Generate Material
Once a thermodynamic system is defined, it can be used to define a multitude of property functions. The Generate Material option provides a fast route to defining the material properties most commonly required for fluid flow, heat transfer and mass transfer. By specifying the composition and the phase of the mixture, a Material node can automatically be setup. The material node can include properties such as the density, heat capacity, heat capacity ratio, thermal conductivity, viscosity and the diffusivity. Two types of property functions can be used, either functions from the underlying thermodynamics or interpolation functions created from these. For space-dependent models, the interpolation models are more computationally efficient.
Right-click the relevant Thermodynamic System node (or an External Thermodynamic System node or Predefined System node), and select Generate Material to start the Generate Material Wizard.
The Generate Material Wizard contains the following steps:
1
Select Phase
2
Select Species
3
Select Properties
4
Define Material
Select Phase
Use this list to specify the phase of the material. Select among the ones available in the system. This step of the Generate Material Wizard is not available for the Predefined Systems Dry Air and Moist Air.
Click the Next button () to proceed to the next step in the wizard.
Select Species
Select the species to be included in the list. Use the Add All button () to add all species in the thermodynamic system. It is also possible to select a subset of the available species. In that case use the Add Selected button () to add species. The Selected species table is updated as you add species.
Notice that when using Generate Material for the Predefined System Water-steam this step is not included in the wizard.
Material Composition
Specify the mixture composition in terms of the Mole fractions or Mass fractions of all species. The fractions should sum to one. This setting is only available for systems with more than one component, and for materials with more than one selected species.
Click the Next button () to proceed to the next step in the wizard.
Select Properties
Use this step to select the material properties to be included.
For a liquid phase material the following properties are available:
•
Density, (ρ)
•
Diffusion coefficient at infinite dilution
•
Heat capacity (Cp)
•
Thermal conductivity (k)
•
Viscosity (μ)
For a gas phase material, the Heat capacity ratio (γ = Cp/Cv) is also available.
To add a property to the Selected properties list click the Add Selected button (). To remove properties, use the Remove Selected button () or the Remove All button ()
When adding the Diffusion coefficient at infinite dilution, also select which of the species is the solvent. The material will include one diffusion coefficient for each of the remaining (solute) species.
Figure 2-23: Generate Material Wizard; Select Properties with Diffusion coefficient at infinite dilution added.
Additional properties
The below additional properties are defined from the selected properties and added to the output properties of the material.
For a liquid phase material the isobaric coefficient of thermal expansion is defined as:
(2-1)
For a gas phase material, the speed of sound c, and the isentropic compressibility χf are also defined as:
(2-2)
Click the Next button () to proceed to the next step.
Define Material
Component
Use the Component list to select where the Material will be added. The already existing components are shown in the top of the list. A new component can be created by selecting the desired space dimension. Select Global at the end of the list to add the material under Global Definitions. A global material can be utilized in any component, through the use of a Material Link. It can also be used to define phase specific properties when linked to a subnode of a Porous Material.
Function Type
The material can be set up to use functions defined under the thermodynamics system, or interpolation functions defined from these. The interpolation functions are significantly faster to evaluate, especially for space dependent models, but requires that the temperature range and the pressure range are specified.
Select Thermodynamics to base the material properties on functions in the current thermodynamic system. The required functions are created, if not already present, and added to the system. When evaluating material properties, the underlying thermodynamics functions are called.
Select Interpolation to generate interpolation functions for the material properties. In this case the required functions are first created and added to the system. Next, the functions are evaluated in a number of sampling points over a given range, for both temperature and pressure. The result of the evaluation is stored and used to define interpolation functions for all material properties.
For the Interpolation points, select Same for all functions to use the same number of evaluation points for all functions. By selecting Individual, the number of evaluation points can be given per function. The latter can for example be used to increase the number of points for a function that is known to vary faster than the rest of the functions.
Select one of the preset levels for the Maximum number of interpolation points. This is used to provide a maximum size of the underlying data for the interpolation functions. If the total number of evaluation points for any function, varying temperature and pressure, is exceeded, a warning is shown.
Define the temperature range and pressure ranges for the temperature and pressure by providing the Low and High end values. To neglect the variation in either temperature or pressure, give the same value for the low and high end value. This can for example be used when the pressure variation is known to be negligible. For each range, also define the number of evaluation points in the Number of points field. The underlying functions are evaluated at uniformly distributed positions across the temperature and pressure range.
When Individual has been selected for the Interpolation points, the Ranges and interpolation points can be specified per function to be created.
Click the Finish button () to create the specified Material and exit the wizard.