REQUEST FOR SUPPORT I am a PhD student at the department of chemical engineering, University College London (UCL). I am working on the investigation of aggregation and breakage of dense fluidized powders via hybrid CFD and population balance modelling (PBM). I am using ANSYS FLUENT 17.2 for my DQMOM simulations. However, I have encountered some issues which require clarification and support. Initializing the sizes of the secondary phases. The initial diameter of the three secondary phases I am considering are 174, 263 and 409 microns and their initial volume fractions are 0.196, 0.229, and 0.205 respectively. Using these initial values I calculated the initial first six moments (moments are size based) and they gave the following: M0 1.00821904E+11 M1 2.10275304E+07 M2 4.77155758E+03 M3 1.20321137E+00 M4 3.40291094E-04 M5 1.07078940E-07 I used these values to generate the DQMOM values using an Overall moments file format (as reported on pg.39 of the ANSYS FLUENT PBM Manual) and obtained the length, volume fraction and DQMOM-m4 initial values for the three quadrature points QP0, QP1 and QP2 which I also used in the initial fields while specifying boundary conditions. See table below for DQMOM generated values.
The values of the volume fraction and length generated from the Overall Moments’ file coincides with the initial diameters and volume fraction of the three secondary phases. The settings for the Max Diameter, Min Diameter, Reference length and other PBM parameters set as shown below:
Figure 1: Parameters and Phenomena settings Sauter Mean Diameter was selected for each of the secondary phases. Bed height and volume fraction were initialized using UDFs. Initially, I ran the bed with a time step size of 0.0001s and for 1 time step, to check if the bed initialized properly before running my simulation with an extended time step. The diameter of the solid phases at 0.0001s, 3s and 5s are shown in the figures below for each of the phases:
Solid Phase 1
Solid Phase 2
Solid Phase 3 We notice that the diameters did not initialize correctly as solid phase 2 and 3 are both 409 microns at 0.0001s while phase 1 is mostly 173 microns. Hence, solid phase 2 did not initialize correctly. After running the simulation for an extended time of 3 and 5 seconds, the particles of phase 1 increase in size, which is what I expected due to the settings for the kernels for an aggregation dominant case. The other phases on the other hand did not increase in size. Bed expansion was observed instead. In two other simulations, a user defined diameter and a constant value diameter were used respectively. In these simulations, we observed that although the diameters of the solid phases initialized correctly, there was no boundary to show the initial bed height. In addition, the diameters of all three solid phases stayed constant after running the simulation for 10s (See pictures below referring to both cases as they both gave similar results).
Solid Phase 1
Solid Phase 2
Solid Phase 3
Hence my questions: 1. How do I initialize the bed correctly using the sauter mean diameter option which is recommended for PBM simulations. 2. How do I set the MIN DIAMETER, MAX DIAMETER and REFERENCE LENGTH to allow for particle size change for the larger solid phases during aggregation because additional simulations run with different values for these parameters (figure 1 on pg1) initializes the bed to the new values of the min and max
diameters that was entered and an increase in size did not go beyond the value of max diameter in the setting. 3. Is it possible to get an example for the use of the population balance variable macros: C_PB_QMOMI, C_PB_QMOMI_L and C_PB_QMOMI_W like we have for the DEFINE macros for the PBM. I would like to write a UDF to retrieve the moments, abscissas and weights respectively using these macros.
Thanks in anticipation of your prompt and favourable response. Kind regards, Akpan Michael PhD Candidate Department of Chemical Engineering University College London e-mail:
[email protected] mobile: +447448427961
