Running a Simulation
In order to run a simulation/flowsheet, you need to add some Compounds, setup a Property Package, add Objects to the Flowsheet and connect them to each other following the process flow.
Components/Compounds
There are two essential information required by DWSIM in order to correctly start a simulation. The first refers to the available components (or compounds). DWSIM comes with six default compound databases (DWSIM, ChemSep, Biodiesel, CoolProp, ChEDL and Electrolytes), with a total of more than 1500 compounds available for your simulation.
To add a compound to the simulation, select it on the list. To remove an added compound, just deselect it.
Property Packages
The Property Package consists in a set of methods and models for the calculation of physical and chemical properties of material streams in the simulation. It is composed of a thermodynamic model - an equation of state or a hybrid model - and methods for property calculation, like the surface tension of the liquid phase.
If the selected property package has any editable property, the "Configure" button becomes clickable and the user can click on it to show the property package configuration window.
Property Package configuration options
? Use Ideal Mixing Rule for Liquid Phase Density
If the liquid phase has small amounts of supercritical components, the default calculation method may fail. If that is the case, change this option to 1 to force an ideal mixing rule for the liquid density (use a molar weighted average of individual component liquid densities).
Additional Property Package configuration options
Some Property Packages have extra configuration options in order to allow a deeper control of the thermodynamic calculations for the user. They are:
? Use EOS for Liquid Density
This option forces the calculation of the liquid densities based on the compressibility factor given by the EOS. When disabled, DWSIM will use the Rackett correlation to calculate the liquid density. Please note that this also affects the calculation of partial molar volumes, and, consequently, component liquid volumetric fractions and flow rates.
Use 0 to disable, 1 to enable this option.
? Use Peneloux Volume Translation correction
This option is available for PR and SRK Property Packages. It enables correction of EOS-calculated densities by the inclusion of a correction factor named volume translation coefficient. This option will be effective only if the Use EOS for Liquid Density option is enabled.
Use 0 to disable, 1 to enable this option.
? Use Experimental Liquid Density Data
This option affects ChemSep database compounds only. It forces usage of experimental coefficients present in the database to calculate liquid phase densities.
Use 0 to disable, 1 to enable this option.
? Use Experimental Liquid Thermal Conductivity Data
This option affects ChemSep database compounds only. It forces usage of experimental coefficients present in the database to calculate liquid thermal conductivities.
Use 0 to disable, 1 to enable this option.
? Enthalpy/Entropy/Cp calculation method (Activity Coefficient Property Packages only)
Defines the Enthalpy, Entropy and Heat Capacity calculation model (0 = Lee-Kesler, 1 = Ideal, 2 = Excess).
Flash Algorithms
The Flash Algorithms in DWSIM are the components responsible for determining a particular set of phases at thermodynamic equilibrium, their amounts (and the amounts of the compounds on each phase) at the specified conditions like Temperature, Pressure, Total Enthalpy and Total Entropy. Some Flash Algorithms are capable of predicting equilibrium between one vapor and one liquid phase, while others support another co-existing liquid and/or solid phase. As the amount of phases considered in equilibrium increases, the calculation time/complexity also increases while the results' reliability decreases. Some flash algorithms are more capable/reliable than others, depending on the mixture for which the flash calculation request is being requested. DWSIM features a selection of flash algorithms that are capable of calculating VLE, VLLE and SLE. They are:
1. Nested?Loops?(VLE): recommended for the vast majority of VLE systems;
2. Nested?Loops?(VLLE): recommended for systems where the liquid phase may be unstable (will split in two liquid phases with different compositions);
3. Nested?Loops?for?Eutectic?Solid?Systems (SLE-E): Calculates Solid-Liquid Equilibria for eutectic systems considering the solid phase as being ideal.
4. Nested?Loops?for?Solid?Solution?Systems (SLE-SS): Calculates Solid-Liquid Equilibria for solid solution systems considering the solid phase as being ideal.
Multiple Property Packages and Flash Algorithms
DWSIM allows multiple Property Packages and Flash Algorithms to be added to a single simulation, which can be associated to each unit operation and material stream on a individual basis.
Systems of Units
Three basic units systems are present in DWSIM: SI System (selected by default), CGS System and English (Imperial) System. The simulation's units system can be viewed/modified in the "Units System" section of the "Simulation Settings" panel (bottom-right corner).
