Induction cooking: Difference between revisions
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This form of flameless cooking has an edge over conventional gas flame and electric cookers as it provides rapid heating, vastly improved thermal efficiency, greater heat consistency,<ref>http://www.inductionatmospheres.com/advantages.html</ref> plus the same or greater degree of controllability as gas. Water in a pot begins to boil (at its contact points with the pot) in as few as 5 seconds, and then upon turning down immediately (in a second) transitions to simmering.{{Fact|date=February 2007}} |
This form of flameless cooking has an edge over conventional gas flame and electric cookers as it provides rapid heating, vastly improved thermal efficiency, greater heat consistency,<ref>http://www.inductionatmospheres.com/advantages.html</ref> plus the same or greater degree of controllability as gas. Water in a pot begins to boil (at its contact points with the pot) in as few as 5 seconds, and then upon turning down immediately (in a second) transitions to simmering.{{Fact|date=February 2007}} |
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The amount of time that it takes a pot to boil is proportional to the power or wattage that the induction hob is using |
The amount of time that it takes a pot to boil is proportional to the power or wattage that the induction hob is using. Thus, the time can be from 3 minutes to around 10 minutes for 3600 watts to 1200 watts induction hobs, much faster than conventional electric coil or radiant cookers. |
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Induction cookers are safer to use than conventional hobs because there are no open flames and the element itself |
Induction cookers are safer to use than conventional hobs because there are no open flames and the "element" itself reaches only the temperature of the cooking vessel; only the pan becomes hot. [[Robert Bosch GmbH|Bosch]] brochures, for example, show a person touching the ceramic cover to the inductor while along side is a pan of boiling water heated by the same induction source. However it must be remembered that that pan was at 100 degrees Celsius, and in deep fat frying could be as hot as 200 degrees Celsius. |
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Induction cookers are also easier to clean because the cooking surface is flat and smooth, even though it may have several zones of heating induction. In addition, food cannot burn onto the cooking surface as it is not hot. |
Induction cookers are also easier to clean because the cooking surface is flat and smooth, even though it may have several zones of heating induction. In addition, food cannot burn onto the cooking surface as it is not hot. |
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In induction cooking, Heat is generated in two ways. In [[hysteresis#Magnetic hysteresis|magnetic hysteresis]], the rapidly oscillating [[magnetic field]] causes power in the magnetic field to be converted to [[heat]] in the [[ferromagnetic]] base of the pot due to [[hysteresis]]. The amount of [[heat]] produced is proportional to the area of the hysteresis loop. This is the primary source of heat. With [[eddy current]]s, the magnetic field produces electric currents (known as eddy currents) in the metal base of the pot, and these cause [[electrical resistance|resistive]] heating of the metal. |
In induction cooking, Heat is generated in two ways. In [[hysteresis#Magnetic hysteresis|magnetic hysteresis]], the rapidly oscillating [[magnetic field]] causes power in the magnetic field to be converted to [[heat]] in the [[ferromagnetic]] base of the pot due to [[hysteresis]]. The amount of [[heat]] produced is proportional to the area of the hysteresis loop. This is the primary source of heat. With [[eddy current]]s, the magnetic field produces electric currents (known as eddy currents) in the metal base of the pot, and these cause [[electrical resistance|resistive]] heating of the metal. |
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The heat from the pot is then transferred to the food by [[heat conduction|conduction]], but very little heat is transferred to the actual stovetop. After boiling a pot of water, the surface of an induction stove is |
The heat from the pot is then transferred to the food by [[heat conduction|conduction]], but very little heat is transferred to the actual stovetop. After boiling a pot of water, the surface of an induction stove is warm to touch but not so warm as to burn or human flesh. |
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A pot or saucepan with a [[copper]] base or made of [[aluminium]] will not work on an induction cooktop. As an induction cooktop relies on the two methods itemised above to generate heat, copper and aluminium, which are not ferromagnetic materials, will perform poorly. Note that eddy currents will be generated in the copper and aluminium, but commercially available induction cooking cannot generate sufficient heat via eddy currents alone for effective heating. [[Pyrex]] glass and [[ceramic]] containers will not be heated by either method, as such containers are neither ferromagnetic, nor capable of carrying eddy currents. |
A pot or saucepan with a [[copper]] base or made of [[aluminium]] will not work on an induction cooktop. As an induction cooktop relies on the two methods itemised above to generate heat, copper and aluminium, which are not ferromagnetic materials, will perform poorly. Note that eddy currents will be generated in the copper and aluminium, but commercially available induction cooking cannot generate sufficient heat via eddy currents alone for effective heating. [[Pyrex]] glass and [[ceramic]] containers will not be heated by either method, as such containers are neither ferromagnetic, nor capable of carrying eddy currents. |
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EARLY PRODUCTION |
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The concept of using high frequency magnetic fields to cook with is an old one; first patents date from the early 20th century. |
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Modern implementation in the USA dates from the early 1970s, with work done at the Research & Development Center of Westinghouse Electric Corporation at Churchill Borough, near Pittsburgh, PA. |
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This work was first put on public display at the 1971 National Association of Home Builders convention in Houston, TX, as part of the Westinghouse Consumer Products Division display. The stand-alone single “burner” range was named the Cool Top Induction Range. It used transistors developed for automotive electronic ignition systems to drive the 25 kHz current. |
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Westinghouse decided to make a few hundred production units to further develop the market. These were named Cool Top 2 (CT2) Induction ranges. The development work was done at the same R&D location by a team led by Bill Moreland & Terry Malarkey. The ranges were priced at $1500 each. This included a set of high quality cookware made of Quadraply, a stainless steel/carbon steel/aluminum/stainless steel laminate (outside to inside). |
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Production took place in 1973 through 1975, and stopped coincidentally with Westinghouse Consumer Products Division being sold to White Consolidated Industries Inc. |
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CT2 had 4 burners of sufficient power, about 1600 thermal watts. The range top was a ceramic sheet surrounded by a stainless steel bezel upon which 4 magnetic sliders adjusted 4 matching potentiometers set below. This design, using no through-holes, made the range proof against spills. The electronic section was made in 4 identical modules. Provision was made for fan cooling of the electronics package. |
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In each of the electronics modules the 240 V 60 Hz domestic line power was converted to variable DC by a phase-controlled rectifier. This DC power was in turn converted to 25 kHz AC by 2 arrays of 6 paralleled automotive ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator of which the inductor component was the induction heating coil & its load, the cooking pan. |
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Control electronics included functions such as protection against over-heated cook-pans & overloads. Provision was made to reduce radiated electrical & magnetic fields. There was magnetic pan detection also. |
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CT2 was UL ® Listed and received FCC approval, both firsts. Numerous patents were issued. |
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Raymond Baxter demonstrated the CT2 on his BBC series, Tomorrow’s World. He showed how the CT2 could cook through a slab of ice. |
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== Vendors == |
== Vendors == |
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Revision as of 14:09, 24 May 2007
An induction cooker uses induction heating for cooking. Usually a ferromagnetic or ferrimagnetic coated pot is placed above an induction coil for the heating process to take place. This type of hob (or, in American English stove top or cooktop) does not work with non-ferromagnetic cookware, such as glass, aluminum, and most stainless steel, nor with ferromagnetic material covered with a conductive layer, such as a copper-bottomed pan.
Induction cookers are faster and more energy-efficient than traditional hobs. Additionally, the risk of accidental burning is diminished since the hob itself only gets marginally hot (due to heat conduction down from cookware), allowing direct contact with a reduced chance of harm. Also, no heat is lost to the air directly from the hob, keeping the kitchen containing the cooker cooler.
Since heat is being generated from an electric current induced by an electric coil, the range can detect when cookware is removed or its contents boil out by monitoring the resistance to the current. In theory, this creates additional functions, such as keeping a pot at minimal boil or automatically turning off when the cookware is removed.
Benefits
This form of flameless cooking has an edge over conventional gas flame and electric cookers as it provides rapid heating, vastly improved thermal efficiency, greater heat consistency,[1] plus the same or greater degree of controllability as gas. Water in a pot begins to boil (at its contact points with the pot) in as few as 5 seconds, and then upon turning down immediately (in a second) transitions to simmering.[citation needed]
The amount of time that it takes a pot to boil is proportional to the power or wattage that the induction hob is using. Thus, the time can be from 3 minutes to around 10 minutes for 3600 watts to 1200 watts induction hobs, much faster than conventional electric coil or radiant cookers.
Induction cookers are safer to use than conventional hobs because there are no open flames and the "element" itself reaches only the temperature of the cooking vessel; only the pan becomes hot. Bosch brochures, for example, show a person touching the ceramic cover to the inductor while along side is a pan of boiling water heated by the same induction source. However it must be remembered that that pan was at 100 degrees Celsius, and in deep fat frying could be as hot as 200 degrees Celsius.
Induction cookers are also easier to clean because the cooking surface is flat and smooth, even though it may have several zones of heating induction. In addition, food cannot burn onto the cooking surface as it is not hot.
Economic considerations
Induction cookers are considerably more expensive than traditional cookers, but consume half as much electricity as electric cookers and are more efficient in heat transfer, achieving an absolute efficiency of 84% in US Dept of energy tests (compared to a typical 40% for a gas cooker).[citation needed] According to CEG Electric Glass Company, "[Induction cooking] power savings of 40-70% are realistically achievable in comparison to conventional cooktops." CEG Electric Glass Company also states induction cooking has an efficiency rate of 90%, while Electric and Gas have efficiency rates of less than 50%.[2]
Common usage
Most induction cooking is done on stovetop units, which may be built into a countertop or may be a portable unit. In this style of cooking, the electromagnet is usually sealed beneath a heat-resisting glass-ceramic sheet which is easily cleaned. The pot is placed on the glass coating, and begins to heat up along with its contents. In Japan, a large percentage of rice cookers are powered by induction heating.
Heat generation
In induction cooking, Heat is generated in two ways. In magnetic hysteresis, the rapidly oscillating magnetic field causes power in the magnetic field to be converted to heat in the ferromagnetic base of the pot due to hysteresis. The amount of heat produced is proportional to the area of the hysteresis loop. This is the primary source of heat. With eddy currents, the magnetic field produces electric currents (known as eddy currents) in the metal base of the pot, and these cause resistive heating of the metal.
The heat from the pot is then transferred to the food by conduction, but very little heat is transferred to the actual stovetop. After boiling a pot of water, the surface of an induction stove is warm to touch but not so warm as to burn or human flesh.
A pot or saucepan with a copper base or made of aluminium will not work on an induction cooktop. As an induction cooktop relies on the two methods itemised above to generate heat, copper and aluminium, which are not ferromagnetic materials, will perform poorly. Note that eddy currents will be generated in the copper and aluminium, but commercially available induction cooking cannot generate sufficient heat via eddy currents alone for effective heating. Pyrex glass and ceramic containers will not be heated by either method, as such containers are neither ferromagnetic, nor capable of carrying eddy currents.
EARLY PRODUCTION
The concept of using high frequency magnetic fields to cook with is an old one; first patents date from the early 20th century.
Modern implementation in the USA dates from the early 1970s, with work done at the Research & Development Center of Westinghouse Electric Corporation at Churchill Borough, near Pittsburgh, PA.
This work was first put on public display at the 1971 National Association of Home Builders convention in Houston, TX, as part of the Westinghouse Consumer Products Division display. The stand-alone single “burner” range was named the Cool Top Induction Range. It used transistors developed for automotive electronic ignition systems to drive the 25 kHz current.
Westinghouse decided to make a few hundred production units to further develop the market. These were named Cool Top 2 (CT2) Induction ranges. The development work was done at the same R&D location by a team led by Bill Moreland & Terry Malarkey. The ranges were priced at $1500 each. This included a set of high quality cookware made of Quadraply, a stainless steel/carbon steel/aluminum/stainless steel laminate (outside to inside).
Production took place in 1973 through 1975, and stopped coincidentally with Westinghouse Consumer Products Division being sold to White Consolidated Industries Inc.
CT2 had 4 burners of sufficient power, about 1600 thermal watts. The range top was a ceramic sheet surrounded by a stainless steel bezel upon which 4 magnetic sliders adjusted 4 matching potentiometers set below. This design, using no through-holes, made the range proof against spills. The electronic section was made in 4 identical modules. Provision was made for fan cooling of the electronics package.
In each of the electronics modules the 240 V 60 Hz domestic line power was converted to variable DC by a phase-controlled rectifier. This DC power was in turn converted to 25 kHz AC by 2 arrays of 6 paralleled automotive ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator of which the inductor component was the induction heating coil & its load, the cooking pan.
Control electronics included functions such as protection against over-heated cook-pans & overloads. Provision was made to reduce radiated electrical & magnetic fields. There was magnetic pan detection also.
CT2 was UL ® Listed and received FCC approval, both firsts. Numerous patents were issued.
Raymond Baxter demonstrated the CT2 on his BBC series, Tomorrow’s World. He showed how the CT2 could cook through a slab of ice.
Vendors
Market for induction hobs is dominated by German players, such as AEG, Bosch and Siemens. The Italian firm Smeg is also a key player in this market. Prices range from about 400 to 1000 UK Pounds. In 2006, Stoves launched the UK's first domestic induction hob on a range cooker.
Taiwanese and Japanese electronics companies are the dominant players in induction cooking for East Asia. Certain companies have also started marketing in the West; such as Tatung, Sunpentown, Panasonic and Hitachi. However, their products available in Western markets are a small fraction of what is available in their home markets. Interestingly, some Japanese electronics giants only sell domestically.
Small stand-alone induction hobs are relatively inexpensive, around $150 USD. These units may run 110 volts, which is less than the typical 220 volts in Europe.
Units may have two, three, four or five induction zones, but four is the most common. Some have touch sensitive controls. Some induction stoves have a memory setting, one per hob, that is able to time the amount of heat required.
References
See also
External links
- US Department of Energy- Technical Support Document for Residential Cooking Products
- PATH Technology Inventory: Induction Cooktops
- Michigan University