I'm studying the combustion of boron particles in a combustion chamber. Because the surface of boron particles is covered with boron oxide, the combustion of boron particles is divided into two stages, ignition stage and combustion stage. The removal of boron oxide is realized in the ignition stage, and the combustion of pure boron is realized in the combustion stage. Therefore, I need to write a DPM UDF code to define the thickness and material of boron particle oxide layer. This material can be called directly from the fluent library. How do you write a UDF code that defines the thickness and material of the multilayer particles? Look forward to your help, thank you.
Dear friend Xianju Wu
Defining the thickness and material of multilayer particles using UDF in Fluent can be achieved by using the discrete phase model (DPM) in Fluent. You can define the material properties of the boron oxide layer and the thickness of the oxide layer using a UDF.
Here's an example of how to define the thickness and material of the multilayer particles using UDF in Fluent:
DEFINE_DPM_PROPERTIES(boron_oxide_properties, cell, thread, dpm)
{
real thickness = 1e-6; // set the oxide layer thickness
real oxide_density = 2500; // set the density of the oxide layer
real oxide_specific_heat = 1000; // set the specific heat of the oxide layer
real oxide_thermal_conductivity = 0.5; // set the thermal conductivity of the oxide layer
dpm->density = (1 - thickness/dpm->diam)*dpm->material_density +
(thickness/dpm->diam)*oxide_density;
dpm->cp = (1 - thickness/dpm->diam)*dpm->material_cp +
(thickness/dpm->diam)*oxide_specific_heat;
dpm->kt = (1 - thickness/dpm->diam)*dpm->material_kt +
(thickness/dpm->diam)*oxide_thermal_conductivity;
}
In this UDF, the thickness of the oxide layer is set to 1 micrometer, and the properties of the oxide layer are defined by setting its density, specific heat, and thermal conductivity. These properties are calculated based on the thickness of the oxide layer and the properties of the boron particle.
You can use Fluent's material library to specify the material properties of the oxide layer. For example, you can define the material properties of boron oxide using the following Fluent command:
mat B2O3;
B2O3 density 2340;
B2O3 specific-heat 1096;
B2O3 conductivity 0.147;
Once you have defined the material properties of the oxide layer and the thickness of the oxide layer using the UDF, you can then use Fluent's DPM model to simulate the combustion of the boron particles.
For more information on using UDFs in Fluent, refer to the Fluent UDF Manual.
Dear my friend Kaushik Shandilya
It is a great honor for you to answer my question in time. Please forgive me for my slow reply.
After seeing your answer, I tried the UDF program of fluent. Unfortunately, I am not familiar with UDF. I have been reading the Fluent UDF Manual these days and finally got the result now.
The first thing I want to say is that my previous question may not have been clear enough, so I need to add some clarification. To do this, I drew a flowchart in the attachment.. My assumption is as follows: the material physical and chemical properties of B2O3 and B are set in fluent material library (as shown on the left of the figure), instead of being defined by UDF. Then I defined reactions in fluent's Species model→reactions (shown on the right). Finally, the function I realized with UDF is as follows: I told fluent solver that material is B when particle radius is less than the initial radius of 0.99. Here the thickness of the oxide layer (B2O3) is 0.01 initial radius.
I came up with this strategy because I'm not good at UDFs. The advantage of this strategy is that the UDF programming code is very short (as shown in the figure).
The good news is that after my study of UDF in recent days, I have gradually got familiar with it. The method I've come up with so far is to use DEFINE_PR_RATE. When the particle size is greater than 0.99R0, the combustion speed of particle surface is slower. Otherwise, the particle surface burns faster.
if (TP_MASS(tp)>TP_INIT_MASS(tp)*0.99)
{
*rr=-0.1*rate;
}
else
{
*rr=-rate;
}
Here, rate refers to the surface combustion rate of pure boron particles.
So, back to my original conundrum. The problem of how to achieve surface combustion of boron in two stages remains unsolved. Maybe the program you mentioned is useful, I haven't tried it out yet. The code you recommended to me is (mat B2O3;B2O3 density 2340;B2O3 specific-heat 1096;B2O3 conductivity 0.147;), but I don't know exactly how to implement it. Can you tell me?
Thank you again for your kind help.
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