Population Balance Model in Fluent - Surface area of changes due to diffusion of part

adib_mohammad · November 13, 2021, 19:24

I am trying to simulate particles motion in laminar flow using a monodisperse population balance model that uses three transport equations to track number (N_agg), surface area (A_tot), and mass of particles (C_tot). I have used three UDSs to implement the transport equations. The diffusion of particles (due to gradient of N_agg) changes N_agg, A_tot and C_tot.

The problem is that the diffusion of particles is only associated with second derivative of N_agg (d2N_agg/dx2), so the transport equation for N_agg can be expressed in UDS standard form.

BUT, the transport equation for A_tot, and C_tot does not follow the conventional form.

So, the effect of particles diffusion (due to N_agg gradient) becomes source term for A_tot and C_tot. I calculated the RHS expressions using DEFINE_SOURCE for A_tot and C_tot, but I always get diverged simulations.

I couldn't find any similar example in UDF manual.

adib_mohammad · November 14, 2021, 19:21

Any suggestions?

November 13, 2021, 19:24	Population Balance Model in Fluent - Surface area of changes due to diffusion of part	#1
adib_mohammad New Member Join Date: Jan 2015 Posts: 22 Rep Power: 11	I am trying to simulate particles motion in laminar flow using a monodisperse population balance model that uses three transport equations to track number (N_agg), surface area (A_tot), and mass of particles (C_tot). I have used three UDSs to implement the transport equations. The diffusion of particles (due to gradient of N_agg) changes N_agg, A_tot and C_tot. The problem is that the diffusion of particles is only associated with second derivative of N_agg (d2N_agg/dx2), so the transport equation for N_agg can be expressed in UDS standard form. BUT, the transport equation for A_tot, and C_tot does not follow the conventional form. So, the effect of particles diffusion (due to N_agg gradient) becomes source term for A_tot and C_tot. I calculated the RHS expressions using DEFINE_SOURCE for A_tot and C_tot, but I always get diverged simulations. I couldn't find any similar example in UDF manual.

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November 14, 2021, 19:21		#2
adib_mohammad New Member Join Date: Jan 2015 Posts: 22 Rep Power: 11	Any suggestions?