In the production process of battery trays and energy storage liquid cold boxes for new energy vehicles, necessary and appropriate surface treatment is a key step, such as: using coating, oxidation treatment, etc. to form a protective layer on the metal surface to resist the erosion of corrosive media; Components that require electrical isolation, such as battery cells, water-cooling plates, module walls, etc., need to establish an insulating protective film. Insulation is generally achieved by spraying insulating powder or insulating paint. Choosing the appropriate surface treatment technology can not only improve the performance of the tray/liquid cooling box Durability and safety can also meet the needs of different application scenarios. This article summarizes common surface treatment technologies for reference.

1-Cleaning and polishing

During the production process, impurities such as processing oil, engine oil residue, powder, and dust may accumulate on the surface of the pallet. Not only do these impurities affect the service life of the battery tray, they may also adversely affect the performance and safety of the battery. Through cleaning and polishing, these impurities can be effectively removed to ensure the cleanliness of the pallet surface. Cleaning and grinding can effectively remove surface impurities, burrs, and welding slag, making the surface smooth and flat, thus improving the overall quality of the battery tray/box.

a.chemical cleaning

Alkali cleaning: Alkaline cleaning mainly uses alkaline solutions (such as sodium hydroxide, sodium carbonate, etc.) to remove grease, dirt and other organic matter on the surface of aluminum alloys. Alkaline washing removes grease through saponification, emulsification and penetration and wetting, and at the same time generates water-soluble precipitates, thereby achieving a cleaning effect. Alkaline cleaning is usually used to remove grease, dust and organic contaminants from the surface of aluminum alloys.

Pickling: Pickling uses acidic solutions (such as nitric acid, hydrochloric acid, etc.) to remove oxide scale, rust and other inorganic deposits on the surface of aluminum alloys. Pickling converts the oxides on the metal surface into soluble salts through the reaction of acid with the oxides on the metal surface, thereby removing surface impurities. Pickling is mainly used to remove oxide film, rust and inorganic salt scale on the surface of aluminum alloys. Pickling is often used for the final treatment of metal surfaces to improve their finish and flatness.

b.Mechanical grinding

During production, the grinding process can remove processing allowances, correct shape errors, ensure the smoothness and accuracy of the pallet/box surface, meet assembly requirements, and thus improve overall performance and service life.

The cleaned and polished surface can be treated with coating materials or other materials, which is very important for the subsequent construction of anti-corrosion, sealing, thermal conductivity, insulation, thermal insulation and other coatings, and plays a key role in the firm attachment of these materials to the pallet/box.

2-Coating and protective film establishment

In addition to basic cleaning and polishing, the production of pallets/boxes uses a spraying process for surface treatment to form a protective layer to prevent oxidation and corrosion and to meet the needs of different scenarios such as thermal insulation, insulation and voltage resistance.

a.Thermal insulation

Anti-condensation and thermal insulation of battery trays can be achieved through comprehensive design of thermal insulation systems, use of high-efficiency thermal insulation materials, application of aerogels, battery pack insulation design, and spraying of foam insulation materials.

Bottom surface sprayed with PVC and foam material

b.Insulation withstand voltage

The insulation of the battery pack casing and the liquid cooling components is primarily to prevent current leakage, protect personnel from electric shocks, and ensure the normal operation of the battery system. Insulation is typically achieved through two main methods: powder spraying and film lamination. The mainstream film lamination processes include room temperature lamination, hot pressing, and UV exposure.

Internal spraying of insulation powder and insulation paint

3-Logos and Signage

A nameplate or label is set in a prominent position on the battery tray, generally through laser, mechanical engraving, etc. These logos are usually made of wear-resistant and corrosion-resistant media to ensure that they are not easily erased during the entire service life.

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As the core equipment of the energy storage system, the energy storage converter is an important tool for power conversion, energy management, ensuring grid stability, improving energy efficiency, etc. As the energy storage converter power unit moves toward high integration and high efficiency, the development of frequency and large capacity puts higher and higher requirements on heat dissipation.

1-Changes in cooling requirements

a.Matching the larger DC cabin, the converter capacity continues to increase, and efficient heat dissipation technology ensures the reliability of the equipment.

As the capacity of energy storage cells becomes larger and larger, the capacity of energy storage systems is also expanding simultaneously. At the beginning of 2023, the standard 20-foot single-cell battery capacity on the market was only 3.35MWh. In the second half of the year, many battery cell companies have launched 310+Ah energy storage products, and the capacity of the 20-foot single-cell battery has also been expanded to 5MWh. However, less than half a year after the 5MWh model was updated, some leading energy storage systems released 6MWh and 8MWh systems. According to general experience, the energy storage converter is configured at 1.2 times the load capacity. The single unit capacity of a 5MWh energy storage system must be greater than 2.5MW. High power requires more efficient cooling technology to ensure stable operation of the equipment under sustained high loads.

Iterative evolution of energy storage system integration topology scheme

b.The application of DC high-voltage technology requires devices to have higher withstand voltage levels and insulation strength, and the heat dissipation of power devices is severe.

