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Homework Help: Heat,work, thermal efficiency problems

  1. Sep 27, 2011 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    This is the question that I can't really answer

    1. A cycle looks like an ellipse in the T-S diagram. The maximum and minimum temperatures are 1000K and 400K. The maximum and minimum entropies are 0.705 KJ/K and 0.235 Kj/K. Determine
    a. the heat added per cycle, b. the work produced per cycle, c. The thermal efficiency of the cycle.

    I'm trying to answer this question but im pretty confused about having the minimum and maximum values. I dont even know what formua to use.

    There is another question:

    2. There are added 20 BTU to 5lb of carbon dioxide at constant volume. The initial temperature is 90F. (CV= 0.1565 Btu/lb-R) Determine. a the final temperature b. the change of enthalphy. c. The change of internal energy.

    Im trying to answer this but im getting confused about the BTU added to lb. I dont know how could I get BTU from lb to have it added.

    Please help me out. I really need your help. This is a make or break of my grades. Thank you needed your response.:frown:
  2. jcsd
  3. Sep 28, 2011 #2


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    Staff Emeritus
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    In problem 2) it's 20 BTU of heat added to 5 lbs of CO2. It is analogous to adding 20 kJ of heat to 5 kg of CO2.
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