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# Temperature,Heat, and Energy Transfer

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### Temperature,Heat, and Energy Transfer

1. 1. Temperature, Heat, and Energy Transfer Wx 201 Henry Robinson
2. 2. Philosophy <ul><li>It is mused that in physics, when you know the mass, momentum (including rotational) and energy changes in a system, you have the problem solved. </li></ul>
3. 3. Energy - Definitions <ul><li>Energy - Ability to do work. </li></ul><ul><li>Work - move matter over some distance </li></ul><ul><li>Potential Energy – the ability to do work because of position (usually height) </li></ul><ul><li>PE = mgh : m = mass g = gravity h = height </li></ul><ul><li>Kinetic Energy – the energy of a mass because of its motion: v = velocity </li></ul>
4. 4. Potential Energy Maximum Kinetic Energy Maximum
5. 5. Conservation of Energy <ul><li>Energy can not be created or destroyed </li></ul><ul><li>Energy is changed from one form into another. </li></ul><ul><li>Since the atmosphere is a big heat engine, most of our discussions of energy will center around heat transfer </li></ul><ul><li>Heat and Temperature are not the same thing </li></ul>
6. 6. Temperature <ul><li>Temperature is the average kinetic energy of the air molecules. </li></ul><ul><li>High temperature – faster molecules. </li></ul><ul><li>Low temperature – slower molecules. </li></ul><ul><li>animation </li></ul>
7. 7. Fahrenheit Scale <ul><li>Developed in early 1700s by G. David Fahrenheit. </li></ul><ul><li>Zero is the lowest temperature that salt water will freeze. </li></ul><ul><li>32 F o is freezing point of pure water. </li></ul><ul><li>100 F o was to be body temperature (slight mistake) </li></ul><ul><li>212 F o is boiling point of pure water. </li></ul><ul><li>F scale used in US for surface temperature except in METARS. </li></ul><ul><li>Absolute scale is the Rankine scale </li></ul>
8. 8. Celsius Scale <ul><li>Developed in late 1700s </li></ul><ul><li>Also called Centigrade scale. </li></ul><ul><li>Zero is the freezing point of pure water. </li></ul><ul><li>100 is the boiling point of pure water at sea level. </li></ul><ul><li>A change of 1 C o = 1.8 F o </li></ul><ul><li>1.8 C = F - 32 </li></ul>
9. 9. Kelvin Temperature Scale <ul><li>Absolute zero – molecules stop moving. </li></ul><ul><li>Lowest possible temperature. </li></ul><ul><li>Zero K. = –459 degrees F. </li></ul><ul><li>Zero K. = -273 degrees C. </li></ul><ul><li>1 degree K = 1 degree C. </li></ul><ul><li>o K= o C+273 </li></ul><ul><li>Kelvin scale used for all scientific equations, such as gas law, etc. </li></ul>
10. 10. Temperature Scales 311 38 100 300 27 80 289 16 60 277 4 40 273 0 32 266 -7 20 255 -18 0 244 -29 -20 233 -40 -40 K C F
11. 11. US Meteorology Temperature Units <ul><li>Most of the world uses Celsius (metric unit) </li></ul><ul><li>U.S. uses F for surface air temperature. </li></ul><ul><li>U.S. uses C for air temperature above surface </li></ul>
12. 12. Kinetic Theory of Gases <ul><li>Perfect Gas Law (animation) </li></ul>
13. 13. Heat <ul><li>In the absence of chemical or phase changes, Heat is the total Kinetic Energy of the molecules. (Temperature is the average kinetic energy of the air molecules.) </li></ul><ul><li>First law of thermodynamics. </li></ul><ul><li>Animation </li></ul>
14. 14. Heat <ul><li>Transfer of heat energy to a mass changes its temperature and its dimensions. </li></ul><ul><li>Specific Heat – amount of heat needed to raise one gram of material one degree Celsius. </li></ul><ul><li>1 calorie of heat will raise 1 gram of water one degree C. </li></ul>
15. 15. First Law of Thermodynamics <ul><li>Add heat to something and it goes into raising the temperature AND expanding the something </li></ul><ul><li>Adiabatic means not adding heat so compress a gas means the temperature goes up </li></ul><ul><li>The adiabatic lapse rate for air is 10 degrees C per kilometer (5.5 F/ 1000 ft) </li></ul>
16. 16. Specific Heat of Substances Sand Dry Air Clay Ice Water Substance 0.19 0.24 0.33 0.5 1.0 Specific Heat 5.2 C 4.2 C 3.0 C 2.0 C 1.0 C Temp rise for 1 calorie of heat added to one gram of material
17. 17. Radiation <ul><li>Incoming solar radiation is important to life, weather </li></ul><ul><li>We receive 2 cal/cm min to warm us during daylight hours Area = 2  r </li></ul>
18. 18. Surface absorption of heat <ul><li>Sunlight not reflected by clouds or surface moves molecules in surface to increase total and average kinetic energy of molecules </li></ul><ul><li>Some heat moves downward but the rest warms the air just above the surface </li></ul><ul><li>Primary reason for the climatological lapse rate of 3.5 degrees F/1000 ft </li></ul>
19. 19. Cooling the Earth <ul><li>All warm bodies emit infrared radiation </li></ul><ul><li>Earth radiates heat through infrared all the time from entire surface Area =  r 2 </li></ul>
20. 20. Balance <ul><li>When incoming solar radiation equals outgoing infrared, the climate is in balance </li></ul><ul><li>If it is not in balance, the climate warms up or cools down. </li></ul><ul><li>We have had periodic imbalances in the past </li></ul><ul><li>We are probably going through a change right now </li></ul>
21. 21. Greenhouse Effect <ul><li>In the news - but it is a natural process in the atmosphere </li></ul>
22. 23. At Issue <ul><li>If the balance is changing, what sort of weather will result </li></ul><ul><li>Consensus seems to be Global Warming will result in </li></ul><ul><ul><li>Sea level rise </li></ul></ul><ul><ul><li>Increased bacterial activity </li></ul></ul><ul><ul><li>Stronger storms </li></ul></ul><ul><ul><li>Faster winds </li></ul></ul>
23. 24. Radiation Transfers <ul><li>Greenhouse effect is only one transfer </li></ul><ul><li>Reflection from clouds </li></ul><ul><li>Reflection from the oceans, lakes, etc. </li></ul><ul><li>Reflection from the surface </li></ul><ul><li>Direct absorption of air </li></ul>
24. 25. Radiation Effects on Matter <ul><li>Absorption </li></ul><ul><li>Conduction </li></ul><ul><li>Convection </li></ul><ul><li>Latent Heat conversion </li></ul>
25. 27. Some Consequences of Specific Heat <ul><li>Land areas warm up more rapidly than water areas for same heat input. </li></ul>Average air temperature near sea level in July ( o F)
26. 28. Latent Heat <ul><li>Latent heat is the heat required to change state (solid to liquid or liquid to gas) </li></ul><ul><li>Latent heat of fusion (melting or freezing) </li></ul><ul><li>Water latent heat of fusion = 80 cal/g. </li></ul><ul><li>Latent heat of evaporation (or condensation) </li></ul><ul><li>Water latent heat of evaporation = 600 cal/g </li></ul>
27. 29. Latent Heat Transfer to/from Environment <ul><li>When water evaporates it takes heat from the environment (example: sweating cools body). When it condenses it releases heat to the environment. </li></ul><ul><li>Latent Heat of evaporation/condensation is an important sink/source of atmospheric energy </li></ul><ul><li>Latent heat drives hurricanes and thunderstorms. </li></ul>
28. 30. Heat Transfer in Atmosphere <ul><li>Conduction – transfer of heat from molecule to next molecule. Slow process. </li></ul><ul><li>Air is a poor conductor of heat. </li></ul><ul><li>Convection –vertical transfer of heat by fluid motions. (warm air rises by buoyancy) </li></ul><ul><li>Advection – horizontal transfer of heat by fluid motions. </li></ul><ul><li>Mixing of air is more efficient process of heat transfer than conduction. </li></ul>
29. 31. Buoyancy <ul><li>If a parcel is lighter than the fluid it displaces, it will rise. Gravity causes the heavier fluid to sink which forces the lighter parcel to rise. </li></ul><ul><li>Recall gas law PV=RT. </li></ul><ul><li>If all the air at a level warms, nothing will happen. Buoyancy requires localized differences in density caused by temperature differences. </li></ul>
30. 32. Thermals <ul><li>Differences in ground temperature caused hot and cool spots. </li></ul><ul><li>Warm air is forced up by cool air. </li></ul><ul><li>Rising air parcel goes to lower pressure. </li></ul><ul><li>Air parcel expands and cools (gas law). </li></ul><ul><li>If air parcel is still warmer (buoyant) than environment, it will continue to rise. </li></ul><ul><li>If air parcel is the same (or cooler) temperature than environment, it will stop rising. </li></ul>
31. 33. Thermals and Clouds Clouds are cause by rising air parcels.
32. 34. Thermals and Latent Heat <ul><li>Rising parcel cools. If the air temperature reaches the dew point temperature (later chapter), droplets will condense out of the air. </li></ul><ul><li>Condensation will release latent heat (600 calories/gram). </li></ul><ul><li>Latent heat will warm air parcel making it buoyant relative to surrounding air. </li></ul>
33. 35. Summary <ul><li>Definitions: </li></ul><ul><li>Energy - Ability to do work. </li></ul><ul><li>Work - move matter over some distance </li></ul><ul><li>Kinetic Energy – mass moving =1/2 mv 2 </li></ul><ul><li>Temperature - average kinetic energy of the air molecules. </li></ul>
34. 43. Summary (cont 1) <ul><li>Temperature Scales – Kelvin ( o K) Fahrenheit ( o F), and Celsius ( o C) scales </li></ul><ul><li>0 o K = -273 o C = -459 o F absolute zero </li></ul><ul><li>273 o K = 0 o C = 32 o F water freezing </li></ul><ul><li>373 o K = 100 o C = 212 o F water boiling </li></ul><ul><li>C=5/9(F-32) ; o K= o C+273 </li></ul>
35. 44. Summary (cont 2) <ul><li>Heat -transfer of energy to a mass which changes its temperature. </li></ul><ul><li>Specific Heat – amount of heat needed to raise one gram of material one degree Celsius. </li></ul><ul><li>1 Calorie of heat will raise 1 gram of water one degree C. </li></ul><ul><li>Specific heat: water=1.0; air=.24; sand=.19 </li></ul>
36. 45. Summary (cont 3) <ul><li>Latent heat is the heat required to change state (solid to liquid or liquid to gas) </li></ul><ul><li>Water latent heat of fusion = 80 cal/g. </li></ul><ul><li>Water latent heat of evaporation = 600 cal/g </li></ul><ul><li>Latent heat drives hurricanes and thunderstorms </li></ul><ul><li>Convection –vertical transfer of heat by fluid motions. (warm air rises by buoyancy) </li></ul><ul><li>Buoyancy requires localized differences in density caused by temperature differences. </li></ul><ul><li>Advection – horizontal transfer of heat by fluid motions. </li></ul>