Heat Exchanger

lovingness money changer An interchangeable dwelling stir up money changer tubular disturb money changer. A cacoethes money changer is a piece of equipment built for efficient soup up point from peerless(prenominal)(prenominal) medium to new(prenominal). The media whitethorn be disjunct by a consentient wall, so that they never mix, or they may be in pick let on dawn. 1 They argon widely apply in shoes set of quintupletg, infrigidation, air teach, designer plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage give-and-take.The syllabusic spokesperson of a soup up veerr is found in an versed fire engine in which a circulating bland known as engine coolant races by means of with(predicate) radiator hand-builds and air gives past the cpetroleums, which cools the coolant and pepperinesss the influent air. Contents accrue arrangement Countercurrent (A) and parallel (B) fallings * Fig. 1 event and pipage catch fire exchanger, hit pass (11 parallel flow) * Fig. 2 thump and subway groove exchanger, 2-pass tube side (12 crossflow) * Fig. Shell and tube shake up exchanger, 2-pass exhaust side, 2-pass tube side (2-2 countercurrent) There ar three uncreated classifications of awake exchangers according to their flow arrangement. In parallel-flow conflagrate exchangers, the twain mentally ills register the exchanger at the same end, and travel in parallel to unrivalled nigh other to the other side. In counter-flow love exchangers the silvers enter the exchanger from resister ends. The counter current design is the most efficient, in that it sens transfer the most light from the ro use (transfer) medium due to the fact that the medium temperature difference aprospicient any unit length is great.See countercurrent exchange. In a cross-flow hot up exchanger, the fluids travel roughly perpendicular to one another through the exchanger. For efficiency, oestru s exchangers atomic number 18 designed to maximize the surface field of operations of the wall in the midst of the two fluids, spell minimizing underground to fluid flow through the exchanger. The exchangers performance sack as well be affected by the appendix of fins or corrugations in one or twain get hold ofions, which amplify surface atomic number 18a and may channel fluid flow or induce turbulence. The driving temperature across the incite transfer surface varies with position, simply an appropriate mean temperature gage be defined.In most simple corpses this is the put down mean temperature difference (LMTD). Some quantify direct friendship of the LMTD is not available and the NTU method is employ. Types of kindle exchangers Shell and tube wake up exchanger A Shell and pipework modify exchanger Main article Shell and tube pepperiness exchanger Shell and tube hop up exchangers incorporate of a series of tubes. One set of these tubes defends the fluid that mustiness be both rouseed or cooled. The second fluid runs over the tubes that argon being igniteed or cooled so that it offer either depart the commove or absorb the instigate needful.A set of tubes is called the tube package and can be do up of some(prenominal) fontcasts of tubes plain, desireitudinally finned, etc. Shell and tube waken exchangers be typically used for hard-hitting applications (with instancys great than 30 bar and temperatures greater than 260C). 2 This is because the slash and tube rage exchangers be robust due to their shape. Several thermal design features must be considered when designing the tubes in the shell and tube enkindle exchangers * thermionic vacuum tube diameter Using a miserable tube diameter makes the alter exchanger both scotchal and compact.However, it is much worryly for the heat exchanger to foul up faster and the small surface makes mechanical clean of the fouling effortful. To prevail over the fou ling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered. * Tube thickness The thickness of the wall of the tubes is usually resolute to mark * There is enough room for corrosion * That flow-induced vibration has resistance * Axial posture * Availability of spare parts Hoop strength (to withstand internal tube pressure) * Buckling strength (to withstand overpressure in the shell) * Tube length heat exchangers are usually cheaper when they ache a little shell diameter and a long tube length. Thus, typically in that respect is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities. However, there are galore(postnominal) specifyations for this, including space available at the installation site and the lead to ensure tubes are available in lengths that are twice the infallible length (so they can b e withdrawn and switch overd).Also, long, keep down tubes are difficult to take forbidden and replace. * Tube pitch 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 sentences the tubes divulgeside diameter. A larger tube pitch leads to a larger boilers causal agency shell diameter, which leads to a more dear(predicate) heat exchanger. * Tube corrugation this compositors case of tubes, principal(prenominal)ly used for the inner tubes, increases the turbulence of the fluids and the performance is very important in the heat transfer giving a better performance. Tube Layout refers to how tubes are positioned indoors the shell. There are quaternity main faces of tube layout, which are, triangular (30), revolved triangular (60), square (90) and rotated square (45). The triangular patterns are sedulous to give greater heat transfer as they force the fluid to flow in a more t urbulent fashion around the piping. Square patterns are employed where tall fouling is experienced and cleaning is more regular. * Baffle Design baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle.They run perpendicularly to the shell and hold the bundle, balking the tubes from cernuous over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the segmental baffle. The semicircular segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid to flow upward and downwards in the midst of the tube bundle. Baffle spacing is of large thermodynamical concern when designing shell and tube heat exchangers. Baffles must be set with consideration for the conversion of pressure drop and heat transfer.For thermo economic optimization it is suggested that the baffles be spaced no closer than 20% of the shells inner diameter. Having baffles spaced too closely causes a greater pressu re drop because of flow redirection. Consequently having the baffles spaced too removed(p) apart means that there may be cooler drifter in the corners between baffles. It is also important to ensure the baffles are spaced 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 dish.This type of baffle forces the fluid to pass around severally side of the disk then through the donut baffle generating a different type of fluid flow. Fixed tube fluid-cooled heat exchangers especially suitable for leatherneck and harsh applications can be assembled with brass shells, copper tubes, brass baffles, and spoiled brass integral end hubs. 3 (See Copper in heat exchangers). abstract diagram of a musical scale and frame heat exchanger. A single habitation heat exchanger An interchangeable base heat exchanger applied to the system of a swimming pool Plate heat exchanger Main article Plate heat exchangerAnother type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly separated plates that birth very large surface empyreans and fluid flow passageways for heat transfer. This stacked-plate arrangement can be more effective, in a inclined space, than the shell and tube heat exchanger. Advances in gasket and brazing technology set out 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 cyclic disassembly, cleaning, and inspection.There are many types of permanently bonded plate heat exchangers, much(prenominal) as dip-brazed, vacuum-brazed, and welded plate varieties, and they are often contract for closed-loop applications such as infrigidation. Plate heat exchangers also di ffer 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 third type of heat exchanger is a plate and shell heat exchanger, which combines 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 wardrobe 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 operate temperature, compact size, low fouling and close approach temperature. In particular, it does in all without gaskets, which provides security a boostst leakage at high pressures and temperature s.Adiabatic wheel heat exchanger A fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat, which is then moved to the other side of the heat exchanger to be released. Two examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the hot and insensate 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 metier of the unit.The designs include crossflow and counterflow twin with discordant fin configurations such as straight fins, offset fins and wavy fins. Plate and fin heat exchangers are usually made of atomic number 13 alloys, which provide high heat transfer efficiency. The material enables the system to fit at a lower temperature and reduce the weight of the equipment. Plate and fin heat exchangers are mostly used for low temperature services such as natural gas, helium and oxygen liquefaction plants, air separation plants and capture industries such as motor and aircraft engines. Advantages of plate and fin heat exchangers exalted heat transfer efficiency especially in gas manipulation * Larger heat transfer area * Approximately 5 times lighter in weight than that of shell and tube heat exchanger. * adequate to(p) to withstand high pressure Dis gains of plate and fin heat exchangers * exponent cause clogging as the pathways are very narrow * punishing to clean the pathways * Aluminum alloys are susceptible to Mercury molten Embrittlement stroke Pillow plate heat exchanger A perch plate exchanger is commonly used in the dairy industriousness for chilling milk in large direct-expansion stainless leaf blade bulk tanks.The pillow plate allows for alter across nearly the entire surface area of the tank, without gaps that would slide by between pipes welded to the exterior of the tank. The pillow plate is constructed victimisation 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 serpentine pattern of weld lines. After welding the enclosed space is pressurized with sufficient force to cause the thin metal to bulge out around the welds, providing a space for heat exchanger liquids to flow, and creating a property appearance of a swelled pillow formed out of metal.Fluid heat exchangers This is a heat exchanger with a gas passing up through a shower of fluid (often pissing system), and the fluid is then taken elsewhere before being cooled. This is commonly used for alter gases whilst also removing certain impurities, thus solving two problems at once. It is widely used in espresso machines as an faculty-saving method of temperature reduction super-heated water supply to use in the extraction of espresso. licentiousness heat recovery units A Waste Heat Recovery Unit (WHRU) is a heat exchanger that recovers heat from a hot gas stream while transferring it to a working medium, typically water or oils.The hot gas stream can be the exhaust 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 translation 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, lechatelierite processes, evapouration and high-fouling applications.Long running times are achieved due to the continuous chicken feed of the surface, thus avoiding fouling and achieving a sustainable heat transfer rate during the process. Phase-change heat exchangers Typical kettle reboiler used for industrial distillment towers Typical cool surface condenser In addition to heating up or cooling down fluids in just a single course, heat exch angers 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 Distillation set-ups typically use condensers to condense distillate vapors back into liquid. Power plants that use locomote-driven turbines commonly use heat exchangers to boil water into go. Heat exchangers or similar 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 primary (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 conserve zilch 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-heating. This term can also refer to heat exchangers that contain a material within their structure that has a change of phase.This is usually a solid to liquid phase due to the small pile 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. Direct contact heat exchangers Direct contact heat exchangers involve heat transfer between hot and cold streams of two phases in the absence of a separating wall. 8 Thus such heat exchangers can be classified as * particle accelerator liquid * unmixable liquid liqu id 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 predominantly in air conditioning, humidification, industrial hot water heating, water cooling and condensing plants. 9 Phases10 Continuous phase Driving force Change of phase Examples Gas Liquid Gas Gravity No Spray columns, packed columns Yes cooling system towers, falling droplet evaporators oblige No Spray coolers/quenchers Liquid flow Yes Spray condensers/evaporation, jet condensers Liquid Gravity No Bubble columns, perforated tray columns Yes Bubble column condensers agonistic No Gas spargers Gas flow Yes Direct contact evaporators, submerge electrocution 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 bob up 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, turn out with extremely 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 carryed to handle their particular latent (moisture) as well as the sensible (cooling) loads.The water that is removed is called condensate. For many climates, water or steam HVAC coils can be exposed to freezing conditions. Because water expands upon freezing, these somewhat expensive and difficult to replace thin-walled heat exchangers can easily be damaged or destroyed by just one embarrass. As such, freeze protection of coils is a major concern of HVAC designers, installers, and operators. The introduction 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 icing 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 metal. 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 dangerous situation that requires immediate attention because combustion products may enter living space. Spiral heat exchangers Schematic drawing of a spiral 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 conduct 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 h ighly 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(prenominal) thermal efficiency, and lower energy costs. Construction The distance between the sheets in the spiral channels are maintained by using spacer studs that were welded prior to rolling. Once the main spiral pack has been rolled, alternate sack up and bottom edges are welded and separately 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 inside of the heat exchanger. The low pressure drop lets the SHE handle fouling more easily. The SHE uses a self cleaning mechanism, whereby foul 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. precipitate arrangements Concurrent and countercurrent flow. There are three main types of flows in a spiral heat exchanger 1. Counter-current Flow Fluids flo w in opposite directions.These are used for liquid-liquid, condensing and gas cooling applications. Units are usually mount vertically when condensing vapour and mounted horizontally when handling high concentrations of solids. 2. Spiral Flow/Cross Flow One fluid is in spiral 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 considerably 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 leaves via the top. Hot gases that enter leave as condensate via the bottom outlet. Applications The SHE is good for applications such as past eurization, digester heating, heat recovery, pre-heating (see recuperator), and effluent cooling. For easy lay treatment, SHEs are generally smaller than other types of heat exchangers. citation needed SelectionDue to the many variables involved, selecting best heat exchangers 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 jumply 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, maintenance 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. Small-diameter coil technologies are decorous more popular in modern air 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 manufactur ing industry, several differing types of heat exchangers are used for just the one process or system to fall the final product. For example, a kettle HX for pre-heating, a double pipe HX for the immune carrier fluid and a plate and frame HX for final cooling. With sufficient knowledge of heat exchanger types and operating requirements, an appropriate selection can be made to optimise the process. 17 Monitoring 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 account when cleaning the heat exchanger is economically attractive. Integrity inspection of plate and tubular heat exchanger can be tested in situ by the conductivity or helium gas methods. These methods confirm the ha leness 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 eddy current testing.Fouling Main article Fouling A heat exchanger in a steam power billet 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 * little wall shear stress * Low fluid velocities * High fluid velocities * Reaction product solid haste * Precipitation 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 furnish and Seaton. Crude fossil oil Exchanger Fouling. In commercial fossil oil oil meliorate, 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 asphaltene insolubility. 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 primary order reaction by Ebert and Panchal19 who expanded 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 meaning and suspended colloidal solids. Localized precipitation of dissolved solids occurs at the heat exchange surface due to wall temperatures higher than bulk fluid temperature. Low fluid velocities (less than 3ft/s) allow suspended solids to specify on the hea t 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 to 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 dose cleaning, sandblasting, high-pressure water jet, bullet 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 downplay 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 c ompanies 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 nasal passages serve as a heat exchanger, which solids air being 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 schnoz and then through your mouth. Air exhaled through your nose is substantially cooler. 2021 In species that have external testes (such as humans), the artery to the musket ball is surrounded by a mesh of veins called the pampiniform plexus. This cools the split heading to the testis, while reheating the returning blood. Birds, fish, marine mammalsCountercurrent exchange conservation circuit Further cultivation 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 submit 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 equalizer 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 process depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical 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 source 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 * Pe troleum refining In waste water treatment, heat exchangers play a brisk role in maintaining optimal temperatures within anaerobic digesters to promote the development of microbes that remove pollutants. Common types of heat exchangers used in this application are the double pipe heat exchanger 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 firm 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