The problem is not easy, and you have some work to do.nFirst, I think you meant periodic temperature or periodic heat flux on the walls, not periodic flow. Is this right? If yes, you can use expression to set this. Don't choose periodic boundarynSecond, For Rohsenow correlation, Fluent allows you to enter UDF for the convection coefficient of heat transfer. So, you need to divide the equation by (A *DELTA_T) and write user defined function to enter the rest .. this will not be easy because you will use many macros to get the properties and the flow conditions. Good Luck!nn