{"id":163072,"date":"2021-10-14T07:01:09","date_gmt":"2021-10-14T07:01:09","guid":{"rendered":"\/forum\/forums\/topic\/udf-for-plug-flow-reactor-change-in-concentration-with-change-in-position\/"},"modified":"2021-10-14T23:29:54","modified_gmt":"2021-10-14T23:29:54","slug":"udf-for-plug-flow-reactor-change-in-concentration-with-change-in-position","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/udf-for-plug-flow-reactor-change-in-concentration-with-change-in-position\/","title":{"rendered":"UDF for plug flow reactor, change in concentration with change in position"},"content":{"rendered":"
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Hey all,<\/p>\n

I'm new to CFD and I'm trying to write a UDF that calculates the concentration at any position as a function of its x-coordinate (for example, Ca = .5C – .1x, or dCa\/dx = -kCa). This is my first time trying to write a UDF.<\/p>\n

I think I have the right idea, but I have a feeling there's a more efficient way to do it. Do you mind looking at it and giving me some insight\/critiques? This is for the examples dCa\/dx = -kCa. I tried defining the rate in terms of the derivative of the concentration of species A as a function of time and velocity. You can ignore the real x[ND_ND].<\/p>\n

Two Questions: 1) Are we able to use the DEFINE_VR_RATE macro to define the fraction of a species, or can we only apply it to define reaction rates? 2) Would I use the begin_f_loop in this case? The reactor is supposed to be 2D. <\/p>\n

DEFINE_VR_RATE(pfr_react_rate,c,t,r,w,yi,rate,rr_t)<\/p>\n

{<\/p>\n

real x[ND_ND];  \t  \/* x[ND_ND] is a vector that holds values of face in 1, 2, or 3 dimensions *\/<\/p>\n

float k = 1; \t      \/* reaction rate constant *\/<\/p>\n

float Cao = .5;      \/* initial concentration of A *\/<\/p>\n

real Ca = ;        \/* real value of Ca concentration *\/<\/p>\n

real Y_A;         \/* mass fraction of calculated component *\/<\/p>\n

weight_A = w[0];      \/* assigns the molar mass of A to the molar mass of the first species *\/<\/p>\n

real time = CURRENT_TIME; \/* variable assigned to the present simulation time *\/<\/p>\n

<\/p>\n<\/p>\n

\/* is this the right type of loop to use? *\/<\/p>\n

begin_f_loop(f,t) <\/p>\n

{<\/p>\n

Y_A = yi[0];           \/* Assigns the mass fraction of species to the first member of mass fraction array *\/<\/p>\n

Ca = Cai*exp(-k * NODE_X(node));  \/* Change in concentration as a function of x position *\/<\/p>\n

Y_A = weight_A*Ca \/C_R(c,t);   \/* This is probably unnecessary *\/<\/p>\n

rate = -k*C_U(c,t)*Ca*exp(-k * C_U(c,t) * time));  \/* This is supposed to calculate the rate as a function of velocity and time *\/<\/p>\n

}<\/p>\n

end_loop(f,t,);<\/p>\n

}<\/p>\n

<\/p>\n<\/p>\n

Thanks!<\/p>\n","protected":false},"template":"","class_list":["post-163072","topic","type-topic","status-closed","hentry","topic-tag-2d","topic-tag-ansys-student","topic-tag-cfd","topic-tag-fluent","topic-tag-udf-fluent"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t