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The most comprehensive introduction for heat exchanger types

By Thomas Huang December 8th, 2023 100 views
Contents

I. What is a heat exchanger?

1.1 Description:

A heat exchanger is equipment that transfers part of the heat from a hot fluid to a cold fluid, so the fluid temperature can meet the process-specified indicators.
In chemical plants, it costs about 10% to 20% of the total investment. 
Among the refinery decompression devices, it takes about 35% to 40% of the total investment.
Photos of all kinds of heat exchangers

1.2 Function

The application's purpose is to ensure the specific temperature of the medium required by the process,  improve energy utilization, and recycle waste heat, waste heat, and low-level heat.

1.3 Application

Heat exchangers are widely used equipment in the chemical, oil refining, power, atomic energy, light, food, pharmaceutical, and machinery manufacturing industries. The heat exchanger can be a separate device, such as heaters, coolers condensers, etc.; but also a process equipment component, such as ammonia synthesis tower heat exchanger, batch reactor, and electronic device.

II, Various types of heat exchangers

Heat exchangers apply to different work conditions, media, temperatures, pressures, and structures.
They are specifically categorized as follows:

2.1 Heat exchangers sorted by heat transfer principle

2.1.1 Surface heat exchanger: 

ᆞDescription:
Surface heat exchangers transfer the heat between the two fluids of different temperatures. The two fluids flow in the space separated by the wall. Heat exchanges via the wall of the thermal conductivity and fluid convection on the wall surface. 
ᆞSubclassification:
Surface-type heat exchanger has shell and tube type, casing type, and other types of heat exchangers.

2.1.2 Heat storage type heat exchanger: 

ᆞDescription:
Heat storage type heat exchangers transfer the heat from the high-temperature fluid to the low-temperature fluid through the solid material composition of the heat storage body. The hot medium heats the solid material to reach a certain temperature, and the cold medium is heated by the solid material. In this way, the purpose of heat transfer is achieved. 
ᆞSubclassification:
Heat storage type heat exchanger has a rotary type, valve switching type, and so on.
photo of Heat storage type heat exchanger

2.1.3 Indirect heat exchanger: 

It is also named as an intermediate heat carrier type heat exchanger.
It consists of two surface heat exchangers and a heat carrier which connect and circulate between the heat exchangers. 
The heat carrier brings the heat via the route of high-temperature fluid, high-temperature fluid heat exchanger, low-temperature fluid heat exchanger, and low-temperature fluid.

2.1.4 Direct contact heat exchanger: 

The direct contact heat exchanger is equipment that makes two fluids in direct contact for heat exchange. 
For example: 
Cold water tower, gas condenser, etc.
photo of Direct contact heat exchanger

2.2 Classified as per applications

2.2.1 For heat exchanging: 

Two mediums with different temperatures exchange heat, so that one medium cools down and another medium to warm up to meet their needs.

2.2.2 Condenser: 

Two medium with different temperatures exchange heat, and one of the mediums change from a vapor state to a liquid state.

2.2.3 Evaporator: 

It has the opposite operation of a condenser, one of the media is evaporated from liquid to vapor.

2.2.4 Heating: 

Only to heat a medium.
Difference between evaporator and condenser
It is mainly the difference in the form of work.
The evaporator is the medium to absorb external heat for vaporization, while the condenser is exothermic equipment to cool the medium to liquid.
The evaporator and condenser in the structure are also different.
The evaporator design is based on the evaporation and vapor materials.
In the condenser design, there are different flow paths.  The inlet of different paths should be as close as possible. The outlets should be as close as possible. But the inlets need to be as far away as possible from outlets, to avoid heat loss and the uneven distribution of flows.

2.2.5 Cooling apparatus

The heat exchanger can be called a cooler when the cooling operation of one medium is done by the coolant (e.g., water, air) if the heat doesn't need recycling.
2.2.5.1 Air Cooler
ᆞDescription:
The equipment using air as coolant can be called an air cooler.
It cools or condenses the high-temperature process fluid in the tube with ambient air.
picture of air cooler
ᆞStructures:
Tube bundle, frame, fan, shutters, ladder platform, and other auxiliary parts.
ᆞAdvantages:
Do not consume circulating cooling water.
Low maintenance costs.
ᆞDisadvantages:
Power consumption, 
The Occupies area is large
Its cooling temperature is affected by the dry bulb temperature of the air.
ᆞTypes:
Dry air-cooled, Wet air-cooled
Horizontal, vertical, and slant top type (herringbone type)
ᆞSpecifications:
The rows of tubes are usually 3~8 rows, and the series size of tube bundles is usually 3, 4.5, 6, 9, and 12 meters.
The outer diameter of the tube is often 25 mm and 38 mm, and the height of the fins is usually 12~16 mm.
The tube bundle width is 100~3000 mm.
Finned tube material:
carbon steel, copper, aluminum, and stainless steel.
Fin material:
aluminum in general, copper or stainless steel for special cases.
Fin form:
winding type, inlaid type, rolled type, sleeve type, welded type, elliptical tube type, turbulent flow type.
Fan:
blower, induced draft fan
The wind speed is generally 1.5~4m/s, and the pressure drop is generally 300Pa or less, preferably not more than 200Pa.
2.2.5.2 New Closed Circulation Air Cooling Tower
photo of New Closed Circulation Air Cooling Tower

2.3 Classification of heat exchangers according to their structure

2.3.1 Tubular heat exchanger

ᆞStructure:
The tube heat exchanger is mainly composed of a shell, tube plate, heat exchanger tube, header, folding baffle, and so on. 
When heat exchange is carried out:
One kind of exchanger letting fluid enter at the linking tube of the head, flow in the tube, and flow out from the outlet tube at the other end of the head, which is called the Tube Pass; 
Another kind of exchanger makes fluid enter the receiver of the shell, and flow out from another receiver on the shell, which is called the Shell Pass.
ᆞCharacteristics:
The structure is strong, reliable, adaptable, easy to manufacture, and can withstand high operating pressure and temperature. In high temperature, high pressure, and large heat exchanger, tube heat exchanger is still the absolute advantage, and is currently the most widely used type of heat exchanger.
Heat transfer efficiency, compactness, and metal consumption per unit of heat transfer area are not as good as other new heat exchangers.
2.3.1.1 Coil pipe heat exchanger
2.3.1.1.1 Immersion coil pipe heat exchange
ᆞAdvantages:
Simple structure. 
Low cost. 
Less sensitive to operation.
The pipe can withstand greater fluid medium pressure.
ᆞDisadvantages:
The fluid flow rate outside the pipe is very small, thus the heat transfer coefficient is small.
Low heat transfer efficiency, the need for heat transfer area is large. 
The equipment appears to be bulky.
ᆞApplication:
The equipment is commonly used in high-pressure fluid cooling, reactor heat transfer elements, and container heating.
photo of coil pipe in the reactor

