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Homework Help: Work obtainable from two finite reservoirs

  1. Jan 21, 2014 #1
    The problem is as follows:

    A Carnot engine operates between two finite size reservoirs, one a body of water of mass MH at 100°C and the other a body of water of mass ML at 0°C. Find the maximum work obtainable from the two reservoirs.

    3. The attempt at a solution

    I haven't done thermodynamics in a while and am trying to relearn a lot of this stuff. I first tried expressing the work done by the engine in terms of the 2nd law. I know I can write the efficiency of the engine with the ratio of the two temperatures, but I'm not sure how to find the heat removed from the hot reservoir. If someone could point me in the right direction I would be grateful.
  2. jcsd
  3. Jan 21, 2014 #2


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    Hello, vandergale. Welcome to PF!

    Consider an infinitesimal step during the process. Corresponding to an amount of heat |dQH| removed from the warmer reservoir, there will be a certain amount of heat |dQC| added to the cooler reservoir. Can you express |dQC| in terms of |dQH| and the current temperatures TH and TC of the two reservoirs?
  4. Jan 22, 2014 #3
    Start out by drawing a PV graph of what the reversible Carnot cycle with these reservoirs looks like. Label some schematic temperature points on this graph. You need to get the "lay of the land."
  5. Jan 24, 2014 #4
    Sorry I haven't checked back, thanks you guys, its much clearer now.
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