Heat Exchanger

Heat money changer An interchange open home office horniness money changer vasiform warmth money changer. A mold off exchanger is a piece of equipment built for efficient modify withdraw from one medium to some other. The media may be sepa assessd by a unattackable wall, so that they never mix, or they may be in direct contact. 1 They ar widely utilise in space agitateing, infrigidation, expression conditioning, military unit plants, chemical plants, petrochemical plants, petroleum re vertical fineries, natural throttle valve processing, and sewage treatment.The classic example of a erupting plant exchanger is found in an cozy combustion engine in which a circulating silver-tongued known as engine coolant hunts with radiator coils and air flows past the coils, which cools the coolant and agitates the succeeding(prenominal) air. Contents Flow arrangement rip (A) and parallel (B) flows * Fig. 1 Shell and provide change exchanger, adept throttle (1 1 parallel flow) * Fig. 2 Shell and furnish stir up up exchanger, 2-pass thermionic valve expression (12 crossflow) * Fig. Shell and tube commove exchanger, 2-pass strap side, 2-pass tube side (2-2 countercurrent) There ar three direct classifications of ignite exchangers according to their flow arrangement. In parallel-flow set off exchangers, the twain fluids enter the exchanger at the very(prenominal) finale, and travel in parallel to one another to the other side. In counter-flow ro physical exercise exchangers the fluids enter the exchanger from opposite ends. The counter current design is the some efficient, in that it female genitalia imparting the most catch fire from the heat (transfer) medium due to the fact that the average temperature dis projecte along any unit duration is greater.See countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger. For efficiency, heat exchangers be designed to maximize the dig up bea of the wall amidst the two fluids, p plow of ground minimizing resistance to fluid flow through the exchanger. The exchangers per course of studyance can also be affected by the addition of fins or corrugations in one or twain directions, which increase surface argona and may channel fluid flow or induce turbulence. The driving temperature across the heat transfer surface varies with position, hardly an appropriate mean temperature can be defined.In most simple remainss this is the log mean temperature deflexion (LMTD). Sometimes direct friendship of the LMTD is not forthcoming and the NTU method is apply. Types of heat exchangers Shell and tube heat exchanger A Shell and vacuum tube heat exchanger Main article Shell and tube heat exchanger Shell and tube heat exchangers consist of a series of tubes. One set of these tubes contains the fluid that must(prenominal)iness be each heated or cooled. The second fluid runs everywhere the tubes that ar being heated or cooled so that it can either provide the heat or assimilate the heat required.A set of tubes is called the tube bundle and can be made up of several types of tubes plain, longitudinally finned, etc. Shell and tube heat exchangers are typically utilize for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260C). 2 This is because the plate and tube heat exchangers are robust due to their shape. Several caloric design features must be considered when designing the tubes in the shell and tube heat exchangers * Tube diam Using a small tube diameter makes the heat exchanger both economical and compact.However, it is to a greater extent interchangeablely for the heat exchanger to foul up faster and the small size makes mechanical modify of the fouling difficult. To prevail over the fouling and make clean problems, bounteousr tube diameters can be utilise. Thus to determine the tube diameter, the ava ilable space, cost and the fouling nature of the fluids must be considered. * Tube thickness The thickness of the wall of the tubes is ordinarily determined to ensure * There is enough room for corrosion * That flow-induced vibration has resistance * Axial force- place * Availability of spare parts Hoop strength (to make internal tube pressure) * Buckling strength (to concord overpressure in the shell) * Tube length heat exchangers are usually cheaper when they eat a smaller shell diameter and a long tube length. Thus, typically there is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities. However, there are many limitations for this, including space available at the installation site and the urgency to ensure tubes are available in lengths that are twice the required length (so they can be withdrawn and replaced).Also, long, shrink tubes are difficult to take out and replace. * Tube fork out when designing the tubes, it is practical to ensure that the tube pitch (i. e. , the centre-centre distance of adjoining tubes) is not less than 1. 25 times the tubes outside diameter. A larger tube pitch leads to a larger overall shell diameter, which leads to a more expensive heat exchanger. * Tube corrugation this type of tubes, mainly utilize for the home(a) tubes, increases the turbulence of the fluids and the effect is very important in the heat transfer giving a better cognitive process. Tube Layout link ups to how tubes are positioned within the shell. There are quaternion main types of tube layout, which are, triangular (30), rotated triangular (60), square (90) and rotated square (45). The triangular patterns are employed to give greater heat transfer as they force the fluid to flow in a more turbulent fashion around the piping. Square patterns are employed where high fouling is experience and cleaning is more regular. * Baffle Design baffles are utilize in shell and tube heat exchangers to direct fluid across the tube bundle.They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the divided baffle. The semi visor segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid to flow upwardly and downwards between the tube bundle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must be space with consideration for the conversion of pressure drop and heat transfer.For thermo economic optimization it is suggested that the baffles be spaced no coatingr than 20% of the shells inner diameter. Having baffles spaced too closely causes a greater pressure drop because of flow redirection. Consequently having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are s paced close enough that the tubes do not sag. The other main type of baffle is the disc and donut baffle, which consists of two concentric baffles. An outer, wider baffle looks like a donut, whilst the inner baffle is shaped like a disk.This type of baffle forces the fluid to pass around each(prenominal) side of the disk indeed through the donut baffle generating a assorted type of fluid flow. Fixed tube liquid-cooled heat exchangers especially suitable for devil dog and harsh applications can be assembled with brass shells, hair tubes, brass baffles, and forged brass integral end hubs. 3 (See Copper in heat exchangers). Conceptual diagram of a plate and frame heat exchanger. A single plate heat exchanger An interchangeable plate heat exchanger applied to the arrangement of a move pool eggshell heat exchanger Main article Plate heat exchanger other type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. Advances in gasket and brazing technology have made the plate-type heat exchanger increasingly practical. In HVAC applications, large heat exchangers of this type are called plate-and-frame when used in open loops, these heat exchangers are normally of the gasket type to allow periodic disassembly, cleaning, and inspection.There are many types of permanently bonded plate heat exchangers, such as dip-brazed, vacuum-brazed, and welded plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and in the configurations of those plates. Some plates may be stamped with chevron, dimpled, or other patterns, where others may have machined fins and/or grooves. Plate and shell heat exchanger A threesome type of heat exchanger is a plate and shell heat exchanger, which acquiesces plate heat exchanger with shell and tube heat exchanger technologies.The heart of the heat exchanger contains a fully welded circular plate pack made by pressing and cutting round plates and welding them together. Nozzles carry flow in and out of the platepack (the Plate side flowpath). The fully welded platepack is assembled into an outer shell that creates a second flowpath ( the Shell side). Plate and shell technology offers high heat transfer, high pressure, high operating temperature, compact size, low fouling and close approach temperature. In particular, it does completely without gaskets, which provides security a fixst leakage at high pressures and temperatures.Adiabatic wheel heat exchanger A fourth type of heat exchanger uses an intermediate fluid or solid investment company to hold heat, which is past moved to the other side of the heat exchanger to be released. twain examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the scorching and glacial fluids, and fluid heat exchangers. Plate fin heat exchanger Main article Plate fin heat exchanger This type of heat exchanger uses sandwiched passages containing fins to increase the military posture of the unit.The designs include crossflow and counterflow coupled with assorted fin configurations such as straight fins, offset fins and wavy fins. Plate and fin heat exchangers are usually made of aluminium alloys, which provide high heat transfer efficiency. The material enables the system to plight at a lower temperature and reduce the weight of the equipment. Plate and fin heat exchangers are largely used for low temperature services such as natural gas, atomic number 2 and oxygen liquefaction plants, air breakup plants and transport industries such as motor and aircraft engines. Advantages of plate and fin heat exchangers High heat transfer efficiency especially in gas treat ment * Larger heat transfer area * or so 5 times lighter in weight than that of shell and tube heat exchanger. * Able to withstand high pressure Disadvantages of plate and fin heat exchangers * Might cause clogging as the pathways are very narrow * Difficult to clean the pathways * Aluminum alloys are susceptible to Mercury Liquid Embrittlement misery Pillow plate heat exchanger A pillow plate exchanger is commonly used in the dairy industry for cooling milk in large direct-expansion stainless steel