thermosiphon question
thermosiphon question
(OP)
1 -Is there something like "pressure gradient" or "driving force gradient" in a thermosiphon system?If so,how is it drawn?
2 - Suppose a simple thermosiphon system of a heat source at bottom ,a sink at top and two risers.If there is another sink in the middle of source and sink how the system will work? Which sink will receive more heat?
The question arises from this practical question ;in a multifloor building when the pump is off,which floor will get more heat?
2 - Suppose a simple thermosiphon system of a heat source at bottom ,a sink at top and two risers.If there is another sink in the middle of source and sink how the system will work? Which sink will receive more heat?
The question arises from this practical question ;in a multifloor building when the pump is off,which floor will get more heat?





RE: thermosiphon question
No easy answer to #2, it would depend on the heat transfer occurring at each floor, and the piping layout. One can easily envision a scenario where the nearer floor sucks all the available heat, starving the flow to the upper floors, or the opposite, where the density gradient is high enough to cause the hot fluid to zip right past the first floor tee.
RE: thermosiphon question
RE: thermosiphon question
RE: thermosiphon question
RE: thermosiphon question
RE: thermosiphon question
By "riser" I mean both supply and return pipes.A single supply pipe and a single return one with branches at each floor.
As racookpe1978 has mentioned I have experienced cases where flow tends to stop or tries to go the wrong way. Also as btrueblood has mentioned there were cases where the first floor has starved.
And what about gradient? Can we consider the heat source like a pump and draw the gradient graph with the least head just before the source and the most head just after it?
RE: thermosiphon question
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: thermosiphon question
An efficient, self-starting thermosiphon has to have a large vertical region that can be made to be the hottest place in the system. If the expansion of the water can cause some of the hot fluid to "back up" into the downcomer pipe, then the siphon won't start.
Once started, it becomes a balancing act to try and get the flow equalized - back to my first reply. Thermostatic valves on the radiators (heat sinks) might help (but these can be slow to react). Even better might be some active control systems that sense the temperature of the fluid along the length of the riser, and at the inlet and outlet of the radiators, and open/close motorized valves to vary the flow in/out of each radiator. Check valves in the feed line to each radiator might also help...but the biggest problem happens when a slug of hot fluid gets forced into the downcomer, something only a finely tuned controller can hope to prevent, I'd think.
RE: thermosiphon question
Your summary was what I was trying to get at in my earlier reply: Routine operation may work, but only after all of the "hot parts" are hot and the "cold parts" are cold and the fluid (the working chemical) are moving in the right direction.
RE: thermosiphon question
RE: thermosiphon question