In order to match the large-capacity energy storage system, DC high-voltage technology has become a technical trend. Through the increase of voltage level, energy saving, efficiency and performance improvement can be achieved. The 1500V voltage upgrade originated from photovoltaics, and now photovoltaics are involved in energy storage. However, the high-voltage evolution of energy storage PCS still has a long way to go, and some manufacturers have begun to optimize and push it to 2000V. The application of DC high-voltage technology forces the power electronic devices in energy storage converters to have higher withstand voltage levels and higher insulation strength to adapt to high-voltage working environments. In high-voltage environments, the heat dissipation design of power devices becomes more important. The pn junction temperature of power devices generally cannot exceed 125°C, and the temperature of the package shell does not exceed 85°C.

c.Networked energy storage systems require complex control algorithms, circuit designs and high power density energy storage converters

Unlike the essential characteristics of current sources in grid-forming energy storage systems, grid-forming energy storage systems are essentially voltage sources that can internally set voltage parameters to output stable voltage and frequency. Therefore, it is required that grid-forming converters simulate the characteristics of synchronous generators, providing support for voltage and frequency to enhance the stability of the power system. This control strategy necessitates that converters possess higher power density and more complex control algorithms, as well as higher-performance power devices and more intricate circuit designs to implement the control strategy. Effectively managing the heat generated by high power density and complex control strategies, while reducing the size and cost of the cooling system without compromising performance, has become a new challenge in thermal design.

2- Comparison of common cooling solutions

The cooling solution for energy storage inverters has undergone significant iterative evolution in recent years, mainly reflected in the transition of cooling technology from traditional air cooling to liquid cooling technology.

a.Air cooling solution

Air cooling is the temperature control form used in the early stage of energy storage converters. It uses air as the medium and dissipates heat through fans and radiators. The air cooling solution improves heat dissipation efficiency by continuously reducing energy consumption, optimizing structure, and improving heat dissipation materials. At the 2.5MW power level, air cooling can still meet the requirements.

b.Liquid Cooling Solution

As the power density and energy density of energy storage systems continue to increase, liquid-cooled PCS uses coolant with high thermal conductivity as the medium. The coolant is driven by a water pump to circulate in the cold plate and is not affected by factors such as altitude and air pressure. The liquid cooling system has a more efficient heat dissipation efficiency than the air cooling system. The liquid cooling solution has a higher matching degree and has begun to be explored and popularized in the past one or two years.

In addition to the full liquid cooling energy storage solution, some manufacturers have launched energy storage direct cooling machines, which use phase change direct cooling and no water circulation. Direct cooling solutions are also entering the energy storage field.

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The battery pack is a key component of new energy vehicles, energy storage cabinets and containers. It is an energy source through the shell envelope, providing power for electric vehicles and providing consumption capacity for energy storage cabinets and containers. In combination with actual engineering needs, this article summarizes the key points of profile design for battery packs by analyzing the requirements of mechanical strength, safety, thermal management and lightweight of battery packs.

1-Battery pack housing design requirements

a.Mechanical strength, vibration resistance and impact resistance. After the test, there should be no mechanical damage, deformation or loosening of the fastening, and the locking mechanism should not be damaged.

b.Sealing: The sealing of the battery pack directly affects the working safety of the battery system. It is usually required to reach IP67 protection level to ensure that the battery pack is sealed and waterproof.

c.The design of the battery pack shell needs to take thermal management performance into consideration and ensure that the battery operates within an appropriate range through appropriate thermal management design.

d.For installation and fixation, the shell should have space for nameplate and safety signs, and reserve sufficient space and fixed foundation for the installation of acquisition lines, various sensor elements, etc.

e.e. All connectors, terminals, and electrical contacts of non-polar basic insulation should meet the corresponding protection level requirements when combined.

f.Lightweighting: Lightweighting of the shell is of great significance to improving the energy density of the battery pack. Aluminum alloy is light in weight and high in quality, making it the most feasible choice at present. The lightweighting level can be improved through appropriate extreme design in combination with actual applications.

g.Durability: The design life of the battery pack shell shall not be less than the service life of the overall product. No obvious plastic deformation should occur during the use cycle. The protection level and insulation performance should not be reduced. The structure should be easy to maintain, including the layout of nameplates and safety signs, and protection of connectors.

Figure 1 Typical aluminum alloy welded battery pack shell

2-Typical aluminum alloy battery pack shell solution

Commonly used aluminum alloy materials for battery pack shells include 6061-T6, 6005A-T6 and 6063-T6, etc. These materials have different yield strengths and tensile strengths to meet different structural requirements. The strength of these materials is: 6061-T6＞6005A-T6＞6063-T6.

At present, the battery pack shell forming solutions include aluminum profile welding, aluminum alloy casting, cast aluminum plus profile aluminum, stamped aluminum plate welding, etc. The aluminum profile welding solution has become the mainstream choice due to its flexibility and processing convenience. As shown in Figure 1, the shell is mainly composed of an aluminum alloy profile frame and an aluminum alloy profile bottom plate, which are welded using 6 series aluminum alloy extruded profiles. The aluminum alloy casting solution is regarded as the future development direction due to its simplified process and cost reduction potential.

3- Profile section design

a. Section size and complexity: The section size of the profile is measured by the circumscribed circle. The larger the circumscribed circle, the greater the extrusion pressure required. The section of the profile is usually composed of multiple cavities to improve the structural rigidity and strength. Usually, the frame, middle partition, bottom plate, beam, etc. adopt different section designs to adapt to different structural and functional requirements.

