1 FUNDAMETALS OF ENERGY CONVERSIONS Doc. Ing. Tomáš Dlouhý, CSc.

2 ENERGY What is energy? What is energy? Energy can be defined as the ability to do work 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 If an object does work (exerts a force over a distance to move an object) the object uses energy 1st law of thermodynamic 1st law of thermodynamic energy can be converted from one form to another but cannot be created or destroyed energy can be converted from one form to another but cannot be created or destroyed

3 ENERGY FORMS AND CONVERSIONS The five main forms of energy are: The five main forms of energy are: Heat Heat Chemical – fuels and food Chemical – fuels and food Electromagnetic Electromagnetic radiation radiation electricity electricity Nuclear Nuclear Mechanical Mechanical Energy can be changed from one form to another. Energy can be changed from one form to another. Changes in the form of energy are called energy conversions. Changes in the form of energy are called energy conversions.

4 ENERGY CONVERSIONS Example - automobile engine Example - automobile engine fuel is burned to convert chemical energy into heat fuel is burned to convert chemical energy into heat the heat energy is then changed into mechanical energy the heat energy is then changed into mechanical energy

5 PRIMARY AND SECONDARY ENERGY primary energy - comes from the direct exploitation of energy sources as they exist in the nature primary energy - comes from the direct exploitation of energy sources as they exist in the nature fossil fuels – gas, coal, oil, … fossil fuels – gas, coal, oil, … renewables – solar, hydro, wind, geothermal, ocean, biomass, … renewables – solar, hydro, wind, geothermal, ocean, biomass, … nuclear nuclear secondary energy - is generated from primary energy through a conversions requiring technical means secondary energy - is generated from primary energy through a conversions requiring technical means

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7 ENERGY CONVERSION AND TECHNICAL MEANS fromtotechnical means chemicalthermalcombustor thermalmechanicalheat engine mechanicalelectricalgenerator

8 THERMAL ENERGY CONVERSIONS 2nd law of thermodynamics 2nd law of thermodynamics it is not possible convert ALL of the thermal energy derived from a high temperature source to mechanical energy 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 some thermal energy must be rejected to a low temperature sink efficiency of conversion efficiency of conversion

9 CARNOT VAPOR CYCLE The thermal efficiency of this cycle is given as

10 The thermal efficiency in any power cycle can be improved by The thermal efficiency in any power cycle can be improved by increase of the maximum temperature at which heat is added increase of the maximum temperature at which heat is added decrease of the minimum temperature at which heat is rejected decrease of the minimum temperature at which heat is rejected Reasons why the vapor Carnot cycle is not used: Reasons why the vapor Carnot cycle is not used: 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. 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 T H constant while the steam expands and does work. to superheat the steam to take advantage of a higher temperature, elaborate controls are required to keep T H constant while the steam expands and does work. To resolve the difficulties associated with the Carnot cycle, the Rankine cycle was devised. To resolve the difficulties associated with the Carnot cycle, the Rankine cycle was devised. CARNOT VAPOR CYCLE

11 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 Process Description 1-2 Isentropic compression in pump 1-2 Isentropic compression in pump 2-3Constant pressure heat addition in boiler 2-3Constant pressure heat addition in boiler 3-4Isentropic expansion in turbine 3-4Isentropic expansion in turbine 4-1 Constant pressure heat rejection in condenser 4-1 Constant pressure heat rejection in condenser

12 SIMPLE VAPOR POWER PLANT

13 CYCLE WITH GAS TURBINE Brayton cycle

14 INTERNAL COMBUSTION ENGINES Two-stroke engine Four-stroke engine Diesel engine

15 STIRLING ENGINES external combustion engine

16 SOLAR THERMAL ENERGY CONVERSIONS concentrated solar power plant solar power tower

17 WIND ENERGY CONVERSION Horizontal and vertical - axis wind turbines

18 ENERGY CONVERSIONS OF THE GEOTHERMAL RESOURCE Hot dry rock geothermal system 1:Reservoir2:Pump house3:Heat exchanger4:Turbine hall 5:Production well 6:Injection well 7:Hot water to district heating 8:Porous sediments 9:Observation well 10:Crystalline bedrock

19 OCEAN ENERGY TECHNOLOGY Tidal power Tidal power Wave power Wave power Marine current power Marine current power Osmotic power Osmotic power Ocean thermal energy Ocean thermal energy

20 DIRECT ENERGY CONVERSIONS heating heating chemical – combustion of fuels chemical – combustion of fuels solar – solar colectors solar – solar colectors geothermal geothermal electricity electricity solar – photovoltaic cells solar – photovoltaic cells chemical – fuel cells chemical – fuel cells

21 Solar thermal energy

22 Solar photovoltaic electricity production

23 Fuel cells

24 Requirements Each student is called to elaborate Each 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 plant Steam power plant Gas Turbines Gas Turbines Internal Combustion Engines Internal Combustion Engines Hydraulic Turbines Hydraulic Turbines Stirling Engines Stirling Engines Solar Thermal Energy Conversion Solar Thermal Energy Conversion Wind Energy Conversion Wind Energy Conversion Energy Conversion of the Geothermal Resource Energy Conversion of the Geothermal Resource Ocean Energy Technology Ocean Energy Technology Direct Energy Conversion - Solar Photovoltaic Cells Direct Energy Conversion - Solar Photovoltaic Cells Direct Energy Conversion - Fuel Cells Direct Energy Conversion - Fuel Cells Date of presentation: Date of presentation: