Sciencemadness Discussion Board

Is induction heating still effective with molten copper ?

brubei - 15-11-2022 at 15:00

This is not about any real project but, can we imagine a low tech heating circuit with a flow of molten copper heated by induction ?

However, one can use a similar configuration with heating a copper pipe and pumping low melting point metal (like melted sodium in nuke plants)

[Edited on 15-11-2022 by brubei]

Rainwater - 16-11-2022 at 02:50

As metals are heated their magnetic properties change, for some metals like iron, they become less influenced by the flux and produce fewer eddy currents, so theoretically there is a limit to how hot each element can be heated with this method. I think the theoretical limit for iron is somewhere around 90,000k. But as the limit is reached the energy transfer becomes less efficient. The cool thing tho, as the limit is reached other processes begin to take over and provide energy to the system.

Non-ferrous materials are commonly heated indirectly in a container that is heated by induction.
Not because the metal itself isn't heated by induction, but because the temperature where efficiency drops is lower, usually below the melting point of the material being heated.

To directly heat non-ferrous materials a more controlled frequency is required, a non-sumetrical wayform, first the flux induces small eddy currents into the material, so that the hysteresis becomes saturated, then the next section of the waveform can induce the desired eddy currents. This has been experimented with but i dont know if anyone has gotten it to work in a commercial setting.

j_sum1 - 16-11-2022 at 03:35

Isn't the induction coil made of a water-cooled copper pipe in most instances? My guess is that would make melting copper problematic.

That aside, I find the concept of liquid metal flowing through pipes just weird. Mostly because it is not what I am used to. I can handle a melt in the bottom of a crucible or flowing down an open channel, but my brain bends at the thought of it flowing like water through a pipe. Liquid copper at 1000°C+ is that unfamiliar and that far out on a limb for me, I would be really worried that I had overlooked some critical safety matter.

Junk_Enginerd - 17-11-2022 at 07:58

I've done a lot of tests and research on a hobby induction heater I'm building. The lower electrical resistivity an object has, the more problematic it becomes to heat it via induction. The coil used to transmit the energy is typically copper. Heating copper with it means you'll be right at the point where you're, best case, heating the coil as much as you're heating the object. This will obviously put a huge strain on the cooling, and the efficiency will be really poor. That said, that doesn't make it impossible. In the case of molten copper, it'll also have significantly higher resistivity than room temperature copper, so that helps too.

yobbo II - 21-11-2022 at 18:19

Also if you were using a metal container of some sort (iron/steel) to hold the copper, would the iron be inclined to dissolve into the molten copper?

[Edited on 22-11-2022 by yobbo II]

Junk_Enginerd - 16-12-2022 at 04:59

Yes. Molten copper is *very* corrosive. That said, I know steel stands up to it at least for shorter times, having melted copper in a steel crucible.