Figure 2 Typical aluminum alloy profile section

b. Aluminum profile wall thickness: The minimum wall thickness of a specific aluminum profile is related to the profile circumscribed circle radius, shape and alloy composition. For example, when the wall thickness of 6063 aluminum alloy is 1mm, the wall thickness of 6061 aluminum alloy should be about 1.5mm. The extrusion difficulty of the same section is: 6061-T6＞6005A-T6＞6063-T6. In the design of battery pack profiles, the frame profile is usually made of 6061-T6 aluminum alloy material, and its typical section is composed of multiple cavities, and the thinnest wall thickness is about 2mm; the bottom plate profile is also composed of multiple cavities, and the material is generally 6061-T6, 6065A-T6, and the thinnest wall thickness is also about 2mm; in addition, in the design of the bottom plate load-bearing tray and bottom plate liquid cooling integration, the bottom plate generally adopts a double-sided structure, the bottom plate thickness is generally 10mm, and the wall thickness and the inner wall of the cavity are about 2mm.

c. Tolerance of profile cross-sectional dimensions: The tolerance of cross-sectional dimensions should be determined based on the processing allowance of the aluminum profile, the conditions of use, the difficulty of profile extrusion, and the shape of the profile. For some aluminum profiles that are difficult to extrude, the shape can be changed or the process allowance and dimensional tolerance can be increased to reduce the difficulty of extrusion and extrude aluminum profile products that are close to the requirements, and then they can be reshaped or processed to meet the use requirements.

In addition, when designing the profile section, it is necessary to consider the specific requirements of different welding processes for joints, grooves, wall thickness, etc.

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Battery trays, also known as battery boxes or PACK boxes, are increasingly valued as a very important component in the development of new energy vehicles. The design of battery trays needs to balance the relationship between factors such as weight, safety, cost, and material performance. Aluminum alloys are widely used in automotive lightweight engineering because of their low density and high specific strength, which can ensure rigidity while ensuring vehicle body performance.

1-Battery tray welding location and method selection

Aluminum battery trays are made of extruded aluminum profiles, and the various components are combined into a whole by welding to form a complete frame structure. Similar structures are also widely used in energy storage pack boxes.

The welding parts of the battery tray usually include the bottom plate splicing, the connection between the bottom plate and the side, the connection between the side frame, the horizontal and vertical beams, the welding of liquid cooling system components, and the welding of accessories such as brackets and hanging ears. When selecting welding methods, different welding methods will be selected according to different material and structural requirements, see the table below:

2-Analysis of the influence of welding thermal deformation

Welding is a local heating processing method. Since the heat source is concentrated at the weld, the temperature distribution on the weld is uneven, which eventually leads to welding deformation and welding stress inside the welded structure. Welding thermal deformation is the phenomenon that the shape and size of the welded parts change due to uneven heat input and heat output during the welding process. Combined with actual engineering project experience, the parts that are prone to welding thermal deformation and the influencing factors are summarized:

a. Long straight welding area

In actual production, the bottom plate of the battery tray is generally made of 2 to 4 aluminum alloy profiles spliced together by stir friction welding. The welds are long, and there are also long welds between the bottom plate and the side plate, and between the bottom plate and the spacing beam. Long welds are prone to local overheating in the welding area due to concentrated heat input, resulting in thermal deformation.

Battery tray frame welding

b. Multi-component joints

It is caused by local high temperature heating and subsequent cooling during the welding process at the multi-component weld. During the welding process, the weldment is subjected to uneven heat input, resulting in a significant temperature difference between the weld area and the surrounding parent material, which causes thermal expansion and contraction effects, causing deformation of the welded parts. The electrical installation end of the energy storage pack box is usually equipped with a water nozzle, a wiring harness bracket, a beam, etc., and the welds are dense and very easy to deform.

In the weld-intensive area, the front side of the pallet is warped and deformed

c.Cold plate channel side wall

In the battery tray with integrated design of liquid cooling plate, parts with smaller structural rigidity, such as thin plates and pipe structures, cannot resist thermal deformation well during welding and are prone to deformation. For example, the side wall of the liquid cooling plate flow channel is very thin, generally only about 2mm. When welding beams, wiring harness brackets and other parts on the module mounting surface, it is easy to cause cracks and deformation wrinkles on the side wall of the flow channel, affecting the overall performance.

Thermal crack defects on the liquid cooling channel wall caused by beam welding

3-Welding thermal deformation control method

a. Segment welding, double-sided welding

For parts with relatively low strength requirements, segmented welding is adopted, and the welding process is broken down into multiple small sections. The welds are arranged symmetrically, and the welds are arranged symmetrically near the neutral axis in the construction section, so that the deformations caused by the welds may offset each other. At the same time, the length and number of welds are minimized, and excessive concentration or crossing of welds is avoided, which can reduce the welding temperature gradient and thus reduce welding deformation. For parts with high strength requirements such as the bottom plate, bottom plate and side frame, double-sided welding is adopted to increase strength while reducing bending deformation caused by large parts and long welds.

b.Optimizing welding sequence

Control welding deformation, use joints with lower rigidity, avoid two-way and three-way intersecting welds, and avoid high stress areas. Optimize the welding sequence, weld the weaker rigidity areas first, and the better rigidity areas last, such as welding the fillet welds first, then the short welds, and finally the long welds; weld the transverse welds first, then the longitudinal welds. A reasonable welding sequence can effectively control welding deformation, thereby controlling the weld dimensions.

c. Welding parameter adjustment

Control welding parameters and processes, and reasonably set welding speed, number of welding layers and thickness of each weld. For thicker welds, use multi-layer and multi-channel welding methods, and the thickness of each weld layer should not exceed 4mm. Multi-layer welding can reduce structural microstructure and improve joint performance. Accurately control welding parameters and reasonably select parameters such as welding current, voltage, electrode model and welding speed to ensure consistent shape and size of the molten pool, thereby avoiding errors caused by improper parameter selection.

d.Welding skills improvement

Improve the welder's operating skills (use mechanical processing for large components or nodes with strict requirements) to ensure consistency and standardization of actions during welding and reduce dimensional problems caused by human factors.

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Aluminum alloy is the most widely used non-ferrous metal structural material in industry, especially in scenarios where the thermal conductivity of materials is of great concern, and in situations where efficient heat conduction is required, such as electronic equipment heat dissipation, electric vehicle three-power heat dissipation, and battery energy storage systems. In the fields of heat dissipation and aerospace, it is usually used to manufacture efficient heat transfer equipment such as radiators, heat conduction plates, and electronic components.

Thermal conductivity, also called thermal conductivity, is a parameter index that characterizes the thermal conductivity of materials. It indicates the heat conduction per unit time, unit area, and negative temperature gradient. The unit is W/m·K or W/m·℃. Aluminum alloy is an alloy material composed of aluminum and other metals. Its thermal conductivity is very excellent, and the thermal conductivity coefficient is usually between 140-200W/(m·K). As the metal with the highest content in the earth's crust, aluminum has a relatively low thermal conductivity coefficient. It is favored because of its high height, low density and low price.

1-Thermal conductivity principle of aluminum alloy materials

When there is a temperature difference between adjacent areas of a material, heat will flow from the high-temperature area to the low-temperature area through the contact part, resulting in heat conduction. There are a large number of free electrons in metal materials. Free electrons can move quickly in the metal and can quickly transfer heat. Lattice vibration is another way of metal heat transfer, but it takes a back seat compared to the free electron transfer method.

Comparison of heat conduction methods between metals and non-metals

2-Factors affecting the thermal conductivity of aluminum alloys

a.Alloying is one of the main factors affecting thermal conductivity. Alloying elements exist in the form of solid solution atoms, precipitated phases and intermediate phases. These forms will bring crystal defects, such as vacancies, dislocations and lattice distortion. These defects will increase the probability of electron scattering, resulting in a reduction in the number of free electrons, thereby reducing the Thermal conductivity of alloys. Different alloying elements produce different degrees of lattice distortion on the Al matrix, and have different effects on thermal conductivity. This difference is the result of multiple factors such as the valence of alloy elements, atomic volume differences, extranuclear electron arrangement, and solidification reaction type.

b.Heat treatment is a very important step in the processing of aluminum alloys. By changing the microstructure and phase transformation of aluminum alloys, its thermal conductivity can be significantly affected. Solid solution treatment is to heat the aluminum alloy to a certain temperature to fully dissolve the solute atoms in the matrix, and then quickly cool it to obtain a uniform solid solution. This treatment improves the material's mechanical properties but usually reduces its thermal conductivity. Aging treatment is through appropriate cold deformation and reheating after solid solution treatment, which can optimize the microstructure of the alloy and improve its overall performance. The aging treatment takes into account the mechanical properties and thermal conductivity of the alloy, so that the alloy maintains high strength while also having good thermal conductivity. Annealing improves the microstructure of the alloy by maintaining it at a lower temperature to precipitate and redistribute the second phase in the alloy. Annealing treatment can improve the plasticity and toughness of aluminum alloys, but the effect on thermal conductivity varies depending on the specific situation.

Schematic diagram of crystal structure changes during the aging process of Al-Cu alloy

c.Other factors influence, impurities and second phase particles: Impurities and second phase particles (such as oxides, carbides, etc.) in aluminum alloys can scatter hot carriers (electrons and phonons), thereby reducing thermal conductivity. The higher the impurity content, the coarser the second phase particles and generally the lower the thermal conductivity. The grain size of aluminum alloys also affects thermal conductivity. Generally speaking, the smaller the grain size, the more grain boundaries there are and the lower the thermal conductivity. In addition, the processing method of aluminum alloy (such as rolling, extrusion, forging, etc.) will affect its microstructure and residual stress state, thereby affecting the thermal conductivity. Work hardening and residual stresses reduce thermal conductivity.

In summary, aluminum alloy is an ideal choice for high thermal conductivity materials. Factors such as the type of alloy elements in aluminum alloys and their forms, heat treatment methods, impurities, grain size, and molding methods will all affect the thermal conductivity of aluminum alloy materials. Comprehensive considerations should be taken when designing material composition and process planning.

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The air tightness of the battery pack is a key factor in ensuring the quality and safety of the battery pack. It is related to the safety, reliability and service life of the battery pack. The air tightness test of the battery pack should be carried out not only during the production process, but also during battery maintenance and inspection.

1-Battery Pack Airtightness Requirements

In actual production, the air tightness of the battery pack must meet the following requirements:

Sealing performance, the battery pack shell, interface and connectors must have good sealing performance to prevent dust, water vapor and other external impurities from entering the battery pack, which can be achieved through welding, sealants, waterproof materials, etc.

Waterproof performance, to prevent moisture from entering the battery, causing short circuits, corrosion and other problems. According to the national standard GB38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles", the sealing performance of batteries and their components should meet the IP67 standard. Most new energy vehicles have higher sealing performance requirements for batteries and their components, and must meet the IP68 standard, that is, the battery pack can prevent water from entering within the specified water depth and submersion time.

