fully discreted coaxial borehole heat exchanger

Hallo,

I want to modell a fully discreted coaxial borehole heat exchanger. To model the waterflow in the tube I want to use 1D discrete elements.

Is this a right way to modell this problem?
I connect all nods within the tube (of each slice) with horizontal 1D discrete elements. And I connect all the all  slices of the heat exchanger with vertical 1D discrete elements. I do so for both the pipe-in and the pipe out, just seperated by the pipe wall between. At the bottom of the heat exchanger, where the water changes its flow direction, I connect all the nods of the entire base area with horizontal 1D discrete elements.
Is this the right way? Or should I use just one vertical 1D element with a corresponding hugher diameter?

What kind of wells (4th BC) do I need for the pipe-in (outer part of the coaxial exchanger) and for the pipe out (inner part)?
What diameter do I have to use for the vertical 1D element (if I use an element for each node)?

Thanks a lot for your answers, I also happy with comments or partial answers.

Nils

Dear Nils,

from my point of view you should use 2D vertical elements for the outer ring and a 1D vertical element for the inner pipe.
At the bottom of the BHE you can connect both units with horizontal 2D DFEs.

As boundary conditions (flow) a 2nd kind flow BC at the top of the inner pipe (inflow) and a 1st kind flow BC at the top of all nodes of the outer ring should work. For the temperature solely a 1st kind BC at the inner pipe has to be defined.

Kind regards
Wolfram