1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: Vapor-compression refrigeration cycle

  1. Feb 27, 2013 #1
    1. The problem statement, all variables and given/known data
    A conventional vapor-compression refrigeration cycle uses ammonia as the refrigerant. Evaporation and condensation are at -4°C and 34°C respectively and the refrigeration rate is 5kW. The compressor efficiency is 0.75. Assume that the throttle process is isenthalpic.
    Calculate the work done by the system, the ammonia circulation rate, the rate of heat transferred to the fluid in the condenser, the power requirement, and the COP of the cycle.

    2. Relevant equations

    Work done by the system = work done by compressor = H3-H2

    3. The attempt at a solution
    From the problem statement: H1=H4, S3=S2
    I started by finding the enthalpy of vaporization at -3°C and 34°C for saturated ammonia. Now I have H1, H2, H4. I also found the entropy of vaporization at -3°C, so I have S2 and S3.
    Last edited: Feb 27, 2013
  2. jcsd
  3. Feb 27, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Do you have a question about this problem? Without showing any work, it's hard to figure out why you made this post.
  4. Feb 27, 2013 #3
    Yes, I just posted everything since each one is interrelated.

    So to start off with, calculating the work: I don't understand how get H3. I thought I could get it via the entropy (S2) since S2=S3, but I don't think there is a relation there. Now I'm thinking I could get it via the compressor efficiency, but for that I need to calculate the work first. I guess I'm just stuck on where to begin.
  5. Mar 1, 2013 #4
    Nevermind, figured it out!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted