Um, I don't think that statement makes much sense. No flame intended but,
think about this logically... The radiator gives off a certain amount of
heat, transfered from the water to the metal of the radiator and to the air
passing over the radiator. I think the part of the equation that you are
leaving off is that when water flows faster through the radiator the water
exiting may be hotter but there but more water is cooled (more heat is
extracted from the system).
Think about it this way, the amount of heat released by the radiator is
equal to the amount that the coolant passing through the radiator has been
cooled, (per gallon/volume). Hold airflow constant for a second. If the
entire radiator was at 130 degrees, the amout of heat given off or
transfered to the air passing over it would be large. If the radiator were
at 100 degrees, the amount of heat released to the air would be less. In
order to keep the whole radiator hot, water flow has to be high. When you
slow down the water, the later part of the radiator cools down and less heat
is released from the system. A cooler radiator releases less heat.
Increasing the flow rate through the radiator will maintain a higher
temperature delta over the entire surface of the radiator between the cool
air and the hot coolant and more heat will be extracted from the system.
It is possible that putting a larger pully on the water pump will enhance
cooling but not because the water is flowing slower through the radiator and
giving off more heat. It would be speculation but, a larger pully on the
water pump would reduce the load on the engine at high speed which could in
turn lower the heat output of the engine. It is also possible that the water
pump cavetates or otherwise loses efficiency at high rpm and therefore,
slowing it down would yield better cooling (greater flow of water).
Would slowing down the airflow accross the radiator increase the amount of
heat released? Well, the air coming off the back of the radiator would be
hotter but there would be less of it and less overall heat would be
extracted. It doesn't make sense that less airflow would cool the radiator
better does it? But that is kinda the same arguement that you are making for
why slowwer water through the radiator would cool more. Now someone out
there is going to tell me that they put a bigger cfm fan on their radiator
and it didn't cool as good as the little one because the air was moving too
fast through the radiator. Larger fans have larger motors that block more
airflow than smaller ones. Sometimes the increased flow of air accross a
small part of the radiator does not outweigh the complete loss of airflow
accross another part. Deminishing returns... So my point is, I'm not saying
that what you have witnessed is not possible, just that it is not for the
reasons you may think and applying those ideas to a simlar problem may not
yeild the desired results.
Chris Reichle
----- Original Message -----
From: Max Heim <mvheim@studiolimage.com>
To: Larry Colen <lrcar@red4est.com>
Cc: MG List <mgs@autox.team.net>
Sent: Monday, August 14, 2000 3:41 PM
Subject: Re: Almost enough cooling
> I have heard the exact same trick described on the Barracuda mailing
> list, so there is apparently something to it. I think what is going on is
> that a given airflow through a specific radiator lowers the coolant
> temperature at a specific rate. If this rate is slower than the rate of
> coolant flow through the radiator, you will not receive the maximum
> cooling benefit. High vehicle speed = high airflow = high cooling rate,
> but high RPM = high coolant flow rate; so in a racing situation, as you
> try to keep the engine in the upper end of the RPM range (regardless of
> vehicle speed), the flow rate could easily exceed the cooling rate. It
> makes sense if you consider the flow rate being optimized for general
> driving, not racing.
>
> Larry Colen had this to say:
>
> >Apparently the trick is to get a late model water
> >pump pulley which will slow down the water pump. The problem is that the
> >water pumps the water through the radiator too fast at high speed. I'm
not
> >quite sure how this works because it seems to me that there is a certain
> >amount of water in the radiator the whole time, but maybe it takes time
> >for convection to actually cool the water away from the edges of the
tubes.
> >Anyone know enough thermodynamics to explain this to an ignorant EE?
>
>
> --
>
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the red one with the silver bootlid.
_________________________________________________________
|