I am running a Lagrangian particle tracking calculation in ANSYS CFX where the particle is heated by both radiation and convection heat transfer from the continuous phases and would like be able to assess how much of the heat transfer to the particle comes from radiation and how much from convection on a particle by particle
basis.
How can I do this? - KSVIHLA
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The output file does provide information on the radiation source to the particle as well as the source to due transfer of energy to the particle from the continuous phase. These are overall numbers, however, and if the particle evaporates, the reported continuous phase energy source will have the contribution from the evaporated material as well. Here's an approach which requires you loop over the particles one track at a time. 1. Define a variable which is equal to the net rate of radiation transfer to the particle multipled by the particle number rate and divided by the particle velocity. The expression for net radiative transfer to the particle is given by Eq 39 in the section of the CFX documentation on particle heat transfer. The expression used to define the variable should be equivalent to the following expression (the name of the particle material in this example is H2Ol) :pi*particle_emissivity*H2Ol.Mean Particle Diameter^2*(pi*Radiation Intensity*1.0 [sr]- stefan*fluid_refractive_index^2*H2Ol.Temperature^4)*H2Ol.Particle Number Rate/H2Ol.Velocity 2. Define a variable which is equal to the net rate of convective heat transfer to the particle multipled by the particle number rate and divided by the particle velocity. The expression for net radiative transfer to the particle is given by Eq 34 in the section of the CFX documentation on particle heat transfer. Note that the expression for the Nusselt Number is given as Eq 35. The expression used to define the variable should be equivalent to the following expression (the name of the particle material in this example is H2Ol) : pi*H2Ol.Mean Particle Diameter*Thermal Conductivity*Nu*(T - H2Ol.Temperature)/H2Ol.Velocity*H2Ol.Particle Number Rate Note that Nu depends upon the fluid Prandtl number and the particle Reynolds number based on the slip velocity between the particle and the continuous phases and needs to be defined via an appropriate expression. 2. Create a particle track object with the filter set to track and the desired track number entered. 3. Length integrate each of the variables defined above over the Particle track limited to a single track. This will give you the net rate of radiation and convective heat transfer to the particle. 4. Repeat the length integration for each of the particle tracks in the file. For a large number of particles, this is obviosuly most efficiently accomplished using a session file with embedded Perl scripting. A sample session file for a particle material named H2Ol which loops over ten individual particle tracks is attached. An image file which shows the equations for particle heat transfer is also attached. |
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