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!

Air passes over an electrical heater at a steady rate of 2500cm^3 per second.

  1. Mar 22, 2012 #1
    1. The problem statement, all variables and given/known data

    Air passes over an electrical heater at a steady rate of 2500cm^3 per second. The inlet temperature of the air is 20^oC ( 20 degrees celcius ) and the steady outlet temperature is 40^0C ( 40 degrees celcius)
    a) What heat is absorbed by air passing over the heater in 2 hours
    b) Obtain an estimate for the power rating of the heater
    Density of air ( 1.2 kgcm-3)
    Specific heat capacity of air : 1000 J-1Kg-1K-1


    2. Relevant equations
    So I think that I should use the equation Q=mcΔθ


    3. The attempt at a solution
    Here's what I did :
    2500cm^3=2500g=2.5kg
    Since 2.5kg is heated every second then 2hrs of heating would heat 2.5x7200 = 18,000kg of air.
    ΔθOutlet-Inlet temperature = 40-20 = 20 degree celcius change in temperature,
    Specific Heat capacity of air : 1000 Jkg-1K-1
    Q=mxcxΔθ
    = 18000x1000x20
    =3.6x10^8
    Which is wrong because the answer at the back of the book had 4.32x10^5. I've tried, but I really need some help :) Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 22, 2012 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi Student-! Welcome to PF! :smile:

    (try using the X2 button just above the Reply box :wink:)

    Quickly dividing 4.32 by 3.6, my eye is drawn to …
    :wink:
     
  4. Mar 22, 2012 #3
    I think you have mis- calculated the mass of air.
    The density of air is 1.2kg/m^3 not 1.2kg/cm^3
     
  5. Apr 14, 2012 #4
    Thanks alot :D I got out the question and I saw my error- :)
     
  6. Apr 14, 2012 #5
    Re: Welcome to PF!

    Thanks I got it out eventually :D :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Air passes over an electrical heater at a steady rate of 2500cm^3 per second.
Loading...