thereby agitating the molecules and atoms. More
agitation means more energy and a higher tempera- ture. Energy is transferred to one body from another without
contact or transporting medium such as air or water. In fact, thermal
radiation heat transfer
is the only form of heat transfer
pos- sible in a vacuum.
All bodies emit a certain
amount of radiation. The amount depends upon the body's tem- perature and nature of its surface. Some
bodies only emit a small amount of radiant energy for their temperature, commonly called low emissivity materials
(abbreviated low-E). Low-E win- dows are used to control the heat radiation
in and out of buildings.
Windows can be designed to reflect, absorb and transmit
different parts of the sun's radiant energy.
The condition of a body's
surface will determine the amount of thermal radiation that is absorbed, reflected or re-emitted.
Surfaces that are black and rough, such as black iron, will absorb and re-emit almost all the energy
that strikes them. Polished and smooth surfaces will not absorb, but reflect, a large part of the incoming radiant energy.
Typical units of measure for rate of radiant heat transfer
Metric (SI) Watt per square
meter (W/m2)
Evaporation
The
change by which any substance is converted from a liquid
state and carried off as vapour.
Example: People are
cooled by evaporation of perspiration from the skin and refrigeration is accomplished by evaporating the liquid refrigerant. Evaporation is a cooling process.
Condensation
The change by which any substance
is converted from a gaseous state to liquid state.
Example: Condensation on the other hand is a
heating process. As molecules of vapour con-
dense and become liquid, their latent heat of vapourisation evidences
itself again as sensible heat,
indicated by a rise in temperature. This heating effect of condensation is what
causes the considerable rise in
atmospheric temperature often noted as fog forms and as rain or snow begins to fall.
Steam
Steam has been a popular mode of conveying energy, since the industrial revolution. The fol- lowing characteristics of steam make it so popular and useful to the industry:
•
High specific heat and latent heat
• High heat transfer coefficient
• Easy to control and distribute
• Cheap and inert
Steam is used for
generating power and also used in process industries, such as, sugar, paper, fertilizer, refineries,
petrochemicals, chemical, food, synthetic fibre and textiles. In the process industries, the high pressure
steam produced in the boiler, is first expanded in a steam turbine for generating power. The
extraction or bleed from the turbine, which are generally at low pressure, are used for the process.
This method of producing power,
by using the steam gen- erated for process in the boiler, is called "Cogeneration."
How to read
a Steam Table?
Select the pressure
and temperature of the steam at which you want to find the enthalpy.
Read the intersection of pressure and temperature for enthalpy (Heat content in the steam)
First law of Thermodynamics
It states that energy may be converted
from one form to another, but it is never lost from the system.
Second Law of Thermodynamics
•
In any conversion
of energy from one form to another, some amount of energy will be dis sipated
as heat.
•
Thus no energy conversion is 100 % efficient.
• This principle
is used in energy equipment efficiency calculations.
Law of Conservation of Matter
•
In any physical or chemical change,
matter is neither created nor destroyed, but it may be changed from one form to another.
•
For example, if a sample of coal were
burnt in an enclosed chamber, carbon in coal would end up as CO2 in the air inside the chamber; In
fact, for every carbon atom there would be
one carbon dioxide molecule in the combustion products (each of which
has one carbon atom). So the carbon
atoms would be conserved, and so would every other atom. Thus, no matter
would be lost during this conversion of the coal into heat.
•
This principle is used in energy and material balance
calculations
2.5 Units and Conversions
The energy units are wide and varied. The
usage of units varies with country, industry sector, systems such as FPS, CGS, MKS and SI, and also with generations
of earlier period using FPS and
recent generations using MKS. Even technology/equipment suppliers adopt units
that are different from the one being
used by the user of that technology/equipment. For example some compressor manufacturers specify output
in m3/min while some specify in cubic feet/minute or even in litres/second. All this cause
confusion and hence the need for this chapter on units and conversions.
