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Hi Dave,
I'll give a shot at a simplistic approximation.
At 250HP (approx 13PSI boost) you will need to get rid of approx 7711 BTU/Min through the radiator and another apprx 3855 BTU/min through the oil cooler. Just to give you a comparison at 160 HP NA those figures are 4977 Radiator and 2488 oil cooler.
A gallon of water (specific heat = 1, mass = 8.2 lbm) takes 8.2 BTU to raise a gallon of water's temperature 1 deg F ( it takes 1 Btu to raise 1 lbm water 1 deg F) So trying a few variables with Delta Temperature or the amount of temperature increase you are willing to let the coolant rise to we can play the numbers game.
If willing to accept a 10F rise in coolant temp it would take 82 BTU to rise a gallon of water 10Def F. So 7711/82 = 90 GPM. For a 20F rise it would take 7711/164 = 47 GPM. For a 30 deg F increase it would take 7711/246 = 31 GPM. This assume of course, that the radiator gets rid of the heat at the same rate. It also assumes that your oil cooler can handle its own increase in heat rejection demands - if not then that heat would also have to be rejected by the coolant/radiators. Further assuming that you are sticking with the standard limits on coolant which means limiting the temp of coolant returning to the block to 180F, then a 20F increase will have it at 200F in the block, a 30F delta would have it at 210F. If your return coolant temp was say 210F with a 31 GPM pump then the block temps could be reaching 240F (actually probably more). The slower the flow means the coolant temps must increase in order to carry away the same amount of heat. So you can have slow flow and higher coolant temps or fast flow and lower coolant temps.
Now that is at 250HP. Presuming you are only going to be operating at that power/boost for a limited time(less than a minute or two) then a 31 GPM pump might work - as the rest of the time the heat demands would be considerably less. But for 250HP continuous then I believe you are talking above 50 GPM.
All this is just my SWAG.
Ed A
----- Original Message ----- From: "David Staten" <Dastaten@earthlink.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, September 10, 2005 10:59 AM
Subject: [FlyRotary] Optimal GPM water pump flow.
This may have inadequate variables, but looking for optimum Gallons Per Minute desired water pump flow for a 13B 2nd gen, at 6000 rpm but boosted to 250 hp max (realistic is 200-225, but I dont want to marginalize capacity). Assuming no more than 20 psi and no undue flow restrictions.
Any takers on the math?
Why: spec'ing a racemate direct drive water pump and alternator.. I intend to order in the next week and want to select the right one.. or the "most right" one.
Dave
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