Can anyone tell me how I can use NDSolveValue to model reflective and constant heat flux boundary conditions. I am solving the heat equation. Essentially I have a PDE that is dependent on time, radius, and axial length. I want to solve it such that the spatial derivative of the temperature is equal to 0 on one boundary and equal to a constant on another boundary. Can anyone explain how I can set up NDSolveValue with these types of boundary conditions? I don't think it can be achieved using NeumannValue because that just sets the entire differential equation to a value. I have tried a lot of different approaches but nothing seems to be working for me. Can anyone please recommend a way to achieve this?