Ch1- Introduction Aman

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MEC551 MEC551 THERMAL ENGINEERINGTHERMAL ENGINEERING

MEC551 MEC551 THERMAL ENGINEERINGTHERMAL ENGINEERING

Aman Mohd IhsanAman Mohd Ihsan

03-5543626803-55436268

T1-A16-4CT1-A16-4C

Aman Mohd IhsanAman Mohd Ihsan

03-5543626803-55436268

T1-A16-4CT1-A16-4C

1.01.0 IntroductionIntroduction1.01.0 IntroductionIntroduction

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COURSE INFOCOURSE INFO

CodeCode : MEC551: MEC551

Course Course : THERMAL : THERMAL ENGINEERINGENGINEERING

Contact HrsContact Hrs : 3 (L) & 1 (T) / weeks : 3 (L) & 1 (T) / weeks

Course Status : CoreCourse Status : Core

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Course Outcomes Course Outcomes

Upon Completion of this course, students should be able to :

CO1 Describe the principles of heat transfer mechanisms, combustion, refrigeration and air conditioning systems [PO1, LO1]{C2}.

CO2 Establish relationship between theoretical and practical aspects of heat transfer application [PO1, LO1]{C3}.

CO3 Analyse principles of energy mechanisms to solve a wide range of thermal engineering problems [PO3, LO3, SS1]{C4, P4}.

CO4 Develop solutions for mathematical models and propose appropriate results for thermal engineering applications. [PO3, LO3, SS1]{C5}.

CO5 Show concern on energy utilization and its impact on the environment. [PO9, LO6, SS4]{A3}.

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AssessmentAssessment

CourseworkCoursework 40%40%• Test 1Test 1 15%15%• Test 2Test 2 15%15%• AssignmentsAssignments 10%10%

Final ExamFinal Exam 60%60%

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Course OutlineCourse Outline

1.1. IntroductionIntroduction 3 hrs3 hrs

2.2. ConductionConduction 7 hrs7 hrs

3.3. ConvectionConvection 6 hrs6 hrs

4.4. Heat ExchangersHeat Exchangers 6 hrs6 hrs

5.5. CombustionCombustion 6 hrs6 hrs

6.6. Refrigeration CyclesRefrigeration Cycles 7 hrs7 hrs

7.7. Air-conditoning ProcessesAir-conditoning Processes 7 hrs.7 hrs.

TEST 1 (~ Week 6-7)TEST 1 (~ Week 6-7)

TEST 2 (~ Week 11-12)TEST 2 (~ Week 11-12)

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Text bookText book

• Y.A. CengelY.A. Cengel, Heat and , Heat and Mass Transfer: A Mass Transfer: A Practical Approach, Practical Approach, McGraw-Hill, 3rd Edition, McGraw-Hill, 3rd Edition, 2007. 2007.

• Y.A. Cengel and M.A. Y.A. Cengel and M.A. BolesBoles,Thermodynamics: ,Thermodynamics: An Engineering An Engineering Approach, , Approach, , McGraw-Hill, McGraw-Hill, 6th Edition, 2007.6th Edition, 2007.

1.0 INTRODUCTION

1.1 Fundamental mechanism of Heat Transfer: Conduction, Convection and Radiation.

1.2 Ozone Depleting Substances and Global Warming Issues.

1.3 Renewable Energy Resources and Technologies - Sustainable Energy Management.

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Introductory DefinitionsIntroductory Definitions

• HeatHeat– Form of energy that can be transferred Form of energy that can be transferred

from one system to another as a result of a from one system to another as a result of a temperature difference.temperature difference.

• Heat TransferHeat Transfer– Science that deals with the determination Science that deals with the determination

of of ratesrates of energy transfer. of energy transfer.

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Why Study Heat Transfer?Why Study Heat Transfer?

• ThermodynamicsThermodynamics is concerned with the is concerned with the amountamount of total heat transfer as a of total heat transfer as a system undergoes a process from one system undergoes a process from one equilibrium state to another.equilibrium state to another.

