Hi
I copied it allright while googling for this info. Maybe it got cashed.
Anyways I am pasting the info below.
Harish.
Here's the Basic Idea
"Cooking" is the application of heat to food. Indoor cooking is almost
entirely done either in an oven or on a cooktop of some sort, though
occasionally
a grill or griddle is used.
Cooktops--which may be part of a range/oven combination or independent
built-in units (and which are known outside the U.S.A. as "hobs")--are
commonly considered
to be broadly divided into gas and electric types, but that is an
unfortunate oversimplification.
In reality, there are several very different methods of "electric" heating,
which have little in common save that their energy input is electricity.
Such
methods include, among others, coil elements (the most common and familiar
kind of "electric" cooker), halogen heaters, and induction. Further
complicating
the issue is the sad habit of referring to several very different kinds of
electric cookers collectively as "smoothtops," even though there can be
wildly
different heat sources under those smooth, glassy tops.
woman cooking over open fire
As we said, cooking is the application of heat to food. Food being prepared
in the home is very rarely if ever cooked on a rangetop except in or on a
cooking
vessel of some sort--pot, pan, whatever. Thus, the job of the cooker is not
to heat the food but to heat the cooking vessel--which in turn heats and
cooks
the food. That not only allows the convenient holding of the food--which may
be a liquid--it also allows, when we want it, a more gradual or more uniform
application of heat to the food by proper design of the cooking vessel.
Cooking has therefore always consisted in generating substantial heat in a
way and place that makes it easy to transfer most of that heat to a
conveniently
placed cooking vessel. Starting from the open fire, mankind has evolved many
ways to generate such heat. The two basic methods in modern times have been
the chemical and the electrical: one either burns some combustible
substance--such as wood, coal, or gas--or one runs an electrical current
through a resistance
element (that, for instance, is how toasters work), whether in a "coil" or,
more recently, inside a halogen-filled bulb.
Induction is a third method, completely different from all other cooking
technologies--
it does not involve generating heat which is then transferred to the cooking
vessel,
it makes the cooking vessel itself the original generator of the cooking
heat.
(Microwaving, an oven-only technology, is a fourth method, wherein the heat
is generated directly in the food itself.)
How does an induction cooker do that?
Put simply, an induction-cooker element (what on a gas stove would be called
a "burner") is a powerful, high-frequency electromagnet, with the
electromagnetism
generated by sophisticated electronics in the "element" under the unit's
ceramic surface. When a good-sized piece of magnetic material--such as, for
example,
a cast-iron skillet--is placed in the magnetic field that the element is
generating, the field transfers ("induces") energy into that metal. That
transferred
energy causes the metal--the cooking vessel--to become hot. By controlling
the strength of the electromagnetic field, we can control the amount of heat
being generated in the cooking vessel--and we can change that amount
instantaneously.
Block quote start
(To be technical, the field generates a loop current--a flow of
electricity--within the metal of which the pot or pan is made, and that
current flow through
the resistance of the metal generates heat, just as current flowing through
the resistance element of a conventional electric range's coil generates
heat;
the difference is that here, the heat is generated directly in the pot or
pan itself, not in any part of the cooker.)
Block quote end
diagram of induction process
How Induction Cooking Works:
List of 4 items
1. The element's electronics power a coil (the red lines) that produces a
high-frequency electromagnetic field (represented by the orange lines).
2. That field penetrates the metal of the ferrous (magnetic-material)
cooking vessel and sets up a circulating electric current, which generates
heat. (But
see the note below.)
3. The heat generated in the cooking vessel is transferred to the vessel's
contents.
4. Nothing outside the vessel is affected by the field--as soon as the
vessel is removed from the element, or the element turned off, heat
generation stops.
list end
(Image courtesy of Induction Cooking World)
Block quote start
(Note: the process described at #2 above is called an "eddy current"; heat
is also generated by another process called "hysteresis", which is the
resistance
of the ferrous material to rapid changes in magnetization. The relative
contributions of the two effects is highly technical, with some sources
emphasizing
one and some the other--but the general idea is unaffected: the heat is
generated in the cookware.)
