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Abstract: Plate heat exchangers (PHEs) are widely used in industrial fields such as chemical engineering, food processing, HVAC, and petrochemicals due to their compact structure, high heat transfer efficiency, and flexible scalability. The design of PHEs is closely related to the physical, chemical, and thermal properties of the heat exchange medium. Any change in the medium (including changes in type, composition, and state parameters) will directly affect the core design conditions of PHEs, such as heat transfer efficiency, pressure drop, material selection, plate structure, and operating stability. This paper systematically analyzes the types of medium changes in PHE design, explores the mechanism of medium changes affecting key design parameters, combines practical engineering cases to verify the impact law, and puts forward corresponding design adjustment strategies. The research shows that medium changes will cause chain reactions in the design system of PHEs: changes in physical properties (viscosity, density, thermal conductivity) affect the heat transfer coefficient and pressure drop; changes in chemical properties (corrosivity, reactivity) determine the selection of plate and gasket materials; changes in state parameters (temperature, pressure, phase) affect the plate type selection and flow channel design; and changes in medium composition (impurities, mixed components) increase the risk of fouling and affect long-term operating efficiency. This study provides a theoretical basis and practical guidance for the design optimization, operation adjustment, and maintenance of PHEs under medium change conditions, helping to improve the adaptability and reliability of PHEs in complex industrial environments.
Keywords: Plate heat exchanger; Medium change; Design conditions; Heat transfer performance; Pressure drop; Material selection
Plate heat exchangers are a type of high-efficiency heat transfer equipment composed of a series of corrugated plates, gaskets, frame plates, and tie rods. The heat exchange process is realized through the alternating flow of hot and cold media on both sides of the plates, and the corrugated structure of the plates enhances the turbulence of the medium, thereby improving heat transfer efficiency. Compared with traditional shell-and-tube heat exchangers, PHEs have the advantages of high heat transfer coefficient (3000–7000 W/m²·K for liquid-liquid applications), compact structure (surface-area density of 100–200 m²/m³, 4–5 times that of shell-and-tube heat exchangers), easy disassembly and maintenance, and flexible adjustment of heat transfer area by increasing or decreasing plates. These advantages make PHEs widely used in various industrial fields, and their design rationality directly determines the operating efficiency, energy consumption, and service life of the entire heat exchange system.
In industrial production, the heat exchange medium is often affected by factors such as raw material replacement, process adjustment, product formula modification, and environmental changes, resulting in changes in its type, composition, physical and chemical properties, and state parameters. For example, in the petrochemical industry, the water content in crude oil may increase due to changes in oilfield exploitation conditions; in the food processing industry, the viscosity of milk or syrup may change due to differences in raw material sources; in the chemical industry, the corrosivity of the medium may increase due to the addition of new components. Once the medium changes, the original design parameters of the PHE (such as heat transfer area, plate type, material, and flow rate) will no longer match the actual operating conditions, leading to problems such as reduced heat transfer efficiency, excessive pressure drop, increased energy consumption, material corrosion, and even equipment failure.
At present, most of the existing research on PHE design focuses on the optimization of plate structure, heat transfer calculation, and fouling control, but there is a lack of systematic analysis on the overall impact of medium changes on design conditions. In practical engineering, many enterprises often ignore the impact of medium changes, resulting in the PHE not being able to exert its due performance, and even causing economic losses. For example, when the water cut in crude oil increases, the outlet temperature of the medium will drop, and if the PHE is not redesigned, it is necessary to add burners for preheating, which increases the annual operating cost by 390,000 euros; while extending the plate pack of the PHE can restore the outlet temperature and achieve investment recovery in less than three months. Therefore, it is of great theoretical and practical significance to study the impact of medium changes on the design conditions of PHEs, clarify the impact mechanism, and propose adjustment strategies.
This paper first classifies the types of medium changes in PHE design, then analyzes the impact of different types of medium changes on key design conditions (heat transfer performance, pressure drop, material selection, plate structure, etc.) from the mechanism, combines practical cases to verify, and finally puts forward design adjustment methods and optimization suggestions, providing support for the rational design and stable operation of PHEs under medium change conditions.
