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Re: [TRNSYS-users] Stratification in Tank Type534



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

 

 



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