Block quote end
view of element coil and electronics
(You can see what such a coil and its associated electronics looks like in
the image at the right.)
There is thus one point about induction: with current technology, induction
cookers require that all your countertop cooking vessels be of a "ferrous"
metal
(one, such as iron, that will readily sustain a magnetic field). Materials
like aluminum, copper, and pyrex are not usable on an induction cooker. But
all that means is that you need iron or steel pots and pans. And that is no
drawback in absolute terms, for it includes the best kinds of cookware in
the
world--every top line is full of cookware of all sizes and shapes suitable
for use on induction cookers (and virtually all of the lines will boast of
it,
because induction is so popular with discerning cooks). Nor do you have to
go to top-of-the-line names like All-Clad or Le Creuset, for many very
reasonably
priced cookware lines are also perfectly suited for induction cooking. But
if you are considering induction and have a lot invested, literally or
emotionally,
in non-ferrous cookware, you do need to know the facts. (Check out our page
on
Induction Cookware.)
Block quote start
(And there are now available so-called
"inductions disks"
that will allow non-ferrous cookware to be used on an induction element;
using such a disk loses many of the advantages of induction--from high
efficiency
to no waste heat--but those who want or need, say, a glass/pyrex or ceramic
pot for some special use, it is possible to use it on an induction cooktop
with such a disk.)
Block quote end
On the horizon is newer technology that will apparently work with any metal
cooking vessel, including copper and aluminum, but that technology--though
already
being used in a few units of Japanese manufacture--is probably quite a few
years away from maturity and from inclusion in most induction cookers. If
you
are interested in a new cooktop, it is, in our judgement, not worth waiting
for that technology.
Block quote start
(The trick seems to be using a significantly high-frequency field, which is
able to induce a current in any metal; ceramic and glass, however, would
still
be out of the running for cookware even when this new technology arrives--if
it ever does.)
Block quote end
An AEG MaxiSense unit
There is also now the first of the new generation of "zoneless" induction
cooktops. These essentially make the entire surface of the unit into a
cooking
area: sensors under the glass detect not only the presence of a pot or pan
or whatever, but its size and placement--and then energize only those
mini-elements
directly under the cooking vessel. You can thus put any size or shape of
vessel--from a small, traditional round pot to a gigantic griddle or
grill--down
anywhere, in any alignment, and the unit will heat it, and only it (or, of
course, seveal "its", as may be).
Block quote start
Quoting AEG's brochure: "The hob senses the size of the pan and only heats
the exact area covered by the pan. The Maxi-sense range [uses] 'flexible
sections'
to create an all-over cooking surface. Pans can be placed anywhere on the
hob as long as the section marker is covered, eliminating the restriction of
traditional specific zones [ = elements]. It does not matter how many pans
you have or what size they are, whether it is a fish kettle, a small milk
pan,
or tagine . . . ."
Block quote end
This technology has only been around since about 2006, and in fairness it
must be said that early reports on the prototypes were not all that one
might
have hoped for; De Dietrich, which is to say the Fagor Group, led then, but
the prototype as distributed for testing had problems remembering where
things
were if they were moved about any, and also with uniform heating.
Presumably, the engineers learned from what they heard, because such units
are now in
production and available (sort of--see the note below). We see, though, that
Electrolux is into this technology in a substantial way in some of their
induction
lines, such as AEG. De Dietrich calls it "Continuum", AEG calls it
"Maxi-sense" (as seen at the left). One supposes that soon everyone will
have it; we
feel it is clearly the future of induction, which in a way is to say the
future of cooking, for it won't be so long now before gas for cooking is
looked
back at in the same way we today look back on coal and wood.
Block quote start
The only lines we know of with this technology are Fagor's De Dietrich--its
premium, "upmarket" line--and Electrolux's AEG, neither of which is
regularly
distributed in North America; there is, however, one distributor in
Canada--who apparently also ships to the U.S.--who handles some parts of the
AEG line,
parts which just recently expanded from two induction units to three, the
new one being one of AEG's "zoneless" types, though one of only 6.9 kW total
and three zones (yes, Virginia, even "zoneless" units have zones) and a
somewhat strange profile, wide but shallow. We have no pricing or
availability
data.
Block quote end
There is also now such a thing as an
induction oven.
(It looks as if the usual heating coil on the base of the oven has been
replaced by a ferrous plate, which is energized to heat by embedded
induction coils
beneath it--so any sort of bakeware will work in it.) Expect to see more
such things before long.
Now Let's Take a Closer Look
woman cooking over open fire
(In this part, we use a little math--but don't shudder, it's all just
arithmetic!)
First, let's define some terms. Energy is a quantity: it's like a gallon of
water. In cooking, we aren't really concerned with actual energy--we want to
know at what rate a cooking appliance can supply energy. It's like, say, a
garden hose: if it can only produce a dribble of water, it doesn't matter to
us that if we let it run day and night we could eventually fill many
buckets. What we want to know is how forcefully that hose can spray--how
many gallons
a minute it can put out--because that's what does useful things for us in
some reasonable amount of time.
So, in discussing cooking appliances, we normally talk about energy flow
rates, which are just like the water flow rates expressed in "gallons a
minute"--that
is, we want to be able to know at what rate we can pump heat into the
cooking process. For gas, energy content (quantity) is traditionally
measured in
"British Thermal Units" (BTU), and so the flow rate of gas energy is given
in BTU/hour. For electricity, energy content is normally measured as
"kilowatt-hours"
(kWh) and the flow rate is just kilowatts (kW).
Block quote start
(Let's restate that, because it often confuses people, being sort of "upside
down". A kilowatt is not a quantity, it's a rate, like "knots" to measure
speed
at sea--there are no "knots an hour", knots are the speed, and kilowatts are
the electrical energy-flow rate. To measure total energy--as, for instance,
your electric-supply company does, to know how much to bill you--we multiply
the flow rate, kilowatts, by the time the flow ran, hours, to get
"kilowatt-hours"
of energy. So BTU/hour and kilowatts are both measures of energy flow rates,
not of energy itself.)
Block quote end
abstract design of numbers
The energy in gas and the energy in electricity just happen to be measured
in different-sized numbers, but they're measuring the same thing. It's like
miles
vs. kilometers: we can say a place is about 5 kilometers away, or that it's
a little over 3 miles away, but the actual distance we'd have to walk or
drive
is the same. We can easily convert from miles to kilometers if we know how
many of one make up the other. Likewise, we can easily convert from BTU/hour
to kilowatts (or vice-versa). There are just about 3,400 BTU to a kWh--or,
more exactly, about 3,413. (Keep in mind that a kilowatt is 1,000 watts: 1
kW
= 1000 W).
Superficially, then, comparing cooking technologies looks easy: can't we
just look at the rated kW or BTU/hour of a cooktop, and simply convert one
kind
of measure to the other to compare them? Nope. The complication is that the
various technologies are not all equally effective at converting their
energy
content into cooking heat; for example, gas delivers little more than a
third of its total energy to the actual cooking process, while induction
delivers
about 85 to 90 percent of its energy.
That means that if we have a gas cooker capable of putting out X BTU/hour,
converting that X to kilowatts does not tell the story--because a lot more
of
that X is wasted energy that doesn't do any cooking than is the case with
induction. To truly compare the cooking power of a gas cooker and an
induction
cooker, we indeed need to first convert one measure to the other, say
BTU/hour to kilowatts; but we then need to slice off from each unit's
nominal output
the amount that does not get used for cooking.
Block quote start
(Think again of garden hoses: if we have two hoses and each is getting, say,
5 gallons a minute pumped into it by the water tap it's screwed onto, are
they
the same? Not if one has a pinhole leak while the other has a gaping rip.
The amount of water that comes out the nozzle to do whatever we need done
will
differ drastically from one to the other. Induction cooking has a pinhole
leak, maybe 10% to 15% of the raw energy it takes being wasted; gas cooking
has
the whacking great rip in it, the average unit wasting over 60% of the raw
energy it consumes.)
