Very well done, Mike. Thanks.
Geoff Branch
'74 Meejit "Yellow Peril"
'72 Innocenti 1300 Mini
----- Original Message -----
From "Michael Lupynec" <mlupynec at globalserve.net>
To: "Peter C." <nosimport@mailbag.com>; "Geoff Branch" <gjbranch@mediaone.net>;
"Mike MacLean" <macleans@earthlink.net>
Cc: <spridgets@autox.team.net>
Sent: Friday, September 28, 2001 12:10 PM
Subject: Re: "Oil Pressure" & "old" overheating problem
> ----- Original Message -----
> From: Peter C. <nosimport@mailbag.com>
> > The coolant needs to go slow enough through the engine
> to pick up
> > the heat, but not too slow or the temperature difference between
> iron and
> > coolant wont be great enough.
>
> I barely remember my 4th year thermodynamics - but here goes. The
> RATE of heat transfer between a FIXED surface area of engine metal
> and coolant linearly depends on the temp difference (delta T). So
> cooler coolant equals more transfer. The metal don't care if the
> coolant is moving or at speed.
>
> Therefore slower flow means the coolant next to the metal warms up
> more, the delta T is less, and heat transfer is less (assuming the
> metal temp remains constant, i.e. let's call the metal to be at
> momentary equilibrium). The other thing you cannot avoid with slow
> flow in the engine is that you will wind up with a cool end and a
> hot end of the motor. The potential for design hot spots is
> increased.
>
> Also --- flow rates introduce the topic of turbulence and boundary
> layers (Reynolds numbers) next to the metal. Boundary layers
> (slower flow) are effectively insulators. Turbulence (high speeds)
> is better for heat transfer. I don't know if internal engine water
> passages are experiencing turbulence, except for sure at the water
> pump impellers and probably not at all in the rad cores. Rads are
> more complex in that you have fluid flow on one side and varying
> temperature/speed air flow on the other. Unlike motors rads are
> not so restricted to an "operating temperature" or a "mechanical
> configuration" and therefore can have long passages for increased
> time exposure, can have space shuttle fin technology, can have a
> hot end and a cool end etc. Has anyone noticed that the water
> passages in a motor block have not changed much in 100 years, but
> look at what has happened to rad technology in terms of size,
> weight and efficiency.
>
> There is a long engineering equation that tries to simulate
> reality for practically everything, up to and including rising
> bubbles in a boiling pot. A lot of car stuff such as balancing the
> heat output of the engine with the heat dissipation at the rad and
> in the engine compartment is derived from empirical test data and
> component suppliers specs. This thread is struggling with the end
> result of a 30's Brit low production volume engineering mentality,
> that designed everything with a minimum theoretical calculation
> contingency safety factor. No allowance for loss of strength due
> to corrosion, for Arizona temperatures, for poor owner maintenance
> and lastly they designed RHD cars and converted (with compromises)
> 80% of them to LHD.
>
> Bottom line, with marginal cooling, you have to guess or figure
> out where your weakest and or cheapest link is - and say goodbye.
> My take - speed it up in the engine (without cavitation), slow it
> down in the rad (bigger rad), max air movement (shrouds and fans).
> When you have excess cooling capacity, then the thermostat can
> once again become the Controller.
>
> Mike L
> 60A,67E,59Bug
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