section 4: using thermal energy chapter 9: heat and states of matter
TRANSCRIPT
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Section 4: Using Thermal Energy
Chapter 9:Heat and States of Matter
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44 How is thermal energy used?
1. Fuel is burned in a furnace and heats a volume of air.
2. A fan blows the heated air through a series of large pipes called ducts.
3. The ducts lead to openings called vents in each room.
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HEATING SYSTEMS FORCED-AIR SYSTEMS
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44 RADIATOR SYSTEMS
• A radiator is a closed metal container that contains hot water or steam.
• The thermal energy contained in the hot water or steam is transferred to the air surrounding the radiator by conduction.
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44
ELECTRIC HEATING SYSTEMS
• In an electric heating system, electrically heated coils placed in floors and in walls heat the surrounding air by conduction and convection.
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44 THERMODYNAMICS
• A SYSTEM is anything you can draw a boundary around.
• The energy transferred to a system is the amount of energy flowing into the system across the boundary.
• The work done on a system is the work done by something outside the system’s boundary.
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HEATING AND WORK INCREASE THERMAL ENERGY
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44THE FIRST LAW OF THERMODYNAMICS
• According to the FIRST LAW OF THERMODYNAMICS, the increase in thermal energy of a system equals the work done on the system plus the thermal energy transferred to the system.
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• The increase in energy of a system equals the energy added to the system.
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44CLOSED AND OPEN SYSTEMS
• A system is an OPEN SYSTEM if thermal energy flows across the boundary or if work is done across the boundary.
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• If NO thermal energy flows across the boundary and no outside work is done, the system is a CLOSED SYSTEM.
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44THE SECOND LAW OF THERMODYNAMICS
• SECOND LAW OF THERMODYNAMICS states it is impossible for thermal energy to flow from a cool object to a warmer object unless work is done.
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44
CONVERTING THERMAL ENERGY TO WORK
• No device or process can convert thermal energy completely into work.
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44 HEAT ENGINES
• A device that converts thermal energy into work is called a HEAT ENGINE.
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• When thermal energy is converted into work, some thermal energy always is transferred to the surroundings.
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44INTERNAL COMBUSTION ENGINES
• The heat engine in a car is an internal combustion engine.
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• Each cylinder contains a piston that moves up and down.
• Each up or down movement of the piston is called a stroke.
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44 Internal Combustion Engines
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44 MOVING THERMAL ENERGY• Liquid coolant is pumped through an
expansion valve and changes into a gas.
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• The cold gas is pumped through pipes inside the refrigerator.
• The coolant absorbs thermal energy and the inside of the refrigerator cools.
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44 ENTROPY• According to the laws of thermodynamics,
work can be converted completely into thermal energy, but thermal energy cannot be converted completely into work.
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• ENTROPY is a measure of how spread out, or dispersed, energy is.
• Entropy increases when energy becomes more spread out and less concentrated.
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44ENTROPY ALWAYS INCREASES
• According to the entropy principle, all events that occur cause the entropy of the universe to increase.
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• The energy that becomes spread out is no longer useable.