What should be the minimum size of the passive scalar source? Is meshing have affect on the passive scalar source? Does the size of the passive scalar source affect the concentration in the study domain?
There shouldn’t be an explicit minimum size for a passive scalar source, as long as you can capture it reasonably with the mesh. So yes, the mesh has an indirect impact on scalar sources, in case your mesh is too poor/coarse around the source.
On your last question: it could, because a larger source is going to generate more scalar. This project might give you more insights: SimScale
Sir, can you provide me the example from passive scalar source in term of mg/s or Kg/s (flux).
Can we measure mole fraction in simscale or not?
Passive scalars don’t have any units linked to them. If you assume a unit (units of concentration work best) and keep the assumption consistent in the rest of the setup and post-processing, then you are good to go.
Essentially, if your unit of interest is a concentration, then it should work. This paragraph from another public project description might be interesting.