[Apologies for reposting but I sent this one out yesterday and oddly,
although I can see it on Google, it hasn't shown up on my local news server
(text.news.ntlworld.com), so I'm wondering if the lack of followups is due
to others not having seen it either rather than (or perhaps as well as)
no-one finding it faintly interesting or being able to help :-)]
Anyone know where I can get figures for calculating (allright, guesstimating
:-) rates of heat transfer through pipes for a diy heat store heat
exchanger? I'm planning to hang say a 25m coil of 10mm table Y copper pipe
in a tank connected to the CH primary and wondering what rates I can expect
to get water out at given inlet and outlet (and tank) temperatures.
Obviously I can suck it & see but it'd be nice to have some sort of
theoretical figures to start with (and encourage me to actually have a go
with the idea :-).
Thanks, so maybe it's just NTL losing one of their own [l]users' posts :-)
Presumably it didn't appear on You-Know-Who's server ;-)
Sometimes the only way you can feel good about yourself
is by making someone else look bad.
And I'm tired of making other people feel good about themselves
Oh it probably did, but we all know that he deals mainly in opinions and
suppositions and not in hard figures, and you specifically asked for
...but then that doesn't *usually* stop him ;-)
Martin Angove (it's Cornish for "Smith") - ARM/Digital SA110 RPC
See the Aber Valley -- http://www.tridwr.demon.co.uk/abervalley.html
On Tue, 15 Jul 2003 23:00:16 +0100, "John Stumbles"
Had you thought of contacting one or other of the cylinder
manufacturers and asking them for information on their water
e.g. you could ask for the kW rating of the coil and its water
content. From the water content you can calculate the pipe surface
area. The heat transfer rate will be dependent on surface area.
Another source might be the Copper Development Association who should
be able to give some data at least.
Theoretically, the maximum rate of transfer is going to come from the
famous equation of mass x specific heat x temperature rise.
However, I can see at least two factors that will reduce that.
1) the thermal resistance of the copper and the area.
2) the thermal gradient from the top to bottom of the tank - unless
you stir the water of course.
Are you doing this as an experiment or on a low budget?
If not, I can't help thinking that using a plate heat exchanger
external to the tank might be a better (or rather more predictable
For a slightly different application of coupling a second CH circuit
that feeds my workshop to the main house CH circuit, I used one made
by GEA Ecobraze. This was a small unit, a little larger than a
house brick, but able to transfer up to 200kW. Since that is much
larger than the amount of heat required to be moved (I need less than
10kW) the effect of the exchanger itself can be ignored and the rate
is determined by the flows on each side.
To email, substitute .nospam with .gl
Most heat exchange properties can be calculated using Newton's Laws on
Materials Cooling, The Fourier Modelling Equation and The Stephan-Boltzmann
Rule, all of which give calculations for flow rate and flow restriction
against surface area. I think that they all roughly state that a longer
wider diameter (greater surface area), higher temperature pipe, with a slow
replenishing flow gives the best results.
The same equations are used in the calculations of heat sink properties on
electronics equipment, which I think a few people using the group will be
able to give more details of.
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