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Alain,<br>
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).<br>
Kind regards,<br>
David<br>
<br>
<br>
On 10/14/2011 05:19, Alain Guiavarch wrote:
<blockquote cite="mid:4E980CCF.50600@mines-paristech.fr" type="cite">Dear
All,
<br>
<br>
I did a very simple test : a water storage (type 4c), initialized
at 50°C.
<br>
There is no load, no heat source.
<br>
The only heat transfer is the heat loss by conduction through the
walls of the tank (with an ambient temperature of 20°C)
<br>
Very simple !
<br>
<br>
But there is something I don't understand in the results ( the
tank is is divided in 20 layers) :
<br>
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.
<br>
<br>
Did I someting wrong ? Where is the error (I also attached the
project file)?
<br>
<br>
Thank you !
<br>
<br>
Alain Guiavarch
<br>
<br>
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<br>
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