Minimum angle for evacuated tubes.

[RogerT]

I was rather surprised to see Dick Strawbridge on INEBG last night install some tubes at a very shallow angle. I thought the tubes were more efficient the more upright they are, or have I got it wrong (again) ?

I know the optimum angle will depend on the time of year/height of sun etc, but is there a minimum angle that the tubes should be at ?

[Ivan]

optimum angle is your angle of lattitude (averaged throughout the year). It should be a bit steeper in winter and a bit less steep in summer. My lattitude is 53degrees - and it does not vary enormously across the UK

Ivan

[RogerT]

> optimum angle is your angle of lattitude...

Yes, but what is the MINIMUM angle at which they will work efficiently ?

The ones Dick installed were on a very shallow shed roof, probably less than 20 degrees above horizontal. Doesn't the fluid in the tube have to vapourise and heat the copper bit at the top and then liguify again and flow down the tube ?

[Ivan]

minimum angle for the heatpipes is 15degrees

[RogerT]

Thanks.  Are they 100% efficient above 15 degrees, or is there some sort of efficiency curve ?

[Ivan]

I really don't know. I assume they will be a little less efficient at 15degrees, but I would also assume the effect is marginal. The main concern is that 15degrees is far from optimal for these lattitudes. Might be interesting to experiment a bit.......