Energy Units
1 barrel of oil = 42 U.S. gallons (gal) = 0.16 cubic meters (m3)
|
1 MW |
1,000 kW |
|
1
kW |
1,000 Watts |
|
1
kWh |
3,412 Btu |
|
1
kWh |
1.340 Hp hours |
|
1,000 Btu |
0.293 kWh |
|
1
Therm |
100,000 Btu (British Thermal
Units) |
|
1
Million Btu |
293.1 Kilowatt hours |
|
100,000 Btu |
1
Therm |
|
1
Watt |
3.412 Btu per hour |
|
1
Horsepower |
746
Watts or 0.746 Kilo Watts |
|
1
Horsepower hr. |
2,545 Btu |
|
1 kJ |
0.239005 Kilocalories |
|
1
Calorie |
4.187 Joules |
|
1
kcal/Kg |
1.8
Btu's/lb. |
|
1
Million Btu |
252
Mega calories |
|
1
Btu |
252
Calories |
|
1
Btu |
1,055 Joules |
|
1
Btu/lb. |
2.3260 kJ/kg |
|
1
Btu/lb. |
0.5559 Kilocalories/kg |
|
Power (Energy
Rate) Equivalents |
|
|
1 kilowatt (kW) |
1 kilo joule /second
(kJ/s) |
|
1 kilowatt (kW) |
3413 BTU/hour (Btu/hr.) |
|
1 horsepower (hp) |
746 watts (0.746 kW) |
|
1 Ton of refrigeration |
12000 Btu/hr. |
Pressure:
Gauge pressure is defined relative to the prevailing atmospheric pressure (101.325 kPa at sea level), or as absolute pressure:
Absolute Pressure = Gauge Pressure + Prevailing Atmospheric Pressure
Units of measure of pressure:
Metric (SI) : kilopascals
(kPa) 1 pascal (Pa) = 1 Newton/m2 (N/m2 )
1 physical atmosphere (atm) = 101325 Pa = 760 mm of mercury (mm Hg)
= 14.69 lb-force/in2 (psi)
1 technical
atmosphere (ata) = 1 kilogram-force/cm2 (kg/cm2)= 9.806650
× 104 Pa
Power:
1 W = 1 J/s = 0.9478×10-3 Btu/s = 3.41214 Btu/hr
Fuel to kWh (Approximate conversion)
|
Natural gas |
M3 x 10.6 |
kWh |
|
|
Ft3 x 0.3 |
kWh |
|
LPG (propane) |
therms x 29.3 m3 x 25 |
kWh kWh |
|
Coal |
kg
x 8.05 |
kWh |
|
Coke |
kg
x 10.0 |
kWh |
|
Gas oil |
litres x 12.5 |
kWh |
|
Light fuel oil |
litres x 12.9 |
kWh |
|
Medium fuel oil |
litres x 13.1 |
kWh |
|
Heavy fuel oil |
litres x 13.3 |
kWh |
Prefixes for
units in the International System
|
Prefix |
Symbol |
Power |
Example |
USA/Other |
|
exa |
E |
1018 |
|
quintillion |
|
peta |
P |
1015 |
pentagram (Pg) |
quadrillion/billiard |
|
tera |
T |
1012 |
terawatt (TW) |
trillion/billion |
|
giga |
G |
109 |
gigawatt (GW) |
billion/milliard |
|
mega |
M |
106 |
megawatt (MW) |
million |
|
kilo |
k |
103 |
kilogram (kg) |
|
|
hecto |
h |
102 |
hectoliter (hl) |
|
|
deka |
da |
101 |
dekagram (dag) |
|
|
deci |
d |
10-1 |
decimeter (dm) |
|
|
centi |
c |
10-2 |
centimeter (cm) |
|
|
milli |
m |
10-3 |
millimeter (mm) |
|
|
micro |
m |
10-6 |
micrometer (mm) |
|
|
nano |
n |
10-9 |
nanosecond (ns) |
|
|
pico |
p |
10-12 |
picofarad (pf) |
|
|
femto |
f |
10-15 |
femtogram (fg) |
|
|
atto |
a |
10-18 |
|
|
Energy
|
To: |
TJ |
Gcal |
Mtoe |
MBtu |
GWh |
|
From: |
