Learning Forum

[SEANGHAI]

Hello! I am having a hard time to find out how to input mass flux of a species in fluent, some people told me to write UDF, then I already wrote UDF for mass flux of that species (Define_Profile(mass_y_flux..)), but I am curious that, which boundary condition should I use for the boundary that I need to input species mass flux ? Mass flux boundary condition or Wall Boundary condition? Thank you in advance for your help!n

[Rob]

It depends. Most species enter with the flow, so you set a velocity or mass flow boundary and a mass fraction for the species. n

[SEANGHAI]

Thank you for your reply! Of course, I want to input only mass flux of a species which this species will spread out to the whole domain by the velocity coming from the inlet1, but the boundary that I input mass flux of a species is the Wall Boundary condition, and its name is inlet 2. However, In the Wall BC, there is only one tap to input species, it is mass fraction, so I cannot input mass flux as I want, then, I started to write UDF and interpreted it into the mass fraction tap, and I expected that even though UDF written in mass flux was interpreted in the mass fraction tap, it will become the mass flux according to UDF, but finally it is not like that, the values calculated in the UDF became the mass fraction value as I see in the plot of mass fraction of a species. Or is it because my UDF is wrong ?nI want to confirm you that the reason why I do not use Mass flux boundary condition, because, if use it, there will be Y-velocities on the inlet 2, it is different to the real situation that velocities coming from the inlet 1(Velocity Inlet BC, velocity= 1m/s) and go through the inlet 2 to the outlet and make only X-velocities on the inlet 2, no Y-velocities, this is why I use Wall BC in stead of Mass flux BC. nPlease help me, because I have been having this problem for a few month ago, I am a University student, I have to graduate soon, but because of this problem, I cannot finish my research, then I cannot graduate as well. nPlease see the attached figures below, they are the boundary's names. And also you can see my UDF for mass flux, is it correct or not?nThe following are my UDF code for species mass flux:n#include udf.hnDEFINE_PROFILE(mass_y_flux, thread, var)n{ntface_t f;ntreal Vx;ntbegin_f_loop(f, thread) nt{nttVx = F_U(f, thread);nttF_PROFILE(f, thread, var) = (0.001) + (0.001*Vx);nt}ntend_f_loop(f,thread)n}nnAnd the following are boundary's names:n

[Rob]

Continues here /forum/discussion/20248/how-can-i-calculate-mass-flux-kg-m%C2%B2s-by-only-inputting-the-mass-fraction-of-a-species-in-fluent#latestn

[vikash kumar]

Dear CFD expert,

                                        Greetings! I am working on the interdigitated flow channel, where mating surfaces (internal)  are supposed to diffuse the liquids from one side to the other. I experimented with different boundary conditions: internal as internal, which led to merging the surfaces and making a single entity. Additionally, I made internal as wall, which prevented the liquids to cross and do diffusion is observed . I am intended to observe diffusion at mating surfaces. Could you please suggest a suitable boundary condition?

Well, After consulting the experts , I have been suggested to write UDFs with species mass flow through the porous wall.Can any one suggest on how to proceed with writing UDFs?