Hello Mohsen, I m trying to carry out a numerical study on the gas-solid flow in the riser of pressurized circulating fluidized bed unit. The experimental study is already done by my supervisor. I ve made the geometry and also applied the other boundary conditions. So now i need to write the UDFs. So sir please , if u can help me in writing those and guide me how to implement those UDFs i will be very thankful to you.