CHINESE COOKING: THE INDUCTION HEATER
As a recent Canadian ex-patriate, currently living in the Mysterious East, I find it interesting to note some of the technical differences between the two societies. Architecture, infrastructure, and day-to-day technology often differ in subtle ways. You may or may not be aware that China, as a developing country, has no Three-Phase electric power. Which is what, exactly?
At the conclusion of the Current Wars, at the turn of the 20th century, alternating current became the standard. What this means is that instead of a continuous supply of one-way current coming our way from the electric plant, what we have is a continual switching of the direction of current, many times every second. Imagine a clothesline as your power source, with someone tugging at the other end, only instead of a constant pull in one direction, it is continually jerked back and forth. The reasons for this are varied and technical, but ultimately it turns out to be more efficient than direct current.
But this also means that household electricity has a frequency, i.e., the number of times this directional change takes place every second. And since there is no such thing as an instantaneous change in motion, not even for the flow of electrons, there is also necessarily a moment where the flow of electricity, during each cycle (of which there are usually hundreds per second), is at a standstill. Three Phase power solves this problem with multiple wires, each carefully out of phase with the others. As the first wire begins its cycle, another wire is one-third of a cycle behind, and the other two-thirds behind. As a result, at no given time are all three sources of current at a standstill simultaneously. We have (more) continuous power.
In China, lacking this, the amount of power any given circuit system can draw on at a given time is much more limited. Less demanding appliances are necessary, and that’s one of the reasons all the cookware is based on induction heating.
The types of electric stoves, ovens, etc., which we use in the West could be properly described as conduction heaters. That is, electricity is allowed to flow through a circuit that includes the cooking appliance in question, through the filament, the part that toasts our toast, heats our pan, raises the temperature inside our oven to 350 degrees (Fahrenheit). This works because this part of the circuit has a much higher resistance, so the electrons that force their way through do a lot of colliding, a lot of rubbing as they make their way through, and friction results in the heating of the filament, which we then use to cook our food. The filament will transfer energy to our food primarily via heat conduction, either through direct contact, as on a stove, or via the air itself, in an enclosed oven.
In induction heating, a ferromagnetic pan is placed on the heater, which is itself not hot, but which provides a strong electromagnetic force. As the source is an alternating current, the magnetic field also alternates, and induces eddy currents within the pan itself, little swirling loops of moving electrons, back and forth, clockwise and counter-, resulting in the pan quickly heating itself up through its own internal friction.
Michael Faraday did a neat little experiment just over 175 years ago, where he showed that one can use a changing magnetic field to induce a current. There’s a rather elegant version of this experiment where one creates an electromagnet, creating a magnetic field which is used to induce a similar current in a second circuit that is physically unconnected to the first. This is essentially what is occurring during induction heating.
At no point is electricity conducted through the pan itself, nor is heat conducted from the surface it rests upon, into the pan. The friction and heat in the pan result directly from the eddy currents within the pan. Heat loss is much less, since only the actual cooking surface is being heated, rather than additional surfaces which would result in more wasted heat. Plus, compared with the relatively slow process of heat conduction, heating an induction cooker to the correct temperature is almost instantaneous.
This is a great example of inherent environmental limitations inspiring creative engineering. Although induction heating was developed to fill cooking needs where the power source is insufficient for normal appliances, it is by all accounts superior to traditional cooking appliances.