Multiply by: |
|
|
|
|
|
TJ |
1 |
238.8 |
2.388 x 10-5 |
947.8 |
0.2778 |
|
Gcal |
4.1868 x 10-3 |
1 |
10-7 |
3.968 |
1.163 x 10-3 |
|
Mtoe |
4.1868 x 104 |
107 |
1 |
3.968 x 107 |
11630 |
|
MBtu |
1.0551 x 10-3 |
0.252 |
2.52 x 10-8 |
1 |
2.931 x 10-4 |
|
GWh |
3.6 |
860 |
8.6 x 10-5 |
3412 |
1 |
Mass
|
To: |
kg |
t |
lt |
st |
lb |
|
From: |
multiply by: |
|
|
|
|
|
kilogram (kg) |
1 |
0.001 |
9.84 x 10-4 |
1.102 x 10-3 |
2.2046 |
|
tonne (t) |
1000 |
1 |
0.984 |
1.1023 |
2204.6 |
|
long ton (lt) |
1016 |
1.016 |
1 |
1.120 |
2240.0 |
|
short ton (st) |
907.2 |
0.9072 |
0.893 |
1 |
2000.0 |
|
pound (lb) |
0.454 |
4.54 x 10-4 |
4.46 x 10-4 |
5.0 x 10-4 |
1 |
Volume
|
To: |
gal U.S. |
gal
U.K. |
bbl |
ft3 |
l |
m3 |
|
From: |
multiply by: |
|
|
|
|
|
|
U.S. gallon (gal) |
1 |
0.8327 |
0.02381 |
0.1337 |
3.785 |
0.0038 |
|
U.K. gallon (gal) |
1.201 |
1 |
0.02859 |
0.1605 |
4.546 |
0.0045 |
|
Barrel (bbl) |
42.0 |
34.97 |
1 |
5.615 |
159.0 |
0.159 |
|
Cubic foot (ft3) |
7.48 |
6.229 |
0.1781 |
1 |
28.3 |
0.0283 |
|
Litre (l) |
0.2642 |
0.220 |
0.0063 |
0.0353 |
1 |
0.001 |
|
Cubic metre (m3) |
264.2 |
220.0 |
6.289 |
35.3147 |
1000.0 |
1 |
|
QUESTIONS |
|
|
1. |
Discuss one energy conversion activity with various
losses occurring stage wise. |
|
2. |
The reactive power is represented by (a) kVA (b) kW (c) kVAr (d) PF |
|
3. |
A fluorescent tube light consumes
40 W for the tube and 10 W for choke. If the lamp operates for 8 hours a day for 300 days in a year, calculate the total energy cost per
annum if the energy cost is Rs.3/- per kWh |
|
4. |
Power factor is the ratio of (a)
kW / kVA (b) kVA / kW (c) kVA / kVAr
(d) kVAr / kV |
|
5. |
Define the term load
factor. |
|
6. |
What do you understand by the term calorific value? |
|
7. |
What are the three modes of heat transfer? Explain with examples? |
|
8. |
Explain why steam is used commonly
in industries? |
|
9. |
If an electric heater consumes 4 kWh, what will be the equivalent kilocalories? |
|
10. |
Why a cube of ice at 0oC is more effective in cooling a drink than the same quantity of water at 0oC? |
|
11. |
10 kg of steam at 100oC with latent heat of vapourisation 2260 kJ is cooled to 50oC. If the specific heat of water
is 4200 J/kgoC, find the quantity
of heat given out. |
REFERENCES
1.
Energy Dictionary, Van Nostrand Reinhold
Company, New York - V Daniel Hunt.
2.
Cleaner
Production – Energy Efficiency Manual
for GERIAP, UNEP, Bangkok prepared
by National Productivity Council
www.eia.doe.gov/kids/btudef.html www.calculator.org/properties.html www.katmarsoftware.com
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