There is a button available on this interface to create a custom system of units. It is worth remembering that the units systems can also be modified at any time during the simulation - the changes are applied immediately.
Process modeling (Flowsheeting)
Inserting Flowsheet Objects
To add an object to the flowsheet, go to 'Object' > 'Add New Simulation Object'.
The elements of a simulation (objects) which can be added to the flowsheet are:
? Material Stream: used to represent matter which enters and leaves the limits of the simulation and passes through the unit operations. The user should define their conditions and composition in order for DWSIM to calculate their properties accordingly;
? Energy Stream: used to represent energy which enters and leaves the limits of the simulation and passes through the unit operations;
? Mixer: used to mix up to three material streams into one, while executing all the mass and energy balances;
? Splitter: mass balance unit operation - divides a material stream into two or three other streams;
? Valve: works like a fixed pressure drop for the process, where the outlet material stream properties are calculated beginning from the principle that the expansion is an isenthalpic process;
? Pipe: simulates a fluid flow process (mono or two-phase). The pipe implementation in DWSIM provides the user with various configuration options, including heat transfer to environment or even to the soil in buried pipes. Two correlations for pressure drop calculations are available: Beggs and Brill and Lockhart and martinelli. Both reduces to Darcy equation in the case of single-phase flow;
? Pump: used to provide energy to a liquid stream in the form of pressure. The process is isenthalpic, and the non-idealities are considered according to the pump efficiency, which is defined by the user;
? Separator Vessel: used to separate the vapor and liquid phases of a stream into two other distinct streams;
? Compressor: used to provide energy to a vapor stream in the form of pressure. The ideal process is isentropic (constant entropy) and the non-idealities are considered according to the compressor efficiency, which is defined by the user;
? Expander: the expander is used to extract energy from a high-pressure vapor stream. The ideal process is isentropic (constant entropy) and the non-idealities are considered according to the expander efficiency, which is defined by the user;
? Heater: simulates a stream heating process;
? Cooler: simulates a stream cooling process;
? Conversion Reactor: simulates a reactor where conversion reactions occur;
? Equilibrium Reactor: simulates a reactor where equilibrium reactions occur;
? PFR: simulates a Plug Flow Reactor (PFR);
? CSTR: simulates a Continuous-Stirred Tank Reactor (CSTR);
? Shortcut Column: simulates a simple distillation column with approximate results using shorcut calculations;
? Distillation Column: simulates a distillation column using rigorous thermodynamic models;
? Absorption Column: simulates an absorption column using rigorous thermodynamic models;
? Heat Exchanger: simulates a countercurrent heat exchanger using rigorous thermodynamic models.
? Component Separator: model to simulate a generic process for component separation.
? Solids Separator: model to simulate a generic process for solid compound separation.
Additionally, the following logical operations are available in DWSIM:
? Adjust: used to make a variable to be equal to a user-defined value by changing the value of other (independent) variable;
? Recycle: used to mix downstream material with upstream material in a flowsheet.
Connecting/Disconnecting objects
The material and energy streams represent mass and energy flowing between unit operations. You can connect/disconnect streams to/from Unit Operations or Logical Blocks by selecting the object, clicking with the right mouse button and selecting 'Edit Connections'.
Process data management
Entering process data
The objects' process data (temperature, pressure, flow, composition and/or other parameters) can be entered in the property editor window, accessible through the 'Edit Properties' context menu item.
Running a Simulation
DWSIM is a sequential modular process simulator, that is, all calculations are made in a per-module basis, according to the connections between the objects. The calculator checks if an object has all of its properties defined and, if yes, passes the data for the downstream object and calculates it, repeating the process in a loop until it reaches an object that doesn't have any of its dowstream connections attached to any object. This way, the entire flowsheet can be calculated as many times as necessary without having to "tell" DWSIM which object must be calculated. In fact, this is done indirectly if the user define all the properties and make all connections between objects correctly.
To solve the flowsheet, press F5 or click on 'Solver' > 'Solve Flowsheet'. As DWSIM's solver does its job, messages are shown in the log panel. These messages tell the user if the object was calculated successfully or if there was an error while calculating it.
If the calculation finishes without errors, you can proceed to viewing the results.