Iso-Surface mesh for specific geometry
 

hello,

in the file attached there's the geometry I'm working with, its a part of a 3D shell and tube with phase changing material (marked in green) what's shown in the picture is the geometry in YX plane and its length is across the Z axis. what I'm trying to figure out is how i can see a contour of the melting/solidification on the black line marked (or something like it) where it goes through all the length of the geometry. is it possible to do this with Iso-Surface? the axis is defined to be the center of the arc of the tube.

I don't know the way other than dividing your domain with 3D surface in advance
so later you may select it in the list of available surfaces to plot contour