Cedar Rapids Brewing Society

I've seen the hype on TV about boiling water in "seconds" with these induction hotplates. Interesting but I assume special pots are needed to make them work.

Yes, you need a layer of magnetic metal in the bottom of the pot.

I've thought about building a big coil, and dropping a cast-iron plate (or a block of magnetic stainless) in a kettle.  Never gone anywhere with the idea, though.


-Jim

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Is the cost prohibitive?

I've got a small induction plate that I use sometimes, but I've only got a couple pans that work with it.  I just haven't had the time to look into how to build a big plate.  I saw them make one on Mythbusters for making a huge amount of popcorn.

On Mon, Jun 25, 2012 at 12:05 PM, jjbuck <brew-equipment@crbeernuts.org (brew-equipment@crbeernuts.org)> wrote:

Is the cost prohibitive?

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Induction heating is just another means of energy transfer. By coupling electrical energy into the pot and directly generating heat in the body of the cooking vessel, it eliminates a thermal choke point and lowers the thermal energy transfer time constant. If you were trying to boil a cup of water, you would undoubtedly notice the pot heat up faster relative to a coil-based or flat-top electric stove. If, however, you were trying to boil 10 gallons of water, I doubt you'd see a difference, since the driving factor in that case would be the thermal mass of the water and the power level of the heating element.

From talking to a few guys at work about the topic, it's my understanding that the energy transfer mechanism in an induction heater is a combination of skin effect ohmic loss and bulk magnetic losses. If the cooker is designed to only couple energy into a ferrous plate, then you'll need to use something like a cast iron pot. That being said, if you were to design your own induction heater, you shouldn't need a pot made from a magnetically lossy material or a similar substrate with a good thermal path to your kettle. In a higher frequency induction heater, where the pot acts like a single turn loop on the secondary side of a transformer, the electric currents running through the pot will dissipate and create thermal energy in the walls of the pot. As long as it isn't a super-conductor, almost any metal will create heat nicely.

The first video, below, shows an example of melting an iron bolt (i.e. a ferrous material) with a home-made induction heater. The second video is similar, but they melt an aluminum can (i.e. a non-ferrous material). I suspect that you could build an induction heating loop to go around a stainless keg, but be prepared for an adventure. At a minimum, I would guess you'd need to set up a water cooler to dissipate the several hundred watts of heat coming from the coils, since the energy transfer probably won't be more than 90% efficient.

http://www.youtube.com/watch?v=CyG0Ri0dqI4
http://www.youtube.com/watch?v=d7DBS2Is ... ure=fvwrel

http://www.mindchallenger.com/inductionheater/

Very interesting, but like you said Dr. Paulsen, impractical for large volumes of liquid. Maybe practical for a multistep infusion, might scorch a decoction mash boil however.