2.3.1.1.2 Spray-type coil heat exchanger
ᆞDescription:
For this type of heat exchanger,  the serpentine pipes are fixed in rows on a steel frame. The hot fluid flows inside the pipes, entering from the lowest pipe and exiting from the uppermost pipe. The cold water flows down from the uppermost drench pipe, evenly distributed on the coil pipes, and flows through the surface of the pipes below row by row along their sides, and finally flows into the sink and discharges.  The heat exchange between cold water and fluid inside the pipe happens when cold water flows over the surface of the pipes in each row.
ᆞAdvantages:
The formation of a layer of the liquid film outside the pipe with a high degree of turbulence, and thus the convective heat transferring outside the pipe is good. Compared with the immersion coil heat exchanger, the spray coil type is much better.
Easy maintenance and cleaning.
ᆞDisadvantages:
Huge size. 
Large consumption of cooling water.
Uniform spraying is hard. 
scheme of Spray-type coil heat exchanger
2.3.1.2 Double-pipe heat exchanger 
ᆞDescription:
The double-pipe heat exchanger is a concentric casing made of straight tubes of different sizes connected by U-shaped elbows. 
Each section of casing is called a pass, and the effective length of each pass is about 4 to 6 m. If the pipes are too long, the middle of the tubes will bend downward. 
In the double-pipe heat exchanger, a fluid goes inside the tube, the another fluid goes to the ring gap. So, appropriate selection of the diameter of the two tubes, the two fluids can get a higher flow rate, and the two fluids can be countercurrent, favorable for heat transfer.
ᆞAdvantages:
Both sides of the fluid can improve the flow rate, the heat transfer coefficient is high.
Simple structure.
Can withstand high pressure.
Heat transfer area can be increased or decreased according to the needs.
ᆞDisadvantages:
Occupies a large area.
Large metal consumption.
Too many joints between pipes, easy to leak. The maintenance is troublesome.
ᆞApplications:
Generally suitable for high temperature, high pressure, small flow of fluid and the required heat transfer area is not large occasions.
scheme of double tube exchanger principle
2.3.1.3 Wound-tube heat exchanger
Suitable for simultaneous processing of a variety of media,  in occasions that require a large amount of heat transferring at a high operating pressure of medium with small temperature difference, such as oxygen producing and another low-temperature process.
Application:
Sampler cooling.
photo of Wound-tube heat exchanger
2.3.1.4 Shell-and-tube exchanger
ᆞAdvantages:
Sturdy structure.
High reliability.
Wide adaptability.
Easy to make.
Large processing capacity.
Low production costs.
Wide range of raw material.
Easy to clean heat transfer surface.
principle of shell and tube exchanger
ᆞDisadvantage:
Heat transfer efficiency, compactness, and metal consumption per unit of heat transfer area are not as good as some new high-efficiency compact heat exchangers.
ᆞApplication:
High temperature and high-pressure occasions.
2.3.1.4.1 Fixed tube sheet exchanger
picture of Fixed tube sheet exchanger
ᆞAdvantages 
Simple, compact structure.
Can withstand high pressure.
Low cost.
Easy to clean the pipe pass.
Easy to replace the tube when it is damaged or plugged.
ᆞDisadvantages: 
A large thermal stress will be produced in the shell and the tube bundle when there is a large difference in the linear expansion coefficient of the tube wall's temperature or material.
flow direction of Fixed tube sheet exchanger and it's photo
ᆞApplication:
The occasion when the medium of the shell side is clean, not easy to deposit, and can be dissolved cleaning, and the temperature difference is not large on both sides of the tube and shell or the temperature difference is large but the shell is not under high pressure.
2.3.1.4.2 Floating head heat exchanger
scheme of floating head exchanger
ᆞAdvantages:
Pipe cleaning is easy.
No thermal stress.
ᆞDisadvantages:
The structure is complex.
The cost is higher than the fixed tube sheet heat exchanger.
Bulky equipment.
Material consumption is large. 
The small cover of the floating head end can not be inspected during operation.
High sealing requirements during fabrication.
Picture of floating head exchanger
ᆞApplication:
The occasion when the shell and tube bundles between the wall temperature difference are large or when the shell pass media is easy to deposit.
2.3.1.4.3 U-tube heat exchanger
ᆞAdvantages:
Relatively simple structure.
Inexpensive.
High-pressure resistance.
ᆞDisadvantages:
Shell fluid is easy to short-circuit, and heat transfer is unfavorable. 
When there is tube leakage damage, only the outer U-shaped tube is replaceable, the inner tube can only be plugged. So, one U-shaped tube worn means two tubes are scrapped.
picture of U-tube heat exchanger
ᆞApplication:
The occasion when the temperature difference between the tube and shell wall is large or when shell process media is easy to deposit needs cleaning, however, it is not suitable for floating head type and fixed tube plate exchanger. 
Especially suitable for clean but not easy-to-scale medium, having high temperature, high pressure, and corrosive properties.
2.3.1.4.4 Stuffing box heat exchanger 
ᆞAdvantages: 
Simple structure,  production cost is low. 
Save material. 
The tube bundle from the shell can be withdrawn.
Easy for maintenance.
ᆞDisadvantages:
Easy to leak in the packing area.
picuture of Stuffing box heat exchanger
ᆞApplication:
Working condition below 4MPa. 
Not suitable for medium easy volatile, flammable, explosive, toxic, and precious. 
The temperature is limited by the physical properties of the filler.
2.3.1.4.5 Kettle-type reboiler
ᆞAdvantages:
Easy to maintain like the floating head type, U-shaped tube heat exchanger.
Can deal with unclean, easy-to-scale media.
Can withstand high temperature and high pressure (no temperature stress).
ᆞDisadvantages:
Large space occupation.
ᆞApplication:
Only for reboiler.
photo of Kettle-type reboiler
2.3.1.4.6 Limpet coil exchanger
The limpet coil heat exchanger is also called a half-pipe exchanger. It is a spiral half-pipe welded to the external surface of the reactor vessel wall.
The kettle can be heated or cooled through the spiral tube.
ᆞAdvantages:
Fast heating speed:
The reaction vessel can be heated to the required temperature in a shorter time.
Good heating and cooling effect.
Part of the heat can be recycled, improving the utilization of energy.
Accurate temperature control.
The temperature of the reactor can be accurately controlled, thus ensuring the stability of the reaction.
ᆞDisadvantages:
Requires a high level of welding.