Block quote end
So, to see how induction compares to its only real rival, gas, we have to
make the following calculation:
BTU/hour = kW x 3413 x Eind/Egas
That last term there--Eind/Egas--is simply the ratio of the two methods'
real efficiencies: Eind is the energy efficiency of a typical induction
cooker
and Egas is the energy efficiency of a typical quality gas cooker.
abstract mathematics design
The snag comes when we try to find reliable figures for those efficiencies.
It is remarkable how much misinformation there is (especially on the
internet),
largely from well-meaning but ignorant sources who do not understand the
issues, or are simply repeating what they read elsewhere (from someone else
who
does not understand the issues). For example, the energy-efficiency values
quoted by various induction-cooker makers range from a low of 83% to a high
of 90%, while values given for gas cooking run, depending on the source,
from 55% down to as little as 30%, nearly a 2:1 ratio.
Fortunately, in the last few years some standardized data from disinterested
sources have become available, so we no longer have to rely on figures from
parties with an axe to grind. The U.S. Department of Energy has
established
that the typical efficiency of induction cooktops is 84%, while that of gas
cooktops is 40% (more exactly, 39.9%)--figures right in line with the range
of claims made for each, and thus quite believable.
Using those values (and sparing you the in-between steps), we can say that
gas-cooker BTU/hour figures equivalent to induction-cooker wattages can be
reckoned
as:
BTU/hour = kW x 7185
It is worth noting that the testing method that established the induction
data used, in essence, a slab of ferrous metal as the "vessel". It reliably
established
what might be called a "baseline" efficiency, and that is why we use it
throughout in evaluating energy equivalencies. It remains as a possibility
that
particular items of induction equipment--and, for that matter, of
cookware--may be a bit more or less efficient than the baseline. There are
at least plausible
reports that some makes, coupled with some items of cookware, can achieve
true efficiences close to 90%. On this site, we do not use that value
because
we do not yet know of any definite, reliable data, but you should keep it
clear in your mind that when we discuss the gas heating-power equivalencies
of
induction units, we are using what should be considered rather conservative
numbers; chances are that many induction units are actually somewhat more
powerful
(in BTU/hour equivalents) than we set forth.
In fact, Panasonic states for several of its units that efficiency is 90%,
noting that: Heating-efficiency measurements were taken based on standards
of
the Japanese Electrical Manufacturers' Association and using a Panasonic
standard enamelled iron pot. Also: a University of Hong Kong research
product
showed induction efficiencies from 83.3% to 87.9%, numbers clearly in line
with 84% as a minimum and 90% as possible.
So How Much Power Is What?
image of balance scale with an apple and an orange
Perhaps the most useful way to use that conversion datum is to see what good
gas-cooker BTU values are and work back to what induction-cooker kW values
would have to be to correspond. But what are good gas-cooker BTU values?
Here too, opinions will vary. As a sort of baseline, we can look at what
typical
mid-line gas ranges look like. As numerous sources report, a typical
"ordinary" home gas range will usually have its burners in these power
ranges, give
or take only a little: a small burner of about 5,000 Btu/hour; two
medium-level burners of about 9,000 Btu/hour; and (depending on width, 30
inches or
36 inches) either one or two large burners of anywhere from 12,000 to 16,000
BTU/hour
woman cooking over open fire
When one moves from stock home appliances up to the deluxe level (sometimes
called "pro", though ironically the warranties for such units expressly
forbid
commercial use), gas ranges and cooktops naturally become more powerful. On
these, burner powers run up to 18,000 BTU/hour or thereabouts (one highly
regarded
specimen of this class has four 15,000-BTU/hour burners and two
18,000-BTU/hour burners). One
expert source
remarked of such gear: Most commercial-style home ranges offer 15,000 BTUs
per burner, which is perfectly adequate for most at-home cooks. You won't
always
need all that heat, but if you want to caramelize a bell pepper in seconds,
or blacken a redfish like a pro, well, you'll need all the heat you can get.
My advice: Go for the big-time BTUs (which, in the tests he was discussing,
was that 18,000 BTU/hour level).