Traditional air tightness testing methods include pressure method and immersion method (water test). The immersion method is to immerse the liquid cooling plate in water and observe whether bubbles are generated to judge the sealing.

Liquid Cooling Plate Water Channel Air Tightness Test Tank

Although the IP68 standard is more stringent, in actual applications, the pressure drop method is often used as the main detection method to meet the IP68 requirements by setting appropriate airtightness detection standards. The pressure drop method determines the airtightness of the battery pack by measuring the pressure change inside the battery pack. When performing airtightness testing, multiple parameters need to be paid attention to, such as inflation pressure, inflation time, pressure stabilization time and leakage rate.

                                    Differential pressure basic principle diagram                                             Direct pressure basic principle diagram

2-Analysis of Liquid Cooling Plate Leakage Problem

With the continuous upgrading of market demand for power battery vehicles, battery energy storage systerms, etc., higher energy density and power density battery packs are widely used. Because of the thermal characteristics of batteries, to ensure the stable operation of core equipment such as batteries and improve energy utilization efficiency, liquid cooling technology is one of the mainstream technical routes for energy storage thermal management, and the air tightness test of the liquid cooling system has become a key link.

Liquid cooling plate leakage is a serious problem: the leakage will hinder the normal flow of the coolant, affect the heat dissipation effect of the liquid cooling plate, and reduce the performance of the equipment; the leakage may also cause aging and damage of system components, reducing the reliability of the system; the leakage may also corrode electronic components and circuits, increasing the risk of equipment failure and fire.

Why does the leakage problem still occur after rigorous air tightness testing during the production and manufacturing process of the liquid cooling plate?

Liquid Cooling System Airtightness Test Process

Liquid seepage may be caused by a variety of factors:

l Tiny cracks and defects. Landscape air tightness testing may detect large leakage channels, but tiny cracks and defects may still exist. These tiny cracks may expand under liquid pressure or high temperature environment, causing liquid seepage.

l Coolant surface tension and wettability differences: When the surface tension of the coolant is low, it is easier to penetrate through tiny gaps. If the surface tension design of the liquid cold plate is unreasonable or the coolant is not properly selected, the liquid seepage problem may be aggravated.

Wettability differences: Different coolants have different wettability on solid surfaces. If the material surface roughness of the liquid cold plate is high or there are microstructural defects, the coolant may penetrate more easily.

l Installation or process problems: If the installation process of the liquid cold plate is not fine enough, or there are defects in the welding, connection and other processes, it may also lead to poor sealing and increase the possibility of liquid seepage.

l Environmental conditions: Changes in temperature, especially in high-pressure environments, may affect the permeability of the coolant. Although these environmental factors may not be considered during air tightness testing, in actual operation, temperature fluctuations may cause seal failure.

l Material aging or fatigue: If the material of the liquid cold plate is used for too long, it may age or fatigue, causing its sealing performance to deteriorate, thereby increasing the risk of liquid leakage.

3-Preventive Measures for Liquid Cooling Plate Leakage

l  Improve the design of liquid cooling plate: By optimizing the structure and design of the liquid cooling plate, reduce small cracks and defects, and improve its sealing performance. For example, when welding the module installation beam on the flow channel surface, take anti-leakage measures to avoid coolant leakage.

l Improve the manufacturing process level: In the production process of the liquid cooling plate, high-quality welding processes and materials are used to ensure that the coolant is not easy to penetrate. At the same time, during the assembly process, strictly follow the operating procedures to avoid looseness or incorrect installation.

l Optimize the combination of detection methods to ensure detection efficiency while improving detection accuracy and reducing missed detection rate. The immersion method and pressure drop method are used for air tightness detection, which is simple to operate, economical, and efficient, and is suitable for large-scale routine detection needs. However, the detection accuracy of the two methods is low. The detection accuracy of the pressure drop method is generally a leakage rate of 1×10-4Pa·m³/s, and the accuracy of the detection results is easily interfered by factors such as temperature, humidity, cleanliness, and pressure. Use detection equipment with higher detection accuracy and better effect to increase the detection accuracy to 1×10-6Pa·m³/s, thereby improving the detection effect.

In addition to the preventive measures for the liquid cooling plate itself, it is also necessary to adopt appropriate response strategies in multiple aspects such as coolant selection, seal selection and equipment working environment.

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In heat dissipation design, adopting effective cost-reduction methods can improve the reliability and efficiency of the overall system while reducing unnecessary costs.

1-Derating design  reduces costs

Derating design is a design method that intentionally reduces the electrical, thermal and mechanical stresses that components or products are subjected to during operation. In actual production and use scenarios, the stability of electronic equipment can be improved by reducing the stress borne by components.

Schematic diagram of heat dissipation paths for 2D and 3D packaging

l Reduce working stress: During product design and operation, the working stress of components can be reduced by reducing the workload, controlling the operating frequency, limiting the current and voltage, etc.

l Reduce environmental stress: Reduce environmental stress by selecting appropriate component types, layouts, and packaging forms, such as selecting components with a large temperature margin, or using packaging forms with good sealing to reduce the effects of temperature, humidity, and pressure on components.

l Reliability engineering application: reasonable redundant design, fault detection and isolation, etc., further reduce the failure risk of components.

By reducing the stress on components during operation, their power consumption and heat generation can be reduced. When power devices operate under stress conditions lower than their rated stress, their power consumption and heat generation can be reduced, which helps to improve the energy efficiency and reliability of the system. In the long run, derating design effectively increases the life of components, reduces failure rates, reduces maintenance workload, and thus reduces costs.

2-Optimize layout

The working efficiency of the radiator can be significantly improved through reasonable arrangement of thermal components, and a reasonable component layout strategy can achieve a balance between product performance and cost.

l Distribute heat dissipation components: Disperse components that generate large amounts of heat to reduce the heat load per unit area.

l Location that is conducive to heat dissipation: Place the heating element in a location that is conducive to heat dissipation, such as near a vent or the edge of the device.

l Staggered arrangement: During layout, stagger the heating components with other general components, and try to make the heating components principle temperature-sensitive components to reduce their impact on the heat-sensitive components.

l Improve airflow: By changing the direction design and component layout, the airflow path is optimized, the flow rate is increased, and the heat transfer coefficient is improved.

Spacing recommendations between components

3-Choice of cooling method

As the performance of electronic components improves and the degree of integration increases, the power density continues to increase, resulting in a significant increase in the heat generated by the electronic components during operation. When choosing a heat dissipation method for electronic components, the temperature control requirements mainly include the following aspects:

l Temperature range: Different components have different temperature tolerance ranges. For example, high-performance chips such as CPUs have operating temperature requirements between 85-100°C, while some low-power devices can tolerate higher temperatures, so the cooling system must ensure Components operate within a safe temperature range.

l Temperature control accuracy: In some scenarios with strict temperature control requirements, it is necessary to adopt a heat dissipation solution that can accurately control the temperature to avoid component performance degradation or even damage caused by excessively high or low temperatures.

l Ambient temperature: The heat dissipation effect of electronic equipment not only depends on the heat dissipation capacity of the device itself, but is also affected by the surrounding ambient temperature. The heat dissipation design needs to consider changes in ambient temperature and try to keep the device within a suitable temperature range through heat dissipation means.

l Power consumption and reliability: Some low-power electronic components can use natural heat dissipation when they generate low heat. For high-power consumption equipment, it is necessary to wait for the heat dissipation technology of universities to ensure that it maintains normal performance and prolongs operation under high load. service life.

l Sealing and density: In sealed and high-density assembled devices, if the heat generation is not high, you can rely on natural heat dissipation. When components are densely packed and generate large amounts of heat, more effective heat dissipation technologies such as forced heat dissipation or liquid cooling are needed. Liquid cooling and heat pipe technology are used in scenarios with high power consumption and large heat generation, such as high-power electronic components such as traveling wave tubes, magnetrons, and power amplifier tubes, servers and high-power consumption equipment, and three-electric systems of new energy vehicles. Its unique application advantages.

                    Charging pile air cooling module                                                  Charging pile liquid cooling module

When choosing a cooling method for electronic components, it is necessary to comprehensively consider factors such as heat generation and heat flux, ambient temperature and operating temperature, space constraints and thermal isolation requirements, and cost and feasibility. By using appropriate cooling technology and cooling devices to ensure that components operate at a suitable temperature, the cost of system replacement and maintenance can be effectively reduced. In addition, reusing historical projects is also an effective strategy to reduce development and manufacturing costs and improve reliability.

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Energy storage immersion liquid cooling technology is an advanced battery cooling method that uses the efficient thermal conductivity of liquid to achieve rapid, direct and sufficient cooling of the battery, ensuring that the battery operates in a safe and efficient environment. Its basic principle is to completely immerse the energy storage battery in an insulating, non-toxic liquid with heat dissipation capabilities. This technology uses direct contact between the liquid and the battery for heat exchange, thereby quickly absorbing the heat generated by the battery during charging and discharging, and bringing it to the external circulation system for cooling.

Schematic diagram of the principle of a single-phase immersion liquid-cooled energy storage system

As a key component for carrying the battery pack and ensuring that the battery cells work in a suitable environment, the immersion liquid-cooled energy storage Pack box mainly undertakes functions such as carrying the battery pack and coolant, safety protection, and heat conduction. Therefore, in the design of the box structure, it is necessary to comprehensively consider multiple aspects such as airtightness, cooling efficiency, safety, material selection, and processing technology to ensure efficient, safe, and reliable operation of the system. The box structure design is the basis of the entire liquid cooling system.

1-Unified load

The lower box of the immersion liquid cooling energy storage pack is composed of a bottom plate and side plates. The bottom plate serves as the basic support, while the side plates are fixed around the bottom plate, together forming the main frame of the box. The size of the box is adjusted based on the overall needs and load conditions of the liquid cooling system. In the design of a larger box, an internal partition or process structure can be reasonably set to divide the large space into multiple small spaces, and the uniform load capacity can be improved by increasing the force-bearing area. The internal structure can increase the local load-bearing capacity by adding support ribs and reinforcing ribs, and a load-balancing structure can be set inside the box to balance the load in each corner.

At the same time, in order to reduce the impact of plastic deformation on uniform load-bearing, the processing surfaces of different heights can be designed as the same plane, which can reduce the number of machine tool adjustments and avoid deformation caused by height differences; the width or height of the box can also be increased to disperse the load and reduce deformation.

