Pipe Flow Heat Transfer Question

Hello,

I am trying to simulate the temperature drop in water flowing through an underground copper pipe. I have access to the COMSOL laminar flow module and the Heat transfer in fluids as well as the heat transfer in solids modules. I have read that you only need to use one of the heat transfer modules as long as you define the solid and non solid regions so I am using the solids module.

I am working in 2D asymmetrical mode. I have drawn three cylinders, one for the water (initially at 20 C), one for the copper pipe (initially at 5 C), and one for the surrounding soil (initially at 5 C).

I have been trying to set the inlet temperature of the tube to be a constant 20 C using a temperature boundary condition but I am getting strange results. I initially made my pipe length 1 meter long just to see if I could get the modules working without extended computation time. When I run my simulation to steady state the outlet of the pipe, 1 meter from the inlet, approaches 5 C. This seems physically impossible. I am wondering what mistakes I could be making.

Thank You,

David