Boundary conditions to create a closed loop in comsol

Hi all,

I am trying to build a heat exchanger in comsol with fluid flowing like attached file. Velocity and pressure are given at inlet and outlet. What I need to do is to set the boundary conditions on the left, with fluid flowing from the bottom to the top.

Should I use 'Boundary similarity' to couple the velocity variable on the bottom edge to the top? But velocity is a vector, should I impose each component of velocity? And 'Boundary similarity' seems to only work when the values are the same, how can I make sure the direction of the velocity on these two boundaries are opposite?

Any leads are much appreciate!!!