In addition, the integrated design of the liquid cooling channel and the bottom plate of the box is completed by stir friction welding or laser welding. This design can effectively improve the overall structural strength.

Schematic diagram of the lower box structure of a single-phase immersion liquid-cooled energy storage pack

2-Heat exchange design

Thermal conductivity is an important part of immersion liquid cooling energy storage technology. The design goal is to ensure that the battery can effectively dissipate heat in a high temperature environment, thereby maintaining its performance and safety.

The material of the box should have high thermal conductivity. Commonly used materials are aluminum alloy, copper, and aluminum-based composite materials. The box design also needs to consider the impact of ambient temperature changes. The appropriate thickness of the insulation layer can ensure that the temperature inside the box is within a relatively constant range, thereby improving the overall efficiency of the system.

The structural design of the box directly affects its thermal conductivity. Reasonable flow channel layout ensures that the liquid flows smoothly inside the box and maximizes the contact area, which is the main strategy to improve the thermal conductivity of the box. Multiple flow channels can be set inside the box to increase the coolant circulation path, thereby improving the heat dissipation effect.

               Solution 1:  single item + plate replacement                    Solution 2: single item + box replacement

The liquid cooling system includes a cooling medium, a heat-conducting structure, a liquid cooling pipeline and a supporting structure.

In the first scheme, the same or different types of coolants can be selected to be filled into the liquid cooling plate flow channel cavity and the box cavity respectively, and the two cavities are sealed and not connected to each other. In the box cavity, the coolant immerses the battery module, fully contacts it, cools it without flowing, and absorbs the heat on the battery surface by using the good thermal conductivity of the liquid to reduce the temperature rise. In the liquid cooling plate, the coolant is divided into multiple flow channels in the water inlet manifold and enters the cold plate in parallel, and then converges and flows out in the water outlet manifold, which is mainly responsible for taking out the heat and achieving heat dissipation.

In the second scheme, the coolant with low temperature flows in from the bottom or side, and the coolant with high temperature flows out from the top. The coolant circulates in the battery pack, which can effectively and evenly distribute the heat, improve the overall cooling efficiency, and maintain the consistency of the temperature of the battery cell or battery pack.

In order to further improve the cooling effect, a variety of optimization measures can be taken, such as optimizing the liquid flow and circulation method, selecting a coolant with high heat capacity, and improving the temperature distribution of the liquid. These measures reduce heat buildup and energy loss, ensuring the battery operates in an efficiently cooled state.

3-Sealed design

For liquid cooling pack boxes, the fully sealed design is carried out by adopting advanced sealing materials and structures. The sealing design should not only consider air tightness, but also the sealing of liquid media to ensure that the battery cells are leak-free in all directions.

The design should select the appropriate sealing form and shape according to the specific application requirements, and also consider factors such as the leakage freedom, wear resistance, medium and temperature compatibility, and low friction of the seal, and select the appropriate seal type and material according to the detailed specifications.

In addition, the choice of welding process also has a great influence on the sealing performance. For different materials and thicknesses, choosing the appropriate welding method can effectively improve the quality of the weld to ensure the overall strength and sealing of the system.

Finished picture of the lower box of the single-phase immersion liquid-cooled energy storage pack

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Thank you for your attention to Walmate.

Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Thermal Design

 Use simulation software to analyze the heat dissipation performance of heat sinks and cold plates

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

In a liquid cooling system, the Cold Plate is directly laid at the bottom of the battery or inserted into the gaps between the batteries. After circulating the coolant, it is cooled through a heat exchanger and then circulated back into the system.

The integration of electric vehicle structures can achieve lightweighting, improve space utilization through shared parts, lighten the entire vehicle, enhance endurance, and reduce costs. Based on years of experience in the new energy vehicle industry,Walmate is able to better provide multi in one powertrain components for vehicle manufacturers

New energy vehicles refer to vehicles that use unconventional vehicle fuels as power sources (or use conventional vehicle fuels and new onboard power devices), integrate advanced technologies in vehicle power control and driving, and form advanced technical principles with new technologies and structures.

Structure Design

Stress, load-bearing, and deformation analysis of cold plates and Heatsinks

Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

Clean energy alternative fuel oil：

Climate, environment, resources, energy are closely related to national economy and people's livelihood. Dealing with these related issues well determines whether human society can sustainably develop. Under the pressure of energy shortage and environmental pollution, the two technological routes of energy storage battery vehicles and hydrogen fuel cells have become the main directions for the development of the new energy vehicle industry.

Automotive Light Weighting：

Considering 75 percent of energy consumption is related to vehicle weight, lightweight is an important technological means for new energy vehicles to save energy, reduce consumption, and increase range,

lightweight design is one of the current key drivers to reduce the energy consumption of vehicles. The use of lightweight new materials, structural optimization, and process improvement are the key paths to achieve automotive light weighting.

Thermal Management：

For energy storage electric vehicles, thermal management will become a crucial technology to achieve fast charging and improve range. For hydrogen fuel cell vehicles, water and heat management are key core technologies in the development of fuel cell power systems, which have a decisive impact on the performance, safety, and lifespan of the vehicle's power system.

Generally, external air is used as a heat sink to transfer the heat generated by chip operation to the heat sink through different media and interfaces, and dissipate the heat.

The IGBT power module in the inverter plays a very important role in this process. During the energy conversion process, IBGT will generate a large amount of heat, but when the temperature of IGBT exceeds 150 ℃, IGBT cannot function. Walmate provides various IGBT heat dissipation solutions such as air cooling, single liquid cooling, and phase change.

