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William wrote:
Jim,
Think of it this way, it may help -- When you increase the flow rate through the system, the overall temperature drop/rise across the radiators/engine are decreased. This means the radiators have a higher temperature to reject the heat to the air (beneficial), and the metal components of the engine do not have to get as hot to drive the heat into the coolant going through the engine (beneficial). The price you pay is having more pumping power.
I had looked at it as: High Flow - engine can't heat the water as much as it would if the flow were slower and there was more time to heat the water, resulting in less temp rise in water across engine and more uniform temps in the block. Water emerges from block not much hotter than it went in. Water doesn't stay in the radiator long enough to be exposed to air flow long enough to be cooled very much. Good news: it doesn't *have* to be cooled much - it's not all that hot.
Low Flow - coolant spends more time in engine and gets hotter. Greater dT across engine block, coolant hotter exiting engine and entering radiator. Radiator has to draw more heat out of the coolant to get it back to acceptable block entry temp, but has more time to do it on account of lower flow.
What I hadn't seen, is how apparently wide a range of flows would produce acceptable results. I suppose a better radiator (more flue area, better air flow, etc. - better cooling per in^3) would reduce the volume requirement. Lower limit on flow would seem to be that flow at which the temperature gradient across the engine becomes unacceptable.
Thanks for the details ... Jim S.
With the lower flows of the EWP, greater temperature drop/rise across the radiators/engine are required in order to get the heat out. This means that you have to have a larger or more efficient radiator, and the metal surface inside the engine needs to run at a higher temperature.
It is all a series of trade-offs.
Bill Schertz
KIS Cruiser # 4045
----- Original Message ----- From: "Jim Sower" <canarder@frontiernet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, March 20, 2005 11:04 PM
Subject: [FlyRotary] Re: BMW and EWP
I seem to have missed a lot of posts. When I'm going to be out of town for more than couple of days I stop the list. That could explain some of it. 12 GPM and 34 GPM is a pretty wide window of stuff that apparently works. 34 is like cycling your whole coolant supply through the system every 4 seconds or so. That just seems really really fast to me. It was 40+ years ago last time I studied this stuff, so all I've got is intuitive guesses.
Which is, of course, exactly what I keep complaining about :o) ... Jim S.
Bob White wrote:
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