The medium in PHEs refers to the hot and cold fluids involved in heat exchange, and its changes are diverse, but they can be divided into four categories according to the nature of the change: changes in physical properties, changes in chemical properties, changes in state parameters, and changes in medium composition. These four types of changes are not isolated, and there may be mutual influence (for example, changes in temperature may lead to changes in viscosity and density, and changes in composition may lead to changes in corrosivity).
The physical properties of the medium that affect PHE design mainly include viscosity, density, thermal conductivity, specific heat capacity, and surface tension. Changes in these physical properties will directly affect the flow state of the medium in the flow channel and the heat transfer process. Common changes in physical properties include: increase or decrease in viscosity (such as the increase in viscosity of lubricating oil after aging, the decrease in viscosity of syrup after heating), increase or decrease in density (such as the mixing of light and heavy oils), and changes in thermal conductivity (such as the addition of heat transfer additives to the medium). Among them, viscosity and thermal conductivity are the two most critical physical properties, which have the most significant impact on heat transfer efficiency and pressure drop.
The chemical properties of the medium mainly affect the material selection of PHEs, including corrosivity, reactivity, oxidizability, and reducibility. Changes in chemical properties often occur due to the replacement of raw materials, the addition of new components, or chemical reactions during the heat exchange process. For example, in the chemical industry, the medium may change from neutral to acidic or alkaline due to process adjustment; in the food industry, the medium may produce acidic substances due to fermentation, increasing corrosivity; in the petrochemical industry, the sulfur content in the medium may increase, leading to enhanced corrosion of metal materials. In addition, some media may react with each other or with the plate/gasket materials, leading to material damage and equipment failure.
The state parameters of the medium refer to the temperature, pressure, and phase state (liquid, gas, solid-liquid mixture) during heat exchange. Changes in state parameters are common in industrial production, such as changes in the inlet/outlet temperature of the medium due to process load adjustment, changes in the operating pressure of the system due to pipeline blockage or pump failure, and phase changes of the medium during heat exchange (such as steam condensation, liquid vaporization). Among them, phase changes have the most significant impact on PHE design, as they will change the heat transfer mechanism and require special plate type and flow channel design.
Changes in medium composition refer to the addition of impurities, mixed components, or changes in the proportion of components in the original medium. For example, the medium may contain solid particles (such as sediment in water, catalyst particles in chemical reactions) due to raw material pollution; the mixing of two or more media (such as the mixing of water and oil) changes the overall properties of the medium; the proportion of components in the medium changes (such as the change in the water cut of crude oil). Changes in medium composition will not only affect the physical and chemical properties of the medium but also increase the risk of fouling and blockage of the flow channel, affecting the long-term operation of the PHE.
The design of PHEs is based on the original medium parameters, and any change in the medium will cause a chain reaction in the design system. The following will analyze the impact of medium changes on key design conditions from five aspects: heat transfer performance, pressure drop, material selection, plate structure and flow channel design, and fouling and operating stability.
Heat transfer performance is the core index of PHE design, which is mainly measured by the heat transfer coefficient (U) and heat transfer rate (Q). The heat transfer process of PHEs includes three links: convective heat transfer from the hot medium to the plate wall, conductive heat transfer through the plate wall, and convective heat transfer from the plate wall to the cold medium. Medium changes affect the heat transfer performance by changing the convective heat transfer efficiency and the thermal resistance of the medium.
Viscosity is the most important factor affecting the convective heat transfer coefficient. The higher the viscosity of the medium, the greater the flow resistance, the more difficult it is to form turbulence, and the lower the convective heat transfer coefficient. For example, when the viscosity of the hot medium increases by 50%, the Reynolds number (Re) of the medium in the flow channel will decrease significantly (Re is inversely proportional to viscosity), and the flow state will change from turbulent flow to laminar flow. At this time, the convective heat transfer coefficient will decrease by 30%–50%, resulting in a significant reduction in the heat transfer rate. On the contrary, the decrease in viscosity will increase the Reynolds number, enhance turbulence, and improve the convective heat transfer coefficient.
