[TRNSYS-users] Stratification in Tank Type534

[David BRADLEY]

Alaia,
  Type534 results have been matched against experimental data on 
numerous occasions. If you add heat to the top of a tank by a 
miscellaneous energy flow then there is no physical flow of water 
through the tank that will cause the top node to get hotter and hotter. 
The nodes below will heat up by conduction somewhat but there is no 
other mechanism either in the model or in reality that will cause the 
entire tank to heat up if you are only adding energy to the top node.
   There are a number of parameters that you can use to either enhance 
or decrease stratification if the temperature profiles you are seeing in 
the tank do not match the reality of your experimental data. Type534 
does not directly account for convection cells that form in a tank if 
heat is added to the bottom nodes (note that the top of the tank is node 
1). Such cells need to be accounted for using the inversion mixing flow 
rate. An inversion is defined as a situation where a node nearer the 
bottom of the tank has a higher temperature than a node above.
regards,
  David


On 07/02/2015 01:55, Alaia Sola wrote:
>
> Hi everyone,
>
> I am using Type534 with Plug-in, inserting 1 port and 1 miscellaneous 
> heat flow to it. My doubt is about temperature stratification in the 
> tank. Even if I increase the number of nodes, the temperature 
> difference between the node where I insert the heat flow and the rest 
> of the nodes is too large, i.e. the nodes without external heating 
> barely warm up.
>
> It also happens even if I remove the port and, consequently, simulate 
> it as a tank without any inlet or outlet: the lower nodes barely 
> increase their temperature (I want the miscellaneous heat flow in node 
> 1 or 2), no matter the time length I run the simulation... The upper 
> nodes do reach the desired temperature (I have a controller to the 
> heater that is connected to miscellaneous heat flow for that) but the 
> lower nodes remain almost at constant temperature. I tried to change 
> the “inversion mixing flow rate” to both high and low values, negative 
> and positive values, zero… but the changes in T of the nodes are not 
> visible. I want to increase T of water in tank from 20ºC to 150ºC and 
> I have a quite high water draw from the tank, thus I don’t want that 
> only one or two nodes reach 150ºC, but I want most or all of the tank 
> to do so instead… no matter how much time it takes to heat it up.
>
> How to make the lower nodes to heat up? Which other parameter can I 
> change so the stratification in the tank really works? Is there any 
> other parameter to change rather than “inversion mixing flow rate” to 
> get normal stratification? Should I use another type?
>
> Thank you very much in advance.
>
> Alaia Sola Saura
>
> Project engineer
>
> Thermal Energy and Building Performance Group
>
> *IREC***
>
> *Institut de Recerca en Energia de Catalunya*
>
> www.irec.cat <http://www.irec.cat>
>
>
>
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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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