Inductive stove top heating

It really depends on how much water was in the pan and the power of the inverter driving the coil underneath the pan. Assuming an efficient solid state driver, perhaps 85-90% of the incoming power consumption is directly transformed into heat within a ferromagnetic pan. I've personally witnessed a 1/4" layer of water raised to a boil in a steel frying pan in less than 10 seconds via a 2 kW power inverter driving a Litz wire work coil at about 30-40 kHz. The inverter used a pair of power IGBT's to do very efficient power switching at current zero crossings. In comparison, the efficiency of a gas stove burner is typically less than 40%.

A ferromagnetic pan is placed in close proximity to the work coil (about 1/4" above it), so that most of the oscillating high frequency magnetic field couples into the steel or iron pan. The pan must be made from a magnetic iron alloy so that it will have significant hysterisis losses when driven by the high frequency field). Copper, non-magnetic stainless steel, glass or ceramic pots will not work. Because the energy is directly absorbed by the pan and immediately converted into heat IN the pan, most of the incoming wall plug power ends up directly heating the pan (and the water). Unlike with a flame or electric heater, there is relatively little power loss outside of the pan. The remaining 10-15% losses include primarily IGBT switching losses within the inverter and resistive losses within the work coil.

Here's a good overview of the induction cooking process:

http://theinductionsite.com/how-induction-works.shtml

Bert

Dsdynamics,

I recently made a similar post (http://cr4.globalspec.com/thread/28533#newcomments) to get some more information for a paper I was writing for a paper (I'm a third-year mechanical engineering student in Canada). My final paper can be found here: http://www.appropedia.org/Induction_Annealing and (hopefully) will answer your question of how induction heating works. Some other great resources include:

• http://www.inductionatmospheres.com/induction_heating.html
• http://www.ameritherm.com/aboutinduction.php?source=wp
• http://www.richieburnett.co.uk/indheat.html

A quick synopsis of how induction heating works: An alternating magnetic field induces currents in the workpiece, which heat the part by joule (resistive) heating. As you'll see in my paper, the alternating field can be established by one of two methods: (1) using an alternating current in a coil (similar to an electromagnet; this is the more common method), or (2) by using a semiconductor to develop a static/constant magnetic field in which the workpiece is rotated. In the case of boiling water, the metal pot is heated by induction (induction requires an electromagnetically conductive workpiece, otherwise no currents are generated and no heating can occur) and the water in the pot is heated by conduction (and other methods of heat transfer, from the hot pot).

Some cool videos of induction heating (including levitation melting, where the workpiece melts in mid-air, suspended in the magnetic field), can be found here:

• http://www.youtube.com/watch?v=_uHoZI-ZWyE&feature=channel_page

All the best,

-MechMatt