• However, the study of thermodynamics However, the study of thermodynamics gives gives nono indication of how long it takes. indication of how long it takes.

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Why Study Heat Transfer?Why Study Heat Transfer?

• ThermodynamicsThermodynamics– Deals with equilibrium states and changes Deals with equilibrium states and changes

from one system to anotherfrom one system to another

• Heat TransferHeat Transfer– Deals with systems that lack thermal Deals with systems that lack thermal

equilibrium (e.g. non-equilibrium equilibrium (e.g. non-equilibrium phenomenon).phenomenon).

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Foundational LawsFoundational Laws

• However, the laws of thermodynamics However, the laws of thermodynamics lay out the framework for studying heat lay out the framework for studying heat transfer.transfer.

• 11stst Law – Energy Equation Law – Energy Equation– Rate of energy transfer into a system equal Rate of energy transfer into a system equal

the rate of increase of energy in the the rate of increase of energy in the systemsystem

• 22ndnd Law Law– Heat is transferred in the direction of Heat is transferred in the direction of

decreasing temperature.decreasing temperature.

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Heat Transfer DirectionHeat Transfer Direction

HOT COLD

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1.0 Modes of Heat Transfer1.0 Modes of Heat Transfer

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ConductionConduction

• Transfer of energy from the more Transfer of energy from the more energetic particles of a substance energetic particles of a substance to an adjacent substance with to an adjacent substance with less energetic particles, ones as a less energetic particles, ones as a result of interactions between the result of interactions between the particlesparticles

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ConductionConduction

Conduction can take place in Conduction can take place in solids, liquids, or gasessolids, liquids, or gases

• In In gases and liquidsgases and liquids conduction is due to the conduction is due to the collisionscollisions and and diffusiondiffusion of the of the molecules during their molecules during their random motion.random motion.

• In In solidssolids conduction is due to conduction is due to the combination of the combination of vibrations vibrations of the molecules in a lattice of the molecules in a lattice and the energy transport by and the energy transport by free electronsfree electrons

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Conduction EquationConduction Equation(Fourier’s Law of Heat Conduction)(Fourier’s Law of Heat Conduction)

TT

XX

Temperature Temperature profileprofile

Thickness

DifferenceeTemperaturAreakx

TTAkQcond

21

YY

XX

TT11

TT22

TT

xx

xx11 xx22

Qx

Area (Ax)

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Area Temperature differenceRate of heat conduction

Thickness

(W)cond

dTQ kA

dx

which is called Fourier’s law of heat conduction.

where the constant of proportionality k is the thermal conductivity of the material.

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Conduction EquationConduction Equation(Fourier’s Law of Heat Conduction)(Fourier’s Law of Heat Conduction)

• Fourier’s Law of Heat Conduction (1822) is:Fourier’s Law of Heat Conduction (1822) is:

WdirectionxinconductionofRateQ x

~

Wattsdx

dTkAQ x ~

2

sec~

mflowheatthe

ofdirectionthetonormalareationalCrossA

m

CflowheatofdirectiontheingradienteTemperatur

dx

dT~

Cm

WmaterialtheoftyconductiviThermalk ~

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Thermal conductivityThermal conductivity

• The thermal conductivity (k) of a material is The thermal conductivity (k) of a material is defined as the rate of heat transfer through a defined as the rate of heat transfer through a unit thickness of a material per unit area per unit thickness of a material per unit area per unit temperature difference.unit temperature difference.

• High value for thermal conductivity - good High value for thermal conductivity - good heat conductor heat conductor

• Low value - poor heat conductor or Low value - poor heat conductor or insulator.insulator.

• Symbol: k Symbol: k • Units: W/(mUnits: W/(m··ººC)C)

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• The thermal conductivities of The thermal conductivities of gasesgases such as air vary by a such as air vary by a factor of factor of 101044 from those of from those of pure metalspure metals such as copper. such as copper.

