Fouling is the accumulation of unwanted material on solid surfaces to the detriment of function. The fouling materials can consist of a non-living substance. Fouling is distinguished from other surface-growth phenomena, in that it occurs on a surface of a component, system or plant performing a defined and useful function, that the fouling process impedes or interferes with this function. Other terms used in the literature to describe fouling include: deposit formation, crudding, scaling, scale formation and sludge formation; the last six terms have a more narrow meaning than fouling within the scope of the fouling science and technology, they have meanings outside of this scope. Fouling phenomena are common and diverse, ranging from fouling of ship hulls, natural surfaces in the marine environment, fouling of heat-transfer components through ingredients contained in the cooling water or gases, the development of plaque or calculus on teeth, or deposits on solar panels on Mars, among other examples.
This article is devoted to the fouling of industrial heat exchangers, although the same theory is applicable to other varieties of fouling. In the cooling technology and other technical fields, a distinction is made between macro fouling and micro fouling. Of the three, micro fouling is the one, more difficult to prevent and therefore less important. Following are examples of components that may be subject to fouling and the corresponding effects of fouling: Heat exchanger surfaces – reduces thermal efficiency, decreases heat flux, increases temperature on the hot side, decreases temperature on the cold side, induces under-deposit corrosion, increases use of cooling water. Macro fouling is caused by coarse matter of either biological or inorganic origin, for example industrially produced refuse; such matter enters into the cooling water circuit through the cooling water pumps from sources like the open sea, rivers or lakes. In closed circuits, like cooling towers, the ingress of macro fouling into the cooling tower basin is possible through open canals or by the wind.
Sometimes, parts of the cooling tower internals detach themselves and are carried into the cooling water circuit. Such substances can foul the surfaces of heat exchangers and may cause deterioration of the relevant heat transfer coefficient, they may create flow blockages, redistribute the flow inside the components, or cause fretting damage. Examples Manmade refuse; as to micro fouling, distinctions are made between: Scaling or precipitation fouling, as crystallization of solid salts and hydroxides from water solutions, for example, calcium carbonate or calcium sulfate. Scaling or precipitation fouling involves crystallization of solid salts and hydroxides from solutions; these are most water solutions, but non-aqueous precipitation fouling is known. Precipitation fouling is a common problem in boilers and heat exchangers operating with hard water and results in limescale. Through changes in temperature, or solvent evaporation or degasification, the concentration of salts may exceed the saturation, leading to a precipitation of solids.
As an example, the equilibrium between the soluble calcium bicarbonate - always prevailing in natural water - and the poorly soluble calcium carbonate, the following chemical equation may be written
Hard water is water that has high mineral content. Hard water is formed when water percolates through deposits of limestone and chalk which are made up of calcium and magnesium carbonates. Hard drinking water may have moderate health benefits, but can pose critical problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, other equipment that handles water. In domestic settings, hard water is indicated by a lack of foam formation when soap is agitated in water, by the formation of limescale in kettles and water heaters. Wherever water hardness is a concern, water softening is used to reduce hard water's adverse effects. Water's hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are positively charged metal complexes with a charge greater than 1+; the cations have the charge of 2+. Common cations found in hard water include Ca2+ and Mg2+; these ions enter a water supply by leaching from minerals within an aquifer.
Common calcium-containing minerals are gypsum. A common magnesium mineral is dolomite. Rainwater and distilled water are soft; the following equilibrium reaction describes the dissolving and formation of calcium carbonate and calcium bicarbonate: CaCO3 + CO2 + H2O ⇋ Ca2+ + 2HCO3− The reaction can go in either direction. Rain containing dissolved carbon dioxide can react with calcium carbonate and carry calcium ions away with it; the calcium carbonate may be re-deposited as calcite as the carbon dioxide is lost to atmosphere, sometimes forming stalactites and stalagmites. Calcium and magnesium ions can sometimes be removed by water softeners. Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals; when dissolved, these minerals yield calcium and magnesium cations and carbonate and bicarbonate anions. The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulfate and chloride compounds, this "temporary" hardness can be reduced either by boiling the water, or by the addition of lime through the process of lime softening.
Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water, softer upon cooling. Permanent hardness is hardness; when this is the case, it is caused by the presence of calcium sulfate/calcium chloride and/or magnesium sulfate/magnesium chloride in the water, which do not precipitate out as the temperature increases. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column. Total Permanent Hardness = Permanent Calcium Hardness + Permanent Magnesium Hardness With hard water, soap solutions form a white precipitate instead of producing lather, because the 2+ ions destroy the surfactant properties of the soap by forming a solid precipitate. A major component of such scum is calcium stearate, which arises from sodium stearate, the main component of soap: 2 C17H35COO− + Ca2+ → 2Ca Hardness can thus be defined as the soap-consuming capacity of a water sample, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap.
Synthetic detergents do not form such scums. Hard water forms deposits that clog plumbing; these deposits, called "scale", are composed of calcium carbonate, magnesium hydroxide, calcium sulfate. Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers; this precipitation is principally caused by thermal decomposition of bicarbonate ions but happens in cases where the carbonate ion is at saturation concentration. The resulting build-up of scale restricts the flow of water in pipes. In boilers, the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this overheating can lead to failure of the boiler; the damage caused by calcium carbonate deposits varies on the crystalline form, for example, calcite or aragonite. The presence of ions in an electrolyte, in this case, hard water, can lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal, when both are in contact with an electrolyte.
The softening of hard water by ion exchange does not increase its corrosivity per se. Where lead plumbing is in use, softened water does not increase plumbo-solvency. In swimming pools, hard water is manifested by a cloudy, appearance to the water. Calcium and magnesium hydroxides are both soluble in water; the solubility of the hydroxides of the alkaline-earth metals to which calcium and magnesium belong increases moving down the column. Aqueous solutions of these metal hydroxides absorb carbon dioxide from the air, forming the insoluble carbonates, giving rise to the turbidity; this results from the pH being excessively high. Hence, a common solution to the problem is, while maintaining the chlorine concentration at the proper level, to lower the pH by the addition of hydrochloric acid, the optimum value being in the range of 7.2 to 7.6. It is desirable to soften hard water. Most detergents contain ingredients. For this reason, water soften
The cell is the basic structural and biological unit of all known living organisms. A cell is the smallest unit of life. Cells are called the "building blocks of life"; the study of cells is called cellular biology. Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as multicellular; the number of cells in plants and animals varies from species to species, it has been estimated that humans contain somewhere around 40 trillion cells. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometres. Cells were discovered by Robert Hooke in 1665, who named them for their resemblance to cells inhabited by Christian monks in a monastery. Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, that all cells come from pre-existing cells.
Cells emerged on Earth at least 3.5 billion years ago. Cells are of two types: eukaryotic, which contain a nucleus, prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular. Prokaryotes include two of the three domains of life. Prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling, they are simpler and smaller than eukaryotic cells, lack membrane-bound organelles such as a nucleus. The DNA of a prokaryotic cell consists of a single chromosome, in direct contact with the cytoplasm; the nuclear region in the cytoplasm is called the nucleoid. Most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. A prokaryotic cell has three architectural regions: Enclosing the cell is the cell envelope – consisting of a plasma membrane covered by a cell wall which, for some bacteria, may be further covered by a third layer called a capsule.
Though most prokaryotes have both a cell membrane and a cell wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter; the cell wall consists of peptidoglycan in bacteria, acts as an additional barrier against exterior forces. It prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment; some eukaryotic cells have a cell wall. Inside the cell is the cytoplasmic region that contains the genome and various sorts of inclusions; the genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are circular. Linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid.
Plasmids encode additional genes, such as antibiotic resistance genes. On the outside and pili project from the cell's surface; these are structures made of proteins that facilitate communication between cells. Plants, fungi, slime moulds and algae are all eukaryotic; these cells are about fifteen times wider than a typical prokaryote and can be as much as a thousand times greater in volume. The main distinguishing feature of eukaryotes as compared to prokaryotes is compartmentalization: the presence of membrane-bound organelles in which specific activities take place. Most important among these is a cell nucleus, an organelle that houses the cell's DNA; this nucleus gives the eukaryote its name, which means "true kernel". Other differences include: The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may not be present; the eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins.
