Your explanation started off good and then wandered away, then got back to
point. In my humble opinion. First of all, this is anything but a closed
system as far as heat balances go--the heat sink is the earth. Second, the
heat rejected by the engine is anything but constant--it's a direct
function of energy generated and thermal efficiency. Generation has to do
with how deep your foot is into it and where you are in the power band.
Heat is being carried away thorough all kinds of mechanisms, most of which
are also variable. Direct air cooling of the engine (a function of air
flow through the engine compartment), direct cooling of the engine by the
induction air and the fuel (even though they are one of the primary
sources of heat (friction is another), they also directly cool and they
carry way lots of heat through the exhaust system). Pumping oil both
generates heat and carries it away to the oil cooler. Complicated system.
Way too complicated to do even an approximately accurate heat balance
without big league calculation and a lot of empirical measurements that
would get stuffed into constants. Not that anyone would really care that
wasn't working for a carmaker.
I suspect that Greg Solow is absolutely correct. A fusty brit radiator
designed more than 50 years ago is marginal in a touring application, much
less racing. I think they assemble them with old waxoil instead of solder.
Four pounds of radiator cap is more than enough for them, and even that
can spawn leaks. A dirty TR3 radiator with a crank hole in the middle
probably has a lower temperature drop than the radiator hoses do. Just
FEEL the exit hose sometime--it's as hot as the inlet (I swear mine felt
hotter). I do think the Chevy guy that wants to install a 25# radiator cap
is on to something--it will turn the radiator into a showerhead and then
you can justify a good one.
-----Original Message-----
From: Larry Young [mailto:cartravel@pobox.com]
Sent: Wednesday, March 05, 2003 12:06 PM
To: fot@autox.team.net
Subject: Re: Head Cooling Problems
I thought I was starting a thread on head sealing, but it evolved into one
on cooling. My plans are to install a larger radiator and a higher
pressure cap. This is going to involve a lot of replumbing and other
modifications, so it may be a while before I report back on the results
I've studied heat transfer and have pondered the "flows to fast theory"
quite a bit. I've even written down all the energy balances. The
explanation at the stewartcomponents link is one of the better ones I've
seen. I think what people forget is that this is about removing the heat
generated by the engine not about cooling water. The important point is
that we are dealing with a closed system. At a given set of operating
conditions, the heat generated by the engine is more or less constant. The
amount of heat removed is proportional to the change in temperature times
the flow rate, i.e. if you double the flow rate, then half the
temperature change removes the same amount of heat. If the water is
flowing
too fast to cool down, then its flowing too fast to heat up when it passes
through the engine. I believe a restriction may be beneficial for a
system which is starting to boil, because it will put a bit higher
pressure on the block. The water will tend to remain liquid at the higher
pressure in the block and then flash downstream from the restriction.
This will improve heat transfer, because steam is a poor heat conductor.
However, it seems to me you'd be better off using a higher pressure cap.
Larry Young
elliottd wrote:
> Michael - Your explanation is very interesting.
>
> Let's hope that Larry Young who started this thread comes back to
> explain what he did to solve his overheating problem that caused him
> to have to let up with his right foot after 20 minutes of leading the
> pack in hard competitive racing.
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