• Pure Pure crystals crystals andand metals metals have the have the highest thermal highest thermal conductivitiesconductivities, and gases , and gases and insulating materials the and insulating materials the lowest.lowest.

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• The thermal conductivities The thermal conductivities of materials vary with of materials vary with temperature.temperature.

• The temperature The temperature dependence of thermal dependence of thermal conductivity causes conductivity causes considerable complexity in considerable complexity in conduction analysis.conduction analysis.

• A material is normally A material is normally assumed to be assumed to be isotropic.isotropic.

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100 cm 100 cm x x

50 cm50 cm

ConductionConduction(Example 1.1)(Example 1.1)

• The inside and outside of the The inside and outside of the surface of a window glass are at surface of a window glass are at 2020ºC and -5ºC respectively. If the ºC and -5ºC respectively. If the glass is 100 cm x 50 cm in size glass is 100 cm x 50 cm in size and 1.5 cm thick, with a thermal and 1.5 cm thick, with a thermal conductivity of 0.78 W/(m·ºC). conductivity of 0.78 W/(m·ºC).

• Determine the heat loss through Determine the heat loss through the glass over a period of 2 hours.the glass over a period of 2 hours.

2020ºCºC -5-5ºCºC

1.5 cm1.5 cm

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ConductionConduction(Example 1.1)(Example 1.1)

TT11 = 20 = 20 ººCC

TT22 = -5 = -5 ººCC

A = (100x50)= 5,000 cmA = (100x50)= 5,000 cm2 2 = 0.5 m= 0.5 m22

k = 0.78 W/(mk = 0.78 W/(m··ººC)C)

dx= 0.015 mdx= 0.015 m100 cm 100 cm

x x 50 cm50 cm

2020ºCºC -5-5ºCºC

1.5 cm1.5 cm

W

m

CCm

x

TTAkQ

CmW 650

015.0

5205.078.0 2

21

hrkWhourskW

hoursoverLossHeatTotal

3.1265.0

:2

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ConvectionConvection

• Is the mode of energy Is the mode of energy transfer between a solid transfer between a solid surface and the adjacent surface and the adjacent liquid or gas that is in liquid or gas that is in motion. motion.

• Convection involves the Convection involves the combined effects of combined effects of conduction and fluid motion.conduction and fluid motion.

Convection = Conduction + Advection (fluid motion)

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ConvectionConvection

• Convection is commonly Convection is commonly classified into three sub-classified into three sub-modes:modes:– Forced convection,Forced convection,– Natural (or free) Natural (or free)

convection,convection,– Change of phase Change of phase

(liquid/vapor, solid/liquid, (liquid/vapor, solid/liquid, etc.) etc.)

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Convection EquationConvection Equation(Newton’s Law of Cooling)(Newton’s Law of Cooling)

• Newton’s Law of Cooling (1701) is:Newton’s Law of Cooling (1701) is:

WattsTTAhQ fluidwallconv ~

u∞yy

xx

T∞

Heated SurfaceHeated Surface

( ) (W)conv s sQ hA T T

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Convection EquationConvection Equation(Newton’s Law of Cooling)(Newton’s Law of Cooling)

WattsTTAhQ fluidwallconv ~

WdirectionyinconvectionofRateQconv

~

Cm

WtcoefficienConvectionh

2~

2~ mareaSurfaceA

CetemperatursurfaceWallTwall ~

CetemperaturFluidTT fluid ~

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Convection Heat Transfer CoefficientConvection Heat Transfer Coefficient

• The convection heat transfer coefficient (h) is The convection heat transfer coefficient (h) is not a property of a fluid (unlike k). It is an not a property of a fluid (unlike k). It is an experimentally determined parameter whose experimentally determined parameter whose value depends on surface geometry, fluid value depends on surface geometry, fluid motion, fluid properties, and bulk fluid motion, fluid properties, and bulk fluid velocity.velocity.