2.3.2 Plate heat exchanger

ᆞAdvantage:
Its structural characteristics can strengthen heat transfer.
The equipment cost can be reduced when mass-produced.
ᆞDisadvantage:
Pressure resistance is poorer than tubular heat exchangers.
2.3.2.1 Spiral plate heat exchangers
ᆞDescription:
The spiral plate heat exchanger is made of two parallel thin metal plates rolled at regular intervals, forming two concentric spiral channels inside it. 
The heat exchanger is equipped with a spacer in the center, which separates the spiral channels, and fixed-pitch columns are welded between the plates to maintain the channel spacing. 
There is a welded cover on both sides of the spiral plate the welded cover. 
Cold and hot fluids pass through the two channels respectively and flow countercurrently inside the vessel, exchanging heat through the thin plates.
photo of Spiral plate heat exchangers
ᆞAdvantages:
High heat transfer coefficient.
The fluid can achieve turbulence at the related low Reynolds number (generally Re = 1400 ~ 1800 or lower) due to the interference caused by inertial centrifugal force and fixed-pitch column in a spiral flow channel, and it allows to use of a high flow rate (for liquid 2m / s, gas for 20m / s), so the heat transfer coefficient is high. 
For example:
Water-to-water heat transfer. 
The heat transfer coefficient is up to 2000 ~ 3000W / (m².K), while the tubular heat exchanger is only 1000 ~ 2000 W / (m2.K).
Not easy to deposit or clog.
Because of the high velocity of the fluid and the effect of inertial centrifugal force, suspended particles in the fluid are thrown to the outer edge of the spiral channel and flushed by the fluid, so the spiral plate heat exchanger is not easy to deposit and clog. So, it is suitable for dealing with suspensions and viscosity medium.
Ability to utilize low-temperature heat sources.
Due to the long flow path of the fluid flow, the two fluids can be completely counter-current, so they can be operated under a smaller temperature difference.
Compact structure, high material utilization: 
The heat transfer area per unit volume is 3 times that of the column tubular type exchanger.
ᆞDisadvantages:
The operating pressure and temperature should not be too high.
The current maximum operating pressure could not exceed 2Mpa, the temperature should be below 300 ~ 400 ℃.
Not easy to maintain.
Because the whole heat exchanger is welded into one piece, once it is damaged, the repair would be very difficult.
2.3.2.2 Flat plate heat exchangers
Principle of Flat plate heat exchangers
ᆞDescription:
A flat plate heat exchanger is composed of a set of rectangular thin metal plates arranged in parallel, and tightly assembled on the bracket. The edges of the two neighboring plates are lined with the thickness of the gasket to regulate the size of the channel.
There is a circular hole on each corner of the plates. 
A pair of circular holes connects a group of inter-plate flow channels. The other pair of circular holes prevents fluid from entering the group of inter-plate channels by placing gaskets around the holes. 
The positions of these two pairs of holes are staggered on adjacent plates to form separate channels for the two fluids. 
Hot and cold fluids flow staggered on either side of the plates and heat transfer occurs through the plates. 
The plates have a thickness of about 0.5 to 3 mm and are usually pressed into a concave-convex corrugated shape. 
For example, 
Herringbone corrugated plate.
It could increase the rigidity of the plate to prevent deformation when the plate is pressurized, and make the fluid distribution uniform simultaneously, as well as enhance the degree of fluid turbulence and increase the heat transfer conduction and area.
ᆞAdvantages:
High heat transfer coefficient: 
Due to ripples or grooves in the plate surface, it can achieve turbulence at the low Reynolds number (Re = 200 or so). Besides the small thickness of plate thickness, the heat transfer coefficient is large. 
For example, the water-to-water heat transfer coefficient is up to 1500 ~ 4700W / (m2.℃).
Compact structure: 
picture for Flat plate heat exchangers plates
General plate spacing is 4 ~ 6mm, The heat transfer surface that can be provided by unit volume equipment is 250 ~ 1000m2/m3 (tubular heat exchanger is only 40 ~ 150 m²/m3). The flat plate heat exchanger saves 50% of metal consumption.
With removable structure: 
The number of plates is adjustable to increase or decrease the heat transfer area. 
The operation is flexible.
Easy for overhaul and cleaning.
ᆞDisadvantages:
Allowable operating pressure and temperature are relatively low, usually less than 1.5Mpa. The maximum does not exceed 2.0Mpa. Because high pressure is easy to cause leaking.
The operating temperature is limited by the heat resistance of the gasket material and generally does not exceed 250 C. In addition, due to the distance between the two plates being only a few millimeters, the circulation area is small, the flow rate is not large, and the processing capacity is small.
Both spiral plate heat exchangers and flat plate heat exchangers have features of compact structure, low material consumption, and large heat transfer coefficient. They belong to the new high-efficiency compact heat exchangers. 
They could not be used at high temperatures and high-pressure conditions. 
But for the conditions of lower pressure, low temperature, or highly corrosive expensive materials, they show greater superiority.
They have been widely used in the food, light industry, and chemical industries at present.
2.3.2.3 Plate shell heat exchanger ( PSHE)

