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Thread: radiator design

  1. #1
    Can anyone recommend some reading material on heat exchanger design? So far I hav been relying on intercooler theory on the web and old fluids and heat transfer texts as reference for my rad design. What are other teams using?

    Thanks for the help.

  2. #2
    I could use some insight also.

    B.J. Stoney
    University of Cincinnati

  3. #3

  4. #4

    Join Date
    Jan 2003
    Caracas, Distrito Federal, Venezuela
    Firstly excume for my English...

    Colin... I`m Leida from Universidad Simón Bolìvar team in Venezuela. I would like to know if you found the information asked about radiators design. In that case, would you mind on telling me in what sources you found the information?

    How many universities use the original engine radiator?

    Leida Monterrosa

  5. #5
    We had an excelent cooling system last year.
    radiator 350*370*25mm, standard water pump, 8 amp fan. The radiator hang up the back of the car(ugly, but effective)

    This year we had a terrible cooling system.
    radiator 240*295*40mm, electric water pump, 6.5 amp fan (way to small).

    Both units were well shrouded.

    After the engine started overheating, we tested the new system experimentally.

    We got an urn (you now the big things for heating water for coffee that they have at functions)..

    We heated the water to 80 deg C, and ran the electric fan and water pump, using thermometers either side of the radiator.

    we found the system was good for about 6kw.

    we then varied the water flow rate (pump), and air flow rate (fan), outputs by varying the supplied voltage. We measured the air flow rate with an airspeed meter (little fan with a counter). Obviously you can simply wiegh the water after a 1 min run to find mass flow rate.

    We found that both airflow and waterflow rates increased cooling capacity quite linearly (for given flow rate of other). BUT it was proportional with factors quite a bit less than one.

    Both functions also had a quite large scalar constant. ie.. the zero flow rate condition caused cooling (as you would expect)

    cooling= 0.2*wfr + 1.5kw (for given afr)
    cooling= 0.6*afr + 1.2kw (for given wfr)

    Now, for our system, the waterflow rate had quite a low linear constant, the airflow constant was nearer one.

    i cant remember the exact figures, but for example (from the original condition) doubling the waterflow rate gave us 20% more cooling

    doubling the airflow rate gave us 40% more cooling.

    we were in a rush, so more academic statistical analysis wasn't done,we simply said "right put a bigger fan on quick!"

    Now like I said earlier the system initially shifted 6kw.

    We then put the engine on the dyno. When the engine reached about 6kw the cooling system failed (the temperature started rising)

    Several text books suggest that the shaft horsepower from an engine is roughly the same as the heat leaving the (water) cooling system. So this made sense....

    Now we considered the use of a formula SAE at competition. 32mins racing, 3 mins between heats=35mins

    fuel consumption was 4 ltrs
    calorific value of fuel = 48Mj/kg
    SG fuel 0.75
    20% of heat into engine leaves via radiator
    = 14kw (average)

    from talking to engineers at a radiator manufacturer, it is obvious that it ALL the data is derived experimentally, and without prior data you're stuffed. and even when the system is installed it might still not work.

    the most important thing is understanding what a thermostat does. You should use one. and the cooling system temp should be running constant temperature ALL DAY (retrieve the data from Motec computer). ONLY when this is the case do you have a cooling system that is "working".

    my personal advice is a 300*350*25mm radiator, with a "ballsy" fan (8amp) and a good shroud. The unit should be experimentally tested before the car is run. and you should preferably do the testing before the dyno, and use the unit on the dyno.

    keep in mind we're australian, so 35 deg C days are NOT uncommon, so its pretty important here.

    (sorry about the essay)

  6. #6

    Join Date
    Nov 2002
    Calgary, Alberta, Canada
    Any updated on radiator designs now that the Detroit competition is over?

    The radiator (Al, 10"x12"x1.625", 18 FPI) and fan (pulls air @ 26 KPH) combo we used worked fine. The only problem we had was with packaging. This year we plan on using a radiator approximately 14"x7"x2". They are similar volumes just different frontal areas.

    How did everyone size there radiator? Heat transfer data manipulation, experimental methods, or monkeys throwing darts at a wall?

    Any suggestions, or comments?

  7. #7
    I would advise against using the thicker core to give a similar volume, you will probably find that your cooling capacity will decrease.

    due to the low speed these cars run at, even with fan assistance, cooling will most probably be acheived only in the first 1" of core, the rest of the volume will act as a heatsink, slowing heat transfer from the fluid. a thicker radiator wil only benefit from serious airflow.

    PJL.. you may find that your 14X7 radiator will perform better with a 1 - 1.5" core

    I found this out the hard way. see frank's message above...

    Sam Graham
    Engine Group Leader 2003
    UQ Racing

  8. #8

    What kind of airflow rates are you talking about (that thicker radiators are not a benefit)?

    -Charlie Ping
    Auburn University FSAE
    5th Overall Detroit 2003
    ? Overall Aussie 2003.

  9. #9
    Senior Member
    Join Date
    Aug 2003
    Kirkland, Washington
    For good reading I recomend Compact Heat Exchangers by W.M. Kays and A.L. London.

    I was a bit lost until I found this book. I haven't had any fluid or heat transfer classes yet but this book has everything you need to know if you have had the classes or are willing to think a little bit in order to figure out how they are defining their values.
    I'll hopefully be writing a matlab program to calculate radiator sizes this week.

    The reason for thicker cores being less desirable is hotter air travels across the thicker core decreasing effectiveness. So for cores of equal volume a thinner core is more efficient.

    PJL, are you sure about the velocity that your fan pulls air? if so then it would be a a fairly stout fan at nearly 1200 cfm.
    I'm designing the cooling system for this years car using the NTU method with some experimental fluid flow values, though in previous years I believe monkeys threw darts to determine it.

    The radiator on the past 3 or 4 cars has been 8 x 12 x 2 1/2. It works ok at speed but the fan isn't large enough and it doesn't have a real shroud. Prelimnary calculations say a radiator of the same frontal area and about 3/4" thick will be fine.

    With a gas-liquid heat exchanger, increasing gas flow, in this case air, will almost allways be helpful because the heat capacity rate(Heat capacity times mass rate) of the gas is generally less than a quarter of that for the liquid. The closer the rate ratio is to 1 the more efficient the system will be and the smaller it can be in size.

    I haven't found much information on shroud design, just some recomendations from the American Petroleum Institute. Where have you guys found your info?

  10. #10
    Can anyone give me the dimensions on the stock CBR F4i radiator?
    This info would be greatly appreciated.

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