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Question about Units

  1. Jun 22, 2006 #1
    I solved the problem, but I can't get the right unit for the answer.

    A Carnot engine whose low-temperature reservoir is at 16°C has an efficiency of 31%. By how much should the temperature of the high-temperature reservoir be increased to increase the efficiency to 70%?

    My numerical answer is 544.8. I tried Kelvin first - the most obvious choice - but that was wrong. Then I tried celcius and J/K.

    I tried to work it out but I have no earthly idea - the other choices include:
    - C0 (like the celcius sign but the circle is after the C)
    -J/kg*K
    -J/mol*K and
    -kJ/kg

    Any help would be grately appreciated.
     
  2. jcsd
  3. Jun 22, 2006 #2

    Andrew Mason

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    You have to use Kelvin for temperature in thermodynamics. I get 544.5 K as the increase (from 418.8 K to 963.33 K)

    AM
     
  4. Jun 22, 2006 #3
    Well...the thing is, I did use Kelvin. That was my first choice, but it was wrong. Any other sound possibilities?
     
  5. Jun 22, 2006 #4

    Andrew Mason

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    Mind you, this temperature difference is also 544.5 degrees Celsius. It is just that you have to work out the thermodynamics part in K and then convert back to Celsius.

    AM
     
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