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Work density / heat density question

  1. Oct 5, 2011 #1
    A piston-cylinder device holds R-134a at an initial pressure of 400 kPa and a temperature of 40 degrees Celsius. Heat is added until the specific volume is v = 0.07 m^3/kg while the pressure is held constant.

    a. Determine the temperature of the final state.
    Because the pressure is 0.4 MPa and the specific volume v = 0.07 m^3/kg and because it is a superheated gas, I used table A-13 of the thermodynamic tables and found that that temperature is between 80 - 90 degrees Celsius. Using linear interpolation, I get 85.5 degrees Celsius.
    b. Determine the work density associated with this process.
    c. Using enthalpy determine the heat density required for this process.
    d. Determine the heat density required for this process by explicitly
    using boundary work.

    For b, I found the boundary work Wb = integral(P dV) = P(V2 - V1) and realized that I only have the specific volume at both states, but not the volume. For c, I did Q,in = H2 - H1, where H is the enthalpy. Then I realized that I only have the specific enthalpy h. How do I go about solving this problem? Also, can anyone explain what the work and heat density specifically and physically is?
    Last edited: Oct 5, 2011
  2. jcsd
  3. Oct 5, 2011 #2
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