Pressure Required to Circulate Liquid in a Closed System?

[Baluncore]

The elevation difference has to be sufficient, otherwise the density difference between the "up leg" and the "down leg" won't be enough to overcome the flow resistance (friction, bends, change of area).

The flow velocity self regulates, as a slower fluid flow, has longer to heat, to a higher operating temperature, with a greater density change, resulting in a greater hydrostatic drive pressure difference.

A crude guide to the optimum arrangement of the components in a thermal siphon, is "Heat Rises".

 

[gmax137]

It's pretty light in supporting theory, but it guess its legit if they are using it as a deep backup safety in nuclear plants. I still would like to see an analysis.

For a real plant the analysis is more sophisticated than these hand calcs. Also, the startup testing done during plant commissioning includes a natural circulation test to verify the analytical results. Plus, several plants in the US have lost forced circulation (loss of power to the coolant pumps). This causes an immediate shutdown of the reactor, so the flow requirement is much lower than that required at power.

But this is pretty far afield from the greenhouse unit discussed in the OP; the nuclear plant link was just a convenient place to find a schematic drawing of the basic configuration and the pressure balance equations.

 

[erobz]

But this is pretty far afield from the greenhouse unit discussed in the OP; the nuclear plant link was just a convenient place to find a schematic drawing of the basic configuration and the pressure balance equations.

It seems like the OP's system has the cold reservoir lower than the hot reservoir.

 

[Baluncore]

It seems like the OP's system has the cold reservoir lower than the hot reservoir.

Part of the design optimisation process involves finding ways to invert that situation.

 

[gmax137]

I was hoping the OP would provide a schematic elevation sketch, I didn't take the time to figure it out from the video.