1. Tubular heat exchanger
Each section of casing is called “one pass”.
The inner tube (heat transfer tube) of the pass is connected by U-shaped elbow tubes, while the outer tube is connected in rows with short tubes and fixed on the support.
Heat is transferred from one fluid to another through the inner tube wall.
Usually, the hot fluid (fluid A) is introduced from the upper part, while the cold fluid (fluid B) is introduced from the lower part.
Both ends of the outer pipe of the casing are connected with the inner pipe by welding or flange.
The inner tube and U-shaped elbow tube are connected by flanges, which is convenient for the cleaning and increase and decrease of heat transfer tubes.
The effective length of each heat transfer tube is 4 ~ 7 meters.
The heat transfer area of this heat exchanger is up to 18 square meters, so it is suitable for small capacity heat exchange.
It has simple structure and can withstand high pressure.
The heat transfer area can be increased or decreased as needed, which is convenient for application.
There are many joints between pipes, which are easy to leak.
It covers a large area and consumes a large amount of metal per unit heat transfer surface.
2. Floating head heat exchanger
The floating head end structure of floating head heat exchanger is composed of cylinder, outer head cover side flange, floating head tube plate, hook ring, floating head cover, outer head cover, screw hole, steel ring, etc.
The detailed structure of hook and loop floating head is shown in the figure below.
When there is a temperature difference between the heat exchange tube and the shell, the shell or heat exchange tube will not restrict each other and will not produce temperature difference stress.
The tube bundle can be extracted from the shell to facilitate the cleaning inside and between the tubes.
The structure is complex, with large amount of materials and high cost.
If the seal between the floating head cover and the floating tube plate is not tight, internal leakage will occur, resulting in the mixing of the two media.
3. Immersed coil heat exchange
This kind of heat exchanger bends the metal tubes into various shapes suitable for the container, and immerses them in the liquid in the container.
It has simple structure and can withstand high pressure.
It can be made of corrosion-resistant materials.
The turbulence degree of liquid in the container is low, and the heat transfer coefficient outside the tube is small.
In order to improve the heat transfer coefficient, an agitator can be installed in the container.
4. Plate heat exchanger
Plate heat exchanger is an ideal equipment for liquid-liquid and liquid vapor heat exchange.
It is a new type of high-efficiency heat exchanger made of a series of corrugated metal sheets.
Structural principle of plate heat exchanger:
The removable plate heat exchanger is made up of many corrugated sheets pressed at a certain interval, sealed around by gaskets, and overlapped and compressed by frames and compression screws.
The four corner holes of the plates and gaskets form the distribution pipe and collection pipe of the fluid.
At the same time, the cold and hot fluids are reasonably separated, so that they flow in the flow channels on both sides of each plate, and heat exchange is carried out through the plates.
5. Heat exchanger with compensation ring
The heat exchanger is composed of baffle, compensation ring and heat release nozzle.
When the fluid exchanges heat at a high temperature, because the temperature difference between the shell and the tube bundle is too large, resulting in different thermal expansion rates, the compensation ring is to eliminate this thermal stress.
6. Plate fin heat exchanger
It is a more efficient, compact and lightweight heat exchanger.
In the past, due to high manufacturing costs, it was only used in a few departments such as aerospace, electronics, atomic energy, etc.
It has been gradually used in petrochemical and other industrial sectors.
There are many structural forms of plate fin heat exchangers, but the basic elements are the same, that is, between two parallel thin metal plates, corrugated or other shaped metal fins are added to seal the two sides, which becomes a basic element of heat exchange.
- High heat transfer efficiency and good temperature control.
- The fins are thin, compact and small.
- Fins have both heat transfer surface and support function, and have high strength.
- The flow passage is narrow, easy to be blocked, and difficult to clean.
- The diaphragm and fins are very thin, so it is required that the medium will not corrode the aluminum. If it corrodes, it will cause internal leakage, which is difficult to repair.
- The complex structure makes the design more difficult.
7. Jacket heat exchanger
A jacket is installed on the outer wall of the container, and the space formed between the jacket and the container is used as a path for heating medium or cooling medium.
However, the heating surface is limited by the vessel wall, and the heat transfer coefficient is not high.
In order to improve the heat transfer coefficient and make the liquid in the container heated evenly, an agitator can be installed in the container.
When cooling water or heating agent without phase change is introduced into the jacket, spiral baffles or other measures to increase turbulence can also be set in the jacket to improve the heat transfer coefficient on one side of the jacket.
Simple structure and convenient processing.
Small heat transfer area and low heat transfer efficiency.
8. U-tube heat exchanger
The U-shaped tube heat exchanger bends the heat exchange tube into a U shape, and both ends are fixed on the same tube plate.
Since the shell and the heat exchange tube are separated, the heat exchange tube bundle can expand and contract freely, and the temperature difference stress will not be generated due to the temperature difference of the medium.
The U-tube heat exchanger has only one tube plate and no floating head, so its structure is relatively simple.
The tube bundle can be extracted and installed freely, which is convenient for cleaning, and has the advantages of floating head heat exchanger.
However, because the heat exchange tube is made into U-shaped bends with different radii, the outermost heat exchange tube can be replaced after it is damaged, and other tubes can only be blocked if they are damaged.
At the same time, compared with the fixed tubesheet heat exchanger, because the heat exchange tube is limited by the bending radius, there is a gap in the center of its tube bundle, and the fluid is easy to short circuit, which affects the heat transfer effect.
1. The tube bundle of U-shaped heat exchange tube can float freely without considering temperature difference stress, which can be used in large temperature difference occasions;
2. There is only one tube sheet, with less flanges, less leakage points and simple structure;
3. The tube bundle can be cleaned by core pulling;
4. Due to the limitation of the minimum bending radius of the U-shaped pipe, the split distance is wide, so the number of pipes is less;
5. When the flow rate in the pipe is too high, it will cause serious erosion to the U-shaped elbow section and affect the service life.
6. Because the heat exchange tube is U-shaped, it is difficult to clean in the tube, so the medium in the tube should be clean and not easy to scale.
Simple structure, only one tube plate, less sealing surface, reliable operation and low cost;
The tube bundle can be drawn out and the cleaning between tubes is convenient.
It is difficult to clean in the pipe;
Because the tube needs a certain bending radius, the utilization rate of tube sheet is low;
The spacing between the innermost tubes of the tube bundle is large, and the shell side is easy to be short circuited;
If the inner pipe is broken, it can only be blocked and cannot be replaced, so the scrap rate is high.
9. Tube heat exchanger
Tubular exchanger is the most widely used heat exchanger in chemical industry and alcohol production at present.
It is mainly composed of shell, tube sheet, heat exchange tube, head, baffle, etc.
The required materials can be made of ordinary carbon steel, red copper, or stainless steel.
During heat exchange, a fluid enters from the connecting pipe of the head, flows in the pipe, and flows out from the outlet pipe at the other end of the head, which is called the pipe pass; Another fluid enters from the connecting pipe of the shell and flows out from another connecting pipe on the shell, which is called shell side tubular heat exchanger.
10. Spiral plate heat exchanger
Spiral plate is a new type of heat exchanger, which has good heat transfer efficiency and high operation stability, and can work together with multiple units.
High heat transfer efficiency, strong operation reliability and low resistance.
However, the spiral plate heat exchanger requires high welding quality and is difficult to repair.
Due to heavy weight and poor rigidity, special attention should be paid to the transportation and installation of spiral plate heat exchanger.
11. Spray heat exchanger
This kind of heat exchanger is to fix the heat exchange tubes on the steel frame in rows, the hot fluid flows in the tubes, and the cooling water is evenly drenched from the spray device above, so it is also called spray cooler.
There is a layer of liquid film with high turbulence outside the tube of the spray heat exchanger, and the heat transfer coefficient outside the tube is much larger than that of the immersion type.
In addition, this kind of heat exchanger is mostly placed in the place of air circulation, and the evaporation of cooling water also takes away part of the heat, which can reduce the temperature of cooling water and increase the driving force of heat transfer.
Therefore, compared with immersion type, the heat transfer effect of spray type heat exchanger is greatly improved.
12. Heat pipe heat exchanger
Heat pipe is a kind of heat transfer element with high thermal conductivity.
It transfers heat through the evaporation and condensation of working medium in the fully enclosed vacuum shell.
It has a series of advantages, such as high thermal conductivity, good isothermal, arbitrary change of heat transfer area on both sides of cold and hot, long-distance heat transfer, temperature control and so on.
The disadvantage is poor oxidation resistance and high temperature resistance.
This shortcoming can be solved by installing a set of ceramic heat exchanger in the front, which solves the problem of high temperature resistance and corrosion resistance.
At present, it has been widely used in metallurgy, chemical industry, oil refining, boiler, ceramics, transportation, light textile, machinery and other industries.
As an energy-saving equipment for waste heat recovery and thermal energy utilization in the process, it has achieved remarkable economic benefits.