Computational fluid dynamics
Computational fluid dynamics is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, the interaction of the fluid with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, are required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. Initial validation of such software is performed using experimental apparatus such as wind tunnels. In addition performed analytical or empirical analysis of a particular problem can be used for comparison. A final validation is performed using full-scale testing, such as flight tests. CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering and fluid flows, engine and combustion analysis.
The fundamental basis of all CFD problems is the Navier–Stokes equations, which define many single-phase fluid flows. These equations can be simplified by removing terms describing viscous actions to yield the Euler equations. Further simplification, by removing terms describing vorticity yields the full potential equations. For small perturbations in subsonic and supersonic flows these equations can be linearized to yield the linearized potential equations. Methods were first developed to solve the linearized potential equations. Two-dimensional methods, using conformal transformations of the flow about a cylinder to the flow about an airfoil were developed in the 1930s. One of the earliest type of calculations resembling modern CFD are those by Lewis Fry Richardson, in the sense that these calculations used finite differences and divided the physical space in cells. Although they failed these calculations, together with Richardson's book "Weather prediction by numerical process", set the basis for modern CFD and numerical meteorology.
In fact, early CFD calculations during the 1940s using ENIAC used methods close to those in Richardson's 1922 book. The computer power available paced development of three-dimensional methods; the first work using computers to model fluid flow, as governed by the Navier-Stokes equations, was performed at Los Alamos National Lab, in the T3 group. This group was led by Francis H. Harlow, considered as one of the pioneers of CFD. From 1957 to late 1960s, this group developed a variety of numerical methods to simulate transient two-dimensional fluid flows, such as Particle-in-cell method,Fluid-in-cell method,Vorticity stream function method, Marker-and-cell method. Fromm's vorticity-stream-function method for 2D, incompressible flow was the first treatment of contorting incompressible flows in the world; the first paper with three-dimensional model was published by John Hess and A. M. O. Smith of Douglas Aircraft in 1967; this method discretized the surface of the geometry with panels, giving rise to this class of programs being called Panel Methods.
Their method itself was simplified, in that it did not include lifting flows and hence was applied to ship hulls and aircraft fuselages. The first lifting Panel Code was described in a paper written by Paul Rubbert and Gary Saaris of Boeing Aircraft in 1968. In time, more advanced three-dimensional Panel Codes were developed at Boeing, Douglas, McDonnell Aircraft, NASA and Analytical Methods; some were higher order codes, using higher order distributions of surface singularities, while others used single singularities on each surface panel. The advantage of the lower order codes was. Today, VSAERO has grown to be a multi-order code and is the most used program of this class, it has been used in the development of many submarines, surface ships, helicopters and more wind turbines. Its sister code, USAERO is an unsteady panel method, used for modeling such things as high speed trains and racing yachts; the NASA PMARC code from an early version of VSAERO and a derivative of PMARC, named CMARC, is commercially available.
In the two-dimensional realm, a number of Panel Codes have been developed for airfoil analysis and design. The codes have a boundary layer analysis included, so that viscous effects can be modeled. Professor Richard Eppler of the University of Stuttgart developed the PROFILE code with NASA funding, which became available in the early 1980s; this was soon followed by MIT Professor Mark Drela's XFOIL code. Both PROFILE and XFOIL incorporate two-dimensional panel codes, with coupled boundary layer codes for airfoil analysis work. PROFILE uses a conformal transformation method for inverse airfoil design, while XFOIL has both a conformal transformation and an inverse panel method for airfoil design. An intermediate step between Panel Codes and Full Potential codes were codes that used the Transonic Small Disturbance equations. In particular, the three-dimensional WIBCO code, developed by Charlie Boppe of Grumman Aircraft in the early 1980s has seen heavy use. Developers tur
In the physical sciences, a phase is a region of space, throughout which all physical properties of a material are uniform. Examples of physical properties include density, index of refraction and chemical composition. A simple description is that a phase is a region of material, chemically uniform, physically distinct, mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, the humid air is a third phase over the ice and water; the glass of the jar is another separate phase. The term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter; the term phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. Because phase boundaries relate to changes in the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal structure to another, this latter usage is similar to the use of "phase" as a synonym for state of matter.
However, the state of matter and phase diagram usages are not commensurate with the formal definition given above and the intended meaning must be determined in part from the context in which the term is used. Distinct phases may be described as different states of matter such as gas, solid, plasma or Bose–Einstein condensate. Useful mesophases between solid and liquid form other states of matter. Distinct phases may exist within a given state of matter; as shown in the diagram for iron alloys, several phases exist for both the liquid states. Phases may be differentiated based on solubility as in polar or non-polar. A mixture of water and oil will spontaneously separate into two phases. Water has a low solubility in oil, oil has a low solubility in water. Solubility is the maximum amount of a solute that can dissolve in a solvent before the solute ceases to dissolve and remains in a separate phase. A mixture can separate into more than two liquid phases and the concept of phase separation extends to solids, i.e. solids can form solid solutions or crystallize into distinct crystal phases.
Metal pairs that are mutually soluble can form alloys, whereas metal pairs that are mutually insoluble cannot. As many as eight immiscible liquid phases have been observed. Mutually immiscible liquid phases are formed from water, hydrophobic organic solvents, silicones, several different metals, from molten phosphorus. Not all organic solvents are miscible, e.g. a mixture of ethylene glycol and toluene may separate into two distinct organic phases. Phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of immiscible phase pair combinations that do not physically separate. Left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ. Water in a closed jar with an air space over it forms a two phase system. Most of the water is in the liquid phase, where it is held by the mutual attraction of water molecules.
At equilibrium molecules are in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to break away from the liquid phase and enter the gas phase. Every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid. At equilibrium and condensation processes balance and there is no net change in the volume of either phase. At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%; this percentage increases. At 100 °C and atmospheric pressure, equilibrium is not reached. If the liquid is heated a little over 100 °C, the transition from liquid to gas will occur not only at the surface, but throughout the liquid volume: the water boils. For a given composition, only certain phases are possible at pressure; the number and type of phases that will form is hard to predict and is determined by experiment. The results of such experiments can be plotted in phase diagrams; the phase diagram shown here is for a single component system.
In this simple system, which phases that are possible depends only on pressure and temperature. The markings show points. At temperatures and pressures away from the markings, there will be only one phase at equilibrium. In the diagram, the blue line marking the boundary between liquid and gas does not continue indefinitely, but terminates at a point called the critical point; as the temperature and pressure approach the critical point, the properties of the liquid and gas become progressively more similar. At the critical point, the liquid and gas become indistinguishable. Above the critical point, there are no longer separate liquid and gas phases: there is only a generic fluid phase referred to as a supercritical fluid. In water, the critical point occurs at 22.064 MPa. An unusual feature of the water phase diagram is that the solid–liquid phase line has a negative slope. For most substances, the slope is positive; this unusual feature of water is related to ice having a lowe
The kraft process is a process for conversion of wood into wood pulp, which consists of pure cellulose fibers, the main component of paper. The kraft process entails treatment of wood chips with a hot mixture of water, sodium hydroxide, sodium sulfide, known as white liquor, that breaks the bonds that link lignin and cellulose; the technology entails both mechanical and chemical. It is the dominant method for producing paper. In some situations, the process has been controversial because kraft plants can release odorous products and in some situations produce substantial liquid wastes; the kraft process was invented by Carl F. Dahl in 1879 in Danzig, Germany. U. S. Patent 296,935 was issued in 1884, a pulp mill using this technology started in 1890; the invention of the recovery boiler by G. H. Tomlinson in the early 1930s was a milestone in the advancement of the kraft process, it enabled the recovery and reuse of the inorganic pulping chemicals such that a kraft mill is a nearly closed-cycle process with respect to inorganic chemicals, apart from those used in the bleaching process.
For this reason, in the 1940s, the kraft process superseded the sulfite process as the dominant method for producing wood pulp. Common wood chips used in pulp production are 12–25 millimetres long and 2–10 millimetres thick; the chips first enter the presteaming where they are wetted and preheated with steam. Cavities inside fresh wood chips are filled with liquid and with air; the steam treatment causes about 25 % of the air to be expelled from the chips. The next step is to saturate the chips with white liquor. Air remaining in chips at the beginning of liquor impregnation is trapped within the chips; the impregnation can be done before or after the chips enters the digester and is done below 100 °C. The cooking liquors consist of a mixture of white liquor, water in chips, condensed steam and weak black liquor. In the impregnation, cooking liquor penetrates into the capillary structure of the chips and low temperature chemical reactions with the wood begin. A good impregnation is important to get a homogeneous cook and low rejects.
About 40–60% of all alkali consumption in the continuous process occurs in the impregnation zone. The wood chips are cooked in pressurized vessels called digesters; some digesters operate in some in a continuous process. There are several variations of the cooking processes both for the batch and the continuous digesters. Digesters producing 1,000 tonnes or more of pulp per day are common, with the largest producing more than 3,500 tonnes per day. In a continuous digester, the materials are fed at a rate that allows the pulping reaction to be complete by the time the materials exit the reactor. Delignification requires several hours at 170 to 176 °C. Under these conditions lignin and hemicellulose degrade to give fragments that are soluble in the basic liquid; the solid pulp is washed. At this point the pulp is known as brown stock because of its color; the combined liquids, known as black liquor, contain lignin fragments, carbohydrates from the breakdown of hemicellulose, sodium carbonate, sodium sulfate and other inorganic salts.
One of the main chemical reactions that underpin the kraft process is the scission of ether bonds by the nucleophilic sulfide or bisulfide ions. The excess black liquor contains about 15% solids and is concentrated in a multiple effect evaporator. After the first step the black liquor has about 20–30% solids. At this concentration the rosin soap is skimmed off; the collected soap is further processed to tall oil. Removal of the soap improves the evaporation operation of the effects; the weak black liquor is further evaporated to 65% or 80% solids and burned in the recovery boiler to recover the inorganic chemicals for reuse in the pulping process. Higher solids in the concentrated black liquor increases the energy and chemical efficiency of the recovery cycle, but gives higher viscosity and precipitation of solids. During combustion sodium sulfate is reduced to sodium sulfide by the organic carbon in the mixture: 1. Na2SO4 + 2 C → Na2S + 2 CO2This reaction is similar to thermochemical sulfate reduction in geochemistry.
The molten salts from the recovery boiler are dissolved in a process water known as "weak wash". This process water known as "weak white liquor" is composed of all liquors used to wash lime mud and green liquor precipitates; the resulting solution of sodium carbonate and sodium sulfide is known as "green liquor", although it is not known what causes the liquor to be green. This liquid is mixed with calcium oxide, which becomes calcium hydroxide in solution, to regenerate the white liquor used in the pulping process through an equilibrium reaction: 2. Na2S + Na2CO3 + Ca2 ←→ Na2S + 2 NaOH + CaCO3Calcium carbonate precipitates from the white liquor and is recovered and heated in a lime kiln where it is converted to calcium oxide. 3. CaCO3 → CaO + CO2Calcium oxide is reacted with water to regenerate the calcium hydroxide used in Reaction 2: 4. CaO + H2O → Ca2The combination of reactions 1 through 4 form a closed cycle with respect to sodium and calcium and is the main concept of the so-called recausticizi
A theoretical plate in many separation processes is a hypothetical zone or stage in which two phases, such as the liquid and vapor phases of a substance, establish an equilibrium with each other. Such equilibrium stages may be referred to as an equilibrium stage, ideal stage, or a theoretical tray; the performance of many separation processes depends on having series of equilibrium stages and is enhanced by providing more such stages. In other words, having more theoretical plates increases the efficiency of the separation process be it either a distillation, chromatographic, adsorption or similar process; the concept of theoretical plates and trays or equilibrium stages is used in the design of many different types of separation. The concept of theoretical plates in designing distillation processes has been discussed in many reference texts. Any physical device that provides good contact between the vapor and liquid phases present in industrial-scale distillation columns or laboratory-scale glassware distillation columns constitutes a "plate" or "tray".
Since an actual, physical plate can never be a 100% efficient equilibrium stage, the number of actual plates is more than the required theoretical plates. N a = N t E where N a is the number of actual, physical plates or trays, N t is the number of theoretical plates or trays and E is the plate or tray efficiency. So-called bubble-cap or valve-cap trays are examples of the vapor and liquid contact devices used in industrial distillation columns. Another example of vapor and liquid contact devices are the spikes in laboratory Vigreux fractionating columns; the trays or plates used in industrial distillation columns are fabricated of circular steel plates and installed inside the column at intervals of about 60 to 75 cm up the height of the column. That spacing is chosen for ease of installation and ease of access for future repair or maintenance. An example of a simple tray is a perforated tray; the desired contacting between vapor and liquid occurs as the vapor, flowing upwards through the perforations, comes into contact with the liquid flowing downwards through the perforations.
In current modern practice, as shown in the adjacent diagram, better contacting is achieved by installing bubble-caps or valve caps at each perforation to promote the formation of vapor bubbles flowing through a thin layer of liquid maintained by a weir on each tray. To design a distillation unit or a similar chemical process, the number of theoretical trays or plates, Nt, required in the process should be determined, taking into account a range of feedstock composition and the desired degree of separation of the components in the output fractions. In industrial continuous fractionating columns, Nt is determined by starting at either the top or bottom of the column and calculating material balances, heat balances and equilibrium flash vaporizations for each of the succession of equilibrium stages until the desired end product composition is achieved; the calculation process requires the availability of a great deal of vapor–liquid equilibrium data for the components present in the distillation feed, the calculation procedure is complex.
In an industrial distillation column, the Nt required to achieve a given separation depends upon the amount of reflux used. Using more reflux decreases the number of plates required and using less reflux increases the number of plates required. Hence, the calculation of Nt is repeated at various reflux rates. Nt is divided by the tray efficiency, E, to determine the actual number of trays or physical plates, Na, needed in the separating column; the final design choice of the number of trays to be installed in an industrial distillation column is selected based upon an economic balance between the cost of additional trays and the cost of using a higher reflux rate. There is a important distinction between the theoretical plate terminology used in discussing conventional distillation trays and the theoretical plate terminology used in the discussions below of packed bed distillation or absorption or in chromatography or other applications; the theoretical plate in conventional distillation trays has no "height".
It is a hypothetical equilibrium stage. However, the theoretical plate in packed beds and other applications is defined as having a height. Distillation and absorption separation processes using packed beds for vapor and liquid contacting have an equivalent concept referred to as the plate height or the height equivalent to a theoretical plate. HETP arises from the same concept of equilibrium stages as does the theoretical plate and is numerically equal to the absorption bed length divided by the number of theoretical plates in the absorption bed. N t = H H E T P where N t is the number of theoretical plates, H is the total bed height and HETP is the height equivalent to a theoretical plate; the material in packed beds can either be random dumped packing such as Raschig rings or structured sheet metal. Liquids tend to wet the surface of the packing and the vapors contact the wetted surface, where mass transfer occurs; the theoretical plate concept was adapted for chromatographic processes by Martin
Sulzer Ltd. is a Swiss industrial engineering and manufacturing firm, founded by Salomon Sulzer-Bernet in 1775 and established as Sulzer Brothers Ltd. in 1834 in Winterthur, Switzerland. Today it is a publicly traded company with international subsidiaries; the company's shares are listed on the Swiss Stock Exchange. Sulzer's core strengths are flow control and applicators; the company specializes in pumping solutions and services for rotating equipment, as well as separation and application technology. Sulzer Brothers helped develop shuttleless weaving, their core business was loom manufacture. Rudolf Diesel worked for Sulzer in 1879, in 1893 Sulzer bought certain rights to diesel engines. Sulzer built their first diesel engine in 1898; the company is organized into four divisions: Pumps Equipment: Pump technology and solutions Rotating Equipment Services: Service and repair solutions for rotating equipment such as turbines, compressors and generators. Chemtech: Components and services for separation columns and static mixing Applicator Systems: Systems for liquid applications The Sulzer Ltd shares are registered at the SIX Swiss Exchange.
As of April 11, 2018, Renova Group held a total of 48.83% of Sulzer's share capital. The company "Gebrüder Sulzer, Foundry in Winterthur" was founded in 1834 by Johann Jacob Sulzer, his sons Johann Jakob and Solomon produced cast iron, built fire extinguishers and apparatus for the textile industry. In 1836 the workforce grew to around forty journeymen and apprentices. In 1839 a foundry was added, a mechanical workshop was set up and the first steam engine was built in Winterthur. In 1859, the first "partnership agreement" between the Sulzer brothers was signed. New products were introduced, first steam engines also ships, new organization, production methods. Around 1860 Sulzer opened his first foreign sales office in Turin, in 1867 the company participated in the world exhibition in Paris; the workforce had grown to more than 1,000 workers. From 1880, steam engines, in particular, contributed to the growth to around 2,000 employees. In 1881 a branch was founded in Ludwigshafen am Rhein. In 1898, the first Sulzer diesel engine was developed in cooperation with Rudolf Diesel.
Around 1900 the company had over 3,000 employees and sales offices in Milan, Cairo, London and Bucharest, from 1914 in the Japanese Kobe. As a family business, the company had grown over the years in the form of a general partnership, in June 1914 it was converted into two stock corporations with registered offices in Winterthur and Ludwigshafen am Rhein, both of which were renamed Gebrüder Sulzer Aktiengesellschaft. In 1917, both companies were bundled in a holding structure under the name Sulzer-Unternehmungen AG and subsequently the foreign sales offices were transferred to independent companies. During the 1930s, production fell by two thirds as a result of the global economic crisis, personnel was massively reduced. Out of political and personal considerations, Sulzer decided to sell its subsidiaries in Germany by the beginning of the war. Sulzer was blacklisted by the Allies during World War II due to an increase in trade with Axis countries. Sulzer refused to sign an agreement to limit the future sale of marine diesel engines to the Axis countries, was blacklisted by the Allies as a result.
From 1945, a growth phase began with a flourishing economy and strong expansion of foreign activities. In the 1950s, increasing production was carried out by guest workers from southern Europe. New divisions for energy, plant engineering and textile machinery were created, accompanied by better working conditions, expansion of social benefits, women's work for "lighter factory work" and housing subsidies in surrounding communities. During the second heyday after the Second World War, the Sulzer Tower was built in the early 1960s - the company's new headquarters, a landmark of Winterthur and the tallest building in Switzerland at the time. In 1961, Schweizerische Lokomotiv- und Maschinenfabrik in Winterthur was acquired, the large diesel engine became Sulzer's flagship product worldwide. In 1966, Sulzer acquired a 53 percent stake in Maschinenfabrik Escher Wyss AG in Zurich, reaching an all-time high of over 30,000 employees. In 1969, Escher Wyss AG was taken over in full. In the 1970s, the oil crisis announced a new orientation towards the technology group and the development of materials technologies.
Sulzer reacted to the global decline in capital goods in the 1970s after losses in the second half of the 1980s. In 1982, the weaving machine business was expanded. In 1984, Sulzer underwent massive restructuring. Medical technology was expanded by the purchase of the American Intermedics Group for one billion Swiss francs; the Winterthur machine factory was closed in 1990 and the founding site in Winterthur was vacated. For the first time, Sulzer employed more people abroad than in Switzerland. On May 14, 1993, Gebrüder Sulzer, Aktiengesellschaft was renamed Sulzer Ltd. In 1996, a technology centre was built in the Oberwinterthur Industrial Park. In 2000, Sulzer acquired the Finnish company Ahlstrom Pumps. In the middle of the year, the steam locomotive and machine factory DLM became independent, the remains of the former SLM became Winpro AG in 2001 through a management buyout; the time since 2003 is called a new beginning. Since the Group has be
Dixon rings are a form of random packing used in chemical processing. They consist of a stainless steel mesh formed into a ring with a central divider, are intended to be packed randomly into a packed column. Dixon rings provide a large surface area and low pressure drop while maintaining a high mass transfer rate, making them useful for distillations and many other applications. Packed columns are used in a range of industries to allow intimate contact between two immiscible fluids which can be liquid/liquid or liquid/gas; the fluids are passed through in a counter current flow through a column. Random column packing used to characterize the maximum volume fraction of a solid object obtained when they are packed randomly; this method of packing has been used since the early 1820s. However, in 1850 they were replaced by pieces of coke. In the early 20th century Friedrich Raschig realized the importance of a high void fraction and having the internal surface of the packing media take part in the mass transfer.
He designed the Raschig ring, more effective than previous forms of random packing and became popular. Raschig rings are built from ceramic or metal and provided a large surface area within the column for interaction between liquid and gas vapors. In 1946 Dr Olaf Dixon developed a new product for column distillation. Based on the design of the Lessing ring, Dixon developed the Dixon ring, employing a stainless steel mesh to improve the pressure drop of the packed column. Dixon rings are used for for laboratory distillation applications; the enhanced performance of the Dixon ring is based on liquid surface tension: when the mesh is wet its surface area increases with an accompanying increase in the rate of mass transfer. Dixon rings require pre-wetting. While this increases batch processing startup time, the increased performance of the Dixon ring overcomes this. Random column packing
Distillation is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Distillation may result in complete separation, or it may be a partial separation that increases the concentration of selected components in the mixture. In either case, the process exploits differences in the volatility of the mixture's components. In industrial chemistry, distillation is a unit operation of universal importance, but it is a physical separation process, not a chemical reaction. Distillation has many applications. For example: Distillation of fermented products produces distilled beverages with a high alcohol content or separates out other fermentation products of commercial value. Distillation is an traditional method of desalination. In the fossil fuel industry, oil stabilization is a form of partial distillation that reduces vapor pressure of crude oil, thereby making it safe for storage and transport as well as reducing the atmospheric emissions of volatile hydrocarbons.
In midstream operations at oil refineries, distillation is a major class of operation for transforming crude oil into fuels and chemical feed stocks. Cryogenic distillation leads to the separation of air into its components – notably oxygen and argon – for industrial use. In the field of industrial chemistry, large amounts of crude liquid products of chemical synthesis are distilled to separate them, either from other products, from impurities, or from unreacted starting materials. An installation used for distillation of distilled beverages, is called a distillery; the distillation equipment at a distillery is a still. In 1975 Paolo Rovesti a chemist and pharmacist who became known as"father of Phytocosmetics" discovered a terracota distillation apparatus in the Indus valley in West Pakistan which dates from around 3000 BC. Early evidence of distillation was found on Akkadian tablets dated circa 1200 BC describing perfumery operations; the tablets provided textual evidence that an early primitive form of distillation was known to the Babylonians of ancient Mesopotamia.
Early evidence of distillation was found related to alchemists working in Alexandria in Roman Egypt in the 1st century. Distilled water has been in use since at least c. 200, when Alexander of Aphrodisias described the process. Work on distilling other liquids continued in early Byzantine Egypt under Zosimus of Panopolis in the 3rd century. Distillation was practiced in the ancient Indian subcontinent, evident from baked clay retorts and receivers found at Taxila and Charsadda in modern Pakistan, dating back to the early centuries of the Common Era; these "Gandhara stills" were only capable of producing weak liquor, as there was no efficient means of collecting the vapors at low heat. Distillation in China may have begun during the Eastern Han dynasty, but the distillation of beverages began in the Jin and Southern Song dynasties, according to archaeological evidence. Clear evidence of the distillation of alcohol comes from the Arab chemist Al-Kindi in 9th-century Iraq; the process spread to Italy, where it was described by the School of Salerno in the 12th century.
Fractional distillation was developed by Tadeo Alderotti in the 13th century. A still was found in an archaeological site in Qinglong, Hebei province, in China, dating back to the 12th century. Distilled beverages were common during the Yuan dynasty. In 1500, German alchemist Hieronymus Braunschweig published Liber de arte destillandi, the first book dedicated to the subject of distillation, followed in 1512 by a much expanded version. In 1651, John French published The Art of Distillation, the first major English compendium on the practice, but it has been claimed that much of it derives from Braunschweig's work; this includes diagrams with people in them showing the industrial rather than bench scale of the operation. As alchemy evolved into the science of chemistry, vessels called retorts became used for distillations. Both alembics and retorts are forms of glassware with long necks pointing to the side at a downward angle to act as air-cooled condensers to condense the distillate and let it drip downward for collection.
Copper alembics were invented. Riveted joints were kept tight by using various mixtures, for instance a dough made of rye flour; these alembics featured a cooling system around the beak, using cold water, for instance, which made the condensation of alcohol more efficient. These were called pot stills. Today, the retorts and pot stills have been supplanted by more efficient distillation methods in most industrial processes. However, the pot still is still used for the elaboration of some fine alcohols, such as cognac, Scotch whisky, Irish whiskey and some vodkas. Pot stills made of various materials are used by bootleggers in various countries. Small pot stills are sold for use in the domestic production of flower water or essential oils. Early forms of distillation involved batch processes using one condensation. Purity was improved by further distillation of the condensate. Greater volumes were processed by repeating the distillation. Chemists carried out as many as 500 to 600 distillations in order to obtain a pure compound.
In the early 19th century, the basics of modern techniques, including pre-heating and reflux, were developed. In 1822, Anthony Perrier developed one of the first continuous stills, in 1826, Robert Stein improved that design to make his patent still. In 1830, Aeneas Coffey got a patent for improving the design f