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Induction oven, ferromagnetic

by fluidistic
Tags: ferromagnetic, induction, oven
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fluidistic
#1
Jan18-13, 01:11 PM
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I do not understand why ferromagnetic materials are more easily heated by an induction oven than a non/low ferromagnetic material such as copper or aluminum.
Are Eddy currents more easily induced into a ferromagnetic material than a conductor lacking a high ferromagnetic property? Why is it so?
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Enthalpy
#2
Jan21-13, 09:38 PM
P: 661
An induction cooker for instance creates losses by magnetic hysteresis. It works only with iron pans, not copper.

Some other induction heaters are designed for other materials, work at other frequencies, and prefer simple conductive material.
fluidistic
#3
Jan23-13, 02:09 PM
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Quote Quote by Enthalpy View Post
An induction cooker for instance creates losses by magnetic hysteresis. It works only with iron pans, not copper.

Some other induction heaters are designed for other materials, work at other frequencies, and prefer simple conductive material.
According to wikipedia,
Quote Quote by wiki
In an induction cooker, a coil of copper wire is placed underneath the cooking pot. An alternating electric current flows through the coil, which produces an oscillating magnetic field. This field induces an electric current in the pot. Current flowing in the metal pot produces resistive heating which heats the food. While the current is large, it is produced by a low voltage.
and they are talking about
Quote Quote by wiki
a cooking vessel must be made of a ferromagnetic metal
.
And also
Quote Quote by wiki
Some additional heat is created by hysteresis losses in the pot due to its ferromagnetic nature, but this creates less than ten percent of the total heat generated
.
So this does not seem to be the answer. I'm still clueless as why a ferromagnetic material heats much faster than a non/low ferromagnetic material.

Enthalpy
#4
Jan23-13, 07:52 PM
P: 661
Induction oven, ferromagnetic

Possible explanations:
- Wiki botched it. It does happen.
- Losses result from induced current, but only because the skin effect increases the resistance, and the skin is made much thinner in ferromagnetic materials.
Why shouldn't you try to put some figures at it? Search for "Kelvin effect". Cookers use high frequencies, like >20kHz.
pumila
#5
Jan27-13, 05:26 PM
P: 114
Ferromagnetic materials switch their internal magnetism back and forth with every switch of the external magnetic field. However the process has hysteresis, that is it is not completely reversible. The internal magnetic domains lag behind the changing external field, so the sweep back and forth describes a hysteresis loop. The larger the area in this loop the greater the loss on each cycle. This loss turns up as heat. Look up 'hysteresis loop' for graphs and further details.

This effect does not exist in non magnetic materials.


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