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Heat Energy

Heat Energy. Read Textbook: Meteorology Today Chapter 2, Appendix G Homework Problems Chapter 2 Questions for Review: 1, 3-5, 7, 8, 12-14, 17, 21 Questions for Thought: 2, 7, 9-11 Problems and Exercises: 1, 2, 4. Heat Energy. Temperature is our measurement of the average

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Heat Energy

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  1. Heat Energy • Read Textbook: Meteorology Today • Chapter 2, Appendix G • Homework Problems Chapter 2 • Questions for Review: 1, 3-5, 7, 8, 12-14, 17, 21 • Questions for Thought: 2, 7, 9-11 • Problems and Exercises: 1, 2, 4

  2. Heat Energy Temperature is our measurement of the average kinetic energyfound in the random motions and vibrations of countless atoms and molecules. Temperature is a way of quantifying the kinetic energy of countless atoms and molecules. Temperature is Energy.

  3. Distribution of Speeds

  4. Maxwell-Boltzman Velocity Distribution

  5. Temperature and Kinetic Energy T = a mwv2 a = 4.0 x 10-5 Ks2/m2 v2 = average molecular speed (KE) mw = molecular weight Molecule 28.01 N2 32.00 O2 18.02 H2O 44.01 CO2 28.96 Average Atmosphere

  6. Temperature Conversions CELCIUS C = 5/9 (F-32) FAHRENHEIT F = (9/5 C) + 32 ABSOLUTE or KELVIN K = C + 273

  7. Boiling Point of Water CELCIUS C = 5/9 (F-32) C = 100 FAHRENHEIT F = (9/5 C) + 32 F = (9/5 100) + 32 = 180 + 32 ABSOLUTE = 212 or KELVIN K = C + 273 K = 100 + 273 = 373

  8. Freezing Point of Water CELCIUS C = 5/9 (F-32) C = 5/9 (32-32) = 0.0 FAHRENHEIT F = (9/5 C) + 32 F = 32 ABSOLUTE or KELVIN K = C + 273 K = 0 + 273 = 273

  9. Analog Temperature Conversion Plot

  10. Celsius to Fahrenheit Conversion

  11. Day Ground Temperature Official Temperature is read at a height of 1 meter above the ground, in the shade, and out of the wind.

  12. Night Ground Temperature • The ground radiates away the daytime heat faster than the air above it. Air is a very poor conductor.

  13. Air Turbulence • Air motion causes mixing, removing stagnant boundary air • Larger temperature gradients are possible without the wind

  14. Radiation Shield • Thick forest, Clouds can provide radiation shield

  15. Thermal Insulation • Thick Forest, Low Clouds can provide a thermal blanket

  16. Temperature Data Mean Daily Temperature: average over 24 hours Mean Annual Temperature: average of 12 months Average mean daily Temp.: average of mean daily temperatures over 30 years Annual Temperature Range: Difference between largest monthly mean and smallest monthly mean temperature.

  17. Growing Days • Number of days when the mean daily temperature is 1 degree above the base temperature for the particular crop. Growing Degree Day = Temp - Base “Days to Maturity” is inaccurate.

  18. Cooling Degree Days • Used during summer months to estimate energy and power consumption needs for cooling indoor air. Base Temp = 65o # = 1000’s

  19. Heating Degree Days • Used during winter months to estimate energy and power consumption needs for heating indoor air. Base Temp = 65o # = 1000’s

  20. Controls of Temperature • Solar Insolation (Chapter 3) • Date • Time • Latitude • Exposure (wind, humidity) • Geographic • Land • Water • Oceanic • Currents • Topography • Elevation

  21. Heat Index • Appendix G

  22. Humidity Formulas for Calculators Heat Index Formula: RH=relative % humid., T = temp. (F) Heat index or apparent temperature = -42.379 + 2.04901523*T + 10.14333127*RH - 0.22475541*T*RH - 6.83783x10-3*T2 - 5.481717x10-2*RH2 + 1.22874x10-3*T2*RH + 8.5282x10-4*T*RH2 - 1.99x10-6*T2*RH2 Calculations of relative humidity, dewpoint temperature, and other quantities such as air density, absolute humidity, and the height of cloud bases, which are related to the moisture content of air. http://www.usatoday.com/weather/whumcalc.htm

  23. Wind Chill • Wind Chill Equivalent Temperature • If the air temperature is 10 degrees and the wind is 25 mph, the wind chill equivalent temperature is -29 degrees.

