Dave,
With respect to plumbing them in series; The heat transfer rate is dependant upon the delta (temperature difference) temperature between the coolant and the air (for simplicity the thermal conductivity of the radiator medium is snot being considered.) By plumbing in series the second exchanger will have a lower rate of thermal transfer and result in lower BTU rejection if the total system. Plumbing in series is likely to also reduce flow rate ( as you noted by higher pressure.) The lowest return temp may not indicate the optimum system for heat removal. IMO (given the same radiator area, thickness, renolds number, etc.) the higher the coolant to air temp difference and the highest flow rate should yield the system that removes the greatest BTUs.
JOe

    ----- Original Message -----
    *From:* David Staten <mailto:Dastaten@earthlink.net>
    *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
    *Sent:* Sunday, September 11, 2005 9:41 PM
    *Subject:* [FlyRotary] Re: Optimal GPM water pump flow.

    Al.
    What I am after is trying to determine what the minimum required
    flow is for the horsepower generated. More than anything else, I
    do not want to be BELOW that amount, and consider it a minimum.
    Understandably, trying to place twice or nearly 3 times the flow
    through the same circuit will result in higher pressures and
    perhaps some pump cavitation. I will deal with that as I have to..
    more than anything else I want to make sure I am not starting off
    with a DEFICIT of water flow ability.

    I am considering 2 smaller radiators, and originally I intended to
    plumb them in series to get the best cumulative Delta-T across
    them, but if I have "pressure" problems due to the pump's flow, I
    may go to a parralel arrangement.

    Feel free to critique, Al.. My cooling system is a work in
    progress that is evolving. I live in a place that has 100 degree
    temps with 90% humidity at times, and given the other folks
    demonstrated problems with inadequate cooling, I am very much in
    favor of designing in excess cooling capacity, to the point I may
    even incur a slight weight or drag penalty, such that I don't have
    to give constant attention to the risk of overheating.

    Dave

    Al Gietzen wrote:

    *Subject:* [FlyRotary] Re: Optimal GPM water pump flow.

www.racemate.com <http://www.racemate.com>   They were unable to find the photo of the Mazda install but they say the did a few. I am going to take the plunge and get one.. Dave



Just curious what you’re after with the racemate.  You were asking about “optimal” flow – double the needed flow is not optimum; high pressure gradients around the loop, unnecessary pumping power.



Al

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