{"id":310582,"date":"2023-10-09T08:19:31","date_gmt":"2023-10-09T08:19:31","guid":{"rendered":"\/forum\/forums\/topic\/gradient-calculation-fuel-cell\/"},"modified":"2023-10-09T08:19:31","modified_gmt":"2023-10-09T08:19:31","slug":"gradient-calculation-fuel-cell","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/gradient-calculation-fuel-cell\/","title":{"rendered":"Gradient Calculation Fuel-Cell"},"content":{"rendered":"

Dear all, <\/p>\n

I’m currently developing a CFD-Model for a new kind of Fuel Cell using ANSYS Fluent, which is using both a PEM and an AEM Membrane. Because of this, I can’t use the PEM-Fuel Cell Model which is provided in ANSYS Fluent and instead develop a model using User Defined Functions. The Transport of the electrons is accounted for using a UDS-Scalar Transport Equation (like in the PEM-Model provided by ANSYS) which, after solving it, provides me with a potential distribution. This is the potential distribution i get at the moment: <\/p>\n

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This is comparable to potential distributions I found in the literature. (Note that I solve the equation in the Flow-channel as well, which is not physically meaningful, but I didn’t find a way around it). 
The problem I encounter is the following:  
When I calculate the current density in the Y-Direction from the potential distribution (conductivity * gradient of potential in Y- Direction). I get some weird results, as the gradient in the cells right next to the channel is much higher than for the rest. 
You can see the potential distribution in the second photo (phi_e (the first row from the right is the first row under the channel)). As well as the gradient I get (j_e). \"\"<\/p>\n

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At least to me, the difference in potential per cell in the Y-Direction for the third and 4th cell row doesn’t look high enough to explain the significant increase in the gradient, for the 4th row from the left in comparison to the third row.  
In my opinion, a possible explanations for this could be that the Calculation of the gradient of the electrical potential is wrong (I’m using the C_UDSI_G(c,t,0)[1] command to obtain the gradient in the Y-Direction). I think it is odd, that the Gradient in the Y-Direction is so much higher near the Flow-Channel, which leads me to believe that at least some information from the cells in x and z direction goes into the calculation of the gradient? Maybe for the calculation of C_UDSI_G? For spatial discretization, I use the Least Square Cell based method.  In the last photo you can see the code i currently use to calculate my gradient. <\/p>\n

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If anyone has encountered this problem before or has some insight that might be useful and can help me out, I would much appreciate it! <\/p>\n

Best regards <\/p>\n

Thore  <\/p>\n","protected":false},"template":"","class_list":["post-310582","topic","type-topic","status-closed","hentry","topic-tag-fluent-uds","topic-tag-fluent-uds-udf-1","topic-tag-fuel-cell-1","topic-tag-gradient"],"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\n\t\t\n\t\t\n\t\t