Stove
From Wikipedia, the free encyclopedia
A stove is an appliance used to produce heat, either for domestic or industrial use. A stove generates heat by either the combustion of fossil fuels or by the electrical resistance of a heating element.
When used for cooking, a kitchen stove or range is a form of cooker. In industrial usage, stove may refer to the place where fuel is combusted before being fed to a large heat consumer such as an open hearth furnace.
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[edit] Development
Although a good source of light before lamps, an open fireplace is a very inefficient form of heat for two reasons. First, in order to prevent air, and therefore smoke, from spilling back into the room a large updraft pulling air (and therefore heat) out of the chimney is needed. This both pulls heat away and pulls air from the rest of the house into the fire and then up the chimney. A fireplace consumes 200 to 600 cubic feet of air per minute, more for a very large fire. A mostly closed-off fireplace, for example a modern fireplace with glass doors closed, will use 50-150 cubic feet per minute. High airflow creates a draft which pulls heated air out of the house to be replaced with cold air leaking in from the outside. Second, in an open fire some of the combustible gas coming off the wood escapes and thus does not ignite and is lost. To resolve these problems masonry heaters were developed, then metal stoves came into use in the 18th century.
[edit] Metal stoves
An early, and famous, example of a metal stove is the Franklin stove, said to have been invented by Benjamin Franklin in 1742. It had a labyrinthine path for hot exhaust gases to escape, thus allowing heat to enter the room instead of going up the chimney. The Franklin stove, however, was designed for heating, not for cooking. Benjamin Thompson at the turn to the 19th century was among the first to present a working metal kitchen stove. His Rumford fireplace used one fire to heat several pots that were also hung into holes so that they could be heated from the sides, too. It was even possible to regulate the heat individually for each hole. His stove was designed for large canteen or castle kitchens, though. It would take another 30 years until the technology had been refined and the size of the iron stove been reduced enough for domestic use. Stewart's Oberlin stove was a much more compact metal stove, patented in the U.S. in 1834. It became a huge commercial success with some 90,000 units sold in the next 30 years. In Europe, similar designs also appeared in the 1830s. In the following years, these iron stoves evolved into specialised cooking appliances with flue pipes connected to the chimney, oven holes, and installations for heating water. The originally open holes into which the pots were hung were now covered with concentric iron rings on which the pots were placed. Depending on the size of the pot or the heat needed, one could remove the inner rings.
By controlling the inflow of air to allow only what a fire needs to burn, metal stoves reduce the consumption of air to a mere 15-30 cubic feet per minute (this figure is for a modern stoves. All metal stoves operate on the principle of controlled air flow but their consumption will vary).
Modern wood stoves also increase the completeness of combustion. More expensive stoves use a catalytic converter which causes the gas and smoke particles not actually burned to combust. Other models use a design that includes firebox insulation, a large baffle to produce a longer, hotter gas flow path and pre-heating the air prior to its entering the combustion chamber.
[edit] Masonry heaters
A masonry heater is designed to allow complete combustion by burning fuels at full-temperature with no restriction of air inflow. Because the firebox is masonry (not metal) the burn temperature can increase to the point where secondary and complete combustion of the fuel takes place. These heaters capture most of the heat from the combustion and exhaust through an extended system of flues inside a large thermal mass before the exhaust is vented to the outside air. A properly fired masonry heater has little or no particulate pollution in the exhaust and does not contribute to the buildup of creosote in the heater flues or the chimney. Due to its large thermal mass the captured heat is radiated over long periods of time without the need of constant firing, and the surface temperature is generally not dangerous to touch.
In the US, the EPA created stricter emissions standards in the late 1980s. Maximum smoke output is limited to 7.5 grams per hour and some stoves achieve as little as 1 to 4 grams per hour. Put differently, this is roughly 90% less smoke than older stoves, which equates to nearly zero visible smoke from the chimney. This is largely achieved through causing the most possible material to combust, which results in a net efficiency of 60 to 70% as contrasted to zero to 30% for a fireplace. (net efficiency is the amount of heat energy transferred to the room compared to the amount contained in the wood, minus any amount central heating must work to compensate for the airflow problems described elsewhere in this article.)
Modern enclosed stoves are often built with a window to let out some light and to enable the user to view progress of the fire. Glass or semi-translucent manufactured mica are common window materials.
[edit] Gas and electric stoves
The first gas stoves were developed already in the 1820s, but these remained isolated experiments. At the World Fair in London in 1851, a gas stove was shown, but only in the 1880s did this technology start to become a commercial success. The main factor for this delay was the slow growth of the gas pipe network.
A high-end gas stove called the AGA cooker was invented in 1922 by Swedish Nobel prize winner Gustaf Dalén. It is considered to be the most efficient design and is a much sought after kitchen "must have" in certain circles—despite the hefty price tag.[citation needed] The AGA, and similar products such as the Rayburn Range are examples of always-on stoves which continue to burn fuel even when cooking is not being performed. Stoves (or ranges as they are also known) such as these are often used instead of boilers or furnaces to supply hot water and central heating to the rest of the house.
Thomas Ahearn invented the electric stove in 1892 and installed one in the Windsor Hotel in Ottawa. The electric stove was showcased at the Chicago World's Fair in 1893, where an electrified model kitchen was shown. But like the gas stove, the electrical stove had a slow start, partly due to the unstable technology, and partly because first cities and towns needed to be electrified. By the 1930s, the technology had matured and the electrical stove started to slowly replace the gas stove, especially in domestic kitchens.
Gas and electric stoves are the most common today in western countries. Both are equally mature and safe, and the choice between the two is largely a matter of personal preference and preexisting utility outlets: if a house has no gas supply, adding one just to be able to run a gas stove is an expensive endeavour. In particular, professional chefs often prefer gas cooktops, for they allow them to control the heat more finely and more quickly. On the other hand, chefs often prefer electric ovens because they tend to heat food more evenly. Today's major brands offer both gas and electric stoves, and many also offer dual-fuel stoves combining gas cooktops and electric ovens.
[edit] Modern corn, pellet or biofuel stove
A corn stove is a type of pellet stove which is a type of biofuel stove. The shelled dry kernel of corn, also called a corn pellet, creates as much heat as a wood pellet but generates more ash. "Corn pellet stoves and wood pellet stoves look the same from the outside. Since they are highly efficient, they don't need a chimney; instead they can be vented outdoors by a four-inch pipe through an outside wall and so can be located in any room in the home." [1]
A pellet stove uses small, biological fuel pellets which are renewable and very clean-burning. Home heating using a pellet stove is an alternative currently used throughout the world, with rapid growth in Europe. The pellets are made of renewable material –- typically wood sawdust or off-cuts. There are currently more than half a million homes in North America using pellet stoves for heat, and probably a similar number in Europe. The pellet stove typically uses a feed screw to transfer pellets from a storage hopper to a combustion chamber. Air is provided for the combustion by an electric blower. The ignition is automatic, using a stream of air heated by an electrical element. The rotation speed of the feeder and the fan speeds can be varied to modulate the heat output.
Other efficient stoves are based on Top Lit updraft (T-LUD) or Woodgas or Smoke Burner stove a principle applied and made popular by Dr. Thomas Reed, which use small pieces of sticks, chips of wood or shavings, leaves, etc as fuel. The efficiency is very high up to 50 percent. As compared to traditional stoves which are 5 to 15 percent on an average.[citation needed]