Help with Induction heating for steam

[jacobjacob]

Hi,

I'm working on a project that would require the ability to heat water into steam via electric induction, preferably DC or via AC converter if necessary.

I'm thinking a monotube design with an induction coil surrounding it that could produce steam from 2 quarts of water in say 30 seconds or less.

Anyone here have experience with that kind of design?

Thanks,

[engineerscott]

Is it a requirement that you must use induction heating for your project? It really offers little or no advantage in your application.

First a little clarification, you can not heat water to steam directly via induction heating. Induction heating is a method whereby some ferromagnetic material (iron, steel, nickel, etc.) is subjected to an alternating magnetic flux which is generated by an AC voltage and induction coil (there is no such thing as DC induction heating). The mechanism of heating is eddy currents induced into the ferromagnetic magnetic material. Water would be place in a ferromagnetic container (stainless steel would work nicely). Induction heating would heat the container which would in turn heat the water, eventually producing steam.

Some modern stoves use induction heating. Typically a steel pot is placed on a stove top which has an induction coil beneath it. Low voltage, high current AC is used to induce an alternating magnetic field into the steel of the pot. Eddy currents traveling in the steel result in heating via normal I^2 * R power dissipation (there is also some heat generated via magnetic hysteresis but its contribution is normally small). In this application, the advantage over normal electric heating elements is that the stove top is not hot once you remove the pot and it is somewhat more efficient (though not dramatically).

In a closed system steam generator you would have some ferromagnetic container (steel most likely) that you would heat via magnetic induction. The advantage of the stove top example where you can remove the pot and the surface will remain relatively cool is probably a moot point since you are unlikely to take it apart. The efficiency advantage would also be much less since one would assume that the container would have good thermal insulation from the environment. Normal resistive heating would work well in this application since you will need more hardware (probably at least a large step down transformer capable of suppling fairly high current on the secondary) to do the induction. The transformer is likely to be fairly large operating at 60Hz. You could do a high frequency switcher which would be much smaller and more efficient but you would need a pretty decent understanding of electronics to design such a system.

[kristiamy]

Definitely use a single tube. I would use one with vanes on the inside to maximize surface area between the water and the metal.

Get a copy of Davies & Simpson's Induction Heating Handbook through interlibrary-loan.

See also: Induction Heating