bulge tanks.The pillow plate allows for cooling across nearly the entire surface area of the tank, without gaps that would occur between vacuum tubes welded to the exterior of the tank. The pillow plate is constructed using a thin sheet of metal spot-welded to the surface of another thicker sheet of metal. The thin plate is welded in a regular pattern of dots or with a sheer pattern of weld lines. After welding the enclosed space is pressurized with sufficient force to cause the th in metal to bulge out around the welds, providing a space for heat exchanger liquids to flow, and creating a peculiar(prenominal) appearance of a swelled pillow formed out of metal.Fluid heat exchangers This is a heat exchanger with a gas passing upwards through a shower of fluid (often pee), and the fluid is then taken elsewhere before being cooled. This is commonly used for cooling gases whilst also removing certain impurities, and then solving two problems at once. It is widely used in espresso machines as an energy-saving method of cooling super-heated wet to use in the extraction of espresso. pine heat recovery units A Waste Heat convalescence Unit (WHRU) is a heat exchanger that recovers heat from a hot gas stream season transferring it to a working medium, typically piddle or oils.The hot gas stream can be the ingest gas from a gas turbine or a diesel engine or a waste gas from industry or refinery. They can also be integrated into a heatcatcher system that allows an ORCfurther explanation needed generator to produce waste heat to power. Dynamic scraped surface heat exchanger Another type of heat exchanger is called (dynamic) scraped surface heat exchanger. This is mainly used for heating or cooling with high-viscosity products, crystallization processes, evaporation and high-fouling applications.Long running times are achieved due to the continuous scraping of the surface, and then avoiding fouling and achieving a sustainable heat transfer rate during the process. Phase-change heat exchangers Typical kettle reboiler used for industrial distillation towers Typical peeing-cooled surface condenser In addition to heating up or cooling down fluids in just a single kind, heat exchangers can be used either to heat a liquid to evaporate (or boil) it or used as condensers to cool a vapor and condense it to a liquid. In chemical plants and refineries, reboilers used to heat incoming feed for distillation towers are often heat exchangers. 45 Distilla tion set-ups typically use condensers to condense distillate vapors masking into liquid. Power plants that use steamer-driven turbines commonly use heat exchangers to boil water into steam. Heat exchangers or akin(predicate) units for producing steam from water are often called boilers or steam generators. In the nuclear power plants called pressurized water reactors, special large heat exchangers pass heat from the radical (reactor plant) system to the secondary (steam plant) system, producing steam from water in the process. These are called steam generators.All fossil-fueled and nuclear power plants using steam-driven turbines have surface condensers to convert the exhaust steam from the turbines into condensate (water) for re-use. 67 To con attend energy and cooling capacity in chemical and other plants, regenerative heat exchangers can transfer heat from a stream that must be cooled to another stream that must be heated, such as distillate cooling and reboiler feed pre-heati ng. This term can also refer to heat exchangers that contain a material within their structure that has a change of pattern.This is usually a solid to liquid phase due to the small volume difference between these states. This change of phase effectively acts as a buffer because it occurs at a constant temperature but still allows for the heat exchanger to accept additional heat. One example where this has been investigated is for use in high power aircraft electronics. charge contact heat exchangers Direct contact heat exchangers involve heat transfer between hot and ice- chilliness streams of two phases in the absence of a separating wall. 8 Thus such heat exchangers can be classified as * bumble liquid * Immiscible liquid liquid Solid-liquid or solid gas Most direct contact heat exchangers fall under the Gas- Liquid category, where heat is transferred between a gas and liquid in the form of drops, films or sprays. 2 Such types of heat exchangers are used preponderantly in a ir conditioning, humidification, industrial hot water heating, water cooling and condense plants. 9 Phases10 Continuous phase Driving force Change of phase Examples Gas Liquid Gas Gravity No spraying columns, packed columns Yes temperature reduction towers, falling droplet evaporators Forced No Spray coolers/quenchers Liquid flow Yes Spray condensers/evaporation, spring condensers Liquid Gravity No Bubble columns, perforated tray columns Yes Bubble column condensers Forced No Gas spargers Gas flow Yes Direct contact evaporators, submerged combustion HVAC air coils One of the widest uses of heat exchangers is for air conditioning of buildings and vehicles. This class of heat exchangers is commonly called air coils, or just coils due to their often-serpentine internal tubing. Liquid-to-air, or air-to-liquid HVAC coils are typically of modified crossflow arrangement. In vehicles, heat coils are often called heater cores.On the liquid side of these heat exchangers, the common fluids are water, a water-glycol solution, steam, or a refrigerant. For heating coils, hot water and steam are the most common, and this heated fluid is supplied by boilers, for example. For cooling coils, chilled water and refrigerant are most common. Chilled water is supplied from a chiller that is potentially located very far away, but refrigerant must come from a nearby condensing unit. When a refrigerant is used, the cooling coil is the evaporator in the vapor-compression refrigeration cycle. HVAC coils that use this direct-expansion of refrigerants are commonly called DX coils.Some DX coils are microchannel type. 11 On the air side of HVAC coils a significant difference exists between those used for heating, and those for cooling. Due to psychrometrics, air that is cooled often has moisture condensing out of it, except with super dry air flows. Heating some air increases that airflows capacity to hold water. So heating coils need not consider moisture condensation on their air-side, but cooling coils must be adequately designed and selected to handle their particular latent (moisture) as well as the sensible (cooling) loads.The water that is take away is called condensate. For many climates, water or steam HVAC coils can be exposed to freezing conditions. Because water expands upon freezing, these approximately expensive and difficult to replace thin-walled heat exchangers can easily be damaged or finished by just one freeze. As such, freeze protection of coils is a major concern of HVAC designers, installers, and operators. The installation of indentations placed within the heat exchange fins controlled condensation, allowing water molecules to remain in the cooled air.This invention allowed for refrigeration without frost of the cooling mechanism. 12 The heat exchangers in direct-combustion furnaces, typical in many residences, are not coils. They are, instead, gas-to-air heat exchangers that are typically made of stamped steel sheet meta l. The combustion products pass on one side of these heat exchangers, and air to heat on the other. A cracked heat exchanger is therefore a monstrous situation that requires immediate attention because combustion products may enter living space. Spiral heat exchangers conventional drawing of a whorl heat exchanger.A spiral heat exchanger (SHE), may refer to a helical (coiled) tube configuration, more generally, the term refers to a pair of flat surfaces that are coiled to form the two channels in a counter-flow arrangement. Each of the two channels has one long curved path. A pair of fluid ports are connected tangentially to the outer arms of the spiral, and axial ports are common, but optional. 13 The main advantage of the SHE is its highly efficient use of space. This attribute is often leveraged and partially reallocated to gain other improvements in performance, according to well known tradeoffs in heat exchanger design. A notable tradeoff is capital cost vs operating cost. ) A compact SHE may be used to have a smaller footprint and thus lower all-around capital costs, or an over-size SHE may be used to have less pressure drop, less pumping energy, higher thermal efficiency, and lower energy costs. look The distance between the sheets in the spiral channels are maintained by using spacer studs that were welded precedent to rolling. Once the main spiral pack has been rolled, alternate top and bottom edges are welded and each end closed by a gasketed flat or conical cover bolted to the body.This ensures no mixing of the two fluids occurs. Any leakage is from the periphery cover to the atmosphere, or to a passage that contains the same fluid. 14 Self cleaning SHEs are often used in the heating of fluids that contain solids and thus tend to foul the internal of the heat exchanger. The low pressure drop lets the SHE handle fouling more easily. The SHE uses a self cleaning mechanism, whereby befouled surfaces cause a localized increase in fluid velocity , thus increasing the drag (or fluid friction) on the fouled surface, thus helping to dislodge the blockage and keep the heat exchanger clean. The internal walls that make up the heat transfer surface are often rather thick, which makes the SHE very robust, and able to last a long time in demanding environments. They are also easily cleaned, opening out like an oven where any build up of foulant can be removed by pressure washing. Self-Cleaning water filters are used to keep the system clean and running without the need to shut down or replace cartridges and bags. Flow arrangements Concurrent and countercurrent flow. There are three main types of flows in a spiral heat exchanger 1. Counter-current Flow Fluids flow in opposite directions.These are used for liquid-liquid, condensing and gas cooling applications. Units are usually attach vertically when condensing vapour and mounted horizontally when handling high concentrations of solids. 