1 / 51

Energy and Heat Transfer

Energy and Heat Transfer. AOS 101 Section 301 - Feb 16 2009. Heat, Temperature, and Energy Transfer. Some basic definitions: Temperature – Related to the energy content of an object. In a gas, the temperature is defined as the average kinetic energy of the gas particles.

mindyt
Download Presentation

Energy and Heat Transfer

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Energy and Heat Transfer AOS 101 Section 301 - Feb 16 2009

  2. Heat, Temperature, and Energy Transfer • Some basic definitions: Temperature – Related to the energy content of an object. In a gas, the temperature is defined as the average kinetic energy of the gas particles.

  3. Heat, Temperature, and Energy Transfer • Some basic definitions: Heat – Related to the energy transfer between two objects. Heat is the transfer of energy from a warm object to a cool object, obeying the 2nd Law of Thermodynamics: “Things fall apart”

  4. Heat, Temperature, and Energy Transfer • Important Note: Temperature =/= Heat You cannot “feel” the temperature of an object, only the heat exchange between yourself and that object. It is related to the object’s temperature, but not the same thing.

  5. HOT COLD Temp

  6. ENERGY TRANSFER HOT COLD Temp

  7. ROOM TEMP ROOM TEMP Temp

  8. More Terms to Know • Specific Heat Capacity –This is the ratio of the amount of energy 1 Kg of a substance requires in order to change its temperature by 1 Kelvin: Q C = T C = Specific Heat Capacity Q = Energy (J) Δ T = Change in Temperature (K)

  9. Some Sample Specific Heat Capacities:

  10. Kinds of Energy Transfer • There are four kinds of energy transfer: Conduction Convection Advection Radiation

  11. Kinds of Energy Transfer • There are four kinds of energy transfer: Conduction Convection Advection Radiation Conduction, Convection, and Advection require some kind of medium to act through – Radiation does not.

  12. Kinds of Energy Transfer • There are four kinds of energy transfer: Conduction Convection Advection Radiation Air is a poor conductor of heat, therefore Convection, Advection, and Radiation all play large roles in the atmosphere, while Conduction is less important.

  13. Kinds of Energy Transfer Advection • Energy can be transferred from one region to another through the transport of warm or cool air from one place to another – Advection of temperature • Cyclones are especially good at this:

  14. Cool air from the pole is being advected to the south L Warm air from the tropics is being advected to the north

  15. Uniformly cold near the pole L Strong temperature contrast exists along a narrow line Uniformly warm in the tropics

  16. Uniformly cold near the pole Warm Front L Cold Front Uniformly warm in the tropics

  17. L L L L

  18. L L L L “Wave Train”

  19. Kinds of Energy Transfer Convection • Energy can be transferred when a fluid is forced to vertically mix, allowing hot and cold portions of the fluid to make contact and even the temperature out • “Hot air rises and cold air sinks”

  20. Convection • In the atmosphere, convection occurs when relatively warm air is below relatively cool air, forcing the warm air to rise and cold air to sink – “overturning” • Overturning can occur by warming the air at the surface OR cooling the air above

  21. Lake Effect Snow

  22. Lake Effect Snow • “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Cold Warm S N

  23. Lake Effect Snow • “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Cold air from the land is advected over the warm water surface Cold Warm S N

  24. Lake Effect Snow • “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Warm air is now underneath cold air, leading to convective overturning Cold Warm Cold S N

  25. Lake Effect Snow • “Lake effect” snow is a form of convection which occurs when very cold air passes over relatively warm water: Rising warm air creates strong convective clouds and snow – “Lake Effect” snow Cold S N

  26. Videos of Convection • Convection Video 1 http://www.youtube.com/watch?v=QpriSb6uN4A • Convection Video 2 http://www.youtube.com/watch?v=1gvHpO26Xv4&feature=related • Convection Video 3 http://www.youtube.com/watch?v=H1sS1TmXF38&feature=related

  27. Kinds of Energy Transfer Radiation • Energy can be transmitted from one object to another through emission and absorption of electro-magnetic waves • The Earth-Atmosphere-Sun system is the most important aspect of this kind of energy transfer for meteorology

