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Heat Transfer

Heat Transfer by Radiation, Convection and Conduction

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Heat Transfer

  1. 1. in the Atmosphere ©2008 Norm Ivey Heat Transfer
  2. 2. What is Heat Transfer? <ul><li>Heat transfer is the movement of heat energy from one substance to another. </li></ul>
  3. 3. <ul><li>Heat (energy) always moves from a warmer substance to a cooler substance. </li></ul>What is Heat Transfer? Hot Cold
  4. 4. <ul><li>Heat will continue to move until both substances are the same temperature. </li></ul>What is Heat Transfer? Hot Cold Warm Warm
  5. 5. <ul><li>The greater the difference in temperature between the substances, the faster the heat will transfer. </li></ul>What is Heat Transfer?
  6. 6. <ul><li>There are three types of heat transfer: </li></ul><ul><ul><li>Conduction </li></ul></ul><ul><ul><li>Convection </li></ul></ul><ul><ul><li>Radiation </li></ul></ul>What is Heat Transfer?
  7. 7. Examples <ul><li>You touch a black car in the summer and the heat from the car transfers into your hand. </li></ul><ul><li>A breeze makes you feel cooler because the wind transfers heat away from your body. </li></ul><ul><li>You feel the cold of a winter day because the cold air transfers into you. </li></ul><ul><li>Your Coke in a cooler gets cold because the cold from the ice moves into the Coke. </li></ul>Anti-Examples
  8. 8. Conduction <ul><li>Heat transfer by conduction is the transfer of heat through direct contact. </li></ul>
  9. 9. Conduction <ul><li>Molecules transfer energy to the molecules next to them. </li></ul>
  10. 10. Conduction <ul><li>The molecules do not have to be the same substance. </li></ul>http://www.theelusivefish.com/articles/wp-content/uploads/2007/09/hot-stove.jpg
  11. 11. Example 1 http://www.vernier.com/caliper/fall07/images/heat_transfer_large.jpg The metal conducts heat from the cup of warm water to the cup of cool water.
  12. 12. Your Coke becomes cold because the heat from the soda transfers into the ice, not the other way around. http://www.photoanswers.co.uk/ImgGalleryTn/91/10191/2417_16333.jpg Example 2
  13. 13. No matter what it feels like, cold does not transfer into your body. What is really happening here? Why do you wear heavy clothes when it’s cold outside? http://www.alaska-in-pictures.com/data/media/9/man-in-extreme-cold_355.jpg
  14. 14. Radiation <ul><li>Heat transfer by radiation is the transfer of heat through electromagnetic waves. </li></ul>http://www.nmsu.edu/~safety/images/fire_meaney.gif
  15. 15. Radiation <ul><li>There is no direct contact between the substances. </li></ul>
  16. 16. http://www.blog.thesietch.org/wp-content/uploads/2007/04/earth.jpg http:// stardate.org/images/gallery/sun5.jpg Heat from the sun radiates through empty space to earth. Example 1
  17. 17. http://www.lifefamilytraining.com/img/roasting-marshmallows.jpg Example 2 The heat from the campfire transfers into your marshmallow, giving you a yummy, gooey treat! (Direct contact between the fire and your marshmallow will ruin it!)
  18. 18. Convection <ul><li>Heat transfer by convection is the transfer of heat through the fluid (liquids and gases) movement of currents. </li></ul>
  19. 19. Convection <ul><li>Warm fluids rise, cool down, sink, and then are warmed again. </li></ul>
  20. 20. http://www.eeb.ucla.edu/test/faculty/nezlin/Lecture1/Fig0803.jpg The radiator warms the room by warming the air around it. Then the warm air transfers heat to the rest of the room through convection.
  21. 21. http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap07/FG07_03.jpg As air above the road warms up, it rises and is replaced by cooler air, forming a convection current .
  22. 22. http://www.aos.wisc.edu/~aalopez/aos101/wk5/heatrans.jpg This picture illustrates all three type of heat transfer. Can you identify them all? Conduction Radiation Convection