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: Temperature drop when expanding heated compressed air

  1. Dec 3, 2012 #1
    1. The problem statement, all variables and given/known data

    I need to know how much the temperature drops after an inline heater which heats an airflow of 5 lbs/min up to 88 °C with an pressure of 54 PSI. When the air exits the heater it is released into the free air where it is 20 °C.

    I know that the air will expand to a bigger volume then, which will lead to a temperature drop. So I need to know how much this drop will be.

    2. Relevant equations

    P1 * V1^γ=P2 * V2^γ

    T1 * V1^(γ-1)=T2 * V2^(γ-1)

    3. The attempt at a solution

    γ= 1.4
    V1= 5 lbs = 1.853 m3
    T1= 88 °C = 361 K
    P1= 54 PSI = 3723163.9

    P2= 101325 Pa
    V2= ?
    T2= ?

    P1 * V1^γ=P2 * V2^γ
    V2 = 4.69447 m3

    T1 * V1^(γ-1)=T2 * V2^(γ-1)
    T2 = 248 K

    This will say that the temperature decreases to -25 °C which sounds like a wrong answer in my opinion.

    I also thought to use the ideal gas law with --> P*V= m*Rs*T
    But I dont know how I should use it in my case..

    Anybody who can give me a solution?
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted