[SEL] Thermo-syphon Question

[MaytagTwin at aol.com]

Hi Paul,
Based on lab experiments with thermo-siphoning, I don't think you need to  
worry about being too high.  Do keep in mind that your return line to the  
engine should be a couple inches above the bottom of your tank if you want the  
tank to catch sediment and the line leading from the engine to the top of the  
tank must always remain under the surface of the water in the tank.  So  long as 
you don't have any air pockets in the system, it will thermo-siphon to a  
tank as in your picture or would thermo-siphon to a tank many feet higher.  
 
You see, the return water is slightly cooler and more dense which means it  
can push the warmer water up.  Since if you have the tank higher, both the  
lines are longer and the difference in balance is determined by the temperature  
differential.  The water can move easily with only a small difference in  
density.  The top line must be below the water surface for the system to  balance 
and the volume of water in the cooling tank that is above the top pipe  is how 
much can evaporate before you need refill the cooling tank.
 
In the lab experiments we used glass containers and clear tubing to carry  
the water.  We would get it started and running and then add a drop or  two of 
dye to the water so we could see it move through the tubes.  What  really 
surprised us was how fast the water would move through the tubes  with only a small 
temperature difference.  Thermo-siphoning can work very  well in moving heat 
from the engine.
 
Ron
 
 
In a message dated 1/18/2007 7:46:16 P.M. Central Standard Time,  
paulmaples at sbcglobal.net writes:

I am  working on getting a coolant tank built for my 5 HP Stover and I will 
be using  one of the early Stover Cast Iron Stands: See the picture  below:

http://i52.photobucket.com/albums/g36/wheelterrapin/StoverTankStand1.jpg

By  using this stand my tank will be up higher than it normally would be if 
it was  mounted at the same level as the engine. My question is how high can 
you  reasonably expect the thermo-syphon effect to push the water up to the top 
of  the tank? I need to know this so I can properly locate my inlet fitting 
for  the intake of water at the  top.

Thanks,

Paul