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General Physics 1

General Physics 1. Hongqun Zhang The Department of Physics, Beijing Normal University June 2005. The Second Law of Thermodynamics. Heat can travel from higher temperature area to lower temperature area spontaneously . But the reverse process must occur conditionally. How Refrigerators Work?.

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General Physics 1

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  1. General Physics 1 Hongqun Zhang The Department of Physics, Beijing Normal University June 2005

  2. The Second Law of Thermodynamics • Heat can travel from higher temperature area to lower temperature area spontaneously . But the reverse process must occur conditionally.

  3. How Refrigerators Work? • Parts of A Refrigerator • The Refrigeration Cycle • 3. A Relevant Question

  4. Background Question: • Why does it feel cold when rubbing alcohol evaporates from your skin?

  5. Parts of a Refrigerator • Refrigerant (Freon) • Compressor • Heat-exchanging pipes (Condenser) • Expansion valve • Heat-exchanging pipes (Evaporator) Evaporator

  6. The Refrigeration Cycle Higher temperature and higher pressure gas(p2=9.2bar, t2=46oc) Lower temperature and lower pressure gas(p1=1.5bar, t1=-10oc) Lower temperature and higher pressure liquid (p3=9bar, t3=37.4oc) Lower temperature and lower pressure liquid (p4=1.5bar, t4=-20oc)

  7. Conclusion • In refrigeration cycle, Freon absorb heat from freezer compartment and release the heat from condenser to outside, with input of electrical work

  8. Question: • Why does Freon liquid pass through expansion valve with the temperature decreasing ?

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