Heat exchanger

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A heat exchanger is a device used to transfer heat between a solid and a liquid, or between two or more liquids. Liquids can be separated by solid walls to prevent mixing or they may be in direct contact. They are widely used in space heating, cooling, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. A classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through the radiator coil and the airflow passes through the coil, cooling the coolant and heating the incoming air. Another example is a heat sink, which is a passive heat exchanger that transfers heat generated by electronic or mechanical devices to a liquid medium, often air or coolant.

Video Heat exchanger

Pengaturan aliran

There are three main classifications of heat exchangers according to their flow settings. In the parallel-flow heat exchanger, the two liquids enter the exchanger at the same end, and travel in parallel with each other to the other side. In counter-flow the liquid heat exchanger enters the exchanger from the opposite end. The reversal design is the most efficient, since it can transfer the most heat from the heat (transfer) of medium per unit mass due to the fact that the average temperature difference along the unit length is higher . View the exchange of currents. In a cross-flow hot roller, the liquid flows roughly to one another through the exchanger.

For efficiency, heat exchangers are designed to maximize wall surface area between two liquids, while minimizing resistance to fluid flow through the exchanger. Performance exchangers can also be influenced by the addition of fins or wrinkles in one or two directions, which increase the surface area and can channel fluid flow or induce turbulence.

The driving temperatures across the heat transfer surfaces vary with position, but the exact average temperature can be determined. In most simple systems this is the "average log temperature difference" (LMTD). Sometimes direct knowledge of LMTD is not available and NTU methods are used.

Maps Heat exchanger

Type

The double pipe heat exchanger is the simplest exchanger used in industry. On one hand, these heat exchangers are cheap both for design and maintenance, making it a good choice for small industries. On the other hand, their low efficiency coupled with high spaces used on a large scale, has led the modern industry to use more efficient heat exchangers such as shell and tube or plate. However, because of the simple double pipe heat exchangers, they are used to teach the basics of the heat exchanger design to the students because the basic rules for all heat exchangers are the same.

Shell and tube heat exchanger

Shell and tube heat exchangers consist of a series of tubes. A set of these tubes contains liquids that must be heated or cooled. A second liquid flows over a heated or cooled tube so as to provide heat or absorb the required heat. A set of tubes is called a tube bundle and can consist of several types of tubes: plain, longitudinal lengthwise, etc. Tubular and tube heat exchangers are commonly used for high pressure applications (with pressures greater than 30 bar and temperatures greater than 260 ° C). This is because the shell and tube heat exchangers are strong because of their shape Some features of thermal design should be considered when designing tubes in shell and tube heat exchangers: There are many variations on the shell and tube design. Typically, the tip of each tube is connected to the plenum (sometimes called a water box) through a hole in the tubesheets. The tube may be straight or bent in the form of U, called U-tube.

