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Am I wrong with my calculations or using wrong formula?

  1. Apr 29, 2014 #1
    1. The problem statement, all variables and given/known data
    I have a radiator through which water is passed at 90 degrees Celsius, the air speed as it passes through the radiator is 4ms-1. Water temperature difference between inlet and outlet of radiator is 28.33 K. Temperature difference between air before and after passing through radiator is 29K. Area of radiator core is 2.88 x 10^-2 m^2.

    2. Relevant equations
    Equation for heat transfer = W*Cp*ΔT where W is weighted flow and Cp is specific heat capacity of fluid.

    For water heat transfer is = WCpΔT = QwpwCpΔT, where Qw is volumetric flow rate of water, pw is density of water and Cp is specific heat capacity of water at 90 degrees celcius.

    so Qw = 2.5 x 10-5 m3s-1
    pw = 1.0 kgm-3
    Cp = 4.21
    ΔT = 28.33 K

    For air heat transfer is = WCpΔT = = Ar v CpΔT, where Ar is the surface area of radiator core, v is the velocity of air as it passes through the radiator core, Cp is the specific heat of air

    so Ar = 2.88 x 10^-2
    v = 4.0 ms-1
    Cp = 1.0
    ΔT = 29.0 K

    3. The attempt at a solution

    Heat transfer of water = 2.98 x 10^-3 kWatts
    Heat transfer of air = 3.34 kWatts.

    why am I getting such a huge difference between heat transfer of the two fluids ? are my equations wrong ?
  2. jcsd
  3. Apr 29, 2014 #2


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    What is the density of water?
  4. Apr 29, 2014 #3
    That water flow rate seems very low. I don't see a water flow rate in the problem statement. What is the actual problem statement?

  5. May 3, 2014 #4
    thanks for your replies, I figured out I was using the wrong density of water, it should be 1000 instead of 1
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