Re: [TRNSYS-users] Type 557 tube-in-tube ground heat exchanger

["Jeff Thornton" <thornton@tess-inc.com>]

> I would like to model an open concentric tube heat exchanger where the
> circulated water is in direct contact with the ground, in other words there
> is no outer pipe. What is your opinion on using Type 557d with zero
> thickness of the outer pipe to approximate this? Would this be a crude
> approximation?

I'm pretty sure that zero thickness won't work; you'll have to give it a
small thickness to avoid an error.  As to the heat transfer, I guess it
will depend on the type of material in which the pipe is located.  If it's
a smooth bore into rock, with little fissures or groundwater movement then
a small pipe resistance on the outside shouldn't matter much at all.  If
it's a sandy soil where you have local inflows/outflow then you'll
certainly have some differences.  But then again there aren't many models
(if any) that'll account for the local water movement into and out of
bores.  If you're just worried about the resistance of just the small
outer pipe - don't be - it won;t influence the heat transfer much at all. 
The dominant resistance will be the ground.

Jeff


Jeff Thornton
President - TESS, LLC

2916 Marketplace Drive - Suite 104
Madison WI 53719 USA

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