[TRNSYS-users] problem with type 4c

[David BRADLEY]

Alain,
   I think that what happens is that the surface area of the top node is 
greater than the surface area of the other nodes (because of the tank 
top). As a result, the top node loses more energy than the node below 
and thus cools off. The temperature inversion (a colder temperature 
above and a warmer temperature below) causes a mixing between those two 
nodes and the result is that there is a net transfer of energy upwards. 
This continues on down to the bottom node and because there is no node 
(no source of energy) below that, the bottom node cools off and doesn't 
get replenished. Essentially, I think that the phenomenon that you are 
seeing is real (the tank naturally stratifies). In reality, the 
stratification would not be simply between the bottom and the next to 
the bottom node but would extend up in the tank. Bear in mind, however, 
that there are a lot of phenomena that are NOT modeled by Type4 
(convection cells that develop within the tank, for example).
Kind regards,
  David


On 10/14/2011 05:19, Alain Guiavarch wrote:
> Dear All,
>
> 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)?
>
> Thank you !
>
> Alain Guiavarch
>
>
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> TRNSYS-users at cae.wisc.edu
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

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