Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Carnot engine air conditioner

  1. Apr 30, 2010 #1
    A Carnot air conditioner takes energy from the thermal energy of a room at 76°F and transfers it as heat to the outdoors, which is at 96°F. For each joule of electric energy required to operate the air conditioner, how many joules are removed from the room?

    Attempt at problem

    76 + 273 = 349
    96 + 273 = 369

    COP = energy removed / elec energy required

    COP = 349 / (369 - 349) = 17.45

    17.45 = energy removed / 1 Joule

    the system is always saying that my answer is incorrect but i cant figure out what
     
  2. jcsd
  3. Apr 30, 2010 #2

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Your temperatures are in Fahrenheit, not Celsius, so you're converting them to absolute temperatures incorrectly. The rest looks okay, though.
     
  4. Apr 30, 2010 #3
    shoot i didnt notice that but anyways converted now but the system still says i got the wrong answer


    (5/9)(76-32) = 297.44
    (5/9)(96-32) = 308.56

    COP = energy removed / elec energy required

    COP = 308.56 / (308.56 - 297.44) = 27.75

    27.75 = energy removed / 1 Joule

    i cant find out whats wrong
     
  5. Apr 30, 2010 #4

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    You're using the wrong temperature in the numerator.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook