When and how is CFD used in reactor design?

CFD applications: complex geometries where plug flow/well-mixed assumptions fail, multiphase reactors (bubble columns, fluidized beds), mixing studies in stirred tanks, spray systems, and local phenomena (hot spots, dead zones). Approach: geometry creation, mesh generation, select turbulence model and multiphase approach (Euler-Euler, Euler-Lagrange), couple with reaction kinetics (species transport with source terms), solve energy equation for non-isothermal, and validate against experimental data. Challenges: computational cost, model parameter selection, and validation difficulty.