[TRNSYS-users] TRNSYS Type 534 doubt cross sectional area and temperature-dependent properties

[Jeff Thornton via TRNSYS-users]

For the record, the heat exchanger cross sectional area is used to
reduce the conduction heat flow between adjacent nodes. So if the heat
exchanger tube at the nodal boundary was vertical it would simply be
Pi/4*Do^2 But it's likely much closer to horizontal for a coiled tube
heat exchanger. 

2) I would not use variable fluid properties for the tank unless every
component connected to the tank also has a variable properties - or
you'll get an energy balance. 

3) Misc heat flows can be used to account for any other non-specified
energy flow for the tank. Typicall they are set to zero but have proved
useful in several cases. 

Jeff 

---
Jeff Thornton
President - TESS LLC
22 N. Carroll Street, Madison WI USA 53703
Office: (608) 274-2577 Fax: (608) 278-1475
www.tess-inc.com
E-Mail: thornton at tess-inc.com

On 03/03/2017 4:19 am, Oriol Casal via TRNSYS-users wrote: 

> Dear all, 
> 
> I am currently working on a hot sanitary water system with a solar collector and a storage tank, and I have chosen Type 534 for the tank because it seemed to be able to cover all my modeling needs. 
> 
> However I have not found much information on a couple of topics: If I use the version without the plug-in I cannot choose Propylene Glycol as a fluid and instead I have to input a single value for the physical properties. Is there a way to not use the plug-in and be able to have time-dependent properties? 
> 
> Furthermore, I have struggled a lot to try to grasp what "HX cross-sectional area" is, I have finally decided that for the coil HX case it must be pi*(CoilPipeOuterRadius-CoilPipeInnerRadius)^2, however the default value from TRNSYS is quite higher (two orders of magnitude higher), is my interpretation correct? I have also found other default values to be far away from the ones that I am using, such as the HX wall conductivity, which is two orders of magnitude lower than I would expect, does this mean I should not be using TRNSYS default values for those parameters I have no information on? (such as heat transfer phenomena inside the coil). 
> 
> Finally, I have set miscellanous flows to zero, despite not being entirely sure of what they are, I suppossed they would only be used in case of external energy flows, but instead, in order to do that I am using the auxiliary gains. 
> 
> Kind regards, 
> 
> O.C. 
> 
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