Thermal conductivity directly affects the heat transfer capacity of the medium. The higher the thermal conductivity of the medium, the faster the heat transfer between the medium and the plate wall, and the higher the heat transfer coefficient. For example, when the medium is changed from water (thermal conductivity 0.6 W/(m·K)) to engine oil (thermal conductivity 0.14 W/(m·K)), the thermal conductivity is reduced by 77%, and the convective heat transfer coefficient will be significantly reduced, requiring an increase in the heat transfer area to meet the design heat transfer requirements. In addition, changes in density and specific heat capacity will affect the heat capacity flow rate (m·cp) of the medium, thereby affecting the temperature difference between the inlet and outlet of the medium and the heat transfer rate.
Temperature changes affect the heat transfer performance in two ways: on the one hand, changes in temperature will lead to changes in the physical properties of the medium (such as viscosity, thermal conductivity), thereby affecting the convective heat transfer coefficient; on the other hand, changes in the inlet/outlet temperature of the medium will change the log mean temperature difference (LMTD), which is the driving force of heat transfer. For example, if the inlet temperature of the hot medium decreases by 20°C, the LMTD will decrease, and the heat transfer rate will decrease accordingly. To maintain the original heat transfer requirement, it is necessary to increase the heat transfer area or adjust the flow rate of the medium.
Phase changes (such as condensation of steam, vaporization of liquid) will significantly change the heat transfer mechanism. When the medium undergoes phase change, the latent heat of phase change will be released or absorbed, which can greatly improve the heat transfer rate. For example, when the hot medium is changed from saturated water (sensible heat transfer) to saturated steam (latent heat transfer), the heat transfer coefficient can be increased by 2–3 times. However, phase changes also put forward higher requirements for the plate type and flow channel design. For example, steam condensation requires a plate type with good gas-liquid separation performance to avoid liquid film accumulation affecting heat transfer; liquid vaporization requires a flow channel with uniform distribution to ensure that the medium is heated evenly.
When the medium contains solid particles or impurities, the particles will form a fouling layer on the plate surface, increasing the thermal resistance of the fouling layer, thereby reducing the overall heat transfer coefficient. The higher the content of particles, the faster the fouling rate, and the more significant the reduction in heat transfer efficiency. For example, when the water used as the cold medium contains a large amount of calcium and magnesium ions, scaling will occur on the plate surface after long-term operation, and the thermal conductivity of the scaling layer is only 1/10–1/5 of that of the metal plate, which will reduce the heat transfer coefficient by 20%–40% after scaling. In addition, the mixing of different media may lead to mutual dissolution or stratification, changing the overall physical properties of the medium and further affecting the heat transfer performance.
Pressure drop is another key design condition of PHEs, which refers to the pressure loss of the medium when flowing through the flow channel of the PHE. The pressure drop directly affects the energy consumption of the pump (or fan) and the operating stability of the system. The pressure drop of PHEs is mainly determined by the flow resistance of the medium in the flow channel, which is related to the physical properties of the medium, flow rate, flow channel structure, and other factors. Medium changes will affect the pressure drop by changing the flow resistance of the medium.
Viscosity is the most important factor affecting the pressure drop. The higher the viscosity of the medium, the greater the flow resistance, and the higher the pressure drop. According to the fluid mechanics formula, the pressure drop is proportional to the viscosity of the medium under the same flow rate and flow channel structure. For example, when the viscosity of the medium increases by 100%, the pressure drop will increase by about 80%–100% under the same flow rate. In addition, the density of the medium also affects the pressure drop: the higher the density of the medium, the greater the inertial force of the fluid, and the higher the pressure drop under the same flow rate.
Changes in temperature affect the pressure drop by changing the viscosity and density of the medium. For example, when the temperature of the medium increases, the viscosity decreases, and the pressure drop decreases accordingly; on the contrary, when the temperature decreases, the viscosity increases, and the pressure drop increases. Changes in pressure will affect the density and phase state of the medium. For example, when the operating pressure is lower than the saturation pressure of the medium, the medium will vaporize, forming a gas-liquid two-phase flow, which will significantly increase the flow resistance and pressure drop. In addition, the pressure drop of the PHE is also related to the flow rate of the medium. If the medium flow rate increases due to process adjustment, the pressure drop will increase sharply (the pressure drop is proportional to the square of the flow rate).
