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Need some opinions on my experiment

  1. May 7, 2014 #1
    I carried out a wind tunnel test on two radiators. Radiator 1 is a small radiator and radiator 2 is a bigger radiator with nearly twice as much volume and area as radiator 1.

    Flow rate going into radiator 1 is 1.2L/min
    Flow rate going into radiator 2 is 1.5L/min

    the problem is radiator 1 dissipated more heat than radiator 2. Considering the larger area of radiator 2 I would have thought it would dissipate more heat, so the water entering at 90 degrees Celsius should exit at a lower temperature in radiator 2 at say a air speed of 8m/s but it doesnt.

    My conclusion is that the radiator 2 did not get filled up completely due to the small flow rate. Can you guys input your opinions on why this might have happened ?

    other than thinking the radiator wasnt getting filled up completely, I cant really figure out for the life of me why it would not cool the water more than the smaller radiator 1.

    thanks
     
  2. jcsd
  3. May 7, 2014 #2
    In your other thread, you said that radiator 2 was doing more cooling than radiator 1. Has this changed now? Give us some more data to play with. What are the temperature changes, the heat transfer areas, the tube diameters, the fin sizes, etc.

    chet
     
  4. May 7, 2014 #3
    Yes it has because I got a chance to do the experiment again for radiator 2 and realised in my previous experiment for radiator 2, I was setting the wrong fan frequencies so different wind speed. I carried out the experiment once on radiator 1 aswell which showed the same results so results for radiator 1 are still the same. I was half asleep when I carried out the previous experiment for radiator 2.

    I now carried out the experiment three times and this is what I got:

    Radiator 1:
    Water/Coolant:
    T(inlet): 363.15
    T(Outlet): 334.82

    Air at 8m/s:
    Before Passing radiator: 295.15K
    After passing radiator: 323.15K

    Radiator 2:
    Water/Coolant:
    T(Inlet): 363.15
    T(Outlet): 343.15

    Air at 8m/s:
    Before passing radiator:295.15 K
    After passing radiator: 308.48 K

    Radiator 1 geometry:
    Inlet diameter: 25mm
    Outlet diameter: 15mm
    Core Height: 115mm
    Core Width: 250mm
    8 tubes
    Fin height: 14.3 mm

    Radiator 2 geometry:
    Inlet diameter: 25mm
    Outlet diameter: 25mm
    Core Height: 275 mm
    Core width: 200mm
    23 tubes
    Fin height: 11.96 mm

    Do you need anymore info ?
     
  5. May 7, 2014 #4
    What were the tube IDs and ODs? What were the lengths of the tubes between headers? Is that the core width? Fin spacing? Did you calculate the heat loads and the overall heat transfer coefficients?

    Chet
     
  6. May 10, 2014 #5
    Just a thought, but what is the pressure drop across the larger heat exchanger? If this is bigger than the pressure drop of the smaller heat exchanger, it will mean that the flow rate through the larger heat exchanger will be less - provided that the fan speed remains constant for both cases.
    I'm not sure of your experimental set-up but in some wind tunnels, fans provide the air-flow. If this is the case and the pressure drop through the heat exchanger increases (due to more tubes in the heat exchanger) the mass flow of air will be less. This is assuming your wind tunnel fan speed has not changed from testing the small heat exchanger to the larger one. Obviously, the resulting smaller air flow through the heat exchanger will lead to less heat transfer.
     
  7. May 10, 2014 #6
    I checked the air velocities directly at the radiators and the velocity drop was the same for both radiators. I mentioned the water pressure across the larger radiator as it had a slightly higher flow rate coming out of it.

    and chestermiller I am sorry for not replying earlier I was running out of time to complete my report so I didnt come online.
     
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