Capillary Action

I would assume capillary action. If you do not want it to happen you can widen the tube to lessen the effect or maybe use a material or coating that is hydrophobic to prevent the tube from filling so much or at all.

What's the purpose of the small diameter tube and what is the other end used for? What is the purpose of the wire inside the tube? What is the ID of the tube? Are you getting a pressure difference here or is it pure capillary action? That is the question. Maybe we can offer better suggestions with the answers to these questions.

Simply seal the tube at the top (presumably where the wire enters the tube), then air pressure will prevent (almost) the liquid from entering the tube.

The rising of the liquid depends on many factors. The kind of metal wire... the diameter of the tube etc. I dont know what u intend to use the tube for. I would suggest that u try to seal off the opposite end as a part odff your mechanical structural design. That will prevent any water rise nomatter what the reason for its rising.

Looks like capillary action. As not enough information is given, the only solution that comes to mind is to increase the tube section. If you need more help. give us more info.

Wangito.

Look! I have not tried this for myself so i cannot say really. But one thing is.... If it is purely capillary action, then, it will be solved by applying a hydrophobic layer on the inner usrface of the tube and the outer surface of the wire.

The interesting thing is... I feel that it is not just capillary action but also some pressure of the liquid being filled that causes the liquid to rise into the tube. Sealing can solve that. Also if sealing is not possible then... like u wer told above, you may widen the diameter of the tube.

Cheers!

Thanks for all the feedback.

The tube has an ID of .050" (1.25mm). It is about 2 inches long but is actually bent into a "U" shape. One end hangs down a few mms lower than the other.

The wire is a about 2 mils thick and is a platinum alloy.

The final product is an S type thermocouple. The actual liquid is a potting cement, but this capillary action can be observed using water and the wire need not be present.

Closing one or both end is a possible solution.

What hydrophobic coatings are the that can be applied inside the tube, that would not affect the normal function of this sensor, i.e. read temperature in 3000 degree Fahrenheit molten metal?

Your wise advice is greatly appreciated.

Tell me the nature of the liquid you are using. The exact concentration and purity. I may be able to help you find a suitable hydrophobic substance. Also if you could attach a diagram and details of what the other elements are....

Just the composition of the liquid would also do.

Do try the sealing off of both sides. It will also protect your system.

The final potting cement is calcium aluminate with DI water, some alumina, silica and other proprietary dispersants and retarders that I can not divulge. This is a high temperature refractory cement.

This happens with tap water or DI water and since the liquid part of my potting cement is water if a hydrophic treatment would work with work DI water it should work with the potting cement.

OK I looked at a few chemicals in the idustrial sector but couldnt really come up with any specific substance that will effectively reduce the problem.

Maybe someone more qualified and experienced in that particular feild may help. Though I strongly feel that sealing the tube will do the trick!

I doubt you will need anything else.

Try it!

Then again, There is always vaseline.

I can not introduce anything combustible since this thermocouple will always see close to 3000 degrees Fahrenheit.

You could go in for high temperature resistant resin coatings. Many kinds are available and you may be able to choose one suitable for u. It seems like the best option.

It just occured to me, You could reduce the diameter of the tube that is approaching the liquid. Make up for the loss in diameter by increasing the length of the tube. It may improve the setup.

Then seal off if possible.

Most probably you wouldnt require any coating.

(This coating may reduce the thermocouple efficiency nomatter how inert it is.)