Risk of corrosion on evaporator coil

[kay86]

Hello!

I've constructed an evaporator for a cold trap project using a stainless steel pot with two copper coils, each connected to separate compressor systems. Given that copper and steel are dissimilar metals, there's a risk of galvanic corrosion. To mitigate this, I've wrapped the stainless steel pot with several layers of PET foil to insulate the two materials as you can see in the picture.

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I am aware that this reduces thermal efficiency due to the decreased contact between the copper and steel, but I hope this effect is negligible.

Is this insulation adequate? Should I consider adding an additional vapor barrier material on the outside?

Thank you!

[knighty]

is it for long tem use? if not I'd miss out the tape and go direct copper to stainless, with some sort of thermal parte between them - copper grease wuld work fine

[kay86]

yes it's for long term use, also, since it's R290, I'd really like to avoid having the evaporator leaking, even if I will put a low pressure control.

[seanf]

Would stainless coils work?

[kay86]

I have already made the coils, and I doubt I could have sourced the material. The coils needed to have an exact diameter to fit snugly against the chamber walls.

[kay86]

Also, thermal conductivity of ss is way lower than copper, so maybe copper evap + 100 micron of PET film is very close to ss evap?

[knighty]

in that case I think the coils will be fine the way they are - you just need to make sure the're wrapped as tighty as possible (really tight!)

and then insulate the whole thing

[sterl]

Key question: How Cold? If this to function full time at temperatures below freezing, its going to try to ice up. Won't matter how tight the copper is wrapped, the freeze-thaw will loosen it from the pot. If its only going to sweat, it actually will make better heat transfer operating "wet". In fact, if I was going to make the whole thing HT effective and icing resistant, I'd build a tank around it and fill the tank with an appropriate fluid; then insulate only the outside of the tank.