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 Key Questions What are the two main types of heat engines? How do most heating systems distribute thermal energy? How does a heat pump reverse the normal flow of heat?

external combustion engine—an engine that 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 external internal outside inside

External Combustion Engine Heat Engines 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. Newcomen water Watt

Heat Engines 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. piston Hot steam in Slide valve Exhaust steam out Valve rod Piston rod Cylinder Piston

Heat Engines Most __________ use an internal combustion engine that burns gasoline. They involve a piston that moves ________________ in a cylinder. cars up and down Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Heat Engines The linear motion of each stroke, is converted into _________________ motion of the crankshaft, which is connected to the transmission and wheels rotary Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Intake Stroke - ________ and _________ enter the cylinder Heat Engines Intake Stroke - ________ and _________ enter the cylinder air fuel Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Compression Stroke – the piston _____________ the fuel-air mixture. Heat Engines Compression Stroke – the piston _____________ the fuel-air mixture. compresses Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Heat Engines Power Stroke – A spark plug _____________ and _________ the mixture. The hot gas then expands and drives the piston ____________. ignites heats down Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Heat Engines Exhaust Stroke – Gas ______________ the cylinder, and the cycle repeats exits Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

Heat Engines 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 ________________. NOT 1/3 waste-heat

Most heating systems use _______________ to distribute thermal energy. convection 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. central

Heating Systems Thermostat Hot-Water Heating Water heated by a boiler circulates through ________________ in each room, transferring thermal energy Radiator Exhaust vent Expansion tank radiators Boiler Circulating pump

Heating Systems 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. steam old

Electric Baseboard Heating Heating Systems 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. electrical conductor hot coil

The hot air _______ as cooler, denser air in the room ______ Heating Systems Forced-Air Heating Fans are used to circulate warm air through __________ to the rooms in a building The hot air _______ as cooler, denser air in the room ______ Hot air rises Cool air sinks Supply vent ducts Return vent Chimney Duct rises Furnace sinks

Cooling Systems A heat pump is a device that _____________ the normal flow of thermal energy. This is done by circulating a ___________________ through tubing. reverses refrigerant 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 ____________. vaporizes condenses gas liquid

Cooling Systems 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. cold warm motor Coils release

Cooling Systems 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 enters more Temperature in room: 25°C Temperature in refrigerator: 3°C

Cooling Systems In a window air conditioner, outside air is heated as a fan blows it through the condenser coil. Condenser coil Vapor cools to liquid as heat is removed. Warm air out Cold air out Compressor Expansion valve Pressure drops, causing liquid refrigerant to become cold. Warm air in Evaporator coil Liquid absorbs heat to become vapor.

Assessment Questions 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 lost as unused mechanical energy. destroyed by the engine. converted to potential energy. discharged as waste heat.

How is a room heated by an electric baseboard heating system? Assessment Questions How is a room heated by an electric baseboard heating system? Water heated by a boiler circulates through radiators Fans are used to circulate warm air through ducts A hot coil heats air by conduction and radiation Steam-heated radiators transfer heat to rooms

How do refrigerators reverse the normal flow of heat? Assessment Questions How do refrigerators reverse the normal flow of heat? moving cool air from outside to inside the refrigerator separating warm atoms from cool atoms By moving a refrigerant through tubing inside the refrigerator walls By releasing less energy than what enters the refrigerator