So let's summarize by showing representative gas-power levels and their
induction-power equivalents (remember, calculated quite conservatively):
List of 2 items (contains 2 nested lists)
. Typical home stove:
List of 3 items nesting level 1
. small: 5,000 BTU/hour gas = 0.70 kW induction
. medium: 9,000 BTU/hour gas = 1.25 kW induction
. large: 12,000 BTU/hour gas = 1.70 kW induction; or 15,000 BTU/hour gas =
2.10 kW induction
list end nesting level 1
. Typical "pro style" stove:
List of 2 items nesting level 1
. medium: 15,000 BTU/hour gas = 2.10 kW induction
. large: 18,000 BTU/hour gas = 2.50 kW induction
list end nesting level 1
list end
(Even for wok cooking, the most power-hungry kind there is,
experts
consider 10,000 BTU/hour good and 12,000 BTU/hour "hot".)
So how do actual real-world, on-the-market induction cooktops stack up
against gas?
It's an almost comic mismatch. Sticking to build-in units (as opposed to
little free-standing countertop convenience units), it is difficult, perhaps
by
now impossible, to find a unit with any element having less than 1.2 kW
power--which puts the smallest induction element to be found equal to the
average
"medium" burner on a gas stove. The least-expensive 30-inch (four-element)
induction cooktop has:
List of 3 items
. a 1.3-kW small element (between 9,000 and 9,500 BTU/hour),
. two elements of 1.85 kW each (well over 13,000 BTU/hour), and
. one element of 2.4 kW (over 17,000 BTU/hour).
list end
The least-expensive 36-inch (five-element) induction cooktop has:
List of 4 items
. a 1.2-kW small element (8,500 BTU/hour),
. a medium element of 1.8 kW (13,000 BTU/hour),
. a larger element of 2.2 kW (16,000 BTU/hour),
. and two elements of 2.4 kW (over 17,000 BTU/hour).
list end
The very highest-power gas burner to be found in the residential market is
22,000 BTU/hour, and that's a sort of freak monster, whereas a 3.6-kW and
3.7-kW
element--which is around 26,000 BTU/hour of gas!--is found in many induction
cooktops. (Moreover, the elements on some induction units can share power
with one another, so that if not every element is already in use, a given
one can be "boosted" beyond its normal power level, for uses such as
bringing
a large pot of water to a boil, or pre-heating a fry skillet.)
So, in sum, induction is not "as powerful as gas"--it's miles ahead.
Block quote start
(There is, incidentally, a lesson there: even really serious cooking does
not, save for perhaps a few specialty cases, require stupendous amounts of
power,
and you should not be seduced into choosing between units sheerly on the
basis of the maximum available firepower per element. For one thing, most
units
of the same size have total maximum unit capabilities that are nearly
identical: the differences lie in how they distribute that total among the
unit's
elements, which are invariably four on a 30-inch-wide unit and five on a 36-
inch-wide unit. When a pro tells you that really "big-time" power is the
equivalent
of around 2.5 kW of induction, you should ask yourself whether getting
elements with significantly more power than that really should be a major
consideration
in your decision-making process.)
Block quote end
(There is a much more substantial discussion, which we strenuously recommend
anyone at all interested in induction-cooking equipment read, on our site
page
titled
Kitchen Electricity 101).
So now that you know how induction works, and how--at least in raw cooking
power--it compares with gas, let's go on to examine in more detail all the
The Pros and the Cons:
an honest appraisal of the advantages and disadvantages
Kitchen Electricity 101:
important things you should know about power
Replacing Existing Ranges
problems with and solutions for replacing "slide-in" range/oven combination
units
Radiation--a Hazard?
scientifically sound assessments (and no, it's not a hazard)
----- Original Message -----
From: "akhilesh" <[email protected]>
To: <[email protected]>
Sent: Tuesday, July 06, 2010 2:29 PM
Subject: Re: [AI] Induction cooker
The URL is not working sir.
Could you paste the same in your next mail?
Regards,
Akhilesh.
On 7/6/10, Kotian, H P <[email protected]> wrote:
Hello All
I just heard about this induction cooker. I am told it is available in
our
Indian market for Rs. 1,700 upwards.
I suppose it is well suited to the blind and there is good scope to make
it
talking as well.
Anyone using it? Please share your experience.
For more: http://en.wikipedia.org/wiki/Induction_cooker\
Harish Kotian
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