Presentation from Modelica Conference 2015

1. MULTI-PHASE MIXTURE MEDIA
Johan Windahl1, Katrin Prölss1, Maarten Bosmans2,
Hubertus Tummescheit1, Eli van Es2, Awin Sewgobind2
1Modelon, 2Vortech

2. • MODELICAPROP - CleanSky SGO project
 In collaboration with Modelon and Vortech
• Objectives
 Add support for mixtures with multiple phases
 Analyze Modelica.Media structure
 Interface external property databases
BACKGROUND

3. • Meeting in Delft - 17 people
 Academia, Industry, Modelica design group, CO-Lan
• Conclusion
 Performance important (framework should support caching)
 Challenge: Not possible to share interface
BACKGROUND
model Example
replaceable package Medium=MyMedium;
Medium.MyExternalObject eo;
Modelica.SIunits.Density d;
equation
d=Medium.density_pT(1e5,300,eo);
end Example;

4. • Thermal separation
 Distillation processes
MOTIVATION – NEW APPLICATIONS
• Thermodynamic cycle
– Temperature glide
• Transport of flows
– Compositional pipe network
– CPU expensive

5. • Modelica.Media interface
• Limitations
 Single substance medium with two phases (liquid and vapor)
 Designed for power/energy applications (mass-based)
 Different ways of usage – confusing
 Relies on common subexpression elimination
• Find a new structure!
MODELICA MEDIA

6. 1. Structure and user-friendliness
A. Share interface
- Native Modelica media and external C-code based media
B. Easy to use, understand and implement.
- Details should be hidden from the user
2. Multi-component multi-phase (new functionality)
 Phase equilibrium
 Properties for a specified present phase
Identification of phases and compounds
 Mole and mass based properties
Chemical industry works in mole while energy in mass
GENERAL REQUIREMENTS

7. Function based Model based
INTERFACE STRUCTURE
Record based

8. INTERFACE: FUNCTION VS MODEL
• Advantages model based interface
• Share interface between external and native Modelica media
• Hide implementation details (external object)
• Equation based implementation
• Tool solve flash calculations
• User friendly - work graphically
• Minimalistic interface
• Avoid new functions for new input combinations
• Avoid dependency on special trick as common-sub expression
elimination
• Drawbacks
• No usage inside functions
• User unfriendly to calculate parameter
• Not calculate property on demand

9. MULTI-PHASE MIXTURE
• Package with models and helper functions
• ThermoProperties - similar to
BaseProperties in MSL
• parameters: inputs.pTX, init, optimization
• variables: p,T, d, … (mass and mole based)
• MultiPhaseProperties
• Overall (_overall) and single phase (_1ph)[nP]
properties
• phaseComposition, phaseFraction

10. EXAMPLE – THERMO-PROPERTIES

11. • C/C++ Modelica property interface
 Backends to CAPE-OPEN, RefProp, FluidProp
EXTERNAL MULTI-PHASE MIXTURE MEDIA

12. • A few similar functions (calcThermoProperties_XXX)
 Combines flash and property calculation
C-INTERFACE

13. • External property code
 Not designed for dynamic simulation
 Error when calling outside validity area
 Non-converging region
 Limited support for partial derivatives
 No support for providing iteration start values
• General no support for overall derivatives
 One-phase region: analytical calculation
 When multiple phases exist: calculated numerically (Modelica side)
EXTERNAL INTERFACE - CHALLENGES

14. • Modelica tool
 Not possible to calculate iteration start values from a property model
• Modelica specification
 Inconvenient to use a model/block based structure to calculate
parameters
LIMITATIONS

15. • Case 1: Native Modelica Air media
 3 component simple media, incompressible liquid phase and ideal gas
assumptions
 VLE, fugacities polyniominal adapted to data- solved by tool
 Simulate fast (Initialization is a challenge)
TEST CASE 1 - AIR SEPARATION UNIT
0 4000 8000
0
4
8
Simulation time (s)
CPUtime

16. • Case 2: Refprop Air media
 3 component air media, mixture of multi-parameter eos
 Different state selections and media inputs tested
 Solver getting stuck or failure when calling outside validity region
 Needs to be analyzed further
TEST CASE 2 - AIR SEPARATION UNIT

17. • New framework for multi-component multi-phase
 Open up new areas where the Modelica technology can be used
 New model based media
Support both native Modelica and external media
 Finding a structure more challenging than expected
Due to Modelica restrictions, combination of pure and differentiable
functions
CONCLUSION

18. • More testing and evaluation of concept
 New use cases
• Infrastructure for native Modelica implementations
 Equation of state, mixing rules
 Initialization part (homotopy?)
• Extend the C-interface backend
 More property packages: e.g. MultiFlash
 New functionality
• We encourage you to take part in continuing the
development!
 Open-source GitHub Repository
• Thanks EU for the financial support!
FUTURE WORK