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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 lowtemperature region. HEAT FLOW IN A High Temp Heat in Work Heat out Lower Temp 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/propulsi on/propulsion3.html HEAT ENGINES Only some of the heat transferred from the hightemperature region can be transformed into mechanical energy (work). The remainder of the thermal energy is exhausted as waste heat. Phases of Matter Solid Liquid Definite volume and shape Definite volume Undefined shape Plasma Undefined volume and shape Electrically charged gas—High temp! Neon, lightning, stars, auroras, fluorescent bulbs Gas Undefined volume and shape 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 Condensation is a warming process Evaporation causes the temperature of the liquid to decrease (removes thermal energy from surroundings) Condensation causes the temperature of the surroundings to increase (adds thermal energy to the surroundings) 23.8 Energy and Changes of Phase 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. 23.1 Evaporation 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. Starter Question #2 How 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 21.7 The High Specific Heat Capacity of Water Water has a high specific heat and is transparent, so it takes more energy to heat up than land does. 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 21.7 The High Specific Heat Capacity of Water Water stores and hold heat well because of its high specific heat. This affects global climate. Gulf Stream brings warm water northeast from the Caribbean. Thermal Front The Gulf Stream (warm water from equator) meets The Labrador Current (cold water from polar region) Labrador Current Gulf Stream 21.7 The High Specific Heat Capacity of Water 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. 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. 21.7 The High Specific Heat Capacity of Water 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. Marine Climate Continental Climate Cork Edmonton http://www.sampleireland.com/weather-in-ireland-year-round.html Marine Climate Continental Climate Cork Edmonton Same insolation angle, different climate due to proximity to water and the warming effect from the Gulf Stream http://www.sampleireland.com/weather-in-ireland-year-round.html 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 Compare the climates for each using the graphs provided. You will have to convert Celsius to Fahrenheit and mm to inches to make comparison! Cork is 51°47'N Edmonton is 53° 34' N) 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 Seasons 2 Changing Angle of Sunlight • 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). Summer in Northern Hemisphere Identify the Seasons and the Equinox or Solstice, and comment about the number of daylight vs. night hours Season _________ _________ Equinox or Solstice Season _________ Season _________ Equinox or Solstice Equinox or Solstice Season ________ Equinox or Solstice Identify the Seasons and the Equinox or Solstice Equal day and night—12hr and 12 hr Season _________ spring Equinox or Solstice Less night hours, more daylight hours Less daylight hours, more night hours winter Season _________ summer Season _________ Equinox or Solstice Equinox or Solstice fall Season _________ Equinox or Solstice FUNCTION OF A REFRIGERATOR Remove unwanted Thermal Energy from inside By evaporation Deposit unwanted Thermal Energy on the outside By condensation HOW DO AIR CONDITIONERS 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? 24.7 Entropy According to the second law of thermodynamics, in the long run, the entropy of a system always increases for natural processes. 24.6 Order Tends to Disorder 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 pressure Heat flows from hot to cold 24.7 Entropy 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.
