HOW INDUCTON COOKING WORKS - The Physics of it.
How do we cook in our homes? Or, what is meant by "cooking" ?
We put the "raw" food in a pot and then we apply heat to that pot/cooking vessel. The pot in turn transfers the heat to the food which is then cooked. The burner in the gas stove, for example, does NOT heat the food directly but it heats the vessel only. Cooking over the direct fire is done very rarely.
So, the keyword is HEAT. How do we generate this heat? In olden days we used to burn wood (விறகு) or coal. Then we used Gas, a combustible substance. We use electricity also to generate heat.
Now we will talk about a third method:
In the year 1820 the physicist OERSTED discovered that if current is passed through a wire, magnetic field is created around the wire. This sparkling discovery led to electromagnetism and to many researches by Andre AMPERE, Micheal FARADAY, Heinrich HERTZ, MAXWELL etc physicists; in 1873 MAXWELL published his Laws on Electromagnetic Theory; his third Law states that "an electric current in a wire creates a circular magnetic field around the wire."
More research later, FARADAY said that if an electrical conductor ( a metal, say) is placed in such a magnetic field, an electric current is generated in the metal conductor. This current is known as EDDY CURRENTS. Note that the metal conductor and the magnetic-field-generator (wire) are not in contact; they are at a distance. The Eddy currents are generated by inducing (transferring) method.
Flow of electricity is just acceleration of the electrons in the metal. When electrons are moved very fast in a conductor, James Prescott JOULE said in 1841 that heat will be produced in the conductor (JOULE HEATING). The moving particles [Electrons] interact with the atomic ions of the metal and consequently heat is generated.
As per Joule's First Law, the Quantity of heat [ Q ] is proportional to the square of the current [I-squared] multiplied by the Resistance [R]. The SI unit of energy is "Joule" and one Watt is equal to one joule per second.
When charged moving particles (electrons) collide with ions, they lose some of their Kinetic Energy to the ions. The increase of the KE or the vibrational energy of the ions manifest in the form of heat. Thus the energy is transferred from the electrical supply to the conductor as heat.
We know about the two types of present cooking; INDUCTION is a third method, completely different from these. It does not GENERATE HEAT which is then TRANSFERRED to the cooking vessel, but it makes the cooking vessel itself the original GENERATOR OF HEAT.
[Microwave, an oven-only technology, is the fourth method, wherein the heat is generated DIRECTLY in THE FOOD itself]
How does an induction cooker work?
1) Current is passed through the element (coiled copper wire) under the ceramic top, and the coil/element produces electromagnetic field.
2) This field penetrates the metal of the ferrous (magnetic material) cooking vessel (pot/pan) and sets up electric current which generates heat. (EDDY CURRENT). Heat is also generated by another process called "hysteresis", which is the resistance of the ferrous material to rapid changes in magnetisation.
3) The heat generated in the pot/pan is transferred to the food.
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.
Now let us do some arithmetic.
Energy is a quantity like litres (gallons). When discussing cooking appliances, we talk of the energy flow rates - like "litres per hour or litres per minute". For gas, it is BTU per hour (British Thermal Unit or BTU.) The flow rate is BTU/hr. For electricity it is kilowatt-hours or simply kilowatts (kW).
The energy in Gas and in electricity are measured in different numbers but they measure the same thing. Like miles and kilometres for distance. we can easily convert from BTU/hr to kilowatts (or vice-versa). There are just about 3,400 BTU to a kWh--or, more exactly 3,413. (Keep in mind that a kilowatt is 1,000 watts).
Superficially, then, comparing cooking technologies looks easy: can't we just look at the rated kW or BTU/hr of cooktops, and simply convert one kind of measure to the other to compare them? No. 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 only to the actual cooking process, while induction delivers about 85 to 90 percent of its energy.
So, to see how induction compares to its only real rival, gas, we have to make the following calculation:
BTU/hr = kW x 3413 x Eind/Egas [remember one kW equals 3413 BTU]
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.
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%).
Using those values (and sparing you the in-between steps), we can say that gas-cooker BTU/hr figures equivalent to induction-cooker wattages can be reckoned as:
BTU/hr = kW x 7185 [3413 * (84/39.9) = 7185]
This is with a ferrous material for induction cooking. For other materials the figure 7185 may vary. We have used the efficiency as 84 % but many manufacturers have claimed in recent years that the efficiency has gone upto 90 %
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/hr; two medium-level burners of about 9,000 Btu/hr; and (depending on width, 30 inches or 36 inches) either one or two large burners of anywhere from 12,000 to 16,000 BTU/hr
So let's summarize by showing representative gas-power levels and their induction-power equivalents (remember, calculated quite conservatively):
Typical home stove:
small: 5,000 BTU/hr gas = 0.70 kW induction [5000 / 7185=0.70]
medium: 9,000 BTU/hr gas = 1.25 kW induction
large: 12,000 BTU/hr gas = 1.70 kW induction; 15,000 BTU/hr gas = 2.10 kW induction
The least-expensive 30-inch induction cooktop has a 1.3-kW small element (between 9,000 and 9,500 BTU/hr), [1.3 x 7185 = 9341 BTU]
Made in India Induction cooktop PRESTIGE has one 2000 W element (2kW). This will be the equivalent of 2 * 7185 = 14730 BTU/hr gas. Much higher than the largest of gas burners (12000 BTU/hr).
In sum, induction is not "as powerful as gas"-- it is miles ahead.
So now you know how induction works, and how--at least in raw cooking power -- it compares with gas.
Rajappa
17-10-2012
6 PM
*** We purchased a Prestige Induction Cooktop {photo} on Friday 26 Oct 2012. Read here.
How do we cook in our homes? Or, what is meant by "cooking" ?
We put the "raw" food in a pot and then we apply heat to that pot/cooking vessel. The pot in turn transfers the heat to the food which is then cooked. The burner in the gas stove, for example, does NOT heat the food directly but it heats the vessel only. Cooking over the direct fire is done very rarely.
So, the keyword is HEAT. How do we generate this heat? In olden days we used to burn wood (விறகு) or coal. Then we used Gas, a combustible substance. We use electricity also to generate heat.
Now we will talk about a third method:
In the year 1820 the physicist OERSTED discovered that if current is passed through a wire, magnetic field is created around the wire. This sparkling discovery led to electromagnetism and to many researches by Andre AMPERE, Micheal FARADAY, Heinrich HERTZ, MAXWELL etc physicists; in 1873 MAXWELL published his Laws on Electromagnetic Theory; his third Law states that "an electric current in a wire creates a circular magnetic field around the wire."
More research later, FARADAY said that if an electrical conductor ( a metal, say) is placed in such a magnetic field, an electric current is generated in the metal conductor. This current is known as EDDY CURRENTS. Note that the metal conductor and the magnetic-field-generator (wire) are not in contact; they are at a distance. The Eddy currents are generated by inducing (transferring) method.
Flow of electricity is just acceleration of the electrons in the metal. When electrons are moved very fast in a conductor, James Prescott JOULE said in 1841 that heat will be produced in the conductor (JOULE HEATING). The moving particles [Electrons] interact with the atomic ions of the metal and consequently heat is generated.
As per Joule's First Law, the Quantity of heat [ Q ] is proportional to the square of the current [I-squared] multiplied by the Resistance [R]. The SI unit of energy is "Joule" and one Watt is equal to one joule per second.
When charged moving particles (electrons) collide with ions, they lose some of their Kinetic Energy to the ions. The increase of the KE or the vibrational energy of the ions manifest in the form of heat. Thus the energy is transferred from the electrical supply to the conductor as heat.
We know about the two types of present cooking; INDUCTION is a third method, completely different from these. It does not GENERATE HEAT which is then TRANSFERRED to the cooking vessel, but it makes the cooking vessel itself the original GENERATOR OF HEAT.
[Microwave, an oven-only technology, is the fourth method, wherein the heat is generated DIRECTLY in THE FOOD itself]
How does an induction cooker work?
1) Current is passed through the element (coiled copper wire) under the ceramic top, and the coil/element produces electromagnetic field.
2) This field penetrates the metal of the ferrous (magnetic material) cooking vessel (pot/pan) and sets up electric current which generates heat. (EDDY CURRENT). Heat is also generated by another process called "hysteresis", which is the resistance of the ferrous material to rapid changes in magnetisation.
3) The heat generated in the pot/pan is transferred to the food.
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.
Now let us do some arithmetic.
Energy is a quantity like litres (gallons). When discussing cooking appliances, we talk of the energy flow rates - like "litres per hour or litres per minute". For gas, it is BTU per hour (British Thermal Unit or BTU.) The flow rate is BTU/hr. For electricity it is kilowatt-hours or simply kilowatts (kW).
The energy in Gas and in electricity are measured in different numbers but they measure the same thing. Like miles and kilometres for distance. we can easily convert from BTU/hr to kilowatts (or vice-versa). There are just about 3,400 BTU to a kWh--or, more exactly 3,413. (Keep in mind that a kilowatt is 1,000 watts).
Superficially, then, comparing cooking technologies looks easy: can't we just look at the rated kW or BTU/hr of cooktops, and simply convert one kind of measure to the other to compare them? No. 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 only to the actual cooking process, while induction delivers about 85 to 90 percent of its energy.
So, to see how induction compares to its only real rival, gas, we have to make the following calculation:
BTU/hr = kW x 3413 x Eind/Egas [remember one kW equals 3413 BTU]
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.
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%).
Using those values (and sparing you the in-between steps), we can say that gas-cooker BTU/hr figures equivalent to induction-cooker wattages can be reckoned as:
BTU/hr = kW x 7185 [3413 * (84/39.9) = 7185]
This is with a ferrous material for induction cooking. For other materials the figure 7185 may vary. We have used the efficiency as 84 % but many manufacturers have claimed in recent years that the efficiency has gone upto 90 %
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/hr; two medium-level burners of about 9,000 Btu/hr; and (depending on width, 30 inches or 36 inches) either one or two large burners of anywhere from 12,000 to 16,000 BTU/hr
So let's summarize by showing representative gas-power levels and their induction-power equivalents (remember, calculated quite conservatively):
Typical home stove:
small: 5,000 BTU/hr gas = 0.70 kW induction [5000 / 7185=0.70]
medium: 9,000 BTU/hr gas = 1.25 kW induction
large: 12,000 BTU/hr gas = 1.70 kW induction; 15,000 BTU/hr gas = 2.10 kW induction
The least-expensive 30-inch induction cooktop has a 1.3-kW small element (between 9,000 and 9,500 BTU/hr), [1.3 x 7185 = 9341 BTU]
Made in India Induction cooktop PRESTIGE has one 2000 W element (2kW). This will be the equivalent of 2 * 7185 = 14730 BTU/hr gas. Much higher than the largest of gas burners (12000 BTU/hr).
In sum, induction is not "as powerful as gas"-- it is miles ahead.
So now you know how induction works, and how--at least in raw cooking power -- it compares with gas.
Rajappa
17-10-2012
6 PM
*** We purchased a Prestige Induction Cooktop {photo} on Friday 26 Oct 2012. Read here.
A nice post. Great work.
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