All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria contain some DNA. Many eukaryotic cells are ciliated with primary cilia. Primary cilia play important roles in chemosensation and thermosensation. Cilia may thus be "viewed as a sensory cellular antennae that coordinates a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation." Motile eukaryotes can move using motile flagella. Motile cells are absent in flowering plants. Eukaryotic flagella are more complex than those of prokaryotes. All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, regulates what moves in and out, maintains the electric potential of the cell. Inside the membrane, the cytoplasm takes up most of the cell's volume. All cells possess DNA, the hereditary material of genes, RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery.
There are other kinds of biomolecules in cells. This article lists these primary cellular components briefly
Dishwasher detergent is a detergent made for washing dishes in a dishwasher. Dishwasher detergent is different from dishwashing liquid made to wash dishes by hand; when using a dishwasher, the user must select a special detergent for its use. All detergents are designed for use after the user scrapes leftover food from the dishes before washing. To function, the user places dishes in the dishwasher in such fashion that the surface of all dishes is open to the flow of water. Most dishwasher detergents are incompatible for use with silver, cast iron, bronze and goldleaf, they can harm disposable plastic, anything wood, knives with hollow handles, fine glassware. The best dishwasher detergents would be those that clean dishes the best, leave the least cleaner after rinsing, have versatility in cleaning various types of dish surfaces and food, are easiest to use, the best value for price. There is variation in how effective different detergents are in removing dried food from glass and baked-on sticky food from pots.
In the course of washing, a better detergent will both prevent washed-away food from redepositing on the dishes, prevent mineral accumulation or discoloration of the dishes. Different kinds of dishwashing detergent contain different combinations of ingredients. Common ingredients include: Phosphates Bind calcium and magnesium ions to prevent'hard-water' type limescale deposits, they can cause ecological damage, so their use is starting to be phased out. Phosphate-free detergents are sold as eco-friendly detergents. Oxygen-based bleaching agents bleach organic deposits. Non-ionic surfactants Lower the surface tension of the water, emulsifies oil and fat food deposits, prevents droplet spotting on drying. Alkaline salts These are a primary component in older and original-style dishwasher detergent powders. Alkaline salts attack and dissolve grease, but are corrosive if swallowed. Salts used may include metasilicates, alkali metal hydroxides, sodium carbonate etc. Enzymes Break up protein-based food deposits, oil and fat deposits.
Proteases do this by breaking down the proteins into smaller peptides that are more washed away. Anti-corrosion agent Often sodium silicate, this prevents corrosion of dishwasher components. Dishwashing detergent may contain: Anti-foaming agents Foam interferes with the washing action. Additives to slow down the removal of glaze & patterns from glazed ceramics Perfumes Anti-caking agents Starches Gelling agents Sand Dishwasher detergents are alkaline. Inexpensive powders may contain sand; such detergents may harm the dishwasher. Powdered detergents are more to cause fading on china patterns. Besides older style detergents for dishwashers, biodegradable detergents exist for dishwashers; these detergents may be more environmentally friendly than conventional detergents. Hand-washing dish detergent creates a large foam of bubbles. Rinse aid contains surfactants and uses Marangoni stress to prevent droplet formation, so that water drains from the surfaces in thin sheets, rather than forming droplets.
The benefits of using it are that it prevents "spotting" on glassware, can improve drying performance as there is less water remaining to be dried. A thinner sheet of water has a much larger surface-area than a droplet of the same volume, which increases the likelihood of water molecules evaporating
World War I
World War I known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history, it is one of the deadliest conflicts in history, with an estimated nine million combatants and seven million civilian deaths as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide. On 28 June 1914, Gavrilo Princip, a Bosnian Serb Yugoslav nationalist, assassinated the Austro-Hungarian heir Archduke Franz Ferdinand in Sarajevo, leading to the July Crisis. In response, on 23 July Austria-Hungary issued an ultimatum to Serbia. Serbia's reply failed to satisfy the Austrians, the two moved to a war footing. A network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe.