  28. Earth-Atmosphere-Sun System Sun Earth Atmosphere

  29. Earth-Atmosphere-Sun System Sun is at ~6000 K, and emits shortwave radiation to the atmosphere Sun Earth Atmosphere

  30. Earth-Atmosphere-Sun System Atmosphere is selectively transparent to solar radiation, allowing it to pass through to the Earth, where it is absorbed Sun Earth Atmosphere

  31. Earth-Atmosphere-Sun System Earth heats up and emits longwave radiation outward, some of which is selectively absorbed by the atmosphere, also heating the atmosphere (the rest escapes to space) Sun Earth Atmosphere

  32. Earth-Atmosphere-Sun System Atmosphere heats up and emits longwave radiation both toward the Earth, and away from the Earth into space Sun Earth Atmosphere

  33. Earth-Atmosphere-Sun System Earth has TWO sources of radiation heating the surface: the Sun AND the atmosphere. This is why the Earth is warmer than 0oF Sun Earth Atmosphere

  34. Earth-Atmosphere-Sun System The more longwave radiation the atmosphere absorbs from the Earth, the more longwave radiation is radiated back to Earth – “Greenhouse Effect” Sun Earth Atmosphere

  35. Radiation • In general, when radiation strikes an object, it can be: Radiation

  36. Radiation • In general, when radiation strikes an object, it can be: Radiation Radiation Transmitted– radiation passes through the object without being absorbed

  37. Radiation • In general, when radiation strikes an object, it can be: Radiation Transmitted– radiation passes through the object without being absorbed Absorbed– radiation is retained by the object and stored energy is manifest as an increase in temp.

  38. Radiation • In general, when radiation strikes an object, it can be: Radiation Reflected– radiation bounces off of object and travels in a new direction Transmitted– radiation passes through the object without being absorbed Absorbed– radiation is retained by the object and stored energy is manifest as an increase in temp.

  39. Radiation • In general, when radiation strikes an object, it can be: Radiation Reflected– radiation bounces off of object and travels in a new direction Transmitted– radiation passes through the object without being absorbed Scattered– radiation strikes a small object and reflects in all directions (though not necessarily equally) Absorbed– radiation is retained by the object and stored energy is manifest as an increase in temp.

  40. Radiation • When radiation strikes an object, it MUST do one or more of these things. There is no radiation that is not transmitted, absorbed, reflected, or scattered: Rtotal=Rtrans+Rabs+Rref+Rscat Reflected– radiation bounces off of object and travels in a new direction Transmitted– radiation passes through the object without being absorbed Scattered– radiation strikes a small object and reflects in all directions (though not necessarily equally) Absorbed– radiation is retained by the object and stored energy is manifest as an increase in temp.

  41. What About Latent Heat? • Technically, there are five forms of energy transfer to consider: Conduction Convection Radiation Advection

  42. What About Latent Heat? • Technically, there are five forms of energy transfer to consider: Conduction Convection Radiation Advection Latent Heat

  43. What About Latent Heat? • Technically, there are five forms of energy transfer to consider: Conduction Convection “Sensible Heat” Radiation Advection Latent Heat

  44. What About Latent Heat? • “Sensible Heat”– Energy transfer via the manipulation of temperature – an object becoming warmer or colder due to the absorption or emission of thermal energy. Heat transfer you can sense. • Latent Heat – Energy transfer via the manipulation of the phase state of water. Heat transfer latent to the state of water.

  45. Heating Ice Into Water Vapor Temp Energy supplied to ice causes ice to increase in temperature – sensible heat Time

  46. Heating Ice Into Water Vapor Temp Ice reaches melting point, and supplied energy now forces ice to melt – absorbing latent heat Time

  47. Heating Ice Into Water Vapor Ice has completely melted into water, and now supplied heat increases water temperature – sensible heat Temp Time

  48. Heating Ice Into Water Vapor Temp Water reaches boiling point and uses supplied energy to convert to water vapor – absorbing latent heat Time

  49. Heating Ice Into Water Vapor Temp Water boils completely, and supplied energy now increases temperature of water vapor – sensible heat Time

More Related