HEAT ENGINES

HEAT ENGINE

A heat engine is any device that changes thermal energy into mechanical energy so work can be done.

Mechanical work can be done only if heat flows from a high-temperature to low-temperature region.

High Temp

LowerTemp

Work

HEAT FLOW IN A

Heat out

Heat in

HEAT ENGINE (STEAM)

THERMAL ENERGY IN : MECHANICAL ENERGY OUT

The process of an internal combustion engine resembles that of a heat engine.

http://www.planemath.com/activities/pmenterprises/propulsion/propulsion3.html

HEAT ENGINES

Only some of the heat transferred from the high-temperature region can be transformed into mechanical energy (work). The remainder of the thermal energy is exhausted as waste heat.

Phases of Matter

Solid Definite volume and

shape

Liquid Definite volume Undefined shape

Gas Undefined volume

and shape

Plasma Undefined volume and

shape Electrically charged gas—

High temp! Neon, lightning, stars,

auroras, fluorescent bulbs

Melting and Evaporation Require Input of Thermal Energy

Melting (requires heat of fusion) Heat of fusion is released when liquids freeze

Evaporation (requires heat of vaporization) Heat of vaporization is released when gases

condense

Evaporation vs. Condensation

Evaporation is a cooling process

Evaporation causes the temperature of the liquid to decrease (removes thermal energy from surroundings)

Condensation is a warming process

Condensation causes the temperature of the surroundings to increase (adds thermal energy to the surroundings)

If you heat a solid sufficiently, it will melt and become a liquid.

If you heat the liquid, it will vaporize and become a gas.

The change in the internal energy of a substance causes the change of phase.

23.8 Energy and Changes of Phase

The cloth covering on the sides of the canteen promotes cooling when it is wet. As the faster-moving water molecules leave the cloth, the temperature of the cloth decreases.

23.1 Evaporation

Starter Question #2How does a thermometer work?

The kinetic theory be used to explain expansion and contraction of materials when the temperature of the material changes.

As the temperature rises, heat is transferred from the surroundings to the liquid inside the thermometer and the molecules that compose the liquid vibrate faster. This causes the liquid to expand and rise.

As the temperature falls, heat is transferred away from the liquid inside to the surroundings and the molecules that compose this liquid slow down. This causes the liquid to contract.

The liquid in the thermometer stops rising or falling when thermal equilibrium is reached (no more heat flow!)

Air temperature = Liquid temperature

Winter Vs. Summer Heat Flow

In winter-Heat loss from inside

(warmer) to outside (colder)

-Heating system must operate to transfer thermal energy from fuel to fluid to room to keep house warm

In summer-Heat gain from

outside (warmer) to inside (cooler)

- Cooling system must operate to transfer incoming heat entering the house back to the outside

Water has a high specific heat and is transparent, so it takes more energy to heat up than land does.

21.7 The High Specific Heat Capacity of Water

Moderating Effect of Water on Climate

Water has a high specific heat capacity. This means…

It takes a large amount of heat to raise its temperature

It absorbs a large amount of heat It stores a large amount of heat It has to give up a large amount of heat in

order to cool down It takes a long time for water to cool down

Moderating Effect of Water on Climate

During the summer, surrounding air is cooled by the water and keeps the coast cooler than the intercontinental locations.

During the winter, the surrounding air is warmed by the water and keeps the coast warmer than the intercontinental locations.

SAN FRANCISCO, CA

Water stores and hold heat well because of its high specific heat. This affects global climate.

21.7 The High Specific Heat Capacity of Water

Gulf Stream brings warm water northeast from the Caribbean.

The Gulf Stream (warm water from equator)

meets The Labrador

Current (cold water from polar region)

Gulf Stream

Labrador Current

Thermal Front

Climate of America

On the west coast, air moves from the Pacific Ocean to the land.

• In winter, the water warms the air that moves over it and warms the western coastal regions of North America.

• In summer, the water cools the air and the western coastal regions are cooled.

21.7 The High Specific Heat Capacity of Water

The central interior of a large continent usually experiences extremes of temperature.

Land, with a lower specific heat capacity, gets hot in summer but cools rapidly in winter.

Climate of Europe

Look at a world globe and notice the high latitude of Europe.

Both Europe and Canada get about the same amount of the sun’s energy per square kilometer.

