I haven't thought about this deeply, but I'm thinking the rate of heat
transfer to the oil bath depends only on the temperature difference
between the oil (adjacent to the tube anode) and the anode
temperature, as well as the thermal impedance of the tube-oil
interface. Speeding up the oil flow ensures that cool oil is always
present at the interface, thus maximizing the temperature difference
and optimizing heat transfer.
The same reasoning applies to the oil-radiator system, but in reverse.
Here one wants hot oil and a cool radiator, since that maximizes the
heat transfer from the oil to the external environment.
There are a few other considerations influencing cooling (such as the
thermal conductivity of the oil, as well as its specific heat
coefficient), but those are generally not under the control of the
builder. Ideally one wants oil with the thermal conductivity of
diamond, and a swimming pool-sized oil reservoir, but good luck with
that!
73,
Jim w8zr
Sent from my iPad
> On Apr 1, 2015, at 9:20 AM, Bill Turner <dezrat@outlook.com> 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
>> cooling.
>>
>> 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.
>
> REPLY:
>
> "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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