Re: [TRNSYS-users] type 531 stratified storage tank

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

<In order to maintain the stability of the system, the
chosen number of nodes must not be too many, as the amount of
water flowing into the storage tank in a given time step should
not be greater than the amount of water occupied in each node of
the storage tank. Does this statement apply to storage tank type 531?>

It holds for all tanks that use the isothermal noding concept (4,60, 531-4
etc.).  The statement is a warning to carefully check the energy balances
if you put more water in a tank node than it can hold in one timestep. 
There are times when the energy balance is fine with high flows - and
times where it will fail.  However, there is a very simple solution;
simply reduce your timestep.

<Bumping up the number of nodes absolutely shows me greater
stratification. >

Yes but is it real?  Setting the number of nodes to 10,000 will show
wonderful stratification and even exhibit plug-flow like behavior in the
tank (like a pipe).  But inlet flows tend to mix the tank, auxiliary
heaters create plumes which can mix the tank etc.  You need to choose a
number of nodes that reasonably matches with the conditions and the tank
geometry (diffusers etc.).

Jeff


Jeff Thornton
President - TESS, LLC

2916 Marketplace Drive - Suite 104
Madison WI 53719 USA

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