RGP file for CO2
 

I have to perform a calculation on a heat exchanger in which one of the fluid is CO2. I need a CFX RGP file covering the liquid, the gas and the supecritcal region of the phase state diagram. Is there anyone which has one already prepared or at least files covering pieces of the whole diagram?

Re: RGP file for CO2
 

You could use the Redlich Kwong EOS, for which the solver builds the tables internally.

Re: RGP file for CO2
 

So you are going to perform phase change modelling then as well?

What phase change model are you going to use?

The internal (mentioned by Phil) & presupplied tables are only appropriate for the equilibrium model.

You could pick an equation of state and create your own RGP table as well.

Re: RGP file for CO2
 

I think that CFX is suitable only to superheat region, as stated in reference to RGP-file. (at least for version 5.7). Am I wrong?

Re: RGP file for CO2
 

Certainly CFX can calculate flows of both liquids & vapours.

The doc for the RGP file certainly implies that perhaps you can only use it for superheated vapours.

However, if you carefully look at the file format you could use it for subcooled liquids as well. The file just gives material properties a f(T,p).

You just need to appropriately fill the "superheat" tables with subcooled liquid properties instead, for a liquid.

You make one material for the liquid with a liquid RGP file, one for the gas with a gas RGP file and throw the saturation properties into either, doesn't matter.

Since you can put multiple materials into a single RGP file a single file can hold liquid, vapour and saturation data.

One small caveat is that you need to add the following parameter:


PROPERITES:
..
RGP Liquid Properties = Subcooled
END


to the liquid material.

do you know how to write a RGP file about CO2?

Dear HekLeR,

How to define the liquid properties in the RGP file? how to use the above mentioned one small caveat in the RGP file? Can you give me an example about how to define the liquid properties. I will much appreciate it.

Regarding metastable states for CO2 vapor supercooling
 

Dear Members

I am simulating condensation of CO2 with the droplets based non-equilibrium solver in Ansys CFX.

I have two questions:

First: I want to know whether the Spinodal Limits are incorporated into the Redlich Kwong equation of state as done with the IAPWS library.

Second: I request somebody to provide me RGP file generator based on REFPROP which can incorporate the data for metastable states.

Thank you guys.

Regards

Sir
Thank you for your sharing. In fact, I got the result of convergence by coarse grid, but the deviation between the result and the experiment is still large (This should be attributed to the nucleation model）.
However, I refined the computational grid and recalculated, it went to divergence again. In my opinion, there's a luck component in the simulation of supercritical CO2 flow near critical point with CFX.
In addition, the influence of critical diameter is multifaceted, which not only affects the nucleation rate, but also affects the initial size of droplets, etc.
CEL can only partially solve the problem and I don't think there is any way to completely solve the critical diameter problem in CFX.
As long as you use RGP files，CFX will automatically get metastable physical properties.
I recommend that future researchers use fluent's density based solver instead of pressure based solver.
I wanted to send you an email, but it was rejected.

Saeef

Regarding metastable properties of CO2 vapor in Ansys CFX
 

Dear Saeef


Thank you very much for responding.



I simulated condensing flow of water steam in the Moses and Stein nozzle using IAPWS equation of state. I am getting vapor subcooling even with nucleation and phase change switched ON in Ansys CFX as shown in the images.


Then I simulated condensing flow of CO2 in the Nakagawa nozzle with a RGP file for CO2 generated from the program mentioned at


https://studentcommunity.ansys.com/t...w-simulations/


The important point here is that I do not see vapor subcooling when nucleation and phase change are allowed as shown in the image below.


Similar results are obtained if I use Redlich Kwong equation of state for CO2 instead of REFPROP based RGP file.



The solver settings are same in the three cases.


This raises two points:
------------------------------


1) The IAPWS equation of state in CFX has the necessary data from spinodal region in such a form that allows the solver to give vapor supercooling even after phase change.


2) Some expert parameter needs to be switched ON in Ansys CFX to read the spinodal data and subcooled liquid data from RGP files and with Redlich Kwong equation of state?


The Ansys CFX "Solver Modelling Guide" talks about such a parameter on page 368.


The screenshot of this information is also attached.


I request you Saeef and all concerned to please share your views on this topic.


Thanks and Regards


Shyam

two-phase co2
 

dear ssyadav,
I wonder know if you simulated condensing flow of CO2 in the Nakagawa nozzle with a RGP file generated by the 'nisttorgp-ansys' .I use the generator. But I think the RGP generated by 'nisttorgp-ansys' is not correct. My case is hard to convegence even with so small timestep(auto timescale 10-4). I think the spinodal curve in RGP is wrong. but i still cannot solve it. Do you have the same situation?
thank you