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COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

(OP)
My company is working on a project to develop a methodology of accurately measuring the wetted surface on the upper spring line of a large (i.e., 130’ diameter) cylindrical metal container with a domed top; that is, the spring line represents the departure or aperture of the domed top to the vertical sides of the cylinder. There will be a water source delivering 400-500 gallons per minute on the top of the dome, when required to keep the container cool. The measurement of the wetted surface is to ensure that the water distribution system on the dome is effective at covering the required amount of surface to meet the design cooling requirements. The desired measurement technique/methodology needs to be low tech, and repeatable. I am looking for a coating or paint that could be applied at the spring line, which when wet, changes color and when dry or drier, changes back.

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

Presumably, you need this to be reversible, i.e., it needs to go back to a "dry" indication state. Most such indicators are single-use, and are not reversible. Relative humidity stickers are reversible, but require baking to get back to the dry state.

Have you considered using liquid crystal thermometers?

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

It's fairly easy to see a difference in a grey primer coat, from wet (darker) to dry (lighter).

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

My original post was truncated. Here is what I meant to add.

Reversible color indicating dessicants (e.g. Drierite) use cobalt chloride. I imagine that this mineral could be added to a clear paint or even an adhesive, give it a try.

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

Drierite and other desiccants require a certain amount of heat and dry atmosphere to regenerate, which might be difficult to achieve in-situ.

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

Most things that change colour on contact with water, also change colour on contact with water vapour, so you're out of luck.

If you're concerned about temperature, measure temperature. There are liquid crystal filled paints which change colour with temperature- very spendy, not very good, but available.

There are also pH indicating paints, which may vary between the pH of the wetting water and of steam condensate.

RE: COATING/PAINT THAT CHANGES COLOR WHEN WET; REVERTS WHEN DRY

Ever see the beer glasses that change appearance with the presence of condensation? Google thermochromic and hydrochromic inks and paints.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

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