When the medium contains solid particles or impurities, the particles will collide with the plate wall and each other during the flow process, increasing the flow resistance and pressure drop. In addition, the particles will accumulate in the flow channel, narrowing the flow channel cross-section, further increasing the flow rate and pressure drop. For example, when the medium contains 5%–10% solid particles (particle size 10–50 μm), the pressure drop will increase by 30%–50% compared with the clean medium. If the particles are too large (more than 100 μm), they may even block the flow channel, leading to the failure of the PHE to operate normally.
The material selection of PHEs (including plate material and gasket material) is mainly determined by the chemical properties and state parameters of the medium. The core requirement of material selection is corrosion resistance, followed by thermal conductivity, mechanical strength, and cost-effectiveness. Medium changes will directly lead to the mismatch between the original material and the new medium, resulting in material corrosion, gasket aging, and other problems, affecting the service life of the PHE.
Corrosivity is the key factor determining the plate material. Common plate materials include stainless steel (304, 316L), titanium, Hastelloy, and copper alloy. 316L stainless steel is widely used in neutral and weakly corrosive media (such as water, edible oil), but it is not resistant to strong acids, strong alkalis, and chloride-containing media; titanium is resistant to strong corrosion (such as seawater, hydrochloric acid) and is suitable for harsh working conditions; Hastelloy is resistant to most strong acids and alkalis and is used in chemical industries with strong corrosive media. If the medium changes from neutral to acidic (such as pH value from 7 to 3), the original 304 stainless steel plate will be corroded, leading to plate perforation and leakage. At this time, it is necessary to replace the plate with titanium or Hastelloy.
Gasket material is also affected by the chemical properties of the medium. Common gasket materials include nitrile rubber (NBR), ethylene-propylene-diene monomer (EPDM), and fluorine rubber (Viton). NBR is suitable for oil-based media but not resistant to strong acids and alkalis; EPDM is suitable for neutral and weakly corrosive media and has good high-temperature resistance; Viton is resistant to strong acids, strong alkalis, and organic solvents, but the cost is high. If the medium is changed from oil to strong acid, the original NBR gasket will be corroded and aged, leading to medium leakage, and it is necessary to replace it with Viton gasket.
Temperature and pressure changes affect the material selection by changing the corrosion rate of the medium and the mechanical properties of the material. High temperature will accelerate the corrosion rate of the medium and reduce the mechanical strength and service life of the material. For example, when the operating temperature increases from 100°C to 150°C, the corrosion rate of the medium to the stainless steel plate will increase by 2–3 times, and it is necessary to select a material with better high-temperature corrosion resistance (such as Hastelloy). High pressure requires the material to have higher mechanical strength to avoid plate deformation or damage. For example, when the operating pressure increases from 1.6 MPa to 4.0 MPa, the original ordinary stainless steel plate (thickness 0.5 mm) cannot withstand the high pressure, and it is necessary to increase the plate thickness or select a material with higher strength.
When the medium contains chloride ions, sulfur ions, or other corrosive ions, it will accelerate the corrosion of the plate material. For example, even a small amount of chloride ions (more than 200 ppm) will cause pitting corrosion of stainless steel plates, leading to plate damage. At this time, it is necessary to select chloride-resistant materials (such as titanium). In addition, if the medium contains organic solvents, it will dissolve the gasket material, leading to gasket failure. For example, the medium containing acetone will dissolve the NBR gasket, and it is necessary to replace it with a Viton gasket.
The plate structure (plate type, corrugation angle, plate thickness) and flow channel design (flow channel width, flow direction, number of passes) of PHEs are designed according to the flow state and heat transfer requirements of the original medium. Medium changes will affect the flow state and heat transfer requirements of the medium, thus requiring adjustments to the plate structure and flow channel design.
For high-viscosity media, the original narrow flow channel will lead to excessive pressure drop and poor heat transfer. It is necessary to select a plate type with a wider flow channel (such as a plate with a corrugation angle of 30°) to reduce flow resistance and improve the flow state of the medium. For example, when the medium is changed from water (low viscosity) to heavy oil (high viscosity), the flow channel width needs to be increased from 2–3 mm to 4–5 mm to reduce the pressure drop. In addition, high-viscosity media require a plate type with a stronger turbulence effect (such as herringbone corrugated plates) to enhance convective heat transfer.
For media with low thermal conductivity, it is necessary to increase the heat transfer area by increasing the number of plates or selecting plates with a larger specific surface area. For example, when the medium is changed from water to engine oil (low thermal conductivity), the number of plates needs to be increased by 30%–50% to meet the heat transfer requirements. In addition, the corrugation angle of the plate also affects the heat transfer and pressure drop: a larger corrugation angle (60°) can improve the heat transfer coefficient, but the pressure drop is larger; a smaller corrugation angle (30°) can reduce the pressure drop, but the heat transfer coefficient is lower. Medium changes need to balance heat transfer and pressure drop by adjusting the corrugation angle.
When the medium undergoes phase change (such as steam condensation), it is necessary to select a plate type suitable for phase change heat transfer. For example, condensation heat transfer requires a plate with a smooth surface and a large flow channel to facilitate the discharge of condensed liquid and avoid liquid film accumulation. Vaporization heat transfer requires a plate with a uniform flow channel to ensure that the medium is heated evenly and prevent local overheating. In addition, phase change media require a multi-pass flow channel design to extend the residence time of the medium in the PHE and improve the phase change efficiency.
Changes in temperature and pressure also affect the plate thickness. High temperature and high pressure require thicker plates to ensure mechanical strength. For example, when the operating pressure increases from 1.6 MPa to 4.0 MPa, the plate thickness needs to be increased from 0.5 mm to 0.8–1.0 mm. In addition, high-temperature media require plates with good thermal conductivity to reduce thermal stress, such as copper alloy plates or titanium plates.
When the medium contains solid particles or impurities, it is necessary to select a plate type with a wide flow channel and easy cleaning to avoid flow channel blockage. For example, the medium containing solid particles should select a plate with a flow channel width of more than 4 mm, and the plate surface should be smooth to reduce particle accumulation. In addition, the flow direction of the medium should be designed as countercurrent flow to improve the heat transfer efficiency and reduce the accumulation of particles. For media with serious fouling tendency, it is necessary to design a detachable PHE to facilitate regular cleaning and maintenance.
Fouling is a common problem in PHE operation, which refers to the accumulation of impurities, scale, and other substances on the plate surface, leading to reduced heat transfer efficiency, increased pressure drop, and shortened service life. Medium changes are one of the main causes of fouling. In addition, medium changes will also affect the operating stability of the PHE, leading to problems such as medium leakage, plate deformation, and system fluctuation.
Changes in medium composition are the main factor leading to fouling. For example, the increase in calcium and magnesium ions in the medium will lead to scaling; the increase in solid particles will lead to sedimentation fouling; the increase in organic matter will lead to biological fouling or chemical fouling. In addition, changes in temperature and pressure will also accelerate the fouling rate. For example, high temperature will accelerate the crystallization of calcium and magnesium ions, leading to scaling; changes in pressure will lead to the precipitation of dissolved gases in the medium, forming gas film fouling. Fouling not only reduces heat transfer efficiency but also increases pressure drop, leading to increased energy consumption and even flow channel blockage.
Medium changes may lead to medium leakage. For example, changes in the chemical properties of the medium may corrode the gasket or plate, leading to leakage; changes in pressure may cause the gasket to deform or fall off, leading to leakage. In addition, excessive pressure drop caused by medium changes may lead to pump overload, affecting the stable operation of the system. For example, when the pressure drop exceeds the design limit, the pump will work under overload, leading to pump damage or system shutdown. In addition, changes in the flow state of the medium may lead to uneven temperature distribution of the plate, resulting in thermal stress and plate deformation.
To further verify the impact of medium changes on the design conditions of PHEs, this paper analyzes two practical engineering cases, including the impact of medium composition changes in the petrochemical industry and the impact of physical property changes in the food processing industry, and puts forward corresponding adjustment measures.
A petrochemical enterprise uses a PHE to preheat crude oil. The original design medium is crude oil with a water cut of 5% (mass fraction), the inlet temperature of crude oil is 70°C, the outlet temperature is 101°C, and the heat transfer area of the PHE is 120 m². The plate material is 316L stainless steel, and the gasket material is NBR. Due to changes in oilfield exploitation conditions, the water cut of crude oil increases to 20%, leading to changes in the physical properties of the medium: the viscosity increases by 30%, the thermal conductivity decreases by 15%, and the density increases by 8%.
After the water cut increases, the operating problems of the PHE are as follows: (1) The heat transfer efficiency decreases significantly, the outlet temperature of crude oil drops to 99°C, which cannot meet the subsequent process requirements; (2) The pressure drop increases by 40%, leading to overload of the crude oil pump and increased energy consumption; (3) The water in the crude oil causes slight corrosion of the plate, and the gasket is aged and deformed, with potential leakage risks.
According to the medium changes, the following design adjustment measures are adopted: (1) Adjust the plate structure: increase the number of plates, expand the heat transfer area to 150 m², and select a plate type with a corrugation angle of 30° to reduce the pressure drop; (2) Optimize the flow channel design: increase the flow channel width from 2.5 mm to 3.5 mm to adapt to the high-viscosity medium and reduce particle accumulation; (3) Replace the gasket material: replace NBR gasket with EPDM gasket to improve corrosion resistance to water-containing crude oil; (4) Add a pre-treatment device: install a water-oil separation device at the inlet of the PHE to reduce the water cut of crude oil to 10% and reduce the impact of water on the PHE. After adjustment, the outlet temperature of crude oil is restored to 101°C, the pressure drop is reduced to the design level, and the operating stability of the PHE is significantly improved. The investment in the adjustment measures is recovered in less than three months through energy saving and maintenance cost reduction.
A food processing enterprise uses a PHE to cool milk. The original design medium is fresh milk with a viscosity of 1.2 mPa·s, the inlet temperature is 60°C, the outlet temperature is 4°C, and the heat transfer area is 80 m². The plate material is 316L stainless steel, and the gasket material is EPDM. Due to the replacement of raw milk sources, the viscosity of the milk increases to 2.5 mPa·s (due to the increase in fat content), and the density increases by 5%.
After the viscosity increases, the operating problems of the PHE are as follows: (1) The flow state of the milk in the flow channel changes from turbulent flow to laminar flow, the convective heat transfer coefficient decreases by 45%, and the cooling time is prolonged, which cannot meet the production rhythm; (2) The pressure drop increases by 50%, leading to increased energy consumption of the cooling water pump; (3) The high-viscosity milk is easy to adhere to the plate surface, leading to fouling and reduced heat transfer efficiency after long-term operation.
The design adjustment measures are as follows: (1) Replace the plate type: select herringbone corrugated plates with a corrugation angle of 60° to enhance turbulence and improve the convective heat transfer coefficient; (2) Adjust the flow rate: increase the flow rate of milk by 30% to increase the Reynolds number and restore the turbulent flow state; (3) Optimize the flow channel design: adopt a multi-pass flow channel design to extend the residence time of milk in the PHE and improve the cooling effect; (4) Strengthen cleaning: increase the frequency of CIP (clean-in-place) cleaning to avoid fouling accumulation. After adjustment, the cooling time of milk is restored to the original level, the pressure drop is reduced by 20%, and the fouling problem is effectively controlled, ensuring the stable operation of the production line.
To cope with the impact of medium changes on the design conditions of PHEs, it is necessary to formulate scientific and reasonable design adjustment strategies based on the type and degree of medium changes, combined with the actual operating requirements of the system. The following are the key adjustment strategies from five aspects:
When the medium changes lead to a decrease in the heat transfer coefficient, the heat transfer area can be increased by increasing the number of plates or selecting plates with a larger specific surface area to ensure the heat transfer rate. For media with phase changes, the heat transfer calculation model should be adjusted, and the latent heat of phase change should be considered to accurately calculate the heat transfer area. In addition, the flow rate of the medium can be adjusted to change the Reynolds number, enhance turbulence, and improve the convective heat transfer coefficient. For high-viscosity media, the flow rate should be appropriately increased; for low-viscosity media, the flow rate should be adjusted to avoid excessive pressure drop.
When the medium changes lead to excessive pressure drop, the flow channel width can be increased by selecting a plate type with a wider flow channel to reduce flow resistance. The corrugation angle of the plate can be adjusted: a smaller corrugation angle is selected to reduce the pressure drop, and a balance between heat transfer efficiency and pressure drop is achieved. In addition, the number of passes of the flow channel can be reduced to shorten the flow path of the medium and reduce the pressure drop. For media containing solid particles, a pre-treatment device (such as a filter, separator) should be added to remove impurities and reduce the pressure drop and fouling risk.
According to the changes in the chemical properties of the medium, the plate and gasket materials should be replaced in a timely manner. For corrosive media, materials with strong corrosion resistance (such as titanium, Hastelloy) should be selected; for media containing organic solvents, gasket materials with good solvent resistance (such as Viton) should be selected. For high-temperature and high-pressure media, materials with high mechanical strength and high-temperature resistance should be selected, and the plate thickness should be increased to ensure structural stability. Before material replacement, corrosion tests should be carried out to verify the adaptability of the material to the new medium.
For high-viscosity media, select a plate type with a wider flow channel and stronger turbulence effect; for media with phase changes, select a plate type suitable for phase change heat transfer; for media containing solid particles, select a plate type with a smooth surface and easy cleaning. Adjust the flow channel width, flow direction, and number of passes according to the flow state and heat transfer requirements of the new medium to ensure that the medium flows evenly and the heat transfer is efficient. For detachable PHEs, the plate arrangement can be adjusted to change the flow channel structure and adapt to medium changes.
For media with serious fouling tendency, a pre-treatment device should be added to remove impurities and reduce fouling sources. Optimize the operating parameters (such as temperature, flow rate) to slow down the fouling rate. Formulate a regular cleaning plan, adopt CIP cleaning or manual cleaning to remove the fouling layer in time and restore heat transfer efficiency. Strengthen the daily inspection and maintenance of the PHE, check the plate surface and gasket for corrosion, aging, and damage, and replace them in a timely manner to ensure operating stability.
Medium changes are an inevitable problem in the design and operation of plate heat exchangers, and they have a comprehensive and far-reaching impact on the design conditions of PHEs. Changes in the physical properties, chemical properties, state parameters, and composition of the medium will directly affect the heat transfer performance, pressure drop, material selection, plate structure, and operating stability of PHEs, leading to a series of problems such as reduced heat transfer efficiency, increased energy consumption, material corrosion, and equipment failure.
Through systematic analysis, it is found that the impact of medium changes on PHE design is a chain reaction: changes in physical properties (especially viscosity and thermal conductivity) are the core factors affecting heat transfer efficiency and pressure drop; changes in chemical properties determine the material selection of plates and gaskets; changes in state parameters (especially phase changes) affect the plate type and flow channel design; changes in medium composition increase the fouling risk and affect long-term operating efficiency. The engineering cases show that scientific and reasonable design adjustments (such as adjusting heat transfer area, replacing materials, optimizing plate structure, and strengthening fouling control) can effectively cope with the impact of medium changes and ensure the stable and efficient operation of PHEs.
In practical engineering design, it is necessary to fully consider the possibility of medium changes, conduct in-depth analysis of the properties of the new medium, and formulate targeted design adjustment strategies. At the same time, strengthen the monitoring of medium parameters during operation, find and deal with the impact of medium changes in a timely manner, so as to give full play to the advantages of PHEs, reduce energy consumption, and improve the economic and social benefits of the system. In the future, with the development of industrial technology, the types of heat exchange media will become more complex, and the research on the impact of medium changes on PHE design will be more in-depth, which will provide more theoretical support and technical guidance for the optimization and upgrading of PHEs.
