[SEL] Thermo-syphon Question

[Skip Cleveland]

Well, acording to this, sometimes it is and sometimes not. If you kept the 
coolant topped up it was, when it boiled to a low point belowthe top hose it 
wasn't.
Skip
thermosiphon
Thermosiphon (alt. thermosyphon) refers to a method of passive heat exchange 
based on natural convection which circulates liquid in a vertical 
closed-loop circuit without requiring a conventional pump. Its intended 
purpose is to simplify the pumping of liquid and/or heat transfer, by 
avoiding the cost and complexity of a conventional liquid pump.


Simple thermosiphon
Convective movement of the liquid starts when the bottom of the loop is 
heated, causing it to expand and become less dense, and thus more buoyant 
than the cooler water in the top of the loop. Convection moves heated liquid 
upwards in the system as it is simultaneously replaced by cooler liquid 
returning by gravity. In many cases the liquid flows easily because the 
thermosiphon is designed to have very little hydraulic resistance.


Phase change thermosiphon
In other cases when the loop has more resistance to flow, the liquid may be 
heated beyond its boiling point, causing a phase change as the liquid 
evaporates to a gas (such as steam). Since the gas is much more buoyant than 
the hot liquid, the convective pressure is increased considerably. This is 
known as a heat pipe thermosiphon. It allows the cooling and heating of 
objects by changing the phase of a liquid inside a closed system, and 
operates on the principles of buoyancy (gas-phase) and gravity (liquid) to 
move the fluid through the system.

In some situations the flow of liquid may be reduced further, or stopped, 
perhaps because the loop is not entirely full of liquid. In this case, then 
the system no longer operates on convection principles, so it is no longer a 
simple "thermosiphon". Heat can still be transferred in this system by the 
evaporation and condensation of vapor; however, the system is properly 
classified as a heat pipe.

----- Original Message ----- 
From: "Bill Dickerson" <bill at antique-engines.com>
To: "'The SEL email discussion list'" <sel at lists.stationary-engine.com>
Sent: Saturday, January 20, 2007 7:47 PM
Subject: RE: [SEL] Thermo-syphon Question


> Isn't the cooling on a tractor such as the Farmalls - the F20, 
> thermosiphon?
> Or technically not?
>
> Bill
> Runnells, Iowa
>
> -----Original Message-----
> From: sel-bounces at lists.stationary-engine.com
> [mailto:sel-bounces at lists.stationary-engine.com] On Behalf Of John Culp
> Sent: Saturday, January 20, 2007 12:32 PM
> To: The SEL email discussion list
> 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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