[TRNSYS-users] problem with type 4c

[Jeff Thornton]

<I did a very simple test : a water storage (type 4c), initialized at 50°C.
There is no load, no heat source. The only heat transfer is the heat loss
by conduction through the walls of the tank (with an ambient temperature
of 20°C) Very simple ! But there is something I don't understand in the
results ( the tank is is divided in 20 layers) : All layers follow the
same temperature decrease, all except one layer, the bottom layer. The
temperature of the bottom layer (the 20th layer in the figure, the first
layer being the top layer) is not consistent compared the other layers.
Did I someting wrong ? Where is the error (I also attached the project
file)?>

Alain,

No - the results that you are seeing are correct.  If there was no mixing
algorithm in the storage tank, the top and bottom nodes would decay more
quickly than the other nodes due to the added surface area (top and bottom
of the tank).  However, Type 4 does not allow for temperature inversions
in the tank, so the top node temperature falls below the other nodal
temperatures after the initial thermal calculation - but then the mixing
algorithm checks the nodal temperatures from the top down and mixes nodes
1 and 2.  But now nodes 1 and 2 are colder than node 3 so all three of the
nodes then mix.  This process repeats until we hit the bottom node, which
is colder than the mixed nodes above it - so no internal mixing occurs
there.  The result is 19 mixed nodes and a colder bottom node 20.

Hope this helps.

Jeff

Jeff Thornton
President - TESS, LLC

22 North Carroll Street - Suite 370
Madison WI 53703 USA

Phone: 608-274-2577
Fax: 608-278-1475
E-mail: thornton at tess-inc.com
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