21.7 The High Specific Heat Capacity of Water

http://www.sampleireland.com/weather-in-ireland-year-round.html

Cork

Edmonton

Continental Climate

Marine Climate

http://www.sampleireland.com/weather-in-ireland-year-round.html

Cork

Edmonton

Same insolation angle, different climate due to proximity to water and the warming effect from the Gulf Stream

Continental Climate

Marine Climate

The Gulf Stream brings warm winters to Ireland and the prevailing winds off the Atlantic carry with them rain. It means grass can grow almost all year round — creating the lush sweeping pastures of the Emerald Isle. Today they make up 93 percent of all farmland. No other country in Europe has quite as much grass as Ireland.

Comparing Climate Data Cork, Ireland and Edmonton, Alberta, in Canada are close to the

same latitude Cork is 51°47'N Edmonton is 53° 34' N

Find the following for Cork, Ireland Average daily high and low temperatures for Jan. ____ ____ Average daily high and low temperatures for July ____ ____ Temp. variation for winter to summer (hi/low) ____ ____ Average Precipitation for January and July

Find the following for Edmonton, Alberta (you will have to convert Celsius to Fahrenheit and mm to inches) Average daily high and low temperatures for Jan. ____ ____ Average daily high and low temperatures for July ____ ____ Temp. variation for winter to summer (hi/low) ____ ____ Average Precipitation for January and July ____ ____

Why are the climates for these two cities so different? (Read Ch 21.7, pg. 415-416 )

Comparing Climate Data

Cork, Ireland and Edmonton, Alberta, in Canada are close to the same latitude Cork is 51°47'N Edmonton is 53° 34' N)

Compare the climates for each using the graphs provided. You will have to convert Celsius to Fahrenheit and mm to inches to make comparison! Coldest month and average day and night temperatures (data is already averaged!) Warmest month and average day and night temperatures (data is already averaged) Average summer high and low temperatures (you average the temperature over three

summer months) Average winter high and low and temperatures (you average the temperature over

three winter months) Temperature Mean for day and night (average 12 day and 12 night temperatures) Month with greatest precipitation and least precipitation Precipitation variation (amount of change from highest to lowest)—difference between

highest and lowest Temperature variation (amount of change from highest to lowest average day and

night temperatures) Why are the climates for these two cities different? (read attachment on-line)

Reason for the SeasonsReason for the Seasons

22

• The hemisphere tilted toward the Sun receives sunlight at higher angles than the hemisphere tilted away from the Sun.

• Higher insolation angle means greater intensity of radiant energy (the sun shines more directly on a smaller area).

Changing Angle of Sunlight

Summer in Northern Hemisphere

Season _________

Equinox or Solstice

Season _________

Equinox or Solstice

Season ________

Equinox or Solstice

Season _________

Equinox or Solstice

Identify the Seasons and the Equinox or Solstice, and comment about the number of daylight vs. night hours

_________

Season _________

Equinox or Solstice

Season _________

Equinox or Solstice

Season _________

Equinox or Solstice

Season _________

Equinox or Solstice

Identify the Seasons and the Equinox or Solstice

Equal day and night—12hr and 12 hr

Less night hours, more daylight hours

Less daylight hours, more night hours

spring

summer

fall

winter

FUNCTION OF A REFRIGERATORFUNCTION OF A REFRIGERATOR

                              

Remove unwanted Thermal Energy from inside

Deposit unwanted Thermal Energy on the outside

By evaporation

By condensation

HOW DO AIR CONDITIONERS HOW DO AIR CONDITIONERS AND REFRIGERATORS WORK?AND REFRIGERATORS WORK?

Evaporation of refrigerant removes thermal energy from inside. Evaporation occurs when liquid refrigerant is

allowed to expand (pressure release—lowers vaporization point—heat drawn from food causes evaporation)

Condensation of refrigerant releases thermal energy to the outside Work must be done by the compressor to

compress the refrigerant gas so that the thermal energy drawn from food is released outside when the gas is forced to condense under pressure)

22. How do natural systems tend to proceed?

According to the second law of thermodynamics, in the long run, the entropy of a system always increases for natural processes.

24.7 Entropy

Natural systems tend to proceed toward a state of greater disorder.

The universe trends from a higher state to a lower state of organization.

Examples: Air flows from high to low pressureHeat flows from hot to cold

24.6 Order Tends to Disorder

Entropy is the measure of the amount of disorder in a system.

Disorder increases; entropy increases.

24.7 Entropy

This run-down house demonstrates entropy. Without continual maintenance, the house will eventually fall apart.

24.7 Entropy