Defining particle models (ModelGrain)

Particle models (or ModelGrains) define the concentric arrangement of materials in same and different particles. Any number of particle types can be defined to accommodate all the materials. The XML tag for defining particle models is <modelGrain>.

1 Name (String)

Every particle model has to be given a unique case-sensitive name. In the GUI, creating a new particle model with the same name will replace the earlier particle model. This property can be defined as the attribute “name” with the <modelGrain> XML tags.

2 Layers (Material)

Concentric layers of discrete materials can be defined to be present in a ModelGrain. Since diffuse materials are assumed to be mixed with the discrete materials, the layers can only contain discrete materials. All non-universal discrete materials have to be present in one of the ModelGrains and any material can be present only in one of the layers of one of the ModelGrains. Layers can be added using the XML tag <layer>.

3 Initial particle size distribution (String)

The file-name of the file containing the initial particle size distribution of this particle type is assigned to this parameter. The XML tag for defining this property is <filePSD>. This file can have one of the several different formats, as listed in the following subsections.

3.1 Cumulative particle size distribution

In the first possible format, each line of this file should contain a diameter (double) followed by the fraction of the powder by volume that is smaller than this size (double), separated by space or tab. Although the diameters can be listed in any order, if the diameters are listed in ascending order, the fractions listed should be in ascending order as well. The programme renormalises the fractions assuming that 100% of the powder is smaller than the largest diameter listed. The word “Cumulative” (without quotes) can be optionally provided on the first line of the file to denote this format. The distribution will be assumed to be linear between the provided points.

3.2 Differential particle size distribution

In the second possible format, similar to the first format, each line of this file should contain a diameter (double) followed by the fraction (double) of the volume of the powder present that is of this size, separated by space or tab. The diameters can be listed in any order. In most practically observed particle size distributions, a peak in the fraction values is observed for one of the diameters between the first and the last listed diameters exclusive. This format can be automatically recognised if such is the case. The word “Differential” (without quotes) can otherwise be put on the first line of the file to denote this format. The distribution will be assumed to be linear between the provided points.

3.3 Mono-disperse particle size distribution

A powder can be defined to be mono-disperse (having all particles of the same size) using the third file format. In this format the file should contain only one line of data followed by a line-break. This line should contain the diameter of the particles followed by any arbitrary number, preferably 1.0, , separated by space or tab. This format can be automatically recognised if only a single line of text. The word “Single” (without quotes) may otherwise be optionally included on the first line of the file to denote this format. The number of particles is rounded to the nearest integer calculated from the total initial material of the materials present in the particles and the size of these particles.

3.4 Rosin-Rammler particle size distribution

A powder can be defined to have a particle size distribution as defined by a Rosin-Rammler function using the fourth file format. In this format, the word “Rosin-Rammler” (without the quotes) is given on the first line. The median diameter of the distribution (dm) is given on the second line. The distribution width is given on the third line of the file (wd). The fraction (f) of the powder below a certain diameter (d) is given by the function below.

(1)

The list of diameters at which the fractions are to be calculated are then listed on different lines on the input. The diameters can be listed in any order. The fraction below the smallest diameter is assumed to be zero and that below the largest diameters is assumed to be 100%. The distribution is assumed to be linear between the listed diameters.

4 Example setup of a ModelGrain in the XML file

The following XML block shows the setup of a ModelGrain the XML input file.

  1. <modelGrain name="myGrain">

  2. <layer>myInnermostMaterial</layer>

  3. <layer>mySecondMaterial</layer>

  4. <layer>myThirdMaterial</layer>

  5. <filePSD>psdfile.txt</filePSD>

  6. </modelGrain>