• Tuber diameter: Using a small tube diameter makes the heat exchanger to be economical and compact. However, it is more likely for faster heat exchangers and smaller sizes making mechanical cleaning of fouling difficult. To solve the fouling and cleaning problems, larger diameter tubes can be used. So to determine the diameter of the tube, the available space, cost and fluid fouling properties should be considered.
• The thickness of the tube: The thickness of the tube wall is usually determined to ensure:
  • There is enough room for corrosion
  • The vibrations induced by the stream have resilience
  • The axial power
  • Availability of spare parts
  • Strength of circle (to withstand internal tube pressure)
  • Bending strength (to withstand overpressure in shell)
• Tube length: the heat exchanger is usually cheaper when it has a smaller shell diameter and long tube length. Thus, there is usually a goal to make heat exchangers for as long as possible physically while not exceeding production capability. However, there are many limitations to this, including the space available at the installation site and the need to ensure the tube is available in the length that is twice the required length (so they can be withdrawn and replaced). Also, long, thin tubes are difficult to pick up and replace.
• Tube pitch: when designing a tube, it is practical to ensure that the tube pitch (ie, center-center distance of adjoining tube) is not less than 1.25 times the outer diameter of the tube. Larger pitch tubes lead to larger overall shell diameters, leading to more expensive heat exchangers.
• Tube corrugation: This type of tube, especially used for the inner tube, improves fluid turbulence and its effect is critical in heat transfer which provides better performance.
• Tube Layout: refers to how the tube is positioned inside the shell. There are four main types of tube layouts, namely, triangles (30 Â °), triangles rotated (60 Â °), square (90 Â °) and square rotated (45 Â °). Triangle patterns are used to provide greater heat transfer because they force the fluid to flow in a more volatile way around the piping. Square patterns are used when high fouling is experienced and cleaning is more regular.
• Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across tube bundles. They walk perpendicular to the shell and hold the bundle, preventing longer sagging tubes. They can also prevent the tube from vibrating. The most common type of baffle is segmental insulation. Segmental segmental segments that are oriented at 180 degrees to adjacent baffles force fluid to flow up and down between the tube bundles. Baffle spacing is a great thermodynamic concern when designing shell and tube heat exchangers. Baffles should be spaced with consideration for the conversion of pressure drop and heat transfer. For thermo economic optimization it is recommended that baffles be placed no closer than 20% inner diameter of the shell. Having too tightly spaced baffles causes a greater pressure drop due to stream redirection. As a result, having a baffle that is too far away means that there may be cooler points in the corner between the baffles. It is also important to ensure that the baffles are placed close enough so that the tube does not sag. The other main baffle types are disc and baffle donuts, consisting of two concentric baffles. A wider outer baffle looks like a donut, while the inner baffle is shaped like a disc. This type of baffle forces the liquid to pass through each side of the disc then through the baffle donut to produce a different fluid flow.

The fixed tube of liquid-cooled heat exchanger is particularly suitable for marine and hard applications can be assembled with brass shell, copper tube, brass baffles, and forged integral hollow brass tip. (See: Copper in heat exchanger).

Heat exchanger

Another type of heat exchanger is the heat exchanger plate. This exchanger consists of many thin, slightly separated plates that have very large surface area and a small fluid flow portion for heat transfer. Advances in gasket and brazing technology have made plate type heat exchangers more practical. In an HVAC application, this type of large heat exchanger is called plat-and-frame ; when used in open loops, these heat exchangers are usually of the type of gasket to allow periodic disassembly, cleaning, and inspection. There are many types of permanently bonded plate heat exchangers, such as dip-brazed varieties, vacuum-brazing, and welded plates, and they are often specified for closed-loop applications such as cooling. The heat exchanger plate also differs in the type of plate used, and in the configuration of the plate. Some plates can be stamped with "chevron", dimpled, or other patterns, where others may have engine fins and/or grooves.

When compared to a shell and tube exchanger, the stacked plate arrangement usually has lower volume and cost. Another difference between the two is that plate exchangers typically serve low to medium pressure fluids, compared with medium and high shell and tube pressures. The third and important difference is that the exchange plate uses more opposite flows than the flow of cross currents, allowing lower temperature difference approaches, higher temperature changes, and increased efficiency.

plate plate and shell heat plate

The third type of heat exchangers are plate and shell heat exchangers, which incorporate a heat exchanger with a shell and tube heat exchanger technology. The heart of the heat exchanger contains a packet of welded round dishes made by pressing and cutting the round plate and welding it together. Nozzle brings in and out flow from platepack ('Plate side' flow path). The welded platepack is fully assembled into the outer shell that creates a second flow path ('Shell side'). Plate and shell technology offers high heat transfer, high pressure, high operating temperatures, uling and close approach temperatures. In particular, it's completely without gaskets, which provide security against leaks at high pressure and temperature.

Adiabatic wheel adapter

The fourth type of heat exchanger uses a liquid or solid container to withstand heat, which is then transferred to the other side of the heat exchanger to be released. Two examples of these are adiabatic wheels, consisting of large wheels with fine thread spinning through hot and cold liquids, and fluid heat exchanger.

Plates fin heat exchanger

This type of heat exchanger uses a "hollow" section that contains fins to increase the effectiveness of the unit. Designs include crossflow and counterflow coupled with various fin configurations such as straight fins, offset fins and wavy fins.