Product Testing

We offer customized testing procedures to meet our customers’ requirements

Application Scenarios

Working condition: high heat flux density

Layout Location: Single Sided

Typical Applications：Customed

Features：Excellent Cooling Effect

Application Scenarios

Process: Aluminum profile splicing welding

Layout Location: Bottom Liquid Cooling

Typical Applications：Customed

Features：Light Weight ,Excellent Cooling Effect

Under the requirements of higher system energy density, taking into account factors such as heat dissipation and lightweight cost reduction, Walmate continuously optimizes the production process of battery trays to ensure system safety and reliability while improving cost-effectiveness.

The purpose of a heatsink is to acquire higher heat transfer surface area within a given volume by optimizing the structural shape, thereby improving the heat transfer efficiency from its surface to the surrounding fluid. Through surface treatment and other methods, the effective heat transfer area is increased, achieving enhanced cooling and temperature control.

In applications where volumetric power density and heat flux density requirements are not high, rectangular fin heatsinks are favored by engineers due to their simple structure, reasonable manufacturing cost, and good heat dissipation performance.

Comparision of different heat transfer methods

1- Heatsink Fin Design

The heatsink primarily extends its heat-dissipating surface through the fins, focusing on parameters like fin height, shape, spacing, and the thickness of the substrate.

Plate fin heat sink dimensions

According to the formula, the extended surface area of the heatsink can be calculated as:

The area of a single fin: Af = 2L(h+t/2),
The area between fins: Ab = Lh,
Total heat dissipation area: At = nAf + (n±1) Ab  (n is the number of fins).

Fin sectional view

The primary function of the fins is to increase surface area and improve heat transfer efficiency. The spacing, thickness, and height of the fins are critical factors in determining the number of fins, their distribution, and the expanded surface area.

When the surface area of the heatsink increases, the contact area with the air also increases, making it easier for heat to be dissipated. Engineers can further enhance the expansion area of the heatsink by optimizing the shape of the fins, such as using corrugated or serrated designs.

Although a larger surface area generally improves cooling performance, it is not always true that bigger is better. Whether using natural convection or forced cooling, the spacing between the heatsink fins is a crucial factor that determines the heat transfer coefficient of the air flowing over its surface.

The impact of Fin spacing and height on heat dissipation efficiency

In natural convection, the walls of the heatsink will generate natural convection due to temperature changes on the surface, causing airflow in the boundary layer near the fin walls. If the fin spacing is too small, it will hinder the natural convection process. In forced cooling scenarios, the thickness of the fin boundary layer will be compressed, allowing for narrower fin spacing. However, due to manufacturing methods and the driving force of the power components, the spacing cannot be too small. Therefore, balancing the thickness and height of the fins in actual design is very important.

2-Heatsink Substrate Design

The thickness of the substrate is a significant factor affecting the efficiency of the heatsink. When the heatsink substrate is thin, the thermal resistance to the fins farther from the heat source is larger, leading to uneven temperature distribution across the heatsink and weaker thermal shock resistance.

Increasing the substrate thickness can improve the temperature uniformity and enhance the heat shock resistance of the heatsink, but excessively thick substrates can cause heat accumulation, which in turn reduces thermal conductivity.

Heatsink working principle diagrammatic sketch

As shown in the figure above:

When the area of the heat source is smaller than the area of the base plate, heat must diffuse from the center to the edges, creating a diffusion thermal resistance. The position of the heat source also affects the diffusion thermal resistance. If the heat source is closer to the edge of the heatsink, heat can be conducted away more easily through the edges, thus reducing diffusion thermal resistance.

Note: Diffusion thermal resistance refers to the resistance encountered during the process of heat spreading from the center of the heat source to the edges in heatsink design. This phenomenon usually occurs when there is a significant difference between the area of the heat source and the area of the base plate, requiring heat to spread from a smaller area to a larger area.

3-Connection Process of Fins and Substrate

The connection process between heatsink fins and the substrate typically involves various methods to ensure good thermal conduction and mechanical stability between the two, mainly divided into two categories: integrated molding and non-integrated molding.

In integrated molding heatsinks, the fins and the heatsink substrate are formed as one piece, eliminating contact thermal resistance. The main processes include:

l Aluminum Die Casting: Aluminum ingots are melted into liquid form and then filled into metal molds under high pressure, allowing for the creation of complex fin shapes directly through die casting.

l Aluminum Extrusion: Aluminum material is heated and placed into an extrusion cylinder, where pressure is applied to force it through specific die holes, producing the desired cross-sectional shape and dimensions. Further processing includes cutting and machining.

l Cold Forging: This method allows for the creation of fine, dense fins with a high thermal conductivity material, but the costs are relatively high, and it has better capability for complex shapes compared to aluminum extrusion.

l The material for finned heatsinks can be copper, which has a high thermal conductivity. The fins can be made very thin, and they are directly carved from the substrate using cutting tools. However, when the fins are tall and long, they are susceptible to deformation due to stress.

In non-integrated molding, the fins and the heatsink substrate are processed separately and then joined together through welding, riveting, or bonding processes. The main processes include:

l Welding: The fins and substrate are connected together using solder; this can involve high-temperature brazing or low-temperature soldering. Welding has good thermal conductivity; however, using solder for aluminum substrates and fins requires nