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: Thermodynamics - properties of pure substances

  1. Oct 6, 2011 #1
    A piston cylinder device contains .85kg of refrigerant-134a at -10°C. The piston is free to move and has a mass of 12 kg and a diameter of 25cm. The local atmospheric pressure is 88 kPa. Now, heat is transferred to refrigerant-134a until the temperature is 15°C. Determine (a) the final pressure, (b) the change in the volume of the cylinder, and (c) the change in the enthalpy of the refrigerant-134a.

    So far, i managed to calculate the final pressure, which is 90.4kPa. Now, in order to find the change in volume, i am trying to calculate the volume(V) of the initial and final states by using the equation V = vm, where v is the specific volume.

    My problem is that i am unsure how to find the specific volume (v). Do i use some sort of table or is there a calculation involved? Thanks.
  2. jcsd
  3. Oct 7, 2011 #2
    What is the state of 134a at 88Kpa plus the additional pressure due to the weight of the piston? If, initially, it is part gas and part liquid, you'll have to use tables.

    Looks like it's a constant pressure situation where you are given the initial and final states. From the thermo tables for 134a, you can determine specific volume.
    Last edited: Oct 7, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook