Case Detail

Plate heat exchangers (PHEs) are widely used in chemical, petroleum, pharmaceutical, food, HVAC and central heating industries due to their compact structure, high heat transfer efficiency and small floor space. Their performance and applicability vary significantly with different structures and assembly methods. This article systematically introduces the classification of plate heat exchangers based on structural forms, sealing methods and manufacturing processes, as well as the key assembly skills and precautions, aiming to provide practical guidance for their rational application and standard operation, with the total number of words controlled within 5000.

1. Classification of Plate Heat Exchangers

Plate heat exchangers can be divided into several core types according to differences in structural design, sealing methods and manufacturing processes. Each type has unique structural characteristics, advantages and applicable scenarios, which can meet the needs of different working conditions.

1.1 Gasketed Plate Heat Exchanger

As the most common and widely used type of plate heat exchanger, the gasketed plate heat exchanger is composed of a series of corrugated metal sheets, with rubber gaskets sealed between the plates, and fixed by a frame and compression bolts. Its core feature is high flexibility—users can increase or decrease the number of plates according to load changes, and disassembly, cleaning and maintenance are extremely convenient, which only requires loosening the compression bolts to open the equipment.

The corrugated design of the plates not only increases the heat transfer surface area but also enhances the turbulence of the fluid, thereby improving the heat transfer efficiency. The gaskets are embedded in the grooves of the plates, which play a dual role of sealing the channels to prevent external leakage and guiding the two fluids to flow into alternating channels to avoid internal mixing. Common gasket materials include nitrile rubber (NBR) and ethylene-propylene rubber (EPDM): NBR gaskets have a maximum heat resistance of 110℃ and are resistant to oil and water, while EPDM gaskets can withstand temperatures up to 150℃ and are suitable for steam and water media.

This type is suitable for occasions that require frequent cleaning, easy scaling of media or frequent changes in working parameters, such as food and beverage processing, general HVAC systems and light chemical fields. It is also widely used in residential central heating and domestic hot water supply systems due to its convenient maintenance.

1.2 Welded Plate Heat Exchanger

Aiming at high-temperature, high-pressure or strong corrosive media where traditional rubber gaskets cannot meet the requirements, the welded plate heat exchanger connects the contact points of adjacent plates into an integral structure through laser welding or argon arc welding, which greatly improves the pressure resistance and corrosion resistance of the equipment. According to the welding form, it can be further divided into two sub-types:

Semi-welded plate heat exchanger: One side of the fluid channel is sealed by gaskets, and the other side is sealed by welding. It combines the maintenance convenience of detachable type and the high pressure resistance of welding, and is often used in ammonia refrigeration or working conditions containing slightly corrosive media. It retains the flexibility of gasketed type on one side, which is convenient for regular maintenance and cleaning, while the welded side can withstand harsh working conditions such as high pressure and corrosion.

Fully welded plate heat exchanger: All plates are welded together without the limitation of rubber gaskets. Its temperature resistance can reach more than 300℃, and its pressure resistance is significantly improved, which completely eliminates the risk of medium leakage. This type has high structural strength and good stability, and is suitable for harsh environments such as petrochemical industry, high-temperature water-water heat exchange and toxic and harmful medium treatment.

1.3 Brazed Plate Heat Exchanger

The brazed plate heat exchanger is a highly compact heat exchanger. The plates are brazed together in a vacuum furnace with copper or nickel-based brazing filler metal, without the need for a frame and gaskets. Its core advantages are small volume, light weight, excellent high-pressure resistance (usually up to more than 30bar) and almost no maintenance.

The internal flow channel of this type is optimized, which can greatly reduce the pressure drop and improve the heat transfer coefficient, so it has a high energy efficiency ratio. It is mainly used in small refrigeration units, hydraulic system cooling, floor heating heat exchange stations and installation environments with limited space, such as mobile equipment and small industrial devices. Due to its compact structure, it can save a lot of installation space while ensuring heat transfer efficiency.

1.4 Spiral Plate Heat Exchanger

Although its structure is slightly different from that of traditional plate heat exchangers, it is often classified into the broad category of plate heat exchangers. It is made of two parallel metal plates rolled into two spiral channels, and the hot and cold fluids flow in the two spiral channels respectively to realize heat exchange.

Its most prominent advantage is the unique "self-cleaning" function: the fluid generates secondary flow in the spiral channel, which is not easy to scale; at the same time, it can realize real countercurrent heat exchange, with extremely high heat recovery efficiency. In addition, it has good adaptability to media containing particles and high viscosity, and is suitable for sewage treatment, high viscosity fluid heat exchange and cooling of media containing particles.

1.5 Plate and Shell Heat Exchanger

The plate and shell heat exchanger encapsulates the plate bundle in a cylindrical shell, combining the high efficiency of the plate heat exchanger and the high pressure resistance of the shell and tube heat exchanger. Its unit volume heat transfer area is more than 70% larger than that of the traditional shell and tube heat exchanger, and it can withstand higher pressure and temperature impact, without the hidden danger of gasket leakage.

This type is mainly used in large industrial projects, high-pressure gas cooling, steam condensation and other extreme working conditions. It has the advantages of high heat transfer efficiency, good stability and long service life, and is an ideal choice for large-scale industrial heat exchange systems.

1.6 Other Classification Methods

In addition to the above classification based on structural forms, plate heat exchangers can also be classified according to other standards: According to the process purpose, they can be divided into plate heaters, plate coolers, plate condensers and plate preheaters; according to the flow combination, they can be divided into single-pass and multi-pass plate heat exchangers; according to the flow direction of the medium, they can be divided into cocurrent, countercurrent and cross-flow plate heat exchangers; according to the gap size of the flow channel, they can be divided into conventional gap and wide gap plate heat exchangers.

2. Assembly Skills of Plate Heat Exchangers

The assembly quality of plate heat exchangers directly affects their heat transfer efficiency, sealing performance and service life. Although the assembly steps of different types of plate heat exchangers are slightly different, the core principles and key skills are basically the same. The following mainly takes the most commonly used gasketed plate heat exchanger as an example to introduce the detailed assembly steps, skills and precautions.

2.1 Preparation Before Assembly

Adequate preparation before assembly is the premise to ensure the assembly quality. The preparation work mainly includes the following aspects:

2.1.1 Cleaning of Components

All components, especially heat transfer plates and gasket grooves, must be thoroughly cleaned to be free of debris, oil, old adhesive residue and rust stains. Even newly delivered plates may be contaminated with dust and oil during transportation and storage. If they are directly assembled, these impurities will block the flow channels, affect the heat transfer efficiency and even scratch the surface of the plates.

It is recommended to use a neutral cleaning agent, wipe the surface of the plates gently with a soft bristle brush, and never use steel wire balls or hard objects to scrape, so as not to damage the corrugated structure of the plates and affect the turbulence effect. After cleaning, rinse thoroughly with clean water and dry naturally. Wet plates will easily cause corrosion and bacterial growth after assembly.

2.1.2 Inspection of Components

Carefully inspect each component to ensure that there is no damage, deformation or aging. For the plates, check whether there are dents, warping, cracks or scratches on the surface; if the damage is serious, it should be replaced in time to avoid affecting the sealing performance and heat transfer effect. For the gaskets, check whether there are cracks, aging, deformation or uneven thickness; the gaskets that do not meet the requirements should be replaced, and the material of the gaskets should be consistent with the medium to be transported to ensure corrosion resistance and temperature resistance.

In addition, check whether the frame plate, pressure plate, carrying bar, guiding bar, tightening bolts and other components are intact, whether the threads of the bolts are smooth, and whether the supporting columns are firm. At the same time, check the completeness of the components according to the packing list to avoid missing parts.

Prepare the necessary assembly tools, including torque wrench, tape measure, soft bristle brush, cleaning agent, adhesive, etc. The torque wrench should be calibrated in advance to ensure the accuracy of the torque value; the tape measure is used to measure the distance between the pressure plates and the alignment of the plates, and the error should be controlled within ±2mm.

The assembly environment should be clean, dry and dust-free. Avoid assembling in places with strong wind, sand or high humidity, so as to prevent impurities from entering the flow channels or corroding metal components. The installation site should be flat, and an operation and maintenance space of not less than 0.5 meters should be reserved around the equipment.

2.2 Specific Assembly Steps and Skills

2.2.1 Installation of Gaskets

First, apply a thin layer of special adhesive evenly in the gasket groove of the plate. The adhesive can enhance the bonding force between the gasket and the plate, prevent the gasket from shifting during assembly and operation. Then, press the gasket into the groove gently to ensure that the gasket is closely attached to the groove, without deviation, wrinkling or exposure.

It should be noted that the type and size of the gasket must match the plate. For the head plate and tail plate, special gaskets (such as round hole gaskets and blind plate gaskets) should be used according to the design requirements to separate the hot and cold fluids and avoid internal mixing. After installing the gasket, place the plate flat and press it with a proper weight for a period of time to make the gasket fully fit with the plate.

2.2.2 Stacking of Plates

Stack the plates with gaskets in the order specified by the manufacturer. The plate order is usually marked on the plate, and it is strictly forbidden to reverse or mess up the order, otherwise, the flow channel will be blocked, and the heat transfer effect and sealing performance will be affected. For BR-type plate heat exchangers, adjacent plates need to be rotated 180° so that the herringbone direction is opposite; for BRB-type plate heat exchangers, two different types of plates (A plate and B plate) are stacked alternately.

During the stacking process, ensure that each plate is stably hung on the carrying bar and guided by the guiding bar, with upper and lower alignment and no front-back deviation. Every 5 plates stacked, use a flashlight to check whether the gasket is clamped firmly and whether the plate is aligned. If there is jamming or skew, adjust it in time and do not push it forcibly.

2.2.3 Installation of Frame and Compression of Bolts

After stacking all plates, install the pressure plate, align it with the plate pack, and insert the tightening bolts. The key skill of bolt compression is to tighten symmetrically, step by step and evenly, which is the core to ensure uniform pressure distribution of the plate pack and good sealing performance.

The correct operation method is: start from the middle of the bolt, tighten symmetrically to the surroundings, and gradually apply force in 3 to 4 times until the specified torque value or compression dimension required by the manufacturer is reached. It is strictly forbidden to use electric tools to tighten the bolts quickly, which will easily lead to uneven stress on the bolts, deformation of the frame or damage to the plates. During the compression process, continuously measure the distance between the two pressure plates to ensure that the parallelism deviation between the two pressure plates is not greater than 3mm, and the parallelism deviation is not greater than 1mm after compression to the specified dimension, so as to avoid the gasket being pressed skewed or sliding out of the gasket groove.

2.2.4 Connection of Pipes and Installation of Auxiliary Components

Connect the pipeline according to the "hot and cold fluid inlet and outlet" marked on the equipment nameplate, and never connect it reversely, otherwise, the fluid will be short-circuited and the heat transfer efficiency will be greatly reduced. When connecting the pipeline, add a sealing gasket at the flange connection, and tighten the flange bolts evenly to prevent leakage.

According to the actual needs, install thermometers, pressure gauges, safety valves, blowdown valves and other auxiliary components to ensure that the valves can be opened and closed flexibly and the instruments can work normally. The installation of the safety valve should meet the design requirements to prevent overpressure of the equipment and ensure safe operation.

2.3 Inspection and Test After Assembly

After the assembly is completed, it is necessary to carry out strict inspection and test to ensure that the equipment can operate safely and stably. The inspection and test mainly include the following two aspects:

2.3.1 Static Inspection

Visually check whether the bolts are tightened evenly, whether the pipeline connection is firm, whether the gasket is exposed or offset, and whether the plates are aligned correctly. Check whether the surface of the equipment is clean, whether there are sundries left in the flow channel, and whether the auxiliary components are installed in place.

2.3.2 Pressure Test

The pressure test is an important link to check the sealing performance and structural strength of the equipment. It is generally divided into air tightness test and strength test. For the gasketed plate heat exchanger, the pressure test should be carried out separately on one side, and the test pressure is 1.25 times the design pressure of the equipment, and the pressure is maintained for 30 minutes; for the strength test, the pressure is increased to 1.8 times the design pressure, and the pressure is maintained for 30 minutes, with no leakage, no deformation and no pressure drop as the qualification standard.

During the pressure test, slowly inject clean water (or corresponding medium) and gradually increase the pressure to avoid impact on the equipment. After the test is qualified, drain the water in the equipment and dry it to prevent corrosion.

2.4 Key Precautions for Assembly

1. Strictly follow the manufacturer's assembly instructions and do not assemble according to experience. Each type of plate heat exchanger has specific structural parameters and assembly requirements, such as torque value, number of plates and gasket model, which are crucial to the assembly quality.

2. Pay attention to the safety of operation. Before assembly, ensure that the equipment has been safely depressurized, the pressure gauge returns to zero, and avoid disassembly and assembly under pressure to prevent safety accidents such as medium spray烫伤. When lifting the equipment, pay attention to the center of gravity to avoid collision and damage to the plates.

3. The selection of gaskets and plates should be consistent with the medium. For corrosive media, plates made of corrosion-resistant materials (such as SUS316L) and gaskets with corrosion resistance should be selected; for high-temperature media, gaskets with high temperature resistance should be selected to avoid gasket aging and plate corrosion.

4. During the assembly process, avoid collision and scratch of the plates. The surface of the plates is precision processed, and any damage will affect the sealing performance and heat transfer efficiency. If the plates are slightly scratched, they can be polished and repaired; if the damage is serious, they must be replaced.

5. After the assembly is completed, do not start the equipment immediately. It is necessary to conduct a trial run: first pass the cold fluid, then pass the hot fluid, gradually increase the temperature and pressure, observe the operation noise, temperature and pressure changes, and start formal operation only when there is no abnormality.

3. Conclusion

Plate heat exchangers have different types with distinct characteristics, and their selection should be based on specific working conditions such as medium properties, temperature, pressure and space size. The assembly of plate heat exchangers is a detailed and rigorous work, which requires adequate preparation before assembly, standard operation during assembly, and strict inspection after assembly. Only by mastering the correct classification and assembly skills can the plate heat exchanger give full play to its advantages of high heat transfer efficiency, compact structure and convenient maintenance, ensure long-term safe and stable operation, and reduce the occurrence of faults and maintenance costs.

Classification and Assembly Skills of Plate Heat Exchanger