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Date: Fri, 14 Jan 2005 23:01:52 -0600
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: water cooled matrix in oil pan
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<...oil moves in the channels of the oil cooler at about 20 ft/min ... 
oil entered the pan at one end and traversed across it might be moving 
about ½ ft/min ...>

20 fpm through the cooler seems really slow. What is the oil pump output 
volume? I'd have thought something on the order of 10 gpm or so. 20 fpm 
through a foot long oil cooler that holds a quart of oil is only 5 gpm 
output from the pump. Is that right?

Trying to do the math ... Jim S.

Al Gietzen wrote:

> Subject: [FlyRotary] Re: water cooled matrix in oil pan
>
> `The problem with this is that the oil is essentially stagnant in the pan'
>
> Al, this is only 'cause you haven't looked inside when its running - 
> there's
>
> an oil pump driving this stuff round the engine all the time, it just 
> starts
>
> and finishes at the bottom of the oil pan. The flow rate will be the same
>
> as anywhere else on the system that you would choose to oil/air 
> cooler. Its
>
> true that the `dwell time' in the oil pan will be longer as this is your
>
> reservoir but this is a good thing.
>
> The key word is “essentially”; and it’s the velocity that counts. The 
> oil moves in the channels of the oil cooler at about 20 ft/min; enough 
> to give you good convective heat transfer coefficient. If you assume 
> that the oil entered the pan at one end and traversed across it might 
> be moving about ½ ft/min (the actual case would be likely be less 
> because it is moving more from top to bottom). Convective heat 
> transfer would be “essentially” zero, and you would have to rely on 
> conduction; but, of course, the thermal conductivity of oil is not 
> very good, so . . .
>
> It could be done; but it is not simple. A large pan volume with cooled 
> plates and narrow oil channels could do the job. Sounds a bit 
> expensive and maybe heavy; so a nice compact, effective oil/air heat 
> exchanger sounds pretty good.
>
> And BTW, folks. A good balance of theory and experiment is where it’s 
> at. Let’ not forget that without the theory and engineering; there 
> wouldn’t be a rotary engine.
>
> Al
>