FUNDAMETALS OF
ENERGY
CONVERSIONS
Doc. Ing. Tomáš Dlouhý, CSc.
1
ENERGY

What is energy?
Energy can be defined as the ability to do work
 If an object does work (exerts a force over a
distance to move an object) the object uses
energy


1st law of thermodynamic

energy can be converted from one form to another
but cannot be created or destroyed
2
ENERGY FORMS AND
CONVERSIONS

The five main forms of energy are:



Heat
Chemical – fuels and food
Electromagnetic






radiation
electricity
Nuclear
Mechanical
Energy can be changed from one form to
another.
Changes in the form of energy are called energy
conversions.
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ENERGY CONVERSIONS

Example - automobile engine


fuel is burned to convert chemical energy into heat
the heat energy is then changed into mechanical
energy
4
PRIMARY AND
SECONDARY ENERGY

primary energy - comes from the direct
exploitation of energy sources as they
exist in the nature




fossil fuels – gas, coal, oil, …
renewables – solar, hydro, wind, geothermal,
ocean, biomass, …
nuclear
secondary energy - is generated from
primary energy through a conversions
requiring technical means
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6
ENERGY CONVERSION
AND TECHNICAL MEANS
from
to
chemical
thermal
mechanical
thermal
mechanical
electrical
technical
means
combustor
heat engine
generator
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THERMAL ENERGY
CONVERSIONS

2nd law of thermodynamics



it is not possible convert ALL of the thermal
energy derived from a high temperature source to
mechanical energy
some thermal energy must be rejected to a low
temperature sink
efficiency of conversion
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CARNOT VAPOR CYCLE
Carnot Vapor Cycle Using Steam
700
600
T [C]
500
6000 kPa
400
2
300
100 kPa
3
200
0
0.0
4
1
100
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
s [kJ/kg-K]
The thermal efficiency of this cycle is given as
 th , Carnot
Wnet
Qout

 1
Qin
Qin
TL
 1
TH
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CARNOT VAPOR CYCLE

The thermal efficiency in any power cycle can be
improved by



Reasons why the vapor Carnot cycle is not used:



increase of the maximum temperature at which heat is added
decrease of the minimum temperature at which heat is rejected
pumping process 1-2 requires the pumping of a mixture of
saturated liquid and saturated vapor at state 1 and the delivery
of a saturated liquid at state 2.
to superheat the steam to take advantage of a higher
temperature, elaborate controls are required to keep TH
constant while the steam expands and does work.
To resolve the difficulties associated with the Carnot
cycle, the Rankine cycle was devised.
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RANKINE VAPOR CYCLE
The simple Rankine cycle continues the condensation process 4-1 until the
saturated liquid line is reached.
Ideal Rankine Cycle Processes
Process
Description

1-2
Isentropic compression in pump

2-3
Constant pressure heat addition in boiler

3-4
Isentropic expansion in turbine
Rankine
Vapor
Power
Cycle in condenser

4-1 500 Constant
pressure
heat
rejection
6000 kPa
400
3
T [C]
300
200
10 kPa
2
100
4
1
0
0
2
4
6
s [kJ/kg-K]
8
10
12
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SIMPLE VAPOR POWER PLANT
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CYCLE WITH GAS TURBINE
Brayton cycle
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INTERNAL COMBUSTION
ENGINES
Two-stroke engine
Four-stroke engine
Diesel engine
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STIRLING ENGINES
external combustion engine
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SOLAR THERMAL ENERGY
CONVERSIONS
concentrated solar power plant
solar power tower
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WIND ENERGY CONVERSION
Horizontal and vertical - axis wind turbines
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ENERGY CONVERSIONS OF
THE GEOTHERMAL RESOURCE
Hot dry rock geothermal system
1:Reservoir
2:Pump house
3:Heat exchanger
4:Turbine hall
5:Production well
6:Injection well
7:Hot water to district heating
8:Porous sediments
9:Observation well
10:Crystalline bedrock
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OCEAN ENERGY TECHNOLOGY
Tidal power
 Wave power
 Marine current power
 Osmotic power
 Ocean thermal energy

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DIRECT ENERGY
CONVERSIONS

heating




chemical – combustion of fuels
solar – solar colectors
geothermal
electricity


solar – photovoltaic cells
chemical – fuel cells
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Solar thermal energy
21
Solar photovoltaic electricity
production
22
Fuel cells
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Requirements

Each student is called to elaborate

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writen report (3-5 pages)
presentation (10 slides - max. 10 minutes)
describing one of following items:

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Steam power plant
Gas Turbines
Internal Combustion Engines
Hydraulic Turbines
Stirling Engines
Solar Thermal Energy Conversion
Wind Energy Conversion
Energy Conversion of the Geothermal Resource
Ocean Energy Technology
Direct Energy Conversion - Solar Photovoltaic Cells
Direct Energy Conversion - Fuel Cells
Date of presentation: 13.12.2011
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