  24. Matter Phases • In order of increasing Temperature (Energy): • CRYSTAL Occurring at the coldest temperatures • SOLID • LIQUID • GAS • PLASMA Occurring at the highest temperatures

  25. Matter Phases • In order of increasing Temperature (Energy): • CRYSTAL Occurring at the coldest temperatures • SOLID • LIQUID • GAS • PLASMA Occurring at the highest temperatures • In order of decreasing Organization (Symmetry): • CRYSTAL Highly Ordered • SOLID • LIQUID • GAS • PLASMA Highly Disorganized

  26. Water Crystals Atomic and Molecular Structures Lead to Macroscopic Order

  27. CHANGE OF STATE Heat Energy must be absorbed by the solid to break the highly ordered ice crystals. Heat Energy is released by a liquid in order to crystallize.

  28. Phase Transitions

  29. State Changes Energy Increased and Absorbed by Substance: • SOLID to LIQUID Melting • LIQUID to GAS Boiling • SOLID to GAS Sublimation Energy Decreased and Released by Substance: • GAS to SOLID Deposition • GAS to LIQUID Condensation • LIQUID to SOLID Freezing

  30. Phase Diagram

  31. Latent Heat

  32. Latent Heat of Fusion Heat Energy required to convert solid to liquid

  33. Latent Heat of Evaporation Heat Energy required to convert liquid to gas.

  34. Water Latent Heat Exchange Condensation/Evaporation yield/require 6.75 times more heat energy than Fusion/Melting.

  35. Heat Units • CALORIE: the amount of heat required to raise the temperature of 1 kg of water by 1 degree Celsius. • (1 Food calorie = 1,000 calories = 4.184 Joules)

  36. Specific Heat • Q = m c DT Q = HEAT ENERGY Human Perception m = mass DT = Temperature difference c = specific heat responsible for the thermal properties of the substance (Joules/kg/oCelsius) DT = Q/mc

  37. Specific Heat DT = Q/mc For a given amount of heat energy, say 10,000 Joules, what is the temperature change for 1 kg of water and 1 kg of sand? Csand = 838 J/kgoC Cwater = 4180 J/kgoC DTsand = 10,000/1(838) = 11.9 oC DTwater = 10,000/1(4180) = 2.4 oC

  38. North versus South Land masses dominate the Northern Hemisphere while oceans dominate the Southern Hemisphere.

  39. Land Versus Sea Land masses in the North cause more temperature variations than in the South where oceans keep the temperature even and moderate.

  40. Melting DT = Q/mc Amount of heat energy needed to bring a 25 g ice block to a temperature of 50oC? Starting Temp = 0oC Ending Temp = 50oC Q = heat needed to make transition from ice to water + heat needed to heat water from 0 to 50 oC Q= mLf + mcDT

  41. Melting Ice Q = phase transition + mc DT Q = heat needed to make transition from ice to water + heat needed to heat water from 0 to 50 oC = 80 cal/g*(25 g)*(4.186 J/1000 Cal) +25 g *4.186 J/goC *(50-0 oC) = 8.37 J + 5230 J = 5238.4 J

  42. Freezing This latent heat energy is released when water droplets freeze. Water vapor that condenses gives off latent heat as well. Both processes help heat the atmosphere. The opposite (melting or evaporation) causes heat energy to be removed from the atmosphere.

  43. CONDENSATION • GAS to LIQUID (or Freezing, Liquid to Solid) • ENERGY IS RELEASED, Gas has a higher internal energy than the liquid state. • A WARMING PROCESS

  44. EVAPORATION • LIQUID to GAS • ENERGY IS REMOVED, Liquid has a lower internal energy than the gaseous state. • A COOLING PROCESS

  45. Radiation Energy transport via electromagnetic waves

  46. Convection Energy transport by mass motion

  47. Conduction Energy transport by vibrational translation The jostling of atoms and molecules in close proximity in a solid, especially one with high conductivity.

  48. The Sun as a Blackbody Radiator (T=5800K)

  49. Blackbody Radiation Stefan-Boltzman Law Energy Flux E = sT4 Stefan-Boltzmann Constant s = 5.6705 x 10-8 W/m2K4 Speed of Light c = f l f frequency and l wavelength Wein’s Law l = 3,000,000/T Solar Constant 1370 Watts/m2 At the top of the Earth’s Atmosphere

  50. Energy Balance

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