• Symbol: hSymbol: h• Units:Units: W/(mW/(m22··ººC)C)

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ConvectionConvection(Example 1.2)(Example 1.2)

• Atmospheric air at a Atmospheric air at a temperature of 10temperature of 10ººC flows C flows with a velocity 5 m/s with a velocity 5 m/s across a tube with an across a tube with an outer diameter (OD) of 1 outer diameter (OD) of 1 cm and a length of 5 cm. cm and a length of 5 cm. The surface is maintained The surface is maintained at 110at 110ººC. C.

• Determine the rate of heat Determine the rate of heat flow from the tube surface flow from the tube surface to atmospheric air if h is to atmospheric air if h is 85 W/(m85 W/(m22·ººC). C).

AIRAIR

1 cm1 cm

Tw=110ºCºC

5 m5 m

TT∞∞==10ºC10ºC

V = 5 m/sV = 5 m/sh = 85 W/(mh = 85 W/(m22··ºC)ºC)

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ConvectionConvection(Example 1.2)(Example 1.2)

Surface Area:Surface Area:

Heat Transfer per unit area:Heat Transfer per unit area:

Total Heat Flow:Total Heat Flow:

2157.0501.0 mmm

LDA

22 500,81011085mW

CmW

w

CC

TThA

Qq

WmAqQmW 335,1157.0500,8 2

2

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RadiationRadiation

• Unlike conduction or Unlike conduction or convection, the transfer of convection, the transfer of energy by radiation does energy by radiation does not require the presence not require the presence of an intervening medium. of an intervening medium. Energy transfer by Energy transfer by radiation is the fastest radiation is the fastest (speed of light) and (speed of light) and suffers no attenuation in a suffers no attenuation in a vacuum.vacuum.

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The electromagnetic spectrumThe electromagnetic spectrum

• The theoretical foundation of The theoretical foundation of radiation was established in 1864 radiation was established in 1864 by James Maxwell (1831- 1879) of by James Maxwell (1831- 1879) of Scotland, who postulated that Scotland, who postulated that accelerated electric charges or accelerated electric charges or changingchanging electric currents give rise to electric currents give rise to electric and magnetic fields.electric and magnetic fields.

• These rapidly moving fields are These rapidly moving fields are called called electromagnetic radiation – electromagnetic radiation – ((can be explained as waves or can be explained as waves or photon) - and represent the energy photon) - and represent the energy emitted by matter as a result of emitted by matter as a result of changes in the electronic changes in the electronic configurations of atoms or configurations of atoms or molecules.molecules.

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• The heat radiated by a body is comprised of a range The heat radiated by a body is comprised of a range of frequencies.of frequencies.

– Thermal radiationThermal radiation is defined as the portion of the is defined as the portion of the spectrum between: 10spectrum between: 10-7-7 and 10 and 10-4-4 m. m.

– Visible lightVisible light is the portion of the spectrum is the portion of the spectrum between: 3.9x10between: 3.9x10-7-7 and 7.8x10 and 7.8x10-7-7 m. m.

– Solar radiationSolar radiation is the portion of the spectrum is the portion of the spectrum between: 10between: 10-5-5 and 3x10 and 3x10-6-6 m. m.

• Electromagnetic waves transport energy and travel Electromagnetic waves transport energy and travel at the speed of light.at the speed of light.

cc00= 2.9979 = 2.9979 xx 10 1088 m/s m/s

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Thermal radiation Thermal radiation (10(10-7-7 to 10 to 10-4 -4 m)m)

(3.9x10(3.9x10-7-7 to 7.8x10 to 7.8x10-7-7 m) m)


Solar radiationSolar radiation(10(10-5-5 to 3x10 to 3x10-6 -6 m)m)

• All forms of matter above absolute zero (0 K) emit All forms of matter above absolute zero (0 K) emit thermal radiation. thermal radiation.

• Although the rate of energy emission is independent Although the rate of energy emission is independent of the surroundings, the heat transfer rate is: of the surroundings, the heat transfer rate is: – Proportional to the 4Proportional to the 4thth power of temperature of the power of temperature of the

mattermatter

– Depends on the spatial relationships of the Depends on the spatial relationships of the surface and its surroundings. surface and its surroundings.

– Consequently, it is the least efficient means of Consequently, it is the least efficient means of heat transferheat transfer

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Radiation EquationRadiation Equationemissions- (Stefan-Boltzmann Equation)emissions- (Stefan-Boltzmann Equation)

• Stefan-Boltzmann Equation:Stefan-Boltzmann Equation:

WattsTAQrad ~4

KetemperatursurfaceabsoluteT ~

4281067.5

tan~

Km

W

tconsBoltzmannStefan

0.10~ emissivity

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Radiation- EmissionsRadiation- Emissions

• Stefan-Boltzman constant Stefan-Boltzman constant

((σσ = 5.67x10 = 5.67x10-8-8 W/(m W/(m22·K·K44))– The maximum amount of radiation that can be The maximum amount of radiation that can be

emitted from a surface at absolute temperature. emitted from a surface at absolute temperature.

• BlackbodyBlackbody– Idealized surface that emits radiation at this Idealized surface that emits radiation at this

maximum rate (maximum rate (σσ).).

poweremissiveBlackbodyTEb ~4

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Radiation- EmissionsRadiation- Emissions

• The idealized surface that emits radiation at this The idealized surface that emits radiation at this maximum rate is called a blackbody. maximum rate is called a blackbody.

• The radiation emitted by all real surfaces is less than The radiation emitted by all real surfaces is less than the radiation emitted by a blackbody at the same the radiation emitted by a blackbody at the same temperature, and is expressed as temperature, and is expressed as emissivityemissivity of the of the surface (0 surface (0 εε 1 1))– A measure of how closely the surface A measure of how closely the surface

approximates a blackbodyapproximates a blackbody

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Greybody (real) radiationGreybody (real) radiation

• Most objects are actually grey bodies not black Most objects are actually grey bodies not black bodies.bodies.

• The ratio of the total emissive power of a body to The ratio of the total emissive power of a body to that of a blackbody at the same temperature is that of a blackbody at the same temperature is defined as the defined as the emissivityemissivity ( (εε) of the body.) of the body.

10; bE

E

BlackbodyBlackbody GreybodyGreybody

EEbb EE

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Blackbody (ideal) radiationBlackbody (ideal) radiation

• A blackbody is defined as a A blackbody is defined as a perfectperfect emitteremitter and and absorberabsorber of radiation. of radiation.

– At a specified temperature and At a specified temperature and wavelength, no surface can emit more wavelength, no surface can emit more energy than a blackbody.energy than a blackbody.

– A blackbody absorbs all incident radiation A blackbody absorbs all incident radiation energy uniformly in all directions, energy uniformly in all directions, regardless of wavelength and direction.regardless of wavelength and direction.

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Absorptivity, reflectivity, and Absorptivity, reflectivity, and transmissiontransmission

• Whenever radiant Whenever radiant energy is incident energy is incident upon any surface, upon any surface, part may be:part may be:

– Absorbed (Absorbed ())– Reflected (Reflected (ρρ))– Transmitted (Transmitted ())

Incidentradiation

Reflectedradiation

Transmittedradiation

Absorption

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Radiation - AbsorptionRadiation - Absorption

• The fraction of the The fraction of the

radiation energy incident radiation energy incident

on a surface that is on a surface that is

absorbed by the surface is absorbed by the surface is

termed the termed the absorptivity absorptivity ..

• Both Both and and of a surface of a surface depend on the depend on the temperaturetemperature and the and the wavelengthwavelength of the of the radiation.radiation.

0 1

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Radiation AnalysisRadiation Analysis(Introduction)(Introduction)

• Radiation exchange Radiation exchange with the surroundingwith the surrounding

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41 sssrad TTAQ

TTs2s2

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SunSunT = 6,000 KT = 6,000 KAAss= 6.2x10= 6.2x101212 km km22

Earth (Malaysia)Earth (Malaysia)T = 306 KT = 306 KAA = 5.1x10= 5.1x1088 km km2 2 (0.008% of the sun)(0.008% of the sun)

Significant radiation heat transfer from the sun due to a large Significant radiation heat transfer from the sun due to a large temperature difference and large emitting surface area (Atemperature difference and large emitting surface area (Ass). ).

Life on Earth depends on this!Life on Earth depends on this!

Significant radiation heat transfer from the sun due to a large Significant radiation heat transfer from the sun due to a large temperature difference and large emitting surface area (Atemperature difference and large emitting surface area (Ass). ).

Life on Earth depends on this!Life on Earth depends on this!

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Insignificant radiation heat transfer from light bulb, even Insignificant radiation heat transfer from light bulb, even though there is a large temperature difference, due to the light though there is a large temperature difference, due to the light

bulb’s small emitting surface area (Abulb’s small emitting surface area (Ass))

Insignificant radiation heat transfer from light bulb, even Insignificant radiation heat transfer from light bulb, even though there is a large temperature difference, due to the light though there is a large temperature difference, due to the light

bulb’s small emitting surface area (Abulb’s small emitting surface area (Ass))


100-W Light bulb100-W Light bulbT= 3,000 KT= 3,000 KAAss= 6.3x10= 6.3x10-5-5 m m22

PersonPersonT= 300 KT= 300 KA= 1.7 mA= 1.7 m22

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Why the Sky is BlueWhy the Sky is Blue

• Air molecules scatter blue Air molecules scatter blue light much more than they light much more than they do red light. do red light.

• At sunset, the light travels At sunset, the light travels through a thicker layer of through a thicker layer of atmosphere which removes atmosphere which removes most of the blue from the most of the blue from the natural light allowing red to natural light allowing red to dominate.dominate.

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On Mars it is the oppositeOn Mars it is the opposite

• The Martian atmosphere The Martian atmosphere scatters red light much scatters red light much more than blue light giving more than blue light giving it a red appearance.it a red appearance.

• At sunset the light travels At sunset the light travels through a thicker layer of through a thicker layer of atmosphere allowing blue atmosphere allowing blue to dominate.to dominate.

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Radiation EquationRadiation Equation(Example 1.3)(Example 1.3)

• A horizontal pipe, with a 50 A horizontal pipe, with a 50 mm outside diameter, is mm outside diameter, is maintained at a temperature maintained at a temperature of 50of 50ººC in a large room C in a large room where the air and wall where the air and wall temperature are kept at temperature are kept at 2020ººC. The surface emissivity C. The surface emissivity of the steel pipe may be of the steel pipe may be taken as 0.8.taken as 0.8.

• Calculate the heat loss by Calculate the heat loss by

radiation per unit length.radiation per unit length.

Radiation

Radiation

50 mm50 mm

T1=50ºCºC

εε = 0.8 = 0.8

LL

TT22==20ºC20ºC

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Radiation EquationRadiation Equation(Example 1.3)(Example 1.3)

Heat loss by radiation per unit length:Heat loss by radiation per unit length:

KCT

KCT

29327320

32327350

2

1

LLmLDA 157.005.0

mW

KmW KKm

TTDL

Q

03.25

293323157.01067.58.0 448

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41

42

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Heat Transfer MechanismsHeat Transfer Mechanisms

• Now we have Now we have covered all 3 of the covered all 3 of the heat transfer heat transfer mechanisms. mechanisms.

• Most real problems Most real problems will involved will involved combinations of combinations of these these mechanisms.mechanisms.

