How does the induction cooker work?why aluminium pot does not work ?


by magnetar
Tags: aluminium, cooker, induction, work, workwhy
magnetar
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#1
Aug27-08, 09:49 PM
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How does the induction cooker work?why aluminium pot does not work?








Thank you in advance
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mgb_phys
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Aug27-08, 10:03 PM
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It's an eletro-magnet. The field changes very quickly (20-30KHz) each cycle magnetises and demagnetises the pan, each cycle loses some energy - which goes into heating the food.
It is possible to heat aluminium with an inductor but it is less effective and needs a different frequency - I woked on a system that would heat coffee/ready meals with an Aluminium film inside the packaging and an inductor pad on the counter.
jaseh86
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#3
Aug28-08, 12:12 AM
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In addition to hysteresis heat loss as mentioned by mgb_phys, heating occurs due to electrical resistance and eddy currents.

Changing the direction of the magnetic field passing through the cookware induces little so called 'eddy currents' which are circular loops of current due to the effect of electromagnetic induction (see Faraday's Law). In a metal with resistance, the eddy currents dissipate to produce heat because electrons collide with the metal lattice (see Joule heating).

But like mgb_phys said, there is no reason why aluminium wouldn't work. Where did you hear that?

mgb_phys
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Aug28-08, 08:28 AM
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How does the induction cooker work?why aluminium pot does not work ?


Quote Quote by jaseh86 View Post
In addition to hysteresis heat loss as mentioned by mgb_phys, heating occurs due to electrical resistance and eddy currents.
I forgot the numbers but it's largely hysteresis.

But like mgb_phys said, there is no reason why aluminium wouldn't work. Where did you hear that?
The instruction with most domestic cookers tell you to only use magnetic pans. In fact some even have a magnet sensor as a safety feature and will only turn on with a steel/iron pan present.
Topher925
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#5
Aug28-08, 01:25 PM
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This method of heating stuff is called "Induction Heating" and is not only used in cooking but widely used in manufacturing as well. http://en.wikipedia.org/wiki/Induction_heating
jaseh86
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#6
Aug28-08, 07:33 PM
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Quote Quote by mgb_phys View Post
I forgot the numbers but it's largely hysteresis.


The instruction with most domestic cookers tell you to only use magnetic pans. In fact some even have a magnet sensor as a safety feature and will only turn on with a steel/iron pan present.
Ah okay. I didn't know that. So is it actually unsafe to use aluminium or is it just an issue of magnetisation efficiency?
mgb_phys
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Aug28-08, 07:42 PM
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It's safe - but it's likely that it will have no heating effect at the frequencies used.
vijayradnus
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#8
Nov27-08, 11:33 AM
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Quote Quote by mgb_phys View Post
It's safe - but it's likely that it will have no heating effect at the frequencies used.
Just to introdce something new

I have a doubt in all these?

If Aluminium wont work if it is non-magnetic why does Stainless steel? Is it because it is almost Steel?

Also if I earth a ferromagnetic vessel on the top of an induction stove, what will happen?
mgb_phys
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Nov27-08, 12:04 PM
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Quote Quote by vijayradnus View Post
If Aluminium wont work if it is non-magnetic why does Stainless steel? Is it because it is almost Steel?
Domestic induction hobs mostly rely on magnetic hysterisis, as I said you can use eddy currents for heating Aluminium (or indeed Iron) but the frequency is different and it's not as efficent.
Stainless will work, although non-magnetic stainless is much less efficent.
In practice most high quailty stainless pans are 300 series steel (low magnetic / high corrosion resistance) and have a copper base which is not at all magnetic and so don't work on induction hobs.
The copper base is because the thermal conductivity of stainless is low.

Also if I earth a ferromagnetic vessel on the top of an induction stove, what will happen?
If it is heating by eddy currents and you provided a low enough impedance earth (think busbar or welding cable rather than regular electrical wiring) it would reduce the heating, it would have no real effect on magnetic hysterisis.
Phrak
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#10
Nov27-08, 09:43 PM
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Quote Quote by vijayradnus View Post
Also if I earth a ferromagnetic vessel on the top of an induction stove, what will happen?
No current will flow in the ground wire. It's not absolutely zero, but close enough. More than one ground connection with fractional or whole turns around the geometric axis of the magnetic field will cause currents to be induced in the grounds.

mgb. It's likely turn-on is prevented against the low load condition presented by resistive-only loads to protect the silicon drivers, rather than the safety of the operator.
mgb_phys
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Nov29-08, 01:08 PM
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Quote Quote by Phrak View Post
mgb. It's likely turn-on is prevented against the low load condition presented by resistive-only loads to protect the silicon drivers, rather than the safety of the operator.
Yes the safety of the hob was what I meant.
Some even sense the resistivity change in the pan and use this as a thermostat.
Phrak
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#12
Nov29-08, 06:19 PM
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Quote Quote by mgb_phys View Post
Yes the safety of the hob was what I meant.
Some even sense the resistivity change in the pan and use this as a thermostat.
Ah, I should have known. I once spoke to a technician who had been involved in designing MGBT drive circuits for stoves. I never could get much out of him, seeming that he troubleshoot by devining rod.
But this is beginning to sound suspiciously like your forte.


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