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.
I have been following this carefully, because my touring TR3A with
everything in top condition starts to have the needle start climbing on a 80
degree day (faster even if 90 degrees) when on the open road at 75 to 80
miles per hour. The longer I go, the higher it keeps climbing and I'd love
to know his answer. I overdrive I turning about 3200 rpm. Turning on my
electric fan at these speeds didn't help. Water Wetter didn't eliminate the
phenomenon. I accept that the crank hole may be causing a 15% los, but
that's the way I have it and I want it that way. It's not really a problem
if I let up on the gas to let it cool down again at 55 to 60 mph. It's only
touring you know - not like trying to win a race.
Don Elliott, 1958 TR3A, Montreal, Canada
----- Original Message -----
From: "Michael D. Porter" <mporter@zianet.com>
To: "stutzman" <stutzman@adelphia.net>
Cc: "MARK J WEATHERS" <markjwea@email.msn.com>; <fot@autox.team.net>
Sent: Wednesday, March 05, 2003 1:36 AM
Subject: Re: Head Cooling Problems
> stutzman wrote:
> >
> > in the TR4 comp manuel Kas said to break the bellows and re-install the
> > thermostat. "You must have a restriction in the system or the water
pump
> > will force the coolant through the radiator too fast for proper cooling
to
> > take place, and the engine can overheat very quickly." His advice in
the
> > TR6 comp manuel is similar.
>
> With all due respect to Kas, I've weighed this one back and forth for
> some time. Like others here, I've had some training in thermodynamics,
> and think that there are some minor considerations that may interfere
> with any pure thermodynamics theory, but have come to the opinion that
> their effects are small to negligible. The question is of materials, and
> as Bill Babcock says, of boundary layer effects.
>
> Two things regarding materials are of interest--coefficient of heat
> transfer through the radiator material, and coefficient of heat transfer
> off the material to air. Both of these, effectively, are rates, and by
> definition, are time-dependent. Therefore, it would seem that residence
> time of the hot coolant in contact with the radiator material would be
> of consideration.
>
> As for boundary layer effects, if non-compressible fluids behave
> similarly to compressible fluids, the greater the flow, the thinner the
> boundary layer, but, as well, the greater stagnation of the boundary
> layer. In the case of heat transfer, this creates two temperature
> gradients--one from the hot fluid through the stagnant boundary layer
> (which, being stagnant, is closer in temperature to the radiator
> material), and the second is through the radiator material itself. Since
> heat transfer is also linearly dependent upon the temperature gradient,
> better heat transfer through the radiator would occur if there were no
> boundary layer of coolant, which is a heat moderator, rather than a good
> heat conductor as is the metal of the radiator.
>
> All that said, the gross thermodynamic theory still applies. In a closed
> system, temperature equilibrium depends on only two things--the amount
> of heat produced by the engine in a fixed period of time, and the amount
> of heat rejected by the cooling system in that same time. If the heat
> rejection capacity of the radiator exceeds the heat production of the
> engine, under optimum conditions, total heat in the system (and,
> therefore, indicated temperature) can be regulated by thermostat.
>
> If the heat production of the engine exceeds the heat rejection capacity
> of the cooling system, that's where the rate-dependent materials
> considerations come into play in any overheating equation. The materials
> and design of the radiator will determine _how quickly_ the engine will
> overheat if heat production exceeds heat rejection.
>
> The effect of a restriction in the thermostat housing is build pressure
> in the block and the head to minimize nucleate boiling, purely and
> simply. The lower the pressure in the cooling jacketing of the engine,
> the greater the likelihood of nucleate boiling (this phenomenon hasn't
> been adequately explained, I think--it has specifically to do with the
> ability of water vapor to transfer much less heat as compared to liquid
> water--the higher the pressure, the more difficult it is for the coolant
> to boil, and if liquid coolant can't boil, more of the liquid is in
> contact with the surface area transmitting combustion heat--transferring
> much more heat to the coolant than can steam vapor). It has to do with
> how many molecules of coolant are in contact with the cooling jacket,
> and the space between those molecules. The farther apart the molecules,
> the more difficult the heat transfer. As well, with more molecules of
> coolant in contact with hot areas of the jacket, the greater the heat
> transfer.
>
> The intent of increasing water pump pulley diameter, thus reducing speed
> of rotation of the pump at high operating rpm, is to minimize the
> _cavitation_ of a highly inefficient stock pump--cavitation creates
> vacuum bubbles which act much like nucleate boiling--they are a point of
> compressibility in an otherwise non-compressible fluid, which creates an
> effective pressure loss in the system between the pump outlet and the
> outlet to the radiator, and effectively increases nucleate boiling. The
> original stock pumps have simple straight vanes cast into the impeller
> plate, and those create turbulence at high speed which creates those
> vacuum bubbles.
>
> Cheers.
>
> --
> Michael D. Porter
> Roswell, NM (yes, _that_ Roswell)
> [mailto:mporter@zianet.com]
>
> Don't let people drive you crazy when you know it's within walking
> distance.
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