[SEL] Thermo-syphon Question

[Skip Cleveland]

Here is an interesting find.

Thermosyphon

We learnt at school that gases or liquids if heated become less dense and 
can rise through cooler areas by the buoyancy created. Similarly cooler 
liquids are denser and fall. This principal is used in thermosyphon cooling. 
Heat generated in the engine is picked up by the coolant and rises out of 
the top of the cylinder head progressing up the top hose into the radiator 
header. Coolant in the radiator is loosing heat and tends to fall to the 
bottom where it is lead back to the engine at the lowest point. Thus the 
system works well and responds to changes in load etc by using the laws of 
Physics as Scotty from Star Trek would have put it. However the system does 
need certain aspects to be maintained. The radiator top has to be higher 
than the water outlet on top of the cylinder head with as near a vertical 
top hose as possible, within reasonable bounds the higher the better, 
certainly no less than about 4 or 5" and not too far in front of the engine 
to keep the upward slant of the hose. If the water level drops such that the 
radiator and top hose are not flooded, the circulation will stop. Large 
pipes are needed to ensure the limited motion of the coolant isn't 
restricted.

----- Original Message ----- 
From: "John Culp" <johnculp at chartertn.net>
To: "The SEL email discussion list" <sel at lists.stationary-engine.com>
Sent: Saturday, January 20, 2007 1:31 PM
Subject: Re: [SEL] Thermo-syphon Question


>> I found this on google. Doesn't say anything about the water having to be 
>> above either radiator or tank opening. Could this be wrong?
>
> Of course it could. It's not, though, just incomplete. What they're not 
> mentioning, taking it as a given, is that there must be a complete circuit 
> for the flow to occur, just as with a DC electrical circuit.
>
> Let a large enough air bubble into the system to open the liquid circuit, 
> and thermosiphoning can't occur. Percolation driven by rising steam 
> bubbles still can. Remember the old fashioned coffee percolators?
>
> The heat input to a thermosiphoning system doesn't have to be at the 
> bottom, or the cooling at the top, for convection to occur. It just needs 
> to be asymmetrical so that one side of the system contains warmer liquid 
> than the other. That liquid's less dense than the cool liquid in the other 
> line, so it will rise and be displaced by the cooler liquid, that then is 
> heated.
>
> John Culp
> Bristol, Tennessee, USA
>
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