On Friday, February 15, 2013 6:20:36 PM UTC, Colin Stamp wrote:

Surely the something else is convection isn't it? When the hot, light

water goes in at the bottom, it'll float up to the top of the rad,

flooding through the top "tank". Flow rates inside the rad due to the

pump are low, so convection can dominate and the hot water floats up

through the first few channels. If it didn't, BBOE would never work.

The cooler water already in the rad will pool at the bottom, where the

exit ought to be. If the exit is at the top, then it'll be the hottest

water in the rad that gets pushed out by the incoming water - obviously

not what you want. A notional BTOE (as opposed to TBOE) rad will only

get hot up one end and along the top.





It is plausible with TBSE connections,



It is unlikey with TBOE connections. If you look at a TBOE radiator,

there are equal flow distances between the inlet and outlet connections,

regardless of which vertical channel the water passes through.

You would expect there to be equal flow rates through all of the

radiator channels, regardless of which connection was top or bottom.



No. I would expect convection to be the driving force in deciding which

channels the water flows through. If hot water finds itself at the

bottom of a cooler channel, it'll flow strongly up it. With the exit at

the top, a large pool of cold water will accumulate at the bottom of the

rad.

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.

With BBOE plus convection, it works as above, but pump and convection forces work together.

With TBOE (wrongly connected, flow in bottom & return out opposite top) the pump and convection forces are opposing one another. The pump will IMHO overwhelm the convection forces and ther will be little difference. It will be a parallel flow heat exchanger and the air movement will be reduced.

Domestic hot water cylinders are connected F in bottom, R out the top, but no-one has ever claimed it stops them working.