photo of Plate shell heat exchanger ( PSHE)
ᆞAdvantages:
Close arrangement, compact structure, high heat transfer coefficient.
The heat exchange surface provided per unit volume is more than 3.5 times compared with the tubular type exchanger.
The sturdy structure can withstand high pressure and temperature.
Compact structure.
Heat transfer area per unit volume is 70% more than tube-shell exchanger.
High heat transfer efficiency and small pressure drop.
Compared with a flat plate heat exchanger, it provides a better solution to the contradiction between temperature resistance, pressure resistance, and high efficiency because it doesn't need a sealing gasket.
Easy to clean.
Commonly used in heating, cooling, evaporation, condensation, and other processes.
ᆞDisadvantage:
High welding technology requirements.
2.3.2.4 Jacketed heat exchangers
ᆞDescription:
The jacketed heat exchanger type is the simplest plate heat exchanger, which is made by installing a jacket on the external wall of the vessel, and the space formed between the jacket and the vessel is the pathway for the heating medium or cooling medium.
This type of heat exchanger is mainly used for the heating or cooling of the reaction process. 
When heating with steam, the steam enters the jacket from the upper receiver and the condensate from the lower port.
When it is used as a cooler, the refrigerant medium (e.g. cooling water) enters into the lower receiver of the jacket and exits via the upper port.
Picture of jacket exchanger principle and application
ᆞAdvantages:
Simplest structure.
It can be welded together with the reactor and occupies little space.
ᆞDisadvantages:
The heating surface is limited by the vessel. 
The heat transfer coefficient is not high.
ᆞApplication:
To improve the heat transfer coefficient, a stirrer can be installed inside the vessel.  The coil pipe can be installed inside the vessel to support the heat transfer surface.

