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Todd,
Your airflow through your cooler can indeed be below 60 MPH. If an
ideal diffuser it would be approx 20 MPH. Now, that does not mean it could
not be even slower, if your diffuser slows the air more and raises the
pressure more you may still get adequate cooling - but at some point the
airflow mass through the cooler becomes too little to carry away sufficient
heat even thought you are dumping more heat into the air per cubic
centimeter/inch.
Just like the old radiator situation. Folks found that if they slowed the
coolant flow through the radiator that:
1. The temp of the coolant coming out the other end was lower
2. The air flowing through the fins picked up more heat (increased in
temperature)
The problem was their interpretation that "Slow" water cooled better was, of
course, an erroneous interpretation of the data. The slower movement of the
coolant through the core indeed provided more time for the airflow to absorb
the heat (thereby lowering the coolant temperature and increasing the air
temperature.), but the coolant mass flow through the engine also slower and
failed to move as much heat from engine to radiator per unit time. So it was
not good for heat transfer from the engine to the radiator which is what its
really about.
So for OPTIMUM conditions you need a balance between the Core-Air Heat
transfer coefficient (which increases as the air slows) and the air mass
flow rate through the core (which slows as the heat transfer coefficient
increases) which are diametrically opposed to each other.
No telling how much air mass flow/velocity you have through your cores,
but, I think not having the fan ducted will probably help them survive. My
0.02 worth
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
From: "Mike Robert" <pmrobert@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, June 24, 2004 12:47 PM
Subject: [FlyRotary] Re: Oil cooler air velocity was : [FlyRotary] Visit
> Haywire wrote:
>
> > then your air velocity through your cooler will be
> >
> >
> >>approx 0.1 - 0.3
> >>of your airspeed. So for a 200 MPH speed you might have 20 -60 mph air
> >>velocity through your cooler fins not 200. Just though I would
> >>mention it.
> >>
> >>
> >
> >Hi Ed;
> > Do you really think that it will be this fast? Even say through the Evap
> >cores? The reason I ask is that I've just installed a fan on the back
side
> >of one of my evap cores to be used in conjunction with one of my EWP's to
> >reject cowl/engine heat after shutdown. I assumed/guessed that the
airflow
> >exiting through the evap core will be slowed down to <5mph. I don't have
any
> >data to support this, it just seemed reasonable.
> > I didn't add a shroud around the fan as I didn't want to hurt in-flight
> >cooling by forcing all of the air through the fan blades, even though
this
> >will make the fan less efficient. But I think if it does see up to 60 mph
> >airflow then it's lifespan will indeed be short.
> >
> >
> Auto experience: The RX-7 first gens place the oil cooler directly in
> the incoming air flow, no ducting or anything special to slow the air
> down, it's just sitting right there under the front bumper. I have a 12
> volt fan from a 19" computer rack cooling system bolted to the back of
> it and it hasn't exploded/debladed/etc. yet after numerous miles at 80
> mph. I power the fan only when stuck in traffic after a heat soaking
> fast run and the oil temp is creeping past 200F. I'm quite surprised at
> it's longevity. YMMV, obviously. Doesn't John Slade use a Ferrari fan
> for his coolant radiator app?
>
> >S. Todd Bartrim (completing panel modification/upgrade)
> >Turbo 13B RV-9Endurance
> >C-FSTB
> >http://www3.telus.net/haywire/RV-9/C-FSTB.htm
> >
> > "Whatever you vividly imagine, Ardently desire, Sincerely believe in,
> >Enthusiastically act upon, Must inevitably come to pass".
> >
> >
> >
>
> -Mike
>
> >
> >
> >
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
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