[mostic]

Hi everyone,

Hope the community can assist to solve a problem I have faced. At the moment, I am trying to conduct an ejector modeling using an R513a refrigerant, which is the mixture of the R134a/R1234yf (56/44 Mass Fraction).

Shortly about the physics.
A schematic of the ejector is represented in the figure below.
Untitled-1.jpg
The working flow (subcooled liquid) at high pressure and temperature flow through a converging/diverging nozzle, where its pressure drops and flow accelerates during expansion in the nozzle. At the outlet from the nozzle, the fluid is in a two-phase state. The dryness level depends on operating parameters. The secondary fluid (superheated flow) at lower temperature and pressure, flows through the suction pipe, mixes with the working fluid in the mixing chamber, and mixture compresses to an intermediate pressure. A compressed flow out from the ejector.

Fluid Setup
To set up fluid, the following steps were conducted:
1. Imported available in Peng-Robinson library R134av,R134al, R1234yfv and R1234yfl.
2. Created a material R513al (liquid) as a fixed composition mixture, liquid state. Since I have no data, the mixture thermodynamic and transport properties were set to "Ideal Mixture"
3. Created a material R513av (Vapor) as a fixed composition mixture, Gas state. Since I have no data, the mixture thermodynamic and transport properties were set to "Ideal Mixture"
4. Created R513avl (Vapor Liquid Mixture) as Variable Composition Mixture, components R513al and R513av. Did not set any Thermodynamic state or mixture properties. Mixture Properties were set to Ideal Mixture.

Problem
Previously, using the same approach to provided modeling of R134a and reached the results close to calculation. The R134a vapor-liquid mixture is available in CFX libraries, and properties are defined as a real fluid, based on the Peng-Robinson equation. The times to stabilize working fluid parameters and flow through nozzle usually required about 2500-3500 timesteps. However, for R513a the model does not even start to stabilize working flow after 20000 timesteps. The resulting file showed that the calculation of the expansion process in the nozzle accompanied by phase change was not finished. Additional timesteps returned with an error:

Follower:  22  
Follower:  22   Fatal bounds error detected
Follower:  22   ---------------------------
Follower:  22   Variable: Absolute Pressure
Follower:  22   Locale  : Default Domain

 Parallel run: Received message from follower
 --------------------------------------------
 Follower partition:       22
 Follower routine  : ErrAction
 Leader location   : Message Handler
 Message label     : 001100279
 Message follows below - : 
 
 +--------------------------------------------------------------------+
 | ERROR #001100279 has occurred in subroutine ErrAction.             |
 | Message:                                                           |
 | Stopped in routine ENFORCE_BOUNDS                                  |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 +--------------------------------------------------------------------+
 
 +--------------------------------------------------------------------+
 | ERROR #001100279 has occurred in subroutine MESG_RETRIEVE.         |
 | Message:                                                           |
 | Stopping the run due to error(s) reported above                    |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 |                                                                    |
 +--------------------------------------------------------------------+

 +--------------------------------------------------------------------+
 |                An error has occurred in cfx5solve:                 |
 |                                                                    |
 | The ANSYS CFX solver exited with return code 1.   No results file  |
 | has been created.                                                  |
 +--------------------------------------------------------------------+

End of solution stage.

 +--------------------------------------------------------------------+
 | The following user files have been saved in the directory          |
 | ....../dp35_CFX_2_Solution_2/Fluid   |
 | Flow CFX_012:                                                      |
 |                                                                    |
 | trace, mon, pids                                                   |
 +--------------------------------------------------------------------+


 +--------------------------------------------------------------------+
 | For CFX runs launched from Workbench, the final locations of       |
 | directories and files generated may differ from those shown.       |
 +--------------------------------------------------------------------+


This run of the ANSYS CFX Solver has finished.

Assume that the problem is with the fluid setup and during phase change in the nozzle during expansion is not modeled currently.

Could you please advise how to define fluid for the model?

[ghorrocks]

You define R513avl as a Variable Composition Mixture. Shouldn't this be a Homogeneous Binary Mixture to handle the phase change?

[mostic]

Thank you for the reply.
I have tried to set it up as a Homogeneous Binary Mixture. The CFX-Pre show 2 warnings
Screenshot 2022-01-10 135841.jpg

Starting run with the Initial Conditions, returns me an error

 +--------------------------------------------------------------------+
 |                                                                    |
 |                            Partitioning                            |
 |                                                                    |
 +--------------------------------------------------------------------+
 



 +--------------------------------------------------------------------+
 |                                                                    |
 |                     ANSYS(R) CFX(R) Partitioner                    |
 |                                                                    |
 | 2021 R2                                                            |
 | Build 21.2 2021-05-14T23:10:23.832818                              |
 | Sat May 15 02:10:44 GMTDT 2021                                     |
 |                                                                    |
 |                        Executable Attributes                       |
 |                                                                    |
 |           double-64bit-int32-archfort-optimised-std-lcomp          |
 |                                                                    |
 | (C) 1996-2021 ANSYS, Inc.                                          |
 |                                                                    |
 | All rights reserved. Unauthorized use, distribution or duplication |
 | is prohibited. This product is subject to U.S. laws governing      |
 | export and re-export. For full Legal Notice, see documentation.    |
 +--------------------------------------------------------------------+




 +--------------------------------------------------------------------+
 |                  Job Information at Start of Run                   |
 +--------------------------------------------------------------------+

 Run mode:       partitioning run

 Host computer:  ...... (PID:......)

 Job started:    Mon Jan 10 14:00:13 2022
  
 Details of error:-
 ----------------
 Error detected by routine NAMLST1 
 CNAMS = COMLS/NAMES  CVALUE =
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