2.3.3 Finned Heat Exchangers

2.3.3.1 Finned tube heat exchanger
ᆞDescription:
The tube of the exchanger has fins added on. The connection between the fins and the tube surface is tight and seamless to provide good heat transfer.
Fins connection methods:
Heat sleeve, inlay clamp, tension winding, and welding. In addition, it can also use overall rolling, overall casting, or machining methods.
photo of Finned tube heat exchanger
ᆞAdvantages:
When the difference in convective heat transfer coefficients between the two fluids is large, adding fins on the side with the smaller heat transfer coefficient can enhance heat transfer.
For example:
Heating air with water vapor.
The main thermal resistance of the process is the convective heat transfer thermal resistance on the air side. Adding fins on the air side can enhance the heat transfer.
ᆞDisadvantages:
Adding fins will increase the equipment cost.
However, when the ratio of the convective heat transfer coefficients of the two fluids exceeds 3:1, the application of fins is economical.
ᆞApplications:
In recent years the air cooler made of finned tubes has been widely used in the chemical industry. Using air cooling instead of water cooling is not only applicable in water-scarce areas but also in places with sufficient water sources, the use of air cooling can also achieve greater economic results.
2.3.3.2 Plate-fin heat exchangers
ᆞDescription:
The plate-fin heat exchanger is a more efficient, compact, and lightweight heat exchanger.
Structure:
There are many structural forms of plate-fin heat exchanger, but the basic structural elements are the same, i.e., between two parallel thin metal plates, corrugated or other shaped metal fins are added, and seal the two sides, which becomes a basic element of heat exchange.
picture of Plate-fin heat exchangers principle
ᆞProduce process:
To make a plate bundle, need appropriate stacking and arrangement for the basic elements, and fix them by brazing. The plate bundle (or core) supports parallel flow, countercurrent, or staggered flow. 
Weld the collector box with the fluid import and export ports to the plate bundle. 
Type:
Glossy straight fins exchanger, serrated fins exchanger, and multi-hole fins exchanger.
ᆞAdvantages.
High thermal efficiency:
The heat transfer coefficient is 3 to 10 times greater than that of shell and tube heat exchangers.
Higher heat transfer coefficient due to the fins promoting fluid turbulence and destroying the development of the thermal boundary layer.
The heat transfer surface provided by the unit volume equipment can generally reach 2500~4370 m2/m3 (1000x6000, 347m2, 74m2/m3  in tube-shell exchanger).
Unit weight heat transfer area is large:
Its area is ten times to dozens of times more than a tube-shell exchanger.
It is usually made of aluminum alloy, so the weight is light. Its weight is only one-tenth of the tubular exchanger with the same heat transfer area.
Wide adaptability:
Can be used for gas-gas, gas-liquid, and liquid-liquid heat exchange. 
Can also be used for condensation and evaporation.
It applies to a variety of different fluids operating in the same equipment.
It can be used for 0 ~ 1000K range of heat exchanging if selecting appropriate materials.
Aluminum alloy not only has high thermal conductivity, but also has high ductility and tensile strength when operated below zero degrees, which is suitable for low and ultra-low temperature occasions, so it has a wide operating range. It can be used in the range of 200℃ to absolute zero degrees.
High operating pressure:
Because the fins have a supporting effect on the spacer, the allowable operating pressure of the plate-fin heat exchanger can be 5MPa.

ᆞDisadvantages:
Complex structure, high cost.
The equipment flow channel is very small and easy to clog.
Cleaning and maintenance are difficult, so the materials handled should be cleaner or a pre-purification system.
The fins of the partition are made of thin aluminum plates, so the medium can not corrode aluminum.
Application:
Because of the high cost of manufacturing, it was used only in aerospace, electronics, atomic energy, and other minority sectors. However, it has been gradually used in petrochemical and other industrial sectors in recent years.

2.3.4 Heat pipes

ᆞDescription:
Heat pipes are a new type of heat transfer element developed in the mid-1960s. It is a sealed metal tube filled with a certain amount of certain working liquid after the tube is filled then vacuumed with non-condensable gas.
Principle of operation:
The working liquid absorbs heat, boiling, and vaporing at the hot end. The steam flows to the cold end, condenses, and releases the heat. The condensed liquid is back to the hot end and reboil. The heat is constantly transferred from the hot end to the cold end as the cycle repeats.
picture of principle of hot pipe
ᆞTypes:
The reflux of condensate can be realized by different methods:
Capillary action, gravity, centrifugal force.
The most widely used method is capillary action. It is to install the suction core with a capillary structure on the inner wall of the tube. By the capillary effect, condensate reflux from the cold end to the hot end. 
Working liquids:
Ammonia, water, mercury, etc..
ᆞAdvantages:
Heat pipes can be used over a wide range of temperatures.
Heat transfer of heat pipe is in three steps: boiling vaporization, steam flow, and steam condensation. The boiling and condensation of convection heat transfer intensity are large, and the cross-section of the tube surface at both ends is much larger than the cross-section of the tube. The resistance loss of steam flow is small. So the heat pipe at both ends of the temperature difference can be very small, that is, it can transfer a large amount of heat flow at a very small temperature difference. 
Compared with the metal wall of the same cross-section of the heat pipe, the heat pipe's thermal conductivity can be up to 103 to 104 times the best metal heat conductor. Therefore, it is particularly suitable for occasions with small temperature differences as well as occasions with high requirements for isothermal properties.
The heat pipe of this heat transfer characteristics for the device (or room) inside and outside the heat transfer enhancement provides a very favorable means. 
picture of hot pipe application
For example. 
Both sides of the device are gases. 
By installing a heat pipe on the wall of the device, increasing the length of the ends of the heat pipe, and adding fins to the pipe, you can greatly accelerate the heat transfer inside and outside the gas pedal.
In addition, the heat pipe also has the advantages of a simple structure, long service life, reliable operation, and a wide range of applications.
ᆞApplications:
Heat pipes were initially used in the aerospace and electronics industries. In recent years, they have achieved good results in the utilization of industrial waste heat.

2.4 Classification by material: 

2.4.1 Metal materials  heat exchanger 

Steel, copper, aluminum and their alloy, Titanium, Zirconium, Tantalum, Inconel, etc.

2.4.2 Non-metallic materials heat exchanger.

Graphite, glass, plastics, SiC, ceramics, etc.

III, Heat exchanger cleaning


photo of exchanger cleaning

3.1 Heat exchanger cleaning reasons

After a  period of operation, there would be a layer of white scale on the inside and outside the wall of the heat exchanger.

3.1.1 Thermal conductivity of scale is very poor 

The heat exchanging efficiency will drop about 10% when there is a 1mm thick scale.

3.1.2 The scale can cause equipment failure.

It will reduce the heat transfer surface circulation, increase water circulation resistance, reduce the cross-section area, and even block the flow.

3.2 Cleaning method of heat exchanger

3.2.1 Dosing softening treatment

The method is simple with high efficiency, good economy, and does not require special water production equipment.
Types:
Correction agent treatment.  
Anti-foulant treatment.

3.2.2 Ion scale inhibitor

Ion anti-scaling treatment is a new, advanced water treatment equipment for the hot water circulation system, central air conditioning system, and circulating cooling water system. It achieved satisfactory results for the heat exchangers.

3.2.3 Magnetization anti-scaling treatment

Magnetization anti-scaling treatment principle is the use of water molecules, with the polarity of the water molecules combined.
When the fluid is through the high-intensity magnetic field, the multi-molecule associations in the water act with the ion's magnetic field.
The original single scattered multi-ion associations are disassembled into single or short bond associations. They cut the magnetic lines of the external magnetic field with a certain speed perpendicularly and produce an induced current. 
Therefore, each ion and the external magnetic field establish a new field, established in the adjacent polar ions, ordered, mutual attraction compression, the formation of the change in conditions, resulting in changes in crystallization, the formation of crystalline material is very flaccid, compressive strength, tensile strength is poor and is very brittle, cohesion and adhesion is very weak. 
So they are not easy to attach to the heated surfaces on the formation of scale.

3.2.4 High-pressure water flushing method

The high-pressure water flushing method is mostly used for cleaning the tube bundles with serious coking, such as catalytic slurry heat exchangers.
photo of High-pressure water flushing

3.2.5 Sponge ball cleaning method

Put the soft and flexible sponge ball into the tube, and press the sponge ball to make it in contact with the inner wall of the tube. Then manually or mechanically push the sponge ball along the tube wall, and constantly rub the tube wall, so to remove the scale.

3.2.6 Mechanical cleaning method

For serious scaling and clogging, use a tube impact drill to unclog and clean.
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