2. Spiral Flow/Cross Flow One fluid is in s piral flow and the other in a cross flow. Spiral flow passages are welded at each side for this type of spiral heat exchanger. This type of flow is suitable for handling low density gas, which passes through the cross flow, avoiding pressure loss. It can be used for liquid-liquid applications if one liquid has a well greater flow rate than the other. . Distributed Vapour/Spiral flow This design is that of a condenser, and is usually mounted vertically. It is designed to cater for the sub-cooling of both condensate and non-condensables. The coolant moves in a spiral and trusts via the top. Hot gases that enter leave as condensate via the bottom outlet. Applications The SHE is good for applications such as pasteurization, digester heating, heat recovery, pre-heating (see recuperator), and effluent cooling. For sludge treatment, SHEs are generally smaller than other types of heat exchangers. citation needed SelectionDue to the many variables involved, selecting optimal heat exchange rs is challenging. Hand calculations are possible, but many iterations are typically needed. As such, heat exchangers are most often selected via computer programs, either by system designers, who are typically engineers, or by equipment vendors. To select an appropriate heat exchanger, the system designers (or equipment vendors) would firstly consider the design limitations for each heat exchanger type. Though cost is often the primary criterion, several other selection criteria are important * High/low pressure limits * Thermal performance Temperature ranges * Product mix (liquid/liquid, particulates or high-solids liquid) * Pressure drops across the exchanger * Fluid flow capacity * Cleanability, nutriment and repair * Materials required for construction * Ability and ease of future expansion * Material selection, such as copper, aluminum, carbon steel, stainless steel, nickel alloys, and titanium. elfin-diameter coil technologies are becoming more popular in forward-looking a ir conditioning and refrigeration systems because they have better rates of heat transfer than conventional sized condenser and evaporator coils with round copper tubes and aluminium or opper fin that have been the standard in the HVAC industry. Small diameter coils can withstand the higher pressures required by the new generation of environmentally friendlier refrigerants. Two small diameter coil technologies are currently available for air conditioning and refrigeration products copper microgroove15 and brazed aluminium microchannel. 16 Choosing the right heat exchanger (HX) requires some knowledge of the different heat exchanger types, as well as the environment where the unit must operate.Typically in the manufacturing industry, several differing types of heat exchangers are used for just the one process or system to derive the final product. For example, a kettle HX for pre-heating, a double pipe HX for the carrier fluid and a plate and frame HX for final cooling. With sufficie nt knowledge of heat exchanger types and operating requirements, an appropriate selection can be made to optimise the process. 17 observe and maintenance Online monitoring of commercial heat exchangers is done by tracking the overall heat transfer coefficient. The overall heat transfer coefficient tends to decline over time due to fouling.U=Q/A? Tlm By periodically calculating the overall heat transfer coefficient from exchanger flow rates and temperatures, the owner of the heat exchanger can estimate when cleaning the heat exchanger is economically attractive. Integrity inspection of plate and hollow heat exchanger can be tested in situ by the conductivity or helium gas methods. These methods confirm the integrity of the plates or tubes to prevent any cross contamination and the condition of the gaskets. mechanically skillful integrity monitoring of heat exchanger tubes may be conducted through Nondestructive methods such as gimmick current testing.Fouling Main article Fouling A heat exchanger in a steam power station contaminated with macrofouling. Fouling occurs when impurities deposit on the heat exchange surface. Deposition of these impurities can decrease heat transfer effectiveness significantly over time and are caused by * Low wall clip stress * Low fluid velocities * High fluid velocities * Reaction product solid precipitation * heedlessness of dissolved impurities due to elevated wall temperatures The rate of heat exchanger fouling is determined by the rate of particle deposition less re-entrainment/suppression.This model was originally proposed in 1959 by Kern and Seaton. Crude inunct Exchanger Fouling. In commercial harsh oil refining, crude oil is heated from 21 C to 343 C prior to entering the distillation column. A series of shell and tube heat exchangers typically exchange heat between crude oil and other oil streams to heat the crude to 260 C prior to heating in a furnace. Fouling occurs on the crude side of these exchangers due to asp haltene insolvability. The nature of asphaltene solubility in crude oil was successfully modeled by Wiehe and Kennedy. 18 The precipitation of insoluble asphaltenes in crude preheat trains has been successfully modeled as a first order reaction by Ebert and Panchal19 who grow on the work of Kern and Seaton. Cooling Water Fouling. Cooling water systems are susceptible to fouling. Cooling water typically has a high total dissolved solids content and suspended colloidal solids. place precipitation of dissolved solids occurs at the heat exchange surface due to wall temperatures higher than book fluid temperature. Low fluid velocities (less than 3ft/s) allow suspended solids to settle on the heat exchange surface.Cooling water is typically on the tube side of a shell and tube exchanger because its easy to clean. To prevent fouling, designers typically ensure that cooling water velocity is greater than 0. 9 m/s and bulk fluid temperature is maintained less than 60 C. Other approaches t o control fouling control combine the blind application of biocides and anti-scale chemicals with periodic lab testing. Maintenance Plate heat exchangers must be disassembled and cleaned periodically. Tubular heat exchangers can be cleaned by such methods as acid cleaning, sandblasting, high-pressure water jet, biff cleaning, or drill rods.In large-scale cooling water systems for heat exchangers, water treatment such as purification, addition of chemicals, and testing, is used to minimize fouling of the heat exchange equipment. Other water treatment is also used in steam systems for power plants, etc. to minimize fouling and corrosion of the heat exchange and other equipment. A variety of companies have started using water borne oscillations technology to prevent biofouling. Without the use of chemicals, this type of technology has helped in providing a low-pressure drop in heat exchangers. In nature HumansThe human emaciated passages serve as a heat exchanger, which warms air bein g inhaled and cools air being exhaled. You can demonstrate its effectiveness by putting your hand in front of your face and exhaling, first through your nose and then through your mouth. Air exhaled through your nose is substantially cooler. 2021 In species that have external testes (such as humans), the arterial breed vessel to the testis is surrounded by a mesh of veins called the pampiniform plexus. This cools the blood heading to the testis, while reheating the returning blood. Birds, fish, marine mammalsCountercurrent exchange conservation circuit Further information Countercurrent exchange in biological systems Countercurrent heat exchangers occur naturally in the circulation system of fish, whales and other marine mammals. Arteries to the skin carrying warm blood are intertwined with veins from the skin carrying cold blood, causing the warm arterial blood to exchange heat with the cold venous blood. This reduces the overall heat loss in cold waters. Heat exchangers are also set in the tongue of baleen whales as large volumes of water flow through their mouths. 2223 Wading birds use a similar system to limit heat losses from their body through their legs into the water. Carotid rete The carotid rete is a counter-current heat exchanging organ in some ungulates. The blood ascending the carotid arteries on its way to the brain, flows via a network of vessels where heat is discharged to the veins of cooler blood descending from the nasal passages. The carotid rete allows Thomsons gazelle to maintain its brain almost 3C cooler than the rest of the body, and therefore aids in tolerating bursts in metabolic heat roduction such as associated with outrunning cheetahs (during which the body temperature exceeds the maximum temperature at which the brain could function). 24 In industry Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes. The type and size of heat exchanger used can be tailored to suit a proces s depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical physical composition and various other thermodynamic properties.In many industrial processes there is waste of energy or a heat stream that is being exhausted, heat exchangers can be used to recover this heat and put it to use by heating a different stream in the process. This practice saves a lot of money in industry, as the heat supplied to other streams from the heat exchangers would otherwise come from an external reservoir that is more expensive and more harmful to the environment. Heat exchangers are used in many industries, including * Waste water treatment Refrigeration * Wine and beer making * Petroleum refining In waste water treatment, heat exchangers play a vital role in maintaining optimal temperatures within anaerobic digesters to bring up the growth of microbes that remove pollutants. Common types of heat exchangers used in this application are the double pipe heat exc hanger as well as the plate and frame heat exchanger. In aircraft In commercial aircraft heat exchangers are used to take heat from the engines oil system to heat cold fuel. 25 This improves fuel efficiency, as well as reduces the possibility of water entrapped in the fuel freezing in components. 26 Early 2008, a Boeing 777 flying as British Airways Flight 38 crashed just short of the runway. In an early-2009 Boeing-update sent to aircraft operators, the problem was identified as specific to the Rolls-Royce engine oil-fuel flow heat exchangers. 26 Other heat exchangers, or Boeing 777 aircraft powered by GE or Pratt and Whitney engines, were not affected by the problem. 26