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114-471: In 1873, Julius Buch planned and built a steel works near Völklingen on the banks of the Saar river. However, the steel works ceased operation only 6 years later, and were acquired by Karl Röchling. in 1881, construction on a blast furnace for producing iron began, and two years later the first smelter began operation. Four new furnaces were added between 1885 and 1893, and a coking plant was added in 1897. In 1900,

228-410: A hurricane . On astronomical scales, convection of gas and dust is thought to occur in the accretion disks of black holes , at speeds which may closely approach that of light. Thermal convection in liquids can be demonstrated by placing a heat source (for example, a Bunsen burner ) at the side of a container with a liquid. Adding a dye to the water (such as food colouring) will enable visualisation of

342-408: A steam engine replaced a horse-powered pump in 1742. Such engines were used to pump water to a reservoir above the furnace. The first engines used to blow cylinders directly was supplied by Boulton and Watt to John Wilkinson 's New Willey Furnace. This powered a cast iron blowing cylinder , which had been invented by his father Isaac Wilkinson . He patented such cylinders in 1736, to replace

456-542: A blast furnace to melt the iron and remove the gangue (impurities) unless the ore is very high quality. The oxygen blast furnace (OBF) process has been extensively studied theoretically because of the potentials of promising energy conservation and CO 2 emission reduction. This type may be the most suitable for use with CCS. The main blast furnace has of three levels; the reduction zone (523–973 K (250–700 °C; 482–1,292 °F)), slag formation zone (1,073–1,273 K (800–1,000 °C; 1,472–1,832 °F)), and

570-413: A bloomery does not. Another difference is that bloomeries operate as a batch process whereas blast furnaces operate continuously for long periods. Continuous operation is also preferred because blast furnaces are difficult to start and stop. Also, the carbon in pig iron lowers the melting point below that of steel or pure iron; in contrast, iron does not melt in a bloomery. Silica has to be removed from

684-429: A broader sense: it refers to the motion of fluid driven by density (or other property) difference. In thermodynamics , convection often refers to heat transfer by convection , where the prefixed variant Natural Convection is used to distinguish the fluid mechanics concept of Convection (covered in this article) from convective heat transfer. Some phenomena which result in an effect superficially similar to that of

798-458: A candle in a sealed space with an inlet and exhaust port. The heat from the candle will cause a strong convection current which can be demonstrated with a flow indicator, such as smoke from another candle, being released near the inlet and exhaust areas respectively. A convection cell , also known as a Bénard cell , is a characteristic fluid flow pattern in many convection systems. A rising body of fluid typically loses heat because it encounters

912-461: A colder surface. In liquid, this occurs because it exchanges heat with colder liquid through direct exchange. In the example of the Earth's atmosphere, this occurs because it radiates heat. Because of this heat loss the fluid becomes denser than the fluid underneath it, which is still rising. Since it cannot descend through the rising fluid, it moves to one side. At some distance, its downward force overcomes

1026-446: A convective cell may also be (inaccurately) referred to as a form of convection; for example, thermo-capillary convection and granular convection . Convection may happen in fluids at all scales larger than a few atoms. There are a variety of circumstances in which the forces required for convection arise, leading to different types of convection, described below. In broad terms, convection arises because of body forces acting within

1140-416: A greater variation in density between the two fluids, a larger acceleration due to gravity that drives the convection or a larger distance through the convecting medium. Natural convection will be less likely and less rapid with more rapid diffusion (thereby diffusing away the thermal gradient that is causing the convection) or a more viscous (sticky) fluid. The onset of natural convection can be determined by

1254-512: A layer of fresher water will also cause convection. Natural convection has attracted a great deal of attention from researchers because of its presence both in nature and engineering applications. In nature, convection cells formed from air raising above sunlight-warmed land or water are a major feature of all weather systems. Convection is also seen in the rising plume of hot air from fire , plate tectonics , oceanic currents ( thermohaline circulation ) and sea-wind formation (where upward convection

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1368-404: A lifting force (heat). All thunderstorms , regardless of type, go through three stages: the developing stage , the mature stage , and the dissipation stage . The average thunderstorm has a 24 km (15 mi) diameter. Depending on the conditions present in the atmosphere, these three stages take an average of 30 minutes to go through. Solar radiation affects the oceans: warm water from

1482-472: A minor branch of the industry, but Darby's son built a new furnace at nearby Horsehay, and began to supply the owners of finery forges with coke pig iron for the production of bar iron. Coke pig iron was by this time cheaper to produce than charcoal pig iron. The use of a coal-derived fuel in the iron industry was a key factor in the British Industrial Revolution . However, in many areas of

1596-450: A model factory, often as large as the church and only several feet away, and waterpower drove the machinery of the various industries located on its floor." Iron ore deposits were often donated to the monks along with forges to extract the iron, and after a time surpluses were offered for sale. The Cistercians became the leading iron producers in Champagne , France, from the mid-13th century to

1710-451: A result of physical rearrangement of denser portions of the Earth's interior toward the center of the planet (that is, a type of prolonged falling and settling). The Stack effect or chimney effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers due to buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The greater

1824-552: A role in the structure of Earth's atmosphere , its oceans , and its mantle . Discrete convective cells in the atmosphere can be identified by clouds , with stronger convection resulting in thunderstorms . Natural convection also plays a role in stellar physics . Convection is often categorised or described by the main effect causing the convective flow; for example, thermal convection. Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place. Granular convection

1938-425: A square cavity. It is differentially heated between the two vertical walls, where the left and right walls are held at 10 °C and 0 °C, respectively. The density anomaly manifests in its flow pattern. As the water is cooled at the right wall, the density increases, which accelerates the flow downward. As the flow develops and the water cools further, the decrease in density causes a recirculation current at

2052-468: Is a similar phenomenon in granular material instead of fluids. Advection is fluid motion created by velocity instead of thermal gradients. Convective heat transfer is the intentional use of convection as a method for heat transfer . Convection is a process in which heat is carried from place to place by the bulk movement of a fluid and gases. In the 1830s, in The Bridgewater Treatises ,

2166-484: Is a vertical section of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation. The Sun warms the ground, which in turn warms the air directly above it. The warmer air expands, becoming less dense than the surrounding air mass, and creating a thermal low . The mass of lighter air rises, and as it does, it cools by expansion at lower air pressures. It stops rising when it has cooled to

2280-414: Is also a unique location for international exhibitions, festivals and concerts. The Ferrodrom is an interactive science center focusing on the making of iron. Visitors can tour the production areas. Huge gas machines stand in the blower hall. They were driven by blast furnace gas and generated the wind for the blast furnaces. Parts of the blower hall are used for exhibitions today. The Völklingen Ironworks

2394-495: Is also modified by Coriolis forces ). In engineering applications, convection is commonly visualized in the formation of microstructures during the cooling of molten metals, and fluid flows around shrouded heat-dissipation fins, and solar ponds. A very common industrial application of natural convection is free air cooling without the aid of fans: this can happen on small scales (computer chips) to large scale process equipment. Natural convection will be more likely and more rapid with

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2508-613: Is also the venue for the UrbanArt Biennale . The UrbanArt Biennale is a biennial exhibition (since 2011) dealing with urban art. The aim of the Biennale is to highlight the current positions of this art movement, document its development and to give an overview of the world scene of Urban Art. In 2012, the area was the venue of electro magnetic for the first time. As part of the ‘European Festival Awards’ in Groningen, The Netherlands. It

2622-531: Is believed to have produced cast iron quite efficiently. Its date is not yet clear, but it probably did not survive until Henry VIII 's Dissolution of the Monasteries in the late 1530s, as an agreement (immediately after that) concerning the "smythes" with the Earl of Rutland in 1541 refers to blooms. Nevertheless, the means by which the blast furnace spread in medieval Europe has not finally been determined. Due to

2736-411: Is caused by a variable composition of the fluid. If the varying property is a concentration gradient, it is known as solutal convection . For example, gravitational convection can be seen in the diffusion of a source of dry salt downward into wet soil due to the buoyancy of fresh water in saline. Variable salinity in water and variable water content in air masses are frequent causes of convection in

2850-416: Is divided into a number of tectonic plates that are continuously being created and consumed at their opposite plate boundaries. Creation ( accretion ) occurs as mantle is added to the growing edges of a plate. This hot added material cools down by conduction and convection of heat. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in

2964-585: Is imposed on a ferrofluid with varying magnetic susceptibility . In the presence of a temperature gradient this results in a nonuniform magnetic body force, which leads to fluid movement. A ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field . In a zero-gravity environment, there can be no buoyancy forces, and thus no convection possible, so flames in many circumstances without gravity smother in their own waste gases. Thermal expansion and chemical reactions resulting in expansion and contraction gases allows for ventilation of

3078-544: Is located in Fengxiang County , Shaanxi (a museum exists on the site today). There is however no evidence of the bloomery in China after the appearance of the blast furnace and cast iron. In China, blast furnaces produced cast iron, which was then either converted into finished implements in a cupola furnace, or turned into wrought iron in a fining hearth. Although cast iron farm tools and weapons were widespread in China by

3192-422: Is located in the center where the plasma is hotter. The outer edge of the granules is darker due to the cooler descending plasma. A typical granule has a diameter on the order of 1,000 kilometers and each lasts 8 to 20 minutes before dissipating. Below the photosphere is a layer of much larger "supergranules" up to 30,000 kilometers in diameter, with lifespans of up to 24 hours. Water is a fluid that does not obey

3306-408: Is no convection in free-fall ( inertial ) environments, such as that of the orbiting International Space Station. Natural convection can occur when there are hot and cold regions of either air or water, because both water and air become less dense as they are heated. But, for example, in the world's oceans it also occurs due to salt water being heavier than fresh water, so a layer of salt water on top of

3420-507: Is not unlike that of a lava lamp .) This downdraft of heavy, cold and dense water becomes a part of the North Atlantic Deep Water , a south-going stream. Mantle convection is the slow creeping motion of Earth's rocky mantle caused by convection currents carrying heat from the interior of the Earth to the surface. It is one of 3 driving forces that causes tectonic plates to move around the Earth's surface. The Earth's surface

3534-458: Is possible that the technology reached Sweden by this means. The Vikings are known to have used double bellows, which greatly increases the volumetric flow of the blast. The Caspian region may also have been the source for the design of the furnace at Ferriere , described by Filarete , involving a water-powered bellows at Semogo in Valdidentro in northern Italy in 1226. In a two-stage process

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3648-478: Is to use two identical jars, one filled with hot water dyed one colour, and cold water of another colour. One jar is then temporarily sealed (for example, with a piece of card), inverted and placed on top of the other. When the card is removed, if the jar containing the warmer liquid is placed on top no convection will occur. If the jar containing colder liquid is placed on top, a convection current will form spontaneously. Convection in gases can be demonstrated using

3762-456: Is transported outward from the core region primarily by convection rather than radiation . This occurs at radii which are sufficiently opaque that convection is more efficient than radiation at transporting energy. Granules on the photosphere of the Sun are the visible tops of convection cells in the photosphere, caused by convection of plasma in the photosphere. The rising part of the granules

3876-408: Is used to make cast iron . The majority of pig iron produced by blast furnaces undergoes further processing to reduce the carbon and sulphur content and produce various grades of steel used for construction materials, automobiles, ships and machinery. Desulphurisation usually takes place during the transport of the liquid steel to the steelworks. This is done by adding calcium oxide , which reacts with

3990-509: Is wind driven: wind moving over water cools the water and also causes evaporation , leaving a saltier brine. In this process, the water becomes saltier and denser. and decreases in temperature. Once sea ice forms, salts are left out of the ice, a process known as brine exclusion. These two processes produce water that is denser and colder. The water across the northern Atlantic Ocean becomes so dense that it begins to sink down through less salty and less dense water. (This open ocean convection

4104-757: The Chinese examples, were very inefficient compared to those used today. The iron from the Lapphyttan complex was used to produce balls of wrought iron known as osmonds , and these were traded internationally – a possible reference occurs in a treaty with Novgorod from 1203 and several certain references in accounts of English customs from the 1250s and 1320s. Other furnaces of the 13th to 15th centuries have been identified in Westphalia . The technology required for blast furnaces may have either been transferred from China, or may have been an indigenous innovation. Al-Qazvini in

4218-473: The Hadley cell and the polar vortex , with the Hadley cell experiencing stronger convection due to the release of latent heat energy by condensation of water vapor at higher altitudes during cloud formation. Longitudinal circulation, on the other hand, comes about because the ocean has a higher specific heat capacity than land (and also thermal conductivity , allowing the heat to penetrate further beneath

4332-526: The Industrial Revolution . Hot blast was patented by James Beaumont Neilson at Wilsontown Ironworks in Scotland in 1828. Within a few years of the introduction, hot blast was developed to the point where fuel consumption was cut by one-third using coke or two-thirds using coal, while furnace capacity was also significantly increased. Within a few decades, the practice was to have a "stove" as large as

4446-529: The Ironbridge Gorge Museums. Cast iron from the furnace was used to make girders for the world's first cast iron bridge in 1779. The Iron Bridge crosses the River Severn at Coalbrookdale and remains in use for pedestrians. The steam engine was applied to power blast air, overcoming a shortage of water power in areas where coal and iron ore were located. This was first done at Coalbrookdale where

4560-481: The Lehigh Crane Iron Company at Catasauqua, Pennsylvania , in 1839. Anthracite use declined when very high capacity blast furnaces requiring coke were built in the 1870s. The blast furnace remains an important part of modern iron production. Modern furnaces are highly efficient, including Cowper stoves to pre-heat the blast air and employ recovery systems to extract the heat from the hot gases exiting

4674-504: The Rayleigh number ( Ra ). Differences in buoyancy within a fluid can arise for reasons other than temperature variations, in which case the fluid motion is called gravitational convection (see below). However, all types of buoyant convection, including natural convection, do not occur in microgravity environments. All require the presence of an environment which experiences g-force ( proper acceleration ). The difference of density in

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4788-855: The fuel efficiency of the bloomery and improves yield. They can also be built bigger than natural draught bloomeries. The oldest known blast furnaces in the West were built in Durstel in Switzerland , the Märkische Sauerland in Germany , and at Lapphyttan in Sweden , where the complex was active between 1205 and 1300. At Noraskog in the Swedish parish of Järnboås, traces of even earlier blast furnaces have been found, possibly from around 1100. These early blast furnaces, like

4902-430: The hydrologic cycle . For example, a foehn wind is a down-slope wind which occurs on the downwind side of a mountain range. It results from the adiabatic warming of air which has dropped most of its moisture on windward slopes. Because of the different adiabatic lapse rates of moist and dry air, the air on the leeward slopes becomes warmer than at the same height on the windward slopes. A thermal column (or thermal)

5016-459: The iron sulfide contained in the pig iron to form calcium sulfide (called lime desulfurization ). In a further process step, the so-called basic oxygen steelmaking , the carbon is oxidized by blowing oxygen onto the liquid pig iron to form crude steel . Cast iron has been found in China dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in

5130-564: The 'dwarf" blast furnaces were found in Dabieshan . In construction, they are both around the same level of technological sophistication. The effectiveness of the Chinese human and horse powered blast furnaces was enhanced during this period by the engineer Du Shi (c. AD 31), who applied the power of waterwheels to piston - bellows in forging cast iron. Early water-driven reciprocators for operating blast furnaces were built according to

5244-636: The 13th century and other travellers subsequently noted an iron industry in the Alburz Mountains to the south of the Caspian Sea . This is close to the silk route , so that the use of technology derived from China is conceivable. Much later descriptions record blast furnaces about three metres high. As the Varangian Rus' people from Scandinavia traded with the Caspian (using their Volga trade route ), it

5358-411: The 1550s, and many were built in the remainder of that century and the following ones. The output of the industry probably peaked about 1620, and was followed by a slow decline until the early 18th century. This was apparently because it was more economic to import iron from Sweden and elsewhere than to make it in some more remote British locations. Charcoal that was economically available to the industry

5472-495: The 17th century, also using the phosphate -rich slag from their furnaces as an agricultural fertilizer . Archaeologists are still discovering the extent of Cistercian technology. At Laskill , an outstation of Rievaulx Abbey and the only medieval blast furnace so far identified in Britain , the slag produced was low in iron content. Slag from other furnaces of the time contained a substantial concentration of iron, whereas Laskill

5586-479: The 4th century AD. The primary advantage of the early blast furnace was in large scale production and making iron implements more readily available to peasants. Cast iron is more brittle than wrought iron or steel, which required additional fining and then cementation or co-fusion to produce, but for menial activities such as farming it sufficed. By using the blast furnace, it was possible to produce larger quantities of tools such as ploughshares more efficiently than

5700-508: The 5th century BC , employing workforces of over 200 men in iron smelters from the 3rd century onward, the earliest blast furnaces constructed were attributed to the Han dynasty in the 1st century AD. These early furnaces had clay walls and used phosphorus -containing minerals as a flux . Chinese blast furnaces ranged from around two to ten meters in height, depending on the region. The largest ones were found in modern Sichuan and Guangdong , while

5814-460: The Boussinesq approximation. This is because its density varies nonlinearly with temperature, which causes its thermal expansion coefficient to be inconsistent near freezing temperatures. The density of water reaches a maximum at 4 °C and decreases as the temperature deviates. This phenomenon is investigated by experiment and numerical methods. Water is initially stagnant at 10 °C within

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5928-512: The Corsican, was used prior to the advent of Christianity . Examples of improved bloomeries are the Stuckofen, sometimes called wolf-furnace, which remained until the beginning of the 19th century. Instead of using natural draught, air was pumped in by a trompe , resulting in better quality iron and an increased capacity. This pumping of air in with bellows is known as cold blast , and it increases

6042-519: The Equator tends to circulate toward the poles , while cold polar water heads towards the Equator. The surface currents are initially dictated by surface wind conditions. The trade winds blow westward in the tropics, and the westerlies blow eastward at mid-latitudes. This wind pattern applies a stress to the subtropical ocean surface with negative curl across the Northern Hemisphere , and

6156-470: The Soviet Union) worked at the plant in brutal and inhumane conditions. After World War II, only minor maintenance was conducted until the plant closed in 1986 during the economic steel crisis. The ironworks retains its 1930s-era appearance today, with intact blast furnaces and the original coking plant. The Stiftung Industriekultur (Industrial Culture Foundation) was founded at the beginning of 1996 with

6270-520: The West from the High Middle Ages . They spread from the region around Namur in Wallonia (Belgium) in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal. The successful substitution of coke for charcoal is widely attributed to English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating

6384-399: The advantage of being able to treat zinc concentrates containing higher levels of lead than can electrolytic zinc plants. Convection Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid , most commonly density and gravity (see buoyancy ). When the cause of

6498-755: The aim of presenting the history of the Völklingen Ironworks and making the site culturally accessible. Meinrad Maria Grewenig was the first General Director and Managing Director of the World Cultural Heritage Site Völklingen Ironworks. Ralf Beil has been the General Director of the World Cultural Heritage Site at the Völklingen Ironworks since 1 May 2020. Today, the Völklinger Hütte is a museum and it

6612-589: The area with higher temperatures, ranging up to 1200 °C degrees, it is reduced further to iron metal: The carbon dioxide formed in this process is re-reduced to carbon monoxide by the coke : The temperature-dependent equilibrium controlling the gas atmosphere in the furnace is called the Boudouard reaction : The pig iron produced by the blast furnace has a relatively high carbon content of around 4–5% and usually contains too much sulphur, making it very brittle, and of limited immediate commercial use. Some pig iron

6726-432: The blast furnace, such as the Swedish electric blast furnace, have been developed in countries which have no native coal resources. According to Global Energy Monitor , the blast furnace is likely to become obsolete to meet climate change objectives of reducing carbon dioxide emission, but BHP disagrees. An alternative process involving direct reduced iron (DRI) is likely to succeed it, but this also needs to use

6840-475: The bloomery. In areas where quality was important, such as warfare, wrought iron and steel were preferred. Nearly all Han period weapons are made of wrought iron or steel, with the exception of axe-heads, of which many are made of cast iron. Blast furnaces were also later used to produce gunpowder weapons such as cast iron bomb shells and cast iron cannons during the Song dynasty . The simplest forge , known as

6954-435: The chimney, away from the direct influence of the fire, will also indicate a considerable increase of temperature; in this case a portion of the air, passing through and near the fire, has become heated, and has carried up the chimney the temperature acquired from the fire. There is at present no single term in our language employed to denote this third mode of the propagation of heat; but we venture to propose for that purpose,

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7068-434: The combustion air ( hot blast ), patented by Scottish inventor James Beaumont Neilson in 1828. Archaeological evidence shows that bloomeries appeared in China around 800 BC. Originally it was thought that the Chinese started casting iron right from the beginning, but this theory has since been debunked by the discovery of 'more than ten' iron digging implements found in the tomb of Duke Jing of Qin (d. 537 BC), whose tomb

7182-424: The combustion zone (1,773–1,873 K (1,500–1,600 °C; 2,732–2,912 °F)). Blast furnaces are currently rarely used in copper smelting, but modern lead smelting blast furnaces are much shorter than iron blast furnaces and are rectangular in shape. Modern lead blast furnaces are constructed using water-cooled steel or copper jackets for the walls, and have no refractory linings in the side walls. The base of

7296-488: The convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow. Convective flow may be transient (such as when a multiphase mixture of oil and water separates) or steady state (see convection cell ). The convection may be due to gravitational , electromagnetic or fictitious body forces. Heat transfer by natural convection plays

7410-475: The convection of fluid rock and molten metal within the Earth's interior (see below). Gravitational convection, like natural thermal convection, also requires a g-force environment in order to occur. Ice convection on Pluto is believed to occur in a soft mixture of nitrogen ice and carbon monoxide ice. It has also been proposed for Europa , and other bodies in the outer Solar System. Thermomagnetic convection can occur when an external magnetic field

7524-501: The early 20th century. With a shortage of labor during and after World War I, up to 1,446 people from territories occupied by Germany (with most of them from Russia and Belgium) were forced to work involuntarily at the Völklingen Ironworks between 1915 and 1918. Over 143 of these laborers died during that time. Forced labor was again used in World War II, when a total of 12,393 people (including prisoners of war and civilians deported from

7638-410: The first being that preheated air blown into the furnace reacts with the carbon in the form of coke to produce carbon monoxide and heat: Hot carbon monoxide is the reducing agent for the iron ore and reacts with the iron oxide to produce molten iron and carbon dioxide . Depending on the temperature in the different parts of the furnace (warmest at the bottom) the iron is reduced in several steps. At

7752-409: The first gas-blowing engines were introduced to the Völklingen Ironworks, making it the first large-scale ironworks to use furnace gas to operate the blast furnaces. By the 1910s, the Völklingen Ironworks was Germany's largest producer of steel beams. A large conveyor belt system was installed in the plant, and the technology used at the ironworks became a model for other factories across the world during

7866-407: The first type, plumes rise from the lower mantle, and corresponding unstable regions of lithosphere drip back into the mantle. In the second type, subducting oceanic plates (which largely constitute the upper thermal boundary layer of the mantle) plunge back into the mantle and move downwards towards the core-mantle boundary . Mantle convection occurs at rates of centimeters per year, and it takes on

7980-425: The flame, as waste gases are displaced by cool, fresh, oxygen-rich gas. moves in to take up the low pressure zones created when flame-exhaust water condenses. Systems of natural circulation include tornadoes and other weather systems , ocean currents , and household ventilation . Some solar water heaters use natural circulation. The Gulf Stream circulates as a result of the evaporation of water. In this process,

8094-424: The flow. Another common experiment to demonstrate thermal convection in liquids involves submerging open containers of hot and cold liquid coloured with dye into a large container of the same liquid without dye at an intermediate temperature (for example, a jar of hot tap water coloured red, a jar of water chilled in a fridge coloured blue, lowered into a clear tank of water at room temperature). A third approach

8208-490: The fluid is the key driving mechanism. If the differences of density are caused by heat, this force is called as "thermal head" or "thermal driving head." A fluid system designed for natural circulation will have a heat source and a heat sink . Each of these is in contact with some of the fluid in the system, but not all of it. The heat source is positioned lower than the heat sink. Most fluids expand when heated, becoming less dense , and contract when cooled, becoming denser. At

8322-409: The fluid, such as gravity. Natural convection is a flow whose motion is caused by some parts of a fluid being heavier than other parts. In most cases this leads to natural circulation : the ability of a fluid in a system to circulate continuously under gravity, with transfer of heat energy. The driving force for natural convection is gravity. In a column of fluid, pressure increases with depth from

8436-467: The furnace has a chair shape with the lower part of the shaft being narrower than the upper. The lower row of tuyeres being located in the narrow part of the shaft. This allows the upper part of the shaft to be wider than the standard. The blast furnaces used in the Imperial Smelting Process ("ISP") were developed from the standard lead blast furnace, but are fully sealed. This is because

8550-464: The furnace is a hearth of refractory material (bricks or castable refractory). Lead blast furnaces are often open-topped rather than having the charging bell used in iron blast furnaces. The blast furnace used at the Nyrstar Port Pirie lead smelter differs from most other lead blast furnaces in that it has a double row of tuyeres rather than the single row normally used. The lower shaft of

8664-469: The furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt. The resultant heat was used to preheat the air blown into the furnace. Hot blast enabled the use of raw anthracite coal, which was difficult to light, in the blast furnace. Anthracite was first tried successfully by George Crane at Ynyscedwyn Ironworks in south Wales in 1837. It was taken up in America by

8778-475: The furnace. Competition in industry drives higher production rates. The largest blast furnace in the world is in South Korea, with a volume around 6,000 m (210,000 cu ft). It can produce around 5,650,000 tonnes (5,560,000 LT) of iron per year. This is a great increase from the typical 18th-century furnaces, which averaged about 360 tonnes (350 long tons; 400 short tons) per year. Variations of

8892-496: The heat source of a system of natural circulation, the heated fluid becomes lighter than the fluid surrounding it, and thus rises. At the heat sink, the nearby fluid becomes denser as it cools, and is drawn downward by gravity. Together, these effects create a flow of fluid from the heat source to the heat sink and back again. Gravitational convection is a type of natural convection induced by buoyancy variations resulting from material properties other than temperature. Typically this

9006-674: The increased demand for iron for casting cannons, the blast furnace came into widespread use in France in the mid 15th century. The direct ancestor of those used in France and England was in the Namur region, in what is now Wallonia (Belgium). From there, they spread first to the Pays de Bray on the eastern boundary of Normandy and from there to the Weald of Sussex , where the first furnace (called Queenstock) in Buxted

9120-400: The iron's quality. Coke's impurities were more of a problem before hot blast reduced the amount of coke required and before furnace temperatures were hot enough to make slag from limestone free flowing. (Limestone ties up sulphur. Manganese may also be added to tie up sulphur.) Coke iron was initially only used for foundry work, making pots and other cast iron goods. Foundry work was

9234-449: The leather bellows, which wore out quickly. Isaac was granted a second patent, also for blowing cylinders, in 1757. The steam engine and cast iron blowing cylinder led to a large increase in British iron production in the late 18th century. Hot blast was the single most important advance in fuel efficiency of the blast furnace and was one of the most important technologies developed during

9348-567: The moist air rises, it cools, causing some of the water vapor in the rising packet of air to condense . When the moisture condenses, it releases energy known as latent heat of condensation which allows the rising packet of air to cool less than its surrounding air, continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form, which support lightning and thunder. Generally, thunderstorms require three conditions to form: moisture, an unstable airmass, and

9462-523: The molten iron was tapped twice a day into water, thereby granulating it. The General Chapter of the Cistercian monks spread some technological advances across Europe. This may have included the blast furnace, as the Cistercians are known to have been skilled metallurgists . According to Jean Gimpel, their high level of industrial technology facilitated the diffusion of new techniques: "Every monastery had

9576-433: The much slower (lagged) ocean circulation system. The large-scale structure of the atmospheric circulation varies from year to year, but the basic climatological structure remains fairly constant. Latitudinal circulation occurs because incident solar radiation per unit area is highest at the heat equator , and decreases as the latitude increases, reaching minima at the poles. It consists of two primary convection cells,

9690-417: The ocean basin, outweighing the effects of friction with the cold western boundary current which originates from high latitudes. The overall process, known as western intensification, causes currents on the western boundary of an ocean basin to be stronger than those on the eastern boundary. As it travels poleward, warm water transported by strong warm water current undergoes evaporative cooling. The cooling

9804-401: The oceans and atmosphere which do not involve heat, or else involve additional compositional density factors other than the density changes from thermal expansion (see thermohaline circulation ). Similarly, variable composition within the Earth's interior which has not yet achieved maximal stability and minimal energy (in other words, with densest parts deepest) continues to cause a fraction of

9918-483: The order of hundreds of millions of years to complete a cycle of convection. Neutrino flux measurements from the Earth's core (see kamLAND ) show the source of about two-thirds of the heat in the inner core is the radioactive decay of K , uranium and thorium. This has allowed plate tectonics on Earth to continue far longer than it would have if it were simply driven by heat left over from Earth's formation; or with heat produced from gravitational potential energy , as

10032-399: The particle size of the coke or charcoal is of great relevance. Therefore, the coke must be strong enough so it will not be crushed by the weight of the material above it. Besides the physical strength of its particles, the coke must also be low in sulfur, phosphorus , and ash. The main chemical reaction producing the molten iron is: This reaction might be divided into multiple steps, with

10146-457: The pig iron. It reacts with calcium oxide (burned limestone) and forms silicates, which float to the surface of the molten pig iron as slag. Historically, to prevent contamination from sulfur, the best quality iron was produced with charcoal. In a blast furnace, a downward-moving column of ore, flux, coke (or charcoal ) and their reaction products must be sufficiently porous for the flue gas to pass through, upwards. To ensure this permeability

10260-404: The principle of chemical reduction whereby carbon monoxide converts iron oxides to elemental iron. Blast furnaces differ from bloomeries and reverberatory furnaces in that in a blast furnace, flue gas is in direct contact with the ore and iron, allowing carbon monoxide to diffuse into the ore and reduce the iron oxide. The blast furnace operates as a countercurrent exchange process whereas

10374-522: The process of subduction at an ocean trench. This subducted material sinks to some depth in the Earth's interior where it is prohibited from sinking further. The subducted oceanic crust triggers volcanism. Convection within Earth's mantle is the driving force for plate tectonics . Mantle convection is the result of a thermal gradient: the lower mantle is hotter than the upper mantle , and is therefore less dense. This sets up two primary types of instabilities. In

10488-419: The reaction zone. As the material travels downward, the counter-current gases both preheat the feed charge and decompose the limestone to calcium oxide and carbon dioxide: The calcium oxide formed by decomposition reacts with various acidic impurities in the iron (notably silica ), to form a fayalitic slag which is essentially calcium silicate , Ca Si O 3 : As the iron(II) oxide moves down to

10602-463: The reverse across the Southern Hemisphere . The resulting Sverdrup transport is equatorward. Because of conservation of potential vorticity caused by the poleward-moving winds on the subtropical ridge 's western periphery and the increased relative vorticity of poleward moving water, transport is balanced by a narrow, accelerating poleward current, which flows along the western boundary of

10716-418: The rising force beneath it, and the fluid begins to descend. As it descends, it warms again and the cycle repeats itself. Additionally, convection cells can arise due to density variations resulting from differences in the composition of electrolytes. Atmospheric circulation is the large-scale movement of air, and is a means by which thermal energy is distributed on the surface of the Earth , together with

10830-481: The same temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column. The downward moving exterior is caused by colder air being displaced at the top of the thermal. Another convection-driven weather effect is the sea breeze . Warm air has a lower density than cool air, so warm air rises within cooler air, similar to hot air balloons . Clouds form as relatively warmer air carrying moisture rises within cooler air. As

10944-423: The space between the fire and the thermometer, by the process termed radiation . If we place a second thermometer in contact with any part of the grate, and away from the direct influence of the fire, we shall find that this thermometer also denotes an increase of temperature; but here the heat must have travelled through the metal of the grate, by what is termed conduction . Lastly, a third thermometer placed in

11058-479: The structure of horse powered reciprocators that already existed. That is, the circular motion of the wheel, be it horse driven or water driven, was transferred by the combination of a belt drive , a crank-and-connecting-rod, other connecting rods , and various shafts, into the reciprocal motion necessary to operate a push bellow. Donald Wagner suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze . Certainly, though, iron

11172-553: The surface ) and thereby absorbs and releases more heat , but the temperature changes less than land. This brings the sea breeze, air cooled by the water, ashore in the day, and carries the land breeze, air cooled by contact with the ground, out to sea during the night. Longitudinal circulation consists of two cells, the Walker circulation and El Niño / Southern Oscillation . Some more localized phenomena than global atmospheric movement are also due to convection, including wind and some of

11286-410: The term convection is attested in a scientific sense. In treatise VIII by William Prout , in the book on chemistry , it says: [...] This motion of heat takes place in three ways, which a common fire-place very well illustrates. If, for instance, we place a thermometer directly before a fire, it soon begins to rise, indicating an increase of temperature. In this case the heat has made its way through

11400-518: The term convection , [in footnote: [Latin] Convectio , a carrying or conveying] which not only expresses the leading fact, but also accords very well with the two other terms. Later, in the same treatise VIII, in the book on meteorology , the concept of convection is also applied to "the process by which heat is communicated through water". Today, the word convection has different but related usages in different scientific or engineering contexts or applications. In fluid mechanics , convection has

11514-458: The term has usually been limited to those used for smelting iron ore to produce pig iron , an intermediate material used in the production of commercial iron and steel , and the shaft furnaces used in combination with sinter plants in base metals smelting. Blast furnaces are estimated to have been responsible for over 4% of global greenhouse gas emissions between 1900 and 2015, but are difficult to decarbonize. Blast furnaces operate on

11628-408: The thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation and infiltration. Some cooling towers operate on this principle; similarly the solar updraft tower is a proposed device to generate electricity based on the stack effect. The convection zone of a star is the range of radii in which energy

11742-403: The top of the furnace, while a hot blast of air (sometimes with oxygen enrichment) is blown into the lower section of the furnace through a series of pipes called tuyeres , so that the chemical reactions take place throughout the furnace as the material falls downward. The end products are usually molten metal and slag phases tapped from the bottom, and waste gases ( flue gas ) exiting from

11856-524: The top of the furnace. The downward flow of the ore along with the flux in contact with an upflow of hot, carbon monoxide -rich combustion gases is a countercurrent exchange and chemical reaction process. In contrast, air furnaces (such as reverberatory furnaces ) are naturally aspirated, usually by the convection of hot gases in a chimney flue . According to this broad definition, bloomeries for iron, blowing houses for tin , and smelt mills for lead would be classified as blast furnaces. However,

11970-427: The top, where the temperature usually is in the range between 200 °C and 700 °C, the iron oxide is partially reduced to iron(II,III) oxide, Fe 3 O 4 . The temperatures 850 °C, further down in the furnace, the iron(II,III) is reduced further to iron(II) oxide: Hot carbon dioxide, unreacted carbon monoxide, and nitrogen from the air pass up through the furnace as fresh feed material travels down into

12084-493: The water increases in salinity and density. In the North Atlantic Ocean, the water becomes so dense that it begins to sink down. Convection occurs on a large scale in atmospheres , oceans, planetary mantles , and it provides the mechanism of heat transfer for a large fraction of the outermost interiors of the Sun and all stars. Fluid movement during convection may be invisibly slow, or it may be obvious and rapid, as in

12198-503: The weight of the overlying fluid. The pressure at the bottom of a submerged object then exceeds that at the top, resulting in a net upward buoyancy force equal to the weight of the displaced fluid. Objects of higher density than that of the displaced fluid then sink. For example, regions of warmer low-density air rise, while those of colder high-density air sink. This creates a circulating flow: convection. Gravity drives natural convection. Without gravity, convection does not occur, so there

12312-746: The world charcoal was cheaper while coke was more expensive even after the Industrial Revolution: e. g., in the US charcoal-fueled iron production fell in share to about a half ca. 1850 but still continued to increase in absolute terms until ca. 1890, while in João Monlevade in the Brazilian Highlands charcoal-fired blast furnaces were built as late as the 1930s and only phased out in 2000. Darby's original blast furnace has been archaeologically excavated and can be seen in situ at Coalbrookdale, part of

12426-583: The zinc produced by these furnaces is recovered as metal from the vapor phase, and the presence of oxygen in the off-gas would result in the formation of zinc oxide. Blast furnaces used in the ISP have a more intense operation than standard lead blast furnaces, with higher air blast rates per m of hearth area and a higher coke consumption. Zinc production with the ISP is more expensive than with electrolytic zinc plants, so several smelters operating this technology have closed in recent years. However, ISP furnaces have

12540-522: Was awarded ‘Best New Festival in Europe 2012’ and ran successfully until 2019. Blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron , but also others such as lead or copper . Blast refers to the combustion air being supplied above atmospheric pressure . In a blast furnace, fuel ( coke ), ores , and flux ( limestone ) are continuously supplied through

12654-521: Was built in about 1491, followed by one at Newbridge in Ashdown Forest in 1496. They remained few in number until about 1530 but many were built in the following decades in the Weald, where the iron industry perhaps reached its peak about 1590. Most of the pig iron from these furnaces was taken to finery forges for the production of bar iron . The first British furnaces outside the Weald appeared during

12768-473: Was essential to military success by the time the State of Qin had unified China (221 BC). Usage of the blast and cupola furnace remained widespread during the Song and Tang dynasties . By the 11th century, the Song dynasty Chinese iron industry made a switch of resources from charcoal to coke in casting iron and steel, sparing thousands of acres of woodland from felling. This may have happened as early as

12882-471: Was its lower cost, mainly because making coke required much less labor than cutting trees and making charcoal, but using coke also overcame localized shortages of wood, especially in Britain and eleswhere in Europe. Metallurgical grade coke will bear heavier weight than charcoal, allowing larger furnaces. A disadvantage is that coke contains more impurities than charcoal, with sulfur being especially detrimental to

12996-624: Was probably being consumed as fast as the wood to make it grew. The first blast furnace in Russia opened in 1637 near Tula and was called the Gorodishche Works. The blast furnace spread from there to central Russia and then finally to the Urals . In 1709, at Coalbrookdale in Shropshire, England, Abraham Darby began to fuel a blast furnace with coke instead of charcoal . Coke's initial advantage

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