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16.3 Using Heat
Heat engines played a key role in the development of the modern industrial world. Steam locomotives were an important early use of the steam engine. Electric power plants today use steam turbines.
16.3 Using Heat
What are the two main types of heat engines?
16.3 Key Questions
How do most heating systems distribute thermal energy?
How does a heat pump reverse the normal flow of heat?
16.3 Using Heat
16.3 Key Questions
The two main types of heat engines are the __________________ combustion engine and the __________________ combustion engine.
• external combustion engine—an engine that
burns fuel _____________ the engine.
• internal combustion engine—an engine that
burns fuel _____________ the engine.
external
internal
outside
inside
16.3 Using Heat
External Combustion Engine
A steam engine is an external combustion engine—an engine that burns fuel outside the engine.
• Thomas _________________ developed the first practical steam engine in 1712 to pump ________ out of coal mines.
• James ___________ designed an engine in 1765 that operated at a higher temperature and was more efficient.
Heat Engines
Newcomenwater
Watt
16.3 Using Heat
When the valve in a steam engine slides, steam is trapped in the cylinder. The steam expands and cools as it pushes the _____________ to the left.
Heat Engines
Hot steam inSlide valve
PistonCylinder
Exhaust steam out
Valve rod
Piston rod
piston
16.3 Using Heat
Most __________ use an internal combustion engine that burns gasoline. They involve a piston that moves ________________ in a cylinder.
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
cars
up and down
16.3 Using Heat
The linear motion of each stroke, is converted into _________________ motion of the crankshaft, which is connected to the transmission and wheels
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
rotary
16.3 Using Heat
Intake Stroke - ________ and _________ enter the cylinder
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
air fuel
16.3 Using Heat
Compression Stroke – the piston _____________ the fuel-air mixture.
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
compresses
16.3 Using Heat
Power Stroke – A spark plug _____________ and _________ the mixture. The hot gas then expands and drives the piston ____________.
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
ignites
heatsdown
16.3 Using Heat
Exhaust Stroke – Gas ______________ the cylinder, and the cycle repeats
Heat Engines
Intake stroke Compression Stroke Power stroke Exhaust stroke
Cylinder
Piston
Air-fuel mixture
Intake valve
Spark plug
Exhaust valve
Exhaust gases
exits
16.3 Using Heat
Gasoline engines are more efficient than old-fashioned steam engines, but they still are ______ very efficient.
Only about _____ of the energy in a gasoline engine is converted to work. The rest turns into ________________.
Heat Engines
NOT
1/3
waste-heat
16.3 Using Heat
Heating Systems
Most heating systems use _______________ to distribute thermal energy.
A central heating system heats many rooms from one ______________ location.
• Heating systems differ in how they transfer thermal energy to the rest of the building.
convection
central
16.3 Using Heat
Water heated by a boiler circulates through ________________ in each room, transferring thermal energy
Heating Systems
Radiator
Thermostat
Expansion tank
Circulating pump
Boiler
Exhaust vent
Hot-Water Heating
radiators
16.3 Using Heat
Steam Heating
Steam heating is very similar to hot-water heating except that ___________ is used instead of hot water.
• Steam heating often is used in _____________ buildings or when many buildings are heated from one central location.
Heating Systems
steam
old
16.3 Using Heat
Electric Baseboard Heating
An electric baseboard heater uses _________________ energy to heat a room.
• A ________________ is used to convert electrical energy to thermal energy.
• The ______________ heats the air near it by conduction and radiation.
• Convection circulates the warm air to heat the room.
Heating Systems
electricalconductor
hot coil
16.3 Using Heat
Fans are used to circulate warm air through __________ to the rooms in a building
The hot air _______ as cooler, denser air in the room ______
Heating Systems
Cool air sinks
Return vent
Duct
Furnace
Hot air rises
Supply vent
Chimney
Forced-Air Heating
ducts
rises
sinks
16.3 Using Heat
A heat pump is a device that _____________ the normal flow of thermal energy. This is done by circulating a ___________________ through tubing.
Cooling Systems
A refrigerant is a fluid that ________________ and ________________ inside the tubing of a heat pump.
• When the refrigerant absorbs heat, it vaporizes, or turns into a ____________.
• When the refrigerant gives off heat, it condenses, or turns back into a ____________.
reverses
refrigerant
vaporizes
condenses
gas
liquid
16.3 Using Heat
Refrigerators
A refrigerator is a heat pump—it transfers thermal energy from the ____________ food compartment to the __________room.
• A ______________ must do work to move refrigerant through tubing inside the refrigerator walls.
• _____________ of tubing underneath or behind the refrigerator _____________ heat absorbed from the food compartment to the surroundings of the kitchen.
Cooling Systems
cold
warm
motor
Coilsrelease
16.3 Using Heat
When a refrigerator door is open, some thermal energy from the room _________ the refrigerator.
But __________ thermal energy leaves the refrigerator through the coils because it has to work harder
Cooling Systems
Temperature in room: 25°C
Temperature in refrigerator: 3°C
enters
more
16.3 Using Heat
In a window air conditioner, outside air is heated as a fan blows it through the condenser coil.
Cooling Systems
Warm air out
Warm air inEvaporator coil Liquid absorbs heat to become vapor.
Cold air out
Compressor
Expansion valve Pressure drops, causing liquid refrigerant to become cold.
Condenser coilVapor cools to liquid as heat is removed.
16.3 Using Heat
Assessment Questions
1. Only about one-third of the energy in gasoline is converted to work in an internal combustion engine. The rest of the chemical energy is a. lost as unused mechanical energy.
b. destroyed by the engine.
c. converted to potential energy.
d. discharged as waste heat.
16.3 Using Heat
Assessment Questions
2. How is a room heated by an electric baseboard heating system?a. Water heated by a boiler circulates through radiatorsb. Fans are used to circulate warm air through ductsc. A hot coil heats air by conduction and radiationd. Steam-heated radiators transfer heat to rooms
16.3 Using Heat
Assessment Questions
3. How do refrigerators reverse the normal flow of heat? a. moving cool air from outside to inside the refrigerator
b. separating warm atoms from cool atoms
c. By moving a refrigerant through tubing inside the refrigerator walls
d. By releasing less energy than what enters the refrigerator