Plate and fin heat exchangers are usually made of aluminum alloy, which provides high heat transfer efficiency. The material allows the system to operate at lower temperature differences and reduce equipment weight. 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 transportation industries such as motors and aircraft engines.

Advantages of plate and heat exchanger fin:

• High heat transfer efficiency especially in gas treatment
• Greater heat transfer area
• About 5 times lighter than a shell and tube heat exchanger.
• Able to withstand high pressures

Lack of plate and heat exchanger fin:

• May cause a blockage because the path is very narrow
• Difficult to clear paths
• Aluminum alloys are susceptible to Failure of Mercury Liquid Embrittlement

Heat plate cushion plate

The pillow support plate is usually used in dairy industry to cool milk in large bulk tank with direct expansion of stainless steel. The cushion plate allows cooling in almost the entire tank surface area, without the gap that will occur between the pipe being welded to the outside of the tank.

The pillow plate is built using a thin sheet where the metal is welded onto the surface of other thicker metal sheets. The thin plates are welded in ordinary dot patterns or with welded winding pattern lines. After welding the enclosed chamber is pressed with sufficient strength to cause the thin metal to bulge around the weld, providing room for the fluid of the heat exchanger to flow, and creating the characteristic appearance of a swollen cushion formed of metal.

Liquid heat exchanger

It is a heat exchanger with a gas that flows upward through a liquid shower (often water), and the liquid is then taken elsewhere before it is cooled. It's usually used to cool gas while also removing certain impurities, thus solving two problems at once. It is widely used in espresso machines as an energy-saving method of superheated water cooling for use in espresso extraction.

Generates a heat recovery unit

The waste heat recovery unit (WHRU) is a heat exchanger that recovers heat from the flow of hot gas when transferring it to a working medium, usually water or oil. The flow of hot gas may be a flue gas from a gas turbine or a diesel or waste gas from an industrial or refinery.

Large systems with high gas flow volumes and temperatures, typical in industry, can benefit from the Rankine Steam cycle (SRC) in waste heat recovery units, but these cycles are too expensive for small systems. Recovery of heat from low temperature systems requires a different working fluid than steam.

Organic Rankine (ORC) organic cycle cycle units can be more efficient at low temperature ranges using boiling refrigerants at lower temperatures than water. Typical organic refrigerants are ammonia, pentafluoropropane (R-245fa and R-245ca), and toluene.

Refrigerant is boiled by heat source in evaporator to produce super hot steam. This fluid is expanded in the turbine to convert heat energy into kinetic energy, converted into electricity in an electric generator. This energy transfer process lowers the refrigerant temperature which, in turn, condenses. The cycle is closed and finished using the pump to send the liquid back to the evaporator.

Dynamic scratched surface heat exchanger

Another type of heat exchanger is called "dynamic scratched surface heat exchanger". It is mainly used for heating or cooling with high viscosity products, crystallization process, evaporation and high impurity applications. Long run time is achieved due to continuous scratching from the surface, thus avoiding fouling and achieving continuous heat transfer rates during the process.

Phase change heat exchanger

In addition to heating or cooling the liquid in just one phase, the heat exchanger can be used either to heat the liquid until it evaporates (or boils) or is used as a condenser to cool the vapor and condense it into a liquid. In chemical plants and refineries, reboilers are used to heat incoming feeds for distillation towers often heat exchangers.

The distillation set-up usually uses a condenser to condense the distillate vapor back into a liquid.

Power plants that use steam-driven turbines generally use heat exchangers to boil water into steam. Heat exchangers or similar units to produce steam from water are often called boilers or steam generators.

In a nuclear power plant called a pressurized water reactor, a special large heat exchanger passes heat from the primary reactor system to the secondary system (steam mill), producing steam from the water in the process. This is called a steam generator. All fossil and nuclear-fueled power plants using steam-driven turbines have surface condensers to convert exhaust vapors from turbines into condensate (water) for reuse.

To conserve energy and cooling capacity in chemical plants and others, regenerative heat exchangers can transfer heat from the flow to be cooled to other heated streams, such as distillation cooling and pre-heated reboiler feeds.

The term can also refer to heat exchangers containing materials in their structure that have phase changes. This is usually a solid phase to liquid due to the small volume differences between these countries. This phase change effectively acts as a buffer because it occurs at a constant temperature but still allows the heat exchanger to receive additional heat. One example where this has been investigated is for use in high power plane electronics.

Working heat exchanger in the multifase flow regime can be the subject of Ledinegg's instability.

Direct contact heat exchange

Direct contact heat exchanger involves heat transfer between heat and cold flow from two phases in the absence of a separating wall. So the heat exchanger can be classified as:

• Gas - liquid
• Intangible liquid - liquid
• Solid-liquid or solid - gas

Most direct heat exchangers are included in the Gas - Liquid category, where heat is transferred between gas and liquid in the form of drops, films or sprays.

This type of heat exchanger is used mainly in air conditioning, humidification, industrial hot water heaters, water cooling and condensing plants.

Microchannel heat exchanger

Microchannel heat exchangers are multi-pass parallel flow heat exchangers consisting of three main elements: manifolds (inlets and outlets), multi-port tubes with a hydraulic diameter smaller than 1mm, and fins. All elements are usually brazed together using a controlled atmospheric brazing process. Microchannel heat exchanger is characterized by high heat transfer ratio, low refrigerant charge, compact size, and lower air pressure decrease compared with finned tube heat exchanger. Microchannel heat exchangers are widely used in the automotive industry as car radiators, and as condensers, evaporators, and cooling/heating coils in the HVAC industry.

The micro heat exchanger, micro scale heat exchanger, or microstructure heat exchanger is a heat exchanger where (at least one) liquid fluid in a lateral enclosure with a special dimension below 1 mm. The most distinctive containment are microchannels, which are channels with a hydraulic diameter below 1 mm. Microchannel heat exchangers can be made from metal, ceramic, heat exchanger Microchannel can be used for many applications including:

• high-performance aircraft gas turbine engine
• heat pump
• AC

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HVAC air scroll

One of the widest use of heat exchangers is for air conditioning of buildings and vehicles. These heat exchanger classes are commonly called air coils , or just coils due to their often serpentine internal tubing. Liquid-to-air, or air-to-liquid HVAC coils are usually from a modified crossflow arrangement. In vehicles, hot coils are often called heating core.

On the liquid side of this heat exchanger, the general liquid is water, aqueous glycol, steam, or refrigerant solution. For heating coils, hot water and steam are the most common, and this heated liquid is supplied by the boiler, for example. For cooling coils , cold water and refrigerant are the most common. Cold water is supplied from a potentially very remote chiller, but the refrigerant must come from the nearest condensing unit. When refrigerant is used, the cooling coil is the evaporator in the vapor compression refrigeration cycle. HVAC coils that use direct expansion of this refrigerant are commonly called DX coils . Some DX coils are of the "microchannel" type.

On the air side of the HVAC coils there are significant differences between those used for heating, and for cooling. Due to psychrometric, cooled air often has condensation moisture, except with very dry airflow. Air heating increases the airflow capacity to hold water. So the heating coil does not need to consider the condensation of the humidity on their air side, but the cooling coil must be sufficiently designed and selected to handle their latent latitude and cooling) load. The water released is called condensate .

For many climates, water or steam HVAC coils can be exposed to freezing conditions. Since water expands after freezing, it is rather expensive and difficult to replace thin walled heat exchangers can be easily damaged or destroyed with just one freeze. Thus, coil freezing protection is a major concern of HVAC designers, installers and operators.

Indentation recognition is placed inside the condensation controlled heat exchanger, allowing water molecules to remain in the cooled air. The present invention allows for cooling without coating of the cooling mechanism.

Heat exchangers in direct-burning stoves, typical in many dwellings, are not 'coils'. They are, on the other hand, gas-to-air heat exchangers which are usually made of stamped steel sheet steel. The combustion products pass through one side of this heat exchanger, and the air gets hot on the other. A cracked heat exchanger is a dangerous situation that needs immediate attention because the combustion products can enter the living space.

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Helical-coil heat exchanger

Although dual pipe heat exchangers are the simplest for design, a better choice in the following cases is a helical-coil heat exchanger (HCHE):

• The main advantage of HCHE, like that for SHE, is its highly efficient use of space, especially when limited and insufficient straight pipes can be placed.
• Under conditions of low flowrates (or laminar flow), so that regular shell-and-tube exchangers have low heat transfer coefficients and become uneconomical.
• When there is a low pressure in one of the fluids, it is usually from the pressure drop that accumulates in other process equipment.
• When one of the fluids has components in several phases (solids, liquids, and gases), it tends to create mechanical problems during operation, such as inserting small diameter tubes. The cleaning of the helical coils for this double phase liquid proved more difficult than the tube and tube pairs; but the helical coil unit will be cleaned more often.

It has been used in the nuclear industry as a method for the exchange of heat in the sodium system for large metal fast liquid livestock reactors since the early 1970s, using HCHE devices discovered by Charles E. Boardman and John H. Germer. There are several simple methods for designing HCHE for all types of manufacturing industries, such as the Ramachandra K. Patil (et al.) Method of India and the Scott S. Haraburda method of the United States.

However, this is based on the estimating assumption in the heat transfer coefficient, predicting the flow around the outside of the coil, and at constant heat flux. However, recent experimental data reveal that empirical correlations are appropriate for designing circle and square HCHE patterns. During a study published in 2015, some researchers found that the boundary conditions of exterior wall exchangers were essentially conditions of constant heat flux in power plant boilers, condensers and evaporators; while convective heat transfer conditions are more appropriate in the food, automobile, and process industries.

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Spiral heat exchanger

A modification of the perpendicular flow of typical HCHE involves the replacement of the shell with another circular tube, allowing two fluids to flow parallel to one another, and requiring the use of different design calculations. It is a Spiral Heat Exchangers (SHE), which may refer to a helical tube configuration (circular), more generally, the term refers to a pair of flat surfaces that are rolled to form two channels in a counter-flow arrangement. Each of the two channels has a long curved path. A pair of fluid ports are connected tangentially to the outer arm of the spiral, and the axial port is common, but optional.

The main advantage of SHE is the highly efficient use of space. These attributes are often harnessed and some are reallocated to get another improvement in performance, according to the well-known tradeoffs in the heat exchanger design. (Important sacrifice is the cost of capital vs. operating costs.) A compact SHE can be used to have a smaller footprint and thereby lower the cost of all-around capital, or too large SHE can be used to have less pressure drop, less pumping energy , higher thermal efficiency, and lower energy costs.

Construction

The distance between the sheets in the spiral ducts is maintained by using the stud spacer that is welded before rolling. After the main spiral pack has been rolled up, the alternate top and bottom edges are welded and each end is covered with a flat cover or a flat cone that is bolted to the body. This ensures no mixing of the two liquids that occur. Each leak comes from the edge cover to the atmosphere, or to the same fluid-filled portion.

Self-cleaning

Spiral heat exchangers are often used in heating liquids containing solids and thus tend to rot the inside of a heat exchanger. The low pressure drop allows SHE to handle fouling more easily. SHE uses a "self-cleaning" mechanism, in which a dirty surface causes an increase in localized fluid velocity, thereby increasing drag (or friction fluid) on a dirty surface, thereby helping to remove blockages and keep heat exchangers clean. "The internal walls that make up the heat transfer surface are often a bit thick, which makes SHE very powerful, and able to survive in a demanding environment." They are also easy to clean, open like an oven where any dirt buildup can be removed by pressure washing.

Self-service water filters are used to keep the system clean and running without the need to turn off or replace cartridges and bags.

Streaming settings

There are three main types of currents in a spiral heat exchanger:

• Flow-Flow : The liquid flows in the opposite direction. It is used for liquid-liquid, condensing and gas cooling applications. Units are usually mounted vertically when condensing steam and horizontally mounted when handling high solids concentrations.
• Spiral/Cross Flow: One fluid flows in a spiral and the other in a cross flow. The spiral flow section is welded on each side for this type of spiral heat exchanger. This type of flow is suitable for handling gas of low density, which passes through the cross flow, avoiding pressure loss. This can be used for liquid-liquid applications if one liquid has a much larger flow rate than the other.
• Vapor/Spiral Distributed Flow: This design is a condenser, and is usually installed vertically. It is designed to meet both condensate and non-condensate sub-cooling. The cooler moves in a spiral and leaves through the top. The incoming hot gas goes away as condensate through the lower conduit.

Apps

Spiral heat exchanger is good for applications such as pasteurization, heating digester, heat recovery, preheating (see: recuperator), and effluent cooling. For mud processing, SHE is generally smaller than other types of heat exchangers. This is used to transfer heat.

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Options

Because of the many variables involved, choosing an optimal heat exchanger is challenging. Hand calculations are possible, but many iterations are usually required. Thus, heat exchangers are most often chosen through computer programs, either by system designers, who are usually engineers, or by equipment vendors.

To select the right heat exchanger, the system designer (or equipment vendor) will first consider the design limits for each type of heat exchanger. Although cost is often the main criterion, several other selection criteria are important:

• High/low pressure limit
• Thermal performance
• Temperature range
• Mixture of product (liquid/liquid, particulate or high solid liquor)
• Pressure down in the exchanger
• The fluid flow capacity
• Hygiene, maintenance, and repair
• Materials needed for construction
• Capability and ease of future expansion
• Selection of materials, such as copper, aluminum, carbon steel, stainless steels, nickel alloys, ceramics, polymers, and titanium.

Small-diameter coil technologies are becoming more popular in modern cooling and cooling systems because they have better heat transfer rates than regular-sized condensers and evaporator coils with round copper tubes and aluminum or copper fins that have become standard in the HVAC industry. Small diameter coils can withstand the higher pressures required by a new generation of environmentally friendly refrigerants. Two small diameter coil technologies are currently available for air conditioning and refrigeration products: microgroove copper and aluminum brazing microchannel.

Choosing the right heat exchanger (HX) requires knowledge of the different types of heat exchangers, as well as the environment in which the unit should operate. Usually in the manufacturing industry, several different types of heat exchangers are used only for one process or system to obtain the final product. For example, HX boilers for preheating, dual pipes HX for carrier liquids and plates and HX frames for final cooling. With sufficient knowledge about the type of heat exchanger and operating requirements, the right selection can be done to optimize the process.

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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 decrease over time due to fouling.

U = Q/A? T _lm

By periodically calculating the overall heat transfer coefficient of the flow rate and the exchanger temperature, the owner of the heat exchanger can estimate when the heat exchanger cleanup is attractive.

Examination of plate integrity and tubular heat exchangers can be tested in situ with the conductivity or helium gas method. This method confirms the integrity of plates or tubes to prevent cross contamination and gasket conditions.

Monitoring of the mechanical integrity of the heat exchanger can be carried out through the nondestructive method such as the navel currents test.

Fouling

Fouling occurs when dirt accumulates on the surface of the heat exchanger. These dirt deposits may decrease the effectiveness of heat transfer significantly over time and are caused by:

• Low wall shear stress
• Low fluid speed
• High fluid speed
• Solid precipitation product reactions
• Precipitation of dissolved sewage due to high wall temperature

The fouling rate of the heat exchanger is determined by the deposition rate of the less re-entrainment/suppression particle. This model was originally proposed in 1959 by Kern and Seaton.

Crude Oil Exchangers Fouling . In commercial crude oil refining, crude oil is heated from 21 ° C (70 ° F) to 343 ° C (649 ° F) before entering the distillation column. A series of shell and tube heat exchangers typically exchange heat between crude oil and other oil streams to heat crude oil up to 260 Â ° C (500 Â ° F) before heating in the furnace. Fouling occurs on the rough side of this exchanger due to asphaltene insolubility. The nature of asphaltene solubility in crude oil was successfully modeled by Wiehe and Kennedy. The precipitating of insoluble asphaltenes in early warm-up trains has been successfully modeled as a first-order reaction by Ebert and Panchal that expanded on the work of Kern and Seaton.

Cooling Water Fouling . The cooling water system is very susceptible to fouling. Cooling water typically has a high soluble solids content and suspended colloidal solids. Local soluble solid dissolution occurs on the surface of the heat exchanger because the wall temperature is higher than the temperature of the bulk fluid. Low fluid speed (less than 3 feet/s) allows suspended solids to settle on the surface of the heat exchanger. The cooling water is usually on the side of the tube shell and tube exchanger because it is easy to clean. To prevent fouling, the designer usually ensures that the cooling water velocity is greater than 0.9 m/s and the bulk liquid temperature is maintained less than 60 Ã, Â ° C (140Ã, Â ° F). Another approach to controlling fouling controls combines the application of biocides and "blind" anti-crust chemicals with periodic lab testing.

Maintenance

Plate and frame heat exchanger can be disassembled and cleaned periodically. Tubular heat exchangers can be cleared by methods such as acid cleaning, sandblasting, high pressure water jets, bullet cleaning, or drill rods.

In large-scale cooling water systems for heat exchangers, water treatment such as purification, chemical addition, and testing, are used to minimize the fouling of heat exchange equipment. Other water treatment is also used in steam systems for power plants, etc. To minimize fouling and corrosion on heat exchange and other equipment.

Companies have begun to use water oscillation technology to prevent biofouling. Without the use of chemicals, this type of technology has been helpful in providing low pressure drops on heat exchangers.

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In nature

Man

Nasal human nose serves as a heat exchanger, which warms the air inhaled and cools the exhaled air. Its effectiveness can be demonstrated by putting hands in front of the face and exhaling, first through the nose and then through the mouth. The air exhaled through the nose is much cooler. This effect can be enhanced by clothing, with, for example, wearing a scarf on the face while breathing in cold weather.

In species that have external testes (like humans), the arteries to the testicles are surrounded by a vein called the pampiniform plexus. It cools the blood to the testicles, while reheating the blood.

Birds, fish, marine mammals

The "opposite" heat exchanger occurs naturally in the circulatory systems of fish, whales and other marine mammals. The arteries to the skin carry warm blood that exists with the blood vessels of the skin that carry cold blood, causing warm arterial blood to exchange heat with cold venous blood. This reduces overall heat loss in cold waters. Heat exchangers are also present on the tongue of baleen whales as large volumes of water flow through their mouths. Birds use similar systems to limit heat loss from their bodies through their feet into the water.

Carotid rete

The carotid rete is the organ of heat exchanger against the currents in some ungulates. Blood rises the carotid artery on the way to the brain, flowing through the vascular tissue where the heat is dumped into the blood vessels from the cold blood that descends from the nasal passages. The carotid crack allows Thomson's gazelle to keep its brain nearly 3 Ã, Â ° C (5.4 Ã, Â ° F) cooler than the rest of the body, and therefore helps in blocking bursts in metabolic heat production as related to the cheetah that comes out (where the body temperature exceeds the maximum temperature at which the brain can function).

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In industry

Heat exchangers are widely used in industries both for cooling and heating of large-scale industrial processes. The type and size of the heat exchanger used can be adjusted for processes depending on the type of liquid, phase, temperature, density, viscosity, pressure, chemical composition and various other thermodynamic properties.

In many industrial processes there is a waste of energy or an outflow of heat, a heat exchanger can be used to recover this heat and utilize it by heating different streams in the process. This practice saves a lot of money in the industry, because heat supplied to other streams of heat exchangers will instead come from a more expensive and more environmentally harmful external source.

Heat exchangers are used in many industries, including:

• Wastewater treatment
• Cooling
• Making wine and beer
• Petroleum refining
• nuclear power

In wastewater treatment, heat exchangers play an important role in maintaining optimal temperatures in anaerobic milling to promote microbial growth that removes pollutants. The common types of heat exchangers used in this application are dual pipe heat exchangers as well as plate and frame heat exchangers.

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On the plane

In a commercial aircraft heat exchanger is used to extract heat from the engine oil system to heat the cold fuel. It improves fuel efficiency, as well as reduces the possibility of water trapped in fuel freezing in components.

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Current and estimated market

Estimated at US $ 42.7 billion in 2012, global demand for heat exchangers will experience strong growth of around 7.8% per year over the coming years. The market value is expected to reach US $ 57.9 billion in 2016 and close to US $ 78.16 billion by 2020. Tubular heat exchangers and plate heat exchangers are still the most widely applied products.

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Simple heat exchanger model

Sebuah pertukaran panas sederhana mungkin dianggap sebagai dua pipa lurus dengan aliran fluida, yang terhubung secara termal. Biarkan pipa memiliki panjang yang sama L , membawa cairan dengan kapasitas panas ${\ displaystyle C_ {i}}  ÂÂ$ (energi per satuan massa per satuan perubahan suhu) dan biarkan laju aliran massa fluida melalui pipa, keduanya dalam arah yang sama, menjadi ${\ displaystyle j_ {i}}  ÂÂ$ (massa per satuan waktu), di mana subskrip i berlaku untuk pipa 1 atau pipa 2.

Profil suhu untuk pipa adalah ${\ displaystyle T1 (x)} Â$ dan ${\ displaystyle T2 (x)} Â Â$ di mana x adalah jarak sepanjang pipa. Asumsikan kondisi mantap, sehingga profil suhu bukan fungsi waktu. Asumsikan juga bahwa satu-satunya transfer panas dari volume kecil cairan dalam satu pipa adalah ke elemen cairan pada pipa lainnya pada posisi yang sama, yaitu, tidak ada transfer panas sepanjang pipa karena perbedaan suhu dalam pipa itu. Menurut hukum Newton pendinginan laju perubahan energi dari volume kecil cairan sebanding dengan perbedaan suhu antara itu dan elemen yang sesuai di pipa lainnya:

${\ displaystyle {\ frac {du_ {1}} {dt}} = \ gamma (T2-T1)} Â Â$

${\ displaystyle {\ frac {du_ {2}} {dt}} = \ gamma (T_ 1 -T2)} Â Â$

(Ini adalah untuk aliran paralel dalam arah yang sama dan gradien temperatur yang berlawanan, tetapi untuk pertukaran pertukaran arus balik pertukaran arus, tanda berlawanan di persamaan kedua di depan ${\ displaystyle \ gamma (T1-T2)} Â Â$ )

, di mana ${\ displaystyle u_ {i} (x)} Â$ adalah energi thermal per satuan panjang dan? Adalah is constant to connect thermal with satuan panjang before a second pipe. Perubahan dalam energi internal ini menghasilkan perubahan suhu elemen fluida. Tingkat perubahan wake up elemen fluid yang dibawa oleh aliran adalah:

${\ displaystyle {\ frac {du_ 1} {dt}} = J_ {1} {\ frac {dT_ {1}} {dx}} } Â Â$

${\ displaystyle {\ frac {du_ {2}} {dt}} = J_ {2} {\ frac {dT_2} {dx}} } Â Â$

di mana ${\ displaystyle J_ {i} = {C {i}} {j_ {i}}} Â Â$ adalah "laju aliran massa thermal". Differential persuasions yang mengatur penukar panas sekarang dapat ditulis sebagai:

${\ displaystyle J_ {1} {\ frac {\ partial T_ {1}} {\ partial x}} = \ gamma (T_2 -T_ {1})} Â Â$

${\ displaystyle J2 {\ frac {\ partial T_2} {\ partial x}} = \ gamma (T_ 1 -T_ {2}).} Â Â$

Note that, since the system is in a stable state, there is no partial derivative of temperature over time, and since there is no heat transfer along the pipe, there is no second derivative in x as found in the heat equation. These two first-order differential equations can be solved to produce:

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{          T              Â 1                          =          A         -                                    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> B    Â      Â                        Â 1        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â                  Â                                             e                ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÃ, -      Â             <Â> x                                {\ displaystyle T_ {1} = A - {\ frac {bk_ {1}} {k}} \, e ^ {- kx}}  Â}

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$           T               Â 2                          =          A                                            ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> B    Â      Â                                 2        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â                  Â                                             e                Ã

Source of the article : Wikipedia