How to bending double tube heat exchanger

[studboltbkk]

I would like to make double tube heat exchanger for my refrigerator.
and somebody please recommend me for method to avoid inner tube crushing when bending it

 

[FredRosse]

Put larger tube over inner tube. Pack the inner tube with sand and make sure it is completely full,Cap the ends of the inner tube, then bend outer tube with tube bender or coiling machine. If you do not have tubing bender or coiling machine, then you will need to pack the annular space between the inner and outer tubes also with sand, pack and cap before bending.

Best to use Swagelok Heat Exchanger Tees or equal for this process.

 

[Compositepro]

For small tubing paraffin wax might work better than sand as a tube filler while bending.

 

[EdStainless]

You can also by low melting point metals for this (they melt in hot water).
But paraffin has always worked for me.
Just as a note, if you ever need to put tight bends in large tubes use BB's to fill them.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

Any radius you can bend the outer tube to without crushing it, the inner tube will withstand easily without crushing.

We never pack the interiors or the annulus with anything. We pick our tightest bend radius based on the outer tube. We accept quite a bit of oval its but no buckling/kinking. We bend on ordinary flat pipe cylindrical mandrels for the most part.

Don't concern yourself with the fact that the outer and inner tubes will touch at a point and the annulus won't be continuous. In our experience it does not negatively affect heat transfer in most services.