On Saturday, February 16, 2013 6:18:16 PM UTC, Colin Stamp wrote:
On 16/02/2013 15:28, Onetap wrote:



I still don't agree with that. Please note that I'm not saying it won't happen, I'm saying it wouldn't anticipate it happening.



The convection just generates a pressure difference due to the different masses of the H&C water columns.



With BBOE and no convection (air, rad, water at the same

temperature) water will still flow up the first channels and

down the last, the flow rate being such that the frictional pressure

loss equals the pressure difference across the inlet & outlet

provided by the pump.



I wouldn't expect that. The vast majority of the water will go whistling

straight through the bottom tank and out of the other end. To get to the

top of the rad, it would have to fight the restriction of one of the

channels, both up and then back down. in BBOE, it needs convection to

have a reason to do that.

It definitely does do that. It's the electrical resistance analogy with multiple flow paths. You could work it out from the same principles, i.e., flow in = flow out, differential across all the flow paths is the same, flow along any one path is determined by the resistance and the differential.




With BBOE plus convection, it works as above, but pump and

convection forces work together.



Actually, the pump would work against convection with BBOE, but the

effect is very small because the velocity of water in the rad due to the

pump is so low. Convection easily overwhelms it.

Convection assists the pump, driving more of the flow up the alternative flow paths, along the top header, rather than straight through the bottom header.