There is an error in the simulation part, couldn't solve it

I used the attached tutorial.

Hi Mohammad, and welcome to the forum!

The first error you have to solve is the most fundamental one: for a Convective Heat Transfer simulation, your model must have only one part - the one corresponding to the volume occupied by the fluid. All the other parts must be removed form the model (having previously removed their volume from the fluid region).

If you look at the tutorial, you can have a clear idea on how the model must look:

After you have fixed this, then we can check if you still get errors with the boundary condition assignments.

This what I have for the model.

Do you mean I have to remove all the boundary conditions except the inlet and outlet?

I mean, your CAD model.

Still the same issue.