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I am looking to use 1 foot (0.3 meters) of 32 AWG nichrome wire to dissipate roughly 20 watts of power. Assuming the wire was submersed in still transformer oil, would I be able to do this without melting the nichrome?

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  • \$\begingroup\$ It depends on the design of convection flow of circulating oil. and power density of course but thermal conductance is high. You can use vegetable oil for less smell. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 8 '19 at 4:26
  • \$\begingroup\$ @TonyStewartSunnyskyguyEE75 Assuming it is just sitting in still transformer oil, will it likely melt? \$\endgroup\$ – James Li Dec 8 '19 at 4:27
  • \$\begingroup\$ How long is the wire? \$\endgroup\$ – EasyOhm Dec 8 '19 at 4:27
  • \$\begingroup\$ @EasyOhm 1 foot long (0.3 meters) \$\endgroup\$ – James Li Dec 8 '19 at 4:28
  • \$\begingroup\$ have you tested it with water? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 8 '19 at 4:29
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Let's try to ball park this to see if it's reasonable to use only 12" of such thin wire dissipating 20W:

The surface area of your AWG32 wire is \$\pi \cdot \text {(0.008")} \cdot\$12" = 0.3\$\text{in}^2\$, so the watt density is 67W/\$\text{in}^2\$.

Maximum recommended watt density for vegetable oil with operating temperature of 400°F is 30W\$\text{in}^2\$, and even less for lubricating oils with 250°F operating temperature (more like 13-23W\$\text{in}^2\$) so I would say that you are likely well above the maximum watt density for reliable operation using transformer mineral oil.

You would be better off using a commercial cartridge heater with a much lower watt density (much more surface area but similar wattage).

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The value of flash point for transformer oil( mineral oil) is generally 140°C. This is the lowest temperature where vapours can ignite.

The melting point of NiCr is > 1200'C.

If you wanted to a 25W dummy load, use a tungsten halogen bulb. If you wantedto heat oil, do it externally.

Heating wire this thin may be explosive exceeding the flash point.

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