Thermally conductive corrosion resistant polymer

[ddot]

Hi all,

I am looking into the possibility of substituting a polymer material, possiblye HDPE, for titanium in a plate heat exchanger (PHE) application. The working fluids are sea water and ammonia. The approach temperature is fairly ambient and the pressure is below 200 psi. The concern I have with titanium is its cost and availability. The tradeoff I'm willing to make for a substitute is increased area requirement and possibly with lifetime. Any suggestions for a material that could work under these conditions?

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[moltenmetal]

Any of the polymers you might want to choose will probably result in a vastly larger surface area than you might get from a titanium exchanger. In and of itself, that may not be sufficient to turn you away from looking at polymer heat transfer equipment.

The absolute pressure of the two streams is one issue, but the differential pressure between the seawater and the ammonia is the key issue- there will be nothing but a sheet of plastic between the two streams. 200 psid isn't all that modest with respect to polymeric materials in pressure retaining service as opposed to polymer-lined metal components. The effective strengths of the polymeric materials decrease rapidly with modest increases in temperature, making the problem even worse.

The other issue to consider is the permeability of the chosen polymer material to ammonia- not something you would need to worry about with titanium.

 

[ddot]

Thanks for the input. One thing to note is that the 200 psi I mentioned is design pressure rather than working pressure. I've been wrestling with those issues for the past few days. It looks like HDPE and a few others might be possible. However, as you said, there are major blocks to their implementation. Been trying to contact manufacturers and understand what the real issues are, but so far I haven't been having any luck.

Thanks for the input,

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[mjh368]

just an idea

have you looked into coating a less expensive metal?
maybe a teflon,PP, or PVDF coat

 

[ddot]

Thanks for the input. I have been considering the idea of a coating, but not very seriously. Most the plates in PHEs have a thickness of less than 1 mm, so I'm not sure that the coating would make much sense unless coating was an extremely cheap procedure. Otherwise, coating would have to protect the other material from salt water corrosion (so that something like aluminum could be used on the other side). Do you happen to know anything about the procedure and cost of coatings? Also, as I implied above, if I were to use a coating on the seawater side, would the material on the other side still be affected by the seawater? I assumed that diffusion would occur and still cause corrosion. Your input is appreciated (along with any new input too)!

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[mjh368]

sorry i am just looking into some coaitng applications myself, we are not currently doing any.
custom teflon coating quotes can be easily found all over and people often will ofer a free sample. Borealis(sp?) makers of borocoat do alot in pipe coating.