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Combined ExampleCombined Example(Example 1.4)(Example 1.4)

Air blows (at 20Air blows (at 20ººC) over carbon C) over carbon steel [k=43 W/(msteel [k=43 W/(m22··ººC] hot plate C] hot plate which is 0.5 m x 0.75 m and 20 which is 0.5 m x 0.75 m and 20 mm thick maintained at 250mm thick maintained at 250ººC. C. The convection heat transfer The convection heat transfer coefficient is 25 W/(mcoefficient is 25 W/(m22··ººC) and C) and the heat loss from the plate the heat loss from the plate surface by radiation is 300 W. surface by radiation is 300 W.

(a)(a) Calculate the heat transfer. Calculate the heat transfer.

(b)(b) The inside plate temperature.The inside plate temperature.

TT11

k=43 W/(m2·ºC)

Hot plateHot plate

TTww= 250= 250ººCC

Energy Loss by Radiation(300 W)

Air (T∞=20ºC)h= 25 W/(m2·ºC)

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• Heat Transfer from Newton’s Law of Cooling:Heat Transfer from Newton’s Law of Cooling:

• Energy balance:Energy balance:

W

CCm

TTAhQ

CmW

fw

25.156,2

2025075.050.025 22

kWkWkWx

TkA

QQQ radconvcond

456.23.0156.2

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• Solving for the inside plate temperature:Solving for the inside plate temperature:

C

mm

mWAk

xWT

CmW

05.35.075.043

02.0456,2

456,2

2

CCC

TTT

05.25305.325021

1.2(a) OZONE LAYER DEPLETION

• The ozone layer is a concentration of ozone molecules in the stratosphere. About 90% of the planet's ozone is in the ozone layer

• The ozone depletion process begins when CFCs and other ozone-depleting substances (ODS) are emitted into the atmosphere

• It is caused by the release of chlorofluorocarbons (CFCs), hydrofluorocarbons (HCFCs), and other ozone-depleting substances (ODS), which were used widely as refrigerants, insulating foams, and solvents.

• A diminished ozone layer allows more radiation to reach the Earth's surface. For people, over exposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems. Increased UV can also lead to reduced crop yield and disruptions in the marine food chain . (Ref: )

OZONE LAYER DEPLETION



What can be done?

?

1.2(b) Global Warming

• Green House Effect

• GHGs

GREEN HOUSE EFFECT

• Glass transmits over 90 percent of radiation in the visible range but not the longer-wavelength (infrared regions)

• Radiation emitted by surfaces at room temperature falls in the infrared region.

• Consequently glass allows the solar radiation to enter but does not allow the infrared radiation from the interior surfaces to escape.

• This causes a rise in the interior temperature as a result of the energy buildup known as the greenhouse effect,

GREEN HOUSE EFFECT

• The greenhouse effect is also experienced on a larger scale on earth.

• The surface of the earth, which warms up during the day as a result of the absorption of solar energy, cools down at night by radiating its energy into deep space as infrared radiation.

• The combustion gases such as CO2 and water vapor in the atmosphere transmit the bulk of the solar radiation but absorb the infrared radiation emitted by the surface of the earth.

• Thus, there is concern that the energy trapped on earth will eventually cause global warming and thus drastic changes in weather patterns.

GREEN HOUSE EFFECT

GHGs

• The major greenhouse gases in the atmosphere are carbon dioxide (CO2), methane, (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFCs) and ozone (O3). Atmospheric water vapour (H2O) also makes a large contribution to the natural greenhouse

• Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values

• The global increases in CO2 concentration are due primarily to fossil fuel use and land-use change, while those of CH4 and N2O are primarily due to agricultural/industrial activities.

GHGs concentrations

Global Warming

MAJOR STEP IN CO2 REDUCTION

• Improve Energy Management : New (non fossil) resources & Efficiency in utilization.

• Land & Forest usage: Sustainable Development Policy.

CARBON NEUTRAL TARGET

1.3 RENEWABLE ENERGY RESOURCES

RENEWABLE ENERGY RESOURCES

• Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, biomass etc. which are renewable (naturally replenished).

• In 2010, only about 18% of global final energy consumption came from renewables (Ref: )

WIND ENERGY FOR ELECTRICAL POWER GENERATION

• Airflows can be used to run wind turbines. • Modern wind turbines range from around

600 kW to 5 MW of rated power. Turbines with rated output of 1.5–3 MW have become the most common for commercial use.

• In Malaysia, wind energy is not technically commercially viable resource due to low average wind speed. – may be used in micro application.

DIRECT SOLAR ENERGY

• Solar energy could be harnessed by: Actively -Photovoltaic (PV) cells, or Passively (absorbed by building materials etc)

• Although solar energy is sufficient to meet the entire energy needs of the world, currently it is not economical to do so because of the low concentration of solar energy on earth ( W/m2) and the high capital cost of harnessing it due to low conversion efficiency.

• High potential from emerging technologies

Biomass

• Biomass - (plant material, non-fossil), organic materials which can be burned to produce energy or converted into fuels or other products.

• Biomass is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, plants capture the sun's energy.

BIOMASS & BIOFUEL

Two approaches to biomass as fuel :

• growing plants specifically for energy or using the residue from plants used for other things.

• as bio-fuel for petroleum subtitute

GEO-THERMAL

Geothermal

• Geothermal energy is energy obtained by tapping the heat of the earth itself, either from kilometers deep into the Earth's crust, or in some places of the globe from some meters, in geothermal heat pump

HYDRO

Hydro

• Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams .

• Micro hydro systems are hydroelectric power installations that typically produce up to 100 kW of power .

• Ocean energy describes all the technologies to harness energy from the ocean/sea. This includes marine current power, ocean thermal energy conversion (OTEC), and tidal power.

SUSTAINABLE DEVELOPMENT

Sustainable Development

• Sustainable development is a pattern of resource use that aims to meet human needs while preserving the environment so that these needs can be met not only in the present, but also for future generations.

• Sustainable development can be

conceptually devided into three constituent parts: environmental sustainability, economic sustainability and sociopolitical sustainability

Energy RecoveryEnergy Recovery

• Most heat engines convert only approximately 20% to 50% of the Most heat engines convert only approximately 20% to 50% of the supplied energy into mechanical work whereas the remaining supplied energy into mechanical work whereas the remaining energy is lost.energy is lost.

• Many scope for technologies to recover wasted energy that takes Many scope for technologies to recover wasted energy that takes the form of heat discharge from exhaust or cooling water, the form of heat discharge from exhaust or cooling water, unburned fuel and thermal transfer. unburned fuel and thermal transfer.

• There are many waste heat recovery systems which were designed There are many waste heat recovery systems which were designed and used on large scale power generators. For example, some and used on large scale power generators. For example, some industries that use process heat and consume a large amount of industries that use process heat and consume a large amount of electrical power exploit a cogeneration plant in their Rankine or electrical power exploit a cogeneration plant in their Rankine or Brayton engine cycle. Brayton engine cycle.

• Another method of optimising energy recovery in industrial power Another method of optimising energy recovery in industrial power generator is by topping the Brayton engine cycle on Rankine generator is by topping the Brayton engine cycle on Rankine engine cycle. In this combined cycle, the latent energy from the engine cycle. In this combined cycle, the latent energy from the gas turbine exhaust is recovered by transferring to the steam gas turbine exhaust is recovered by transferring to the steam energy in a waste heat exchanger (WHE) that has replaced the energy in a waste heat exchanger (WHE) that has replaced the boiler.boiler. 89

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• Renewable energy is the manifestation of solar energy in different forms.Such energy sources include wind energy, hydroelectric power, ocean thermal-energy, ocean wave energy, and wood. For example, no hydroelectric powerplant can generate electricity year after year unless the water evaporates by absorbing solar energy and comes back as a rainfall to replenish the water source.

• Although solar energy is sufficient to meet the entire energy needsof the world, currently it is not economical to do so because of the low concentration of solar energy on earth and the high capital cost of harnessing it.

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Ch1- Introduction Aman