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: Thermodynamics Change in Gas Temperature along pipe

  1. Jul 1, 2008 #1
    1. The problem statement, all variables and given/known data

    Nitrogen beginning at 50oC is pumped along a 30m length of Stainless Steel pipe at a flow rate of 1.5 litres per minute. The Pipeline is at ambient temperature 20oC. Find the temperature of the Nitrogen upon it leaving the end of the pipeline.

    Pipe OD - 0.00635m
    Pipe ID - 0.00457m
    Pressure - 1bar

    The following data is taken from a copy of 'An Engineering Data Book' -

    Cp - Nitrogen at 20oC and 1 bar is 1.04 kJ/(kgK)

    2. Relevant equations

    From 'An Engineering Data Book' and 'Thermodynamics an Engineering Approach 4th Edition' i believed that i could work at the figures from the following equations -

    Qdot /l = 2Pi.k.(T2-T1)/In(r2/r1)

    Qdot = Heat Loss l = Length k = Thermal Conductivity T = Temperatures r = Radius

    Wdot - Qdot = mdot.Cp.(T2-T1)

    Wdot = Work Energy In Qdot = Heat Loss mdot = mass flow rate Cp = Specific Heat T = Temperatures

    3. The attempt at a solution

    using k = 15 (Which is the k of Stainless Steel)

    I used Qdot /l = 2Pi.k.(T2-T1)/In(r2/r1)

    which gave me a figure of 8.653 x 103 for Qdot

    Then to calculate mdot i used the following -

    mdot = Vdot / v

    where Vdot = Volume flow rate and v = specific volume

    Vdot = V / delta t

    where V = Volume which is 1.5 litres and delta t = 60 seconds (take from flow rate)

    therefore Vdot = 0.025 l/s = 25 x 10-5 m3/s

    v = R.T1 / P

    where R = Gas Constant which is 0.294 kJ/(kg.K) T1 is temperate 1 which is 323K and P is pressure which is 1 bar (1 x 105Pa)

    this gives v to be 9.4962 x 10-4 m3/kg

    using these mdot becomes 26.32632 x 10-3 kg/s

    Now using Wdot - Qdot = mdot.Cp.(T2-T1)
    I rearrage to get T2 on its own

    therefore T2 = (-Qdot / mdot.Cp) + T1
    note that Wdot = 0 and so has been removed

    Therefore i get an answer of 50.3oC which is obviously WAY wrong??? Can someone please help me with this. Even just a point in the right direction of the correct equations. This is not a homework or coursework question this an engineering question at work and i'm not too sure where to go with it.
  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