By July 1914, the great powers of Europe were divided into two coalitions: the Triple Entente—consisting of France and Britain—and the Triple Alliance of Germany, Austria-Hungary and Italy. Russia felt it necessary to back Serbia and, after Austria-Hungary shelled the Serbian capital of Belgrade on the 28th, partial mobilisation was approved. General Russian mobilisation was announced on the evening of 30 July; when Russia failed to comply, Germany declared war on 1 August in support of Austria-Hungary, with Austria-Hungary following suit on 6th. German strategy for a war on two fronts against France and Russia was to concentrate the bulk of its army in the West to defeat France within four weeks shift forces to the East before Russia could mobilise. On 2 August, Germany demanded free passage through Belgium, an essential element in achieving a quick victory over France; when this was refused, German forces invaded Belgium on 3 August and declared war on France the same day. On 12 August and France declared war on Austria-Hungary.
In November 1914, the Ottoman Empire entered the war on the side of the Alliance, opening fronts in the Caucasus and the Sinai Peninsula. The war was fought in and drew upon each power's colonial empire as well, spreading the conflict to Africa and across the globe; the Entente and its allies would become known as the Allied Powers, while the grouping of Austria-Hungary and their allies would become known as the Central Powers. The German advance into France was halted at the Battle of the Marne and by the end of 1914, the Western Front settled into a battle of attrition, marked by a long series of trench lines that changed little until 1917. In 1915, Italy opened a front in the Alps. Bulgaria joined the Central Powers in 1915 and Greece joined the Allies in 1917, expanding the war in the Balkans; the United States remained neutral, although by doing nothing to prevent the Allies from procuring American supplies whilst the Allied blockade prevented the Germans from doing the same the U. S. became an important supplier of war material to the Allies.
After the sinking of American merchant ships by German submarines, the revelation that the Germans were trying to incite Mexico to make war on the United States, the U. S. declared war on Germany on 6 April 1917. Trained American forces would not begin arriving at the front in large numbers until mid-1918, but the American Expeditionary Force would reach some two million troops. Though Serbia was defeated in 1915, Romania joined the Allied Powers in 1916 only to be defeated in 1917, none of the great powers were knocked out of the war until 1918; the 1917 February Revolution in Russia replaced the Tsarist autocracy with the Provisional Government, but continuing discontent at the cost of the war led to the October Revolution, the creation of the Soviet Socialist Republic, the signing of the Treaty of Brest-Litovsk by the new government in March 1918, ending Russia's involvement in the war. This allowed the transfer of large numbers of German troops from the East to the Western Front, resulting in the German March 1918 Offensive.
This offensive was successful, but the Allies rallied and drove the Germans back in their Hundred Days Offensive. Bulgaria was the first Central Power to sign an armistice—the Armistice of Salonica on 29 September 1918. On 30 October, the Ottoman Empire capitulated. On 4 November, the Austro-Hungarian empire agreed to the Armistice of Villa Giusti after being decisively defeated by Italy in the Battle of Vittorio Veneto. With its allies defeated, revolution at home, the military no longer willing to fight, Kaiser Wilhelm abdicated on 9 November and Germany signed an armistice on 11 November 1918. World War I was a significant turning point in the political, cultural and social climate of the world; the war and its immediate aftermath sparked numerous uprisings. The Big Four (Britain, the United States, It
Laundry detergent, or washing powder, is a type of detergent, added for cleaning laundry. While detergent is still sold in powdered form, liquid detergents have been taking major market shares in many countries since their introduction in the 1950s. Laundry detergent pods have been sold in the United States since 2012 when they were introduced by Procter & Gamble as Tide Pods. Earlier instances of laundry detergent pods include Salvo tablets sold in the 1970s. From ancient times, chemical additives were used to facilitate the mechanical washing of clothing with water; the Italians used a mix of water with charcoal to clean cloth. Egyptians added silicates to soften water. Soaps were the first detergents; the detergent effects of certain synthetic surfactants were noted in Germany in 1917, in response to shortages of soap during World War I. In the 1930s, commercially viable routes to fatty alcohols were developed, these new materials were converted to their sulfate esters, key ingredients in the commercially important German brand FEWA, produced by BASF, Dreft, the U.
S. brand produced by Gamble. Such detergents were used in industry until after World War II. By new developments and the conversion of aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of domestic use in the late 1940s. Washing laundry involves removing mixed soils from fiber surfaces. From a chemical viewpoint, soils can be grouped into: Water-soluble soils such as sugars, inorganic salts and perspiration. Solid particulate soils such as rust, metal oxides, carbonates and humus. Hydrophobic soils such as animal fats, vegetable oils, mineral oil, grease. Proteins such as blood, egg and keratin from skin; these require enzymes, heat or alkali to hydrolyze and denature them into smaller parts before they can be removed by the surfactants. Bleachable stains such as wine, tea, fruit juices, vegetable stains. Bleaching is an oxidation reaction which turns the colored substance into a colorless one, which either stays on the fabric or may be easier to wash out.
Soils difficult to remove are pigments and dyes, resins, tar and denatured protein. Laundry detergents may contain builders, bleach, soil antiredeposition agents, foam regulators, corrosion inhibitors, optical brighteners, dye transfer inhibitors, dyes and formulation aids. Builders are water softeners. Hard water contains calcium and metallic cations; these cations react with surfactant anions to form insoluble compounds which precipitate onto fabrics and washing machines and which are difficult to remove. Builders remove the hard water ions through chelation or ion exchange. In addition, they help remove soil by dispersion. In most European regions the water is hard. In North America and Japan, the water is comparatively soft; the earliest builders were sodium silicate. Since the 1930s, phosphates and polyphosphates were introduced, continuing with the introduction of phosphonates; these agents are now known to have serious environmental consequences leading to a drive towards more environmentally benign phosphorus-free agents, such as polycarboxylates, silicates, gluconic acid and polyacrylic acid.
Alkalis like soda ash precipitate hard water ions and are used as builders. Additionally, they enhance washing performance. Hydrophilic fibers like cotton have a negative surface charge in water, whereas synthetic fibers are comparatively neutral; the negative charge is further increased by the adsorption of anionic surfactants. With increasing pH, soil and fibers become more negatively charged, resulting in increased mutual repulsion; this is one of the reasons why alkalis enhance wash performance, apart from effects like the saponification of fats. However, repulsive forces between soil and fibers alone do not produce satisfactory washing results at high pH; the optimum pH range for good detergency is 9-10.5. Builder and surfactant work synergistically to achieve soil removal, the washing effect of the builder may exceed that of the surfactant. With hydrophilic fibres like cotton, wool and polyacrylonitrile, sodium triphosphate removes soil more than a surfactant alone. With hydrophobic fibres like polyesters and polyolefins, the effectiveness of the surfactant surpasses that of the builder.
Surfactants are responsible for most of the cleaning performance in laundry detergent. They provide this by absorption and emulsification of soil into the water and by reducing the water's surface tension to improve wetting. Laundry detergents contain anionic and non-ionic surfactants. Cationic surfactants are incompatible with anionic detergents and have poor cleaning efficiency. Zwitterionic surfactants are employed in laundry detergents for cost reasons. Most detergents use a combination of various surfactants to balance their performance; until the 1950s, soap was the predominant surfactant in laundry detergents. By the end of the 1950s so-called "synthetic detergents" like tetrapropylenebenzenesulfonate had replaced soap in developed countries. Due to their poor biodegradability these branched alkylbenzen
Polysorbates are a class of emulsifiers used in some pharmaceuticals and food preparation. They are used in cosmetics to solubilize essential oils into water-based products. Polysorbates are oily liquids derived from ethoxylated sorbitan esterified with fatty acids. Common brand names for polysorbates include Scattics, Alkest and Tween. Polysorbate 20 Polysorbate 40 Polysorbate 60 Polysorbate 80 The number 20 following the'polyoxyethylene' part refers to the total number of oxyethylene -- groups found in the molecule; the number following the'polysorbate' part is related to the type of fatty acid associated with the polyoxyethylene sorbitan part of the molecule. Monolaurate is indicated by 20, monopalmitate is indicated by 40, monostearate by 60, monooleate by 80. Sorbitan monolaurate Sorbitan monostearate Sorbitan tristearate NIH PEG-60 Household Products Database