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