Automotive Formula car cooling

  1. Ranger Mike

    Ranger Mike 1,675
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    ok racers, here is a subject I have been debating. our formula car uses two aluminum radiators, one on each side. I switched to the Ultra Side pods which are each 5 pounds lighter and 3 inches narrower than the original sets. Benefit is lighter weight and lower aero drag.
    now the questions,
    1. is it more beneficial to plumb the coolant thru the radiators in series or parallel.
    2. Air enters the side pod and exits thru the radiator fins. Is is better to place insulation around the radiator core to smooth the air flow or
    leave the radiator bare to help dissipate heat from the sides.
    3. the red car photo ( as seen from the front of the car) shows a splitter that spits the incoming flow to the front portion and rear portion of the rad core. I am told that is is not needed on 90 percent of the installations. Note the insulation packed around the rad core.

    your keen observations and comments are valued
    i will respond as required and as beer permits.
    thank you

    Attached Files:

    Last edited: Dec 15, 2009
  2. jcsd
  3. TSK! Someones left beer cans on your sidepod!

    From a cooling standpoint, it depends on how effective the radiators are.

    Parallel = potential for more cooling capacity as you are effectively flowing more coolant to the radiators. More complicated as you have to split the plumbing. Series = better cooling on lower flow rates, probably eaaiser to plumb in.

    Your best bet is to estiamte the cooling capacity of the radiator, then calcualte the maximum fluid flow rate with each scenario. Which ever gives a higher heat transfer value is the one to go for. This will also depend on how good the pump is.

    I'd be tempted to say that parallel will probably be better.

    I don't see the point in the splitter in the red case, unless the flow was seperating on entry and stalling a bit in the sidepod or something like that.
  4. Ranger Mike

    Ranger Mike 1,675
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    Thanks Chris
    the car originally had parallel. we switched it over to series when i went to an electric water pump. temps were about the same...its a 2.0 liter 4 cylinder..
    the splitter thing is a last resort i one in our race series runs it. one big benefit is that the series plumbing makes purging trapped air easier.

    who left that beer can there!!!!
  5. Well if there is no difference in cooling capacity, you may as well just do what is easiest and less fiddly. Infact, unless you were marginal on cooling a series system would probably be better overall anyway, purely becuase problems are easier to sort quickly in the pits.

    What sort of single seater is it?
    It looks like a big verson of an old formula ford.
    Last edited: Dec 15, 2009
  6. Ranger Mike

    Ranger Mike 1,675
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    Gold Member

    1988 Reynard racing in Club Formula Continental series in SCCA
    Formula Fords run a 1600 cc engine and little shorter and lighter.
    this car is supposed to have 150 hp and weighs 1190 pounds coming off the track after the race..but we all know about HP and the rule book too
    don't we!!

    Attached Files:

  7. Ranger Mike

    Ranger Mike 1,675
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    Gold Member

    old side pods vs new ultra side pods
    not readily apparent but the new ones are much narrower
    again a trade off as the old pods made a much wider diffusser area under the car which increased down we trade off losing a little down force for high speed cornering but gain less drag overall
    racing is one big compromise

    Attached Files:

  8. Ranger Mike,

    Looks like a LOT of FUN!

    Your first question;
    "1. is it more beneficial to plumb the coolant thru the radiators in series or parallel."

    Pump considerations;
    In series, there will be a greater pressure drop in the coolant piping which will cause your centrifugal water pump to "back up" on its performance curve, delivering lower gpm at higher head. In parallel, the coolant pressure drop seen by the pump will be lower, allowing it to "run out" on its curve to a higher gpm at lower head.

    Radiator considerations;
    The radiator's thermal performance will be affected by the flow rate... of both the coolant and the air. When deciding between series and parallel plumbing, remember that coolant (tube-side) flow should be kept as near to the design flow rate as possible. Lower flow will reduce coolant turbulance which will reduce heat transfer efficiency. Higher flow can cause cavitation which will erode the tubes from the inside out. The air flow (fin-side) should be as uniform as possible across the face of the radiator. To achieve this, some sort of splitter might be beneficial.

    Heat transfer considerations;
    Generally, you want to operate with as high a delta T between the coolant and the air as possible. This is because heat flow goes as the log of the mean temperature difference (LMTD) between the hot (coolant) and cold (air) fluids. Taken alone (without consideration of other factors discussed above) this means that parallel piping will give the greatest cooling efficiency because both radiators will see the maximum inlet coolant temp. In series, the inlet coolant temp to the second radiator will be lower due to pre-cooling through the first radiator.

    Your second question;
    "2. Air enters the side pod and exits thru the radiator fins. Is is better to place insulation around the radiator core to smooth the air flow or leave the radiator bare to help dissipate heat from the sides."

    The "insulation" is most probably there to eliminate by-pass of air around the radiator. The heat exchange (coolant to air) will be most efficient at the extended surface of the fins. Heat exchange at the headers or through the frame of the radiator will be relatively inefficient. Keep the air flow across the fins.

    For your third question, see "Radiator considerations" above.

    Have fun, and remember; "Keep the shiny side up!"

  9. Ranger Mike

    Ranger Mike 1,675
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    excellent advise..this forum is GOLD
    ok i will work on maximum air flow thru the vanes
    and plumb so it is back to parallel for best results..if i can get it to over coool i can then tape off the inlets for the season and narrow the pods even more next winter..thanks again
    ranger mike
  10. Whoa Nellie...

    Before you re-plumb, check on the specs for your radiators and water pump.

    My post simply outlined the "considerations" involved in making your decision, I did not recommend a solution because I do not have sufficient data... you do have (or should be able to get) that data.

    For example, let's make the "ASSUMPTION" that each radiator needs at least 70 gpm to have tube-side turbulent flow but will cavitate if flow is greater than 150 gpm (these specs should be available from the manufacturer).

    Now, "IF" your pump delivers 100 gpm at the pressure required for parallel piping, then (if you plumb the two radiators in parallel) each radiator will get only 50 gpm and tube-side flow might be laminar (which is not good for heat transfer).

    On the other hand, "IF" your pump will deliver only 80 gpm at the higher pressure required for series piping, then (if you plumb the two radiators in series) each radiator will get 80 gpm and tube-side flow will be turbulent (which is good for heat transfer).

    Another case; "IF" your pump will deliver 160 gpm to series-plumbed radiators, then you should not pipe them in series... cavitation. Though the pump will deliver a higher flowrate (say 200 gpm) to parallel plumbed radiators, this flow rate is split between the two (100 gpm each) and you are back inside the design envelope for your radiators.

    So... before you re-plumb, get more info.

    PS: The attached sketch might help you understand the issue. It shows an example where you would want to plumb the radiators in series to avoid laminar flow. Two operating points for a pump are shown (intersection of pump performance curve with two piping system curves -- series and parallel).


    Attached Files:

  11. turbo

    turbo 7,063
    Gold Member

    Hi, RM. If it is allowed by the rules, is there any way for you to tap in on the discharge side of the oil pump and put a small radiator-type oil-cooler? If you could reduce the oil temperature that way, it might lessen the load on the side-radiators and allow you to block them off even more to make your car more slippery. It might not be feasible in your application (unless perhaps you could hook in at the oil-filter connection) but it sure saved the day with my hopped-up Wide-Glide. On hot days running high revs with a high-performance engine, air-cooled mills can use all the help they can get. Due to the high compression ratio, I had to run high-test fuel to avoid pre-ignition, and the oil cooler bought me a little extra cushion. You can simply wrap it or block it off when air temperatures get low.
  12. Ranger Mike

    Ranger Mike 1,675
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    Thanks Turbo and Tyroman
    we run the Hewland transaxel that is aluminum and houses the oil sump..thought about an oil cooler but things are real tight under the good place to hang it in decent air flow...
    we run a remote waterpump ..20 GPM flow rate
    been doing this for 5 years now...
    like i said, the original setup was parallel
    i learned something in this thread..the best heat transfer occurs when the fluid is exposed to the largest temperature difference.
    the remote pump has a 1 inch outlet but..the plumbing is 1 1/4 inch going into 3/4 inch radiator inlet and i guess running 7/8 inch hose will not impact anything,,right?
    i may go to AN 12 fittings to make plumbing easier

    Attached Files:

    Last edited: Dec 17, 2009
  13. The waterpump photo you attached looks like the Meziere model WP136S found here;

    In the specs, they say;
    "Standard motor provides 20 gallons per minute free flow rating"

    So 20 gpm will be the coolant flow rate if nothing is connected to the pump outlet - "free flow".

    I talked with Dave, (an engineer at Meziere 1.800.208.1755) who said the pump "shut-off" is at 6psi. In other words, with 6psi of piping/radiator pressure drop, the pump will deliver 0 gallons per minute. While Dave says they do not publish a performance curve for the pump, he suggested approximating performance as linear... see my sketch attached.

    On your questions about plumbing size, see the spec page above, which says;

    "Single inlet port threaded #12AN to accept a variety of fittings"
    "Single outlet port threaded #12AN to accept a variety of line connection options"
    "#12AN fittings available for #08AN, #10AN, #12AN, #16AN, 5/8", 3/4", 1", or 1 1/4" slip hose."

    So you have several options depending on how much pressure drop you have to play with.

    And that brings me to the radiator specs... do you know the design flow rates (min & max) for the radiators and what the design pressure drop will be for that range?

    With that information and the approximate pump curve attached, we will be able to answer your questions.


    Attached Files:

  14. turbo

    turbo 7,063
    Gold Member

    Remember that you don't need a lot of air flow nor a lot of transfer surface to make a radiative oil cooler work because the oil is much hotter than the ambient air so your heat transfer rate will be high. There are some very small radiative oil coolers made for H-D applications, and I'll bet you'd be able to fit one or two in very easily, perhaps on the discharge ends of your side-radiator housings. The air coming out of your water-radiators is still going to be significantly cooler than the oil circulating through the oil coolers. Just a thought.
  15. turbo

    turbo 7,063
    Gold Member

    BTW, if you try this, run the oil through the filter first, when the heat and the low viscosity will give you the best flow-rate, and then run the oil through the coolers before returning it to the engine. No point in letting viscosity throttle oil-flow in this case.
  16. Ranger Mike

    Ranger Mike 1,675
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    Gold Member

    excellent advise on both counts ..i will add a small oi lcooler after the side mods are completed..i can snake it into the rear wing mount i think..
    i have no specs on the radiator..which brings us to another learning point...
    how to calculate the rad cooling specs..
    i will make some phone calls tommorow to see if the shops selling the radiators have any specs but typically these come from UK where the Reynard was made.

    you guys are SUPER GOOD!!!
    i am glad i got on this web site a year ago!!!
  17. A theoretical calculation of thermal performance and pressure drop for an automotive radiator is extremely complex. The manufacturer will "bench-test" a prototype to come up with these values. They should have this information available if you can track them down.

    Knowing the number and size of tubes in the radiator, you could calculate the minimum flow rate necessary for turbulance fairly easily.

    But cavitation caused by an excessive flow rate will occur at the header end, where flow direction changes suddenly. I do not know how a manufacturer determines this value, but I would expect destructive testing might be used.

    A thermal performance calculation would require detailed information about the radiator (fin thickness, spacing, area, material, method of attachment, etc.) and even if this info was available, the calculation would be very complex and yield only a "theoretical" value. Bench testing with known flow rates, pressures and temperatures is much easier and reliable.

    So... do what you can to track down the manufacturer's data.

  18. Ranger Mike

    Ranger Mike 1,675
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    no such luck on rad specs...but
    the two rads cooled it successfully from day one
    i did rework the plumbing back to parallel with minimum of .800 ID in all the plumbing..if i went to AN 12 fiitings it would be .700 id and don't know impact of this but .100 is a lot in my opinion
    and adding a small oil cooler can only help i figure
    i wish to thank you all...i learned a lot and is this not what it is about?
  19. ranger
    if you end up in Houston for any events, let me know
    i can help with the beer and food situation

  20. Ranger Mike

    Ranger Mike 1,675
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    I just work takes me all over..i was at texas motor speedway a few years back before going to san antonio..lonnnnnnggg drive..

    Merry Christmas Dr.

    and all of you posters...your jaded cynical wry sense of humor keeps me on my toes...
    just remember

    age and deceit will always over come youth and enthusiasm!
  21. happy holidays to you to ranger
    and everyone else here
    glad I found this place

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