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System Advisor Model (SAM)

User Defined Properties for HTF

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Allan54
Topic Author

21 Mar 2018 02:45 #6150 by Allan54

User Defined Properties for HTF was created by Allan54

Hi There

I'm running the physical parabolic trough model using user defined HTF data for high pressure water. For some strange reason when I input my data I'm getting negative energy out of the system. I've checked my water properties and and believe they're reliable. I've also tried converting j/kg to kj/kg for enthalpy but that made the results worse. I've taken out the titles in the csv file. Since I'm new to this program I'd appreciate some help. I'm in the physical trough model.

Thanks
Allan

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pgilman

21 Mar 2018 15:41 #6151 by pgilman

Replied by pgilman on topic User Defined Properties for HTF

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Allan54
Topic Author

21 Mar 2018 16:06 #6152 by Allan54

Replied by Allan54 on topic User Defined Properties for HTF

Thanks Paul. The issue I was trying to avoid was being outside the range of the Pressurized Water module. I was trying to model 2000 psig water which boils in the 340C range. The module said it was outside the range of its data. I think the biggest impact might be in the assumptions of enthalpy at higher temperatures. Comments please.

I'll check my data inputs for consistency to the info you provided. Appreciate the prompt reply and also the knowledge you folks have. Allan

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Allan54
Topic Author

22 Mar 2018 02:52 #6153 by Allan54

Replied by Allan54 on topic User Defined Properties for HTF

HI Paul. I got all my data looking just like yours. Except the enthalpy you've shown is in kJ/kg isn't it and should be 1000 times larger? My other data comes close. Part two, I ran your data above in the model for Calgary. It still returned negative values. I've run two sets of data and my values come out negative. Any thoughts what's going on? Appreciate your time and help. I realize I'm not the only user making demands on you folks. Allan

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srotermund

12 May 2021 12:49 #9588 by srotermund

Replied by srotermund on topic User Defined Properties for HTF

I've noticed it too Allan. The unit for Enthalpy on User Defined Table is wrong. It should be "kJ/kg", as you said.
It can be confirmed if you start a new project with "Parabolic Trough - Heat" model. When you first click to edit User Defined properties, the software show the properties for Pressurized Water at 23 bar. If you compare to any Table of Thermodynamic Properties (or NIST website), you will see that the values for Enthalpy shown are for "kJ/kg" instead of "J/kg".

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pgilman

13 May 2021 15:59 #9595 by pgilman

Replied by pgilman on topic User Defined Properties for HTF

Hi Sabryna,

The J/kg units in the table are correct. However, the default values in the table for the Physical Trough model are in the wrong units (kJ/kg instead J/kg).

That said, it turns out that the model ignores the enthalpy data in the table. The model uses the specific heat capacity Cp instead of enthalpy in the heat balance equations.

Also, the kinematic viscosity is redundant because it is defined as the ratio of viscosity to density, which are both provided in the table.

We will fix these issues for the Fall 2021 release of SAM: github.com/NREL/SAM/issues/619

Best regards,
Paul.

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