[Amps] more - oil bath GS-35b

Chris Wilson chris at chriswilson.tv
Wed Apr 1 11:37:16 EDT 2015

Hello Bill,

On Wednesday, April 1, 2015,  you wrote:

> ------------ ORIGINAL MESSAGE ------------(may be snipped)

> On Mon, 30 Mar 2015 17:20:50 +1300, Gary and Steve wrote:

>>> You do not need to slow the flow down in order to pick up heat. The faster
>>> the flow the more heat will be transferred.
>>Correct!  The faster the oil flow in the tube cooler, the better the 
>>But not so for the radiator.  The oil must slow down and be in the 
>>radiator for a finite time for the heat to be transferred from the oil 
>>to the air.


> "But not so for the radiator."?

> There seems to be something wrong with the logic here. Heat transfer
> doesn't care whether it goes from the tube to the oil or from the oil
> to the radiator, does it? By your logic, if you slow the oil through
> the radiator down to very, very slow the heat transfer will be better.
> But then the tube will overheat and burn up. 

> Likewise, if you slow down the oil past the tube, the heat transfer
> will be maximum, but again the tube will overheat and burn up. 

> Can't both be right. I think faster is better for both tube and
> radiator. 

> Any heat transfer engineers out there? 

> 73, Bill W6WRT
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There are optimum flow rates based on heat exchanger coolant medium,
be it gaseous, or fluid, the type of liquid, and its viscosity. It
also depends on the surface area of the inside and outside elements of
the exchanger and the device being cooled. For sure faster flow is
*NOT* necessarily better. In automotive racing water (or water mix)
coolant is NOT flowed as fast as possible through the engine, but very
careful design has water flow going at different rates in different
parts of the engine. Those who have replaced a cylinder head gasket
may have noticed the flow restriction hoses of varying sizes in the
head and gasket. Different areas of the engine run at different
temperatures, and flow rate is varied to optimize heat extraction.
Water to air radiators have internal turbulators in high end coolers
to increase internal surface areas, thermostats have restrictor plates
to control water flow rates. Current cooling systems use electronic
water pump drives and electronic thermostats to optimize flow
according to load, blah blah.

Air flow through heat exchangers is similarly regulated for optimum
heat exchange speeds.

I am sure in an oil to air heat exchanger with a submerged valve there
will be an optimal flow rate for the oil and the air, that is far away
from the fastest flow rate, and there are big differences between
convection, conduction and radiation. I am most definitely *NOT* a
heat transfer engineer, but I am a race car engineer and I know a lot
of science and experimentation goes on in the engine world to maximize
heat exchanger performance, and engine coolant flow is a lot slower
than you perhaps imagine.

Best regards,
 Chris                            mailto:chris at chriswilson.tv

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