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Was told to ask this here from chat.

I have 32AWG nichrome water that I want to use to heat liquids. I submerged it into water and noticed that the part outside of water is glowing red, but the part submerged is not. This is expected as the water will bring down the temperature of the submerged part.

I'm thinking of putting the wire inside something that has high heat transfer, but low conductivity so that the wire can heat more evenly inside and also provide protection from accidental contact. My questions are:

  1. What is the best material to use?
  2. Is there a better method?
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    \$\begingroup\$ Use a thick wire for the part outside of the liquid so it doesn't get (as) hot there. \$\endgroup\$ – Arsenal Sep 29 '15 at 10:07
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Usually immersion heaters have the element inside a tube of relatively large surface area and the entire element length is immersed in the liquid. The wires that come outside are much more conductive and hence heat less. The reason you want relatively low watt density at the liquid interface is to maintain enough thermal conductivity even if boiling takes place at the interface.

Here is how a commercial immersion heater is made:

enter image description here

The nichrome wire is tightly packed in with MgO ceramic powder to maintain a low thermal resistance path to the corrosion-resistance sheath.

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  • \$\begingroup\$ Ah thanks. I think I'll go look for an outer interface similar to the Incoloy Sheath. Looks like all metals are more or less conductive so most likely will have to be either high heat tolerance paint or plastic. \$\endgroup\$ – PGT Oct 4 '15 at 18:36
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High heat transfer and low conductivity doesn't match together, conductive material has good heat transfer capabilities. You can put one sleeve made of copper that conducts very well, therfore the wire inside will not heat, you have to press it on the wire. Then you cover with high temperature sleeve, one used for heating elements.

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