11

FUNDAMETALS OF FUNDAMETALS OF ENERGY ENERGY

CONVERSIONSCONVERSIONS

Doc. Ing. Tomáš Dlouhý, CSc.Doc. Ing. Tomáš Dlouhý, CSc.

22

ENERGYENERGY What is energy?What is energy?

Energy can be defined as the ability to do workEnergy can be defined as the ability to do work If an object does work (exerts a force over a If an object does work (exerts a force over a

distance to move an object) the object uses distance to move an object) the object uses energyenergy

1st law of thermodynamic1st law of thermodynamic energy can be converted from one form to another energy can be converted from one form to another

but cannot be created or destroyedbut cannot be created or destroyed

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ENERGY FORMS AND ENERGY FORMS AND CONVERSIONSCONVERSIONS

The five main forms of energy are:The five main forms of energy are: HeatHeat ChemicalChemical – fuels and food – fuels and food ElectromagneticElectromagnetic

radiationradiation electricityelectricity

NuclearNuclear MechanicalMechanical

Energy can be changed from one form to Energy can be changed from one form to another.another.

Changes in the form of energy are called Changes in the form of energy are called energy energy conversionsconversions. .

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ENERGY CONVERSIONSENERGY CONVERSIONS Example - Example - automobile engineautomobile engine

fuel is burned to convert fuel is burned to convert chemicalchemical energy into energy into heatheat tthe heat energy is then changed into he heat energy is then changed into mechanicalmechanical

energyenergy

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PRIMARY AND PRIMARY AND SECONDARY ENERGYSECONDARY ENERGY

primary energyprimary energy -- comes from the comes from the directdirect exploitation of energy sources as theyexploitation of energy sources as they exist in the natureexist in the nature fossil fuels – fossil fuels – gas, coal, oil,gas, coal, oil, … … renewables – solar, hydro, wind, geothermal, renewables – solar, hydro, wind, geothermal,

ocean, biomass, … ocean, biomass, … nuclearnuclear

secondary energy secondary energy - - is generated from is generated from primary energy through a primary energy through a conversions conversions requiring requiring technical meanstechnical means

66

77

ENERGY CONVERSIONENERGY CONVERSIONAND TECHNICAL MEANSAND TECHNICAL MEANS

from to technical means

chemical thermal combustorthermal mechanical heat engine

mechanical electrical generator

88

THERMALTHERMAL ENERGY ENERGY CONVERSIONSCONVERSIONS

2nd law of thermodynamics2nd law of thermodynamics it is not possible convert it is not possible convert ALLALL of the thermal of the thermal

energy derived from a high temperature source to energy derived from a high temperature source to mechanical energymechanical energy

some thermal energy some thermal energy must be rejected must be rejected to a low to a low temperature sinktemperature sink

efficiency of conversionefficiency of conversion

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CARNOT VAPOR CYCLECARNOT VAPOR CYCLE

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.00

100

200

300

400

500

600

700700

s [kJ/kg-K]

T [C

] 6000 kPa

100 kPa

Carnot Vapor Cycle Using Steam

1

2 3

4

th Carnot net

in

out

in

L

H

WQ

QQ

TT

,

1

1

The thermal efficiency of this cycle is given asThe thermal efficiency of this cycle is given as

1010

The thermal efficiency in any power cycleThe thermal efficiency in any power cycle can be can be improved byimproved by increase increase of of the maximum temperature at which heat is addedthe maximum temperature at which heat is added dedecreasecrease of of the the minminimum temperature at which heat is imum temperature at which heat is

rejectedrejected Reasons why the Reasons why the vapor vapor Carnot cycle is not used:Carnot cycle is not used:

ppumping process 1-2 requires the pumping of a mixture of umping process 1-2 requires the pumping of a mixture of saturated liquid and saturated vapor at state 1 and the delivery saturated liquid and saturated vapor at state 1 and the delivery of a saturated liquid at state 2.of a saturated liquid at state 2.

tto superheat the steam to take advantage of a higher o superheat the steam to take advantage of a higher temperature, elaborate controls are required to keep temperature, elaborate controls are required to keep TTHH constant while the steam expands and does work.constant while the steam expands and does work.

To resolve the difficulties associated with the Carnot To resolve the difficulties associated with the Carnot cycle, the cycle, the Rankine cycle Rankine cycle was devised. was devised.

CARNOT VAPOR CYCLECARNOT VAPOR CYCLE

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RANKINE VAPOR CYCLERANKINE VAPOR CYCLE

0 2 4 6 8 10 12120

100

200

300

400

500

s [kJ/kg-K]

T [C

]

6000 kPa

10 kPa

Rankine Vapor Power Cycle

1

2

3

4

The simple Rankine cycle continues the condensation process 4-1 until the The simple Rankine cycle continues the condensation process 4-1 until the saturated liquid line is reached.saturated liquid line is reached.Ideal Rankine Cycle Processes Ideal Rankine Cycle Processes Process Process Description Description 1-2 1-2 Isentropic compression in pump Isentropic compression in pump 2-32-3 Constant pressure heat addition in boiler Constant pressure heat addition in boiler 3-43-4 Isentropic expansion in turbine Isentropic expansion in turbine 4-1 4-1 Constant pressure heat rejection in condenser Constant pressure heat rejection in condenser

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SIMPLE VAPOR POWER PLANTSIMPLE VAPOR POWER PLANT

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CYCLE WITH GAS TURBINECYCLE WITH GAS TURBINEBrayton cycleBrayton cycle

1414

INTERNAL COMBUSTION INTERNAL COMBUSTION ENGINESENGINES

Two-stroke engineTwo-stroke engineFour-stroke engineFour-stroke engineDiesel engineDiesel engine

1515

STIRLING ENGINESSTIRLING ENGINESexternal combustion engineexternal combustion engine

1616

SOLAR THERMAL ENERGY SOLAR THERMAL ENERGY CONVERSIONSCONVERSIONS

concentrated solar power plant concentrated solar power plant

solar power towersolar power tower

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WIND ENERGY CONVERSIONWIND ENERGY CONVERSIONHorizontal and vertical - axis wind turbinesHorizontal and vertical - axis wind turbines

1818

ENERGY CONVERSIONS OF ENERGY CONVERSIONS OF THE GEOTHERMAL RESOURCETHE GEOTHERMAL RESOURCE

Hot dry rock geothermal systemHot dry rock geothermal system1:Reservoir 1:Reservoir 2:Pump house 2:Pump house 3:Heat exchanger 3:Heat exchanger 4:Turbine hall 4:Turbine hall 5:Production well 5:Production well 6:Injection well6:Injection well7:Hot water to district heating 7:Hot water to district heating 8:Porous sediments 8:Porous sediments 9:Observation well 9:Observation well 10:Crystalline bedrock10:Crystalline bedrock

1919

OCEAN ENERGY TECHNOLOGYOCEAN ENERGY TECHNOLOGY Tidal powerTidal power Wave powerWave power Marine current powerMarine current power Osmotic powerOsmotic power Ocean thermal energyOcean thermal energy

2020

DIRECT ENERGY DIRECT ENERGY CONVERSIONSCONVERSIONS

heatingheating chemical – combustion of fuelschemical – combustion of fuels solar – solar colectorssolar – solar colectors geothermalgeothermal

electricityelectricity solar – photovoltaic cellssolar – photovoltaic cells chemical – fuel cellschemical – fuel cells

2121

Solar thermal energySolar thermal energy

2222

Solar photovoltaic electricity Solar photovoltaic electricity productionproduction

2323

Fuel cellsFuel cells

2424

RequirementsRequirements Each student is called to elaborateEach student is called to elaborate

writen report (3-5 pages)writen report (3-5 pages) presentation (10 slides - max. 10 minutes)presentation (10 slides - max. 10 minutes)

describing one of following items:describing one of following items: Steam power plantSteam power plant Gas TurbinesGas Turbines Internal Combustion EnginesInternal Combustion Engines Hydraulic TurbinesHydraulic Turbines Stirling EnginesStirling Engines Solar Thermal Energy ConversionSolar Thermal Energy Conversion Wind Energy ConversionWind Energy Conversion Energy Conversion of the Geothermal ResourceEnergy Conversion of the Geothermal Resource Ocean Energy TechnologyOcean Energy Technology Direct Energy Conversion - Solar Photovoltaic CellsDirect Energy Conversion - Solar Photovoltaic Cells Direct Energy Conversion - Fuel CellsDirect Energy Conversion - Fuel Cells

Date of presentation: 13.12.2011Date of presentation: 13.12.2011

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