I am not familiar with using soldering to repair Stainless steel tubular heat exchangers, but we regularly TIG weld T-304 and T-316 stainless steel tubing in the food industry.
I would think you could also TIG weld T-347 SS, but have no experience with this alloy. It maybe that you will need...
I think you are asking about counter current flow (Flow of each fluid across the heat transfer surface is in opposite direction)
as opposed to Con-current flow (Both flows in same direction).
Counter Current flow is generally MUCH more efficient as there is a larger LMTD (Log Mean Temperature...
I am running Autocad 2005 using a Cal-Comp Drawing Tablet III with a 16-button cursor mouse, as well as a Logitec cordless mouseman wheel mouse. So yours can probably be made to work. I do remember something about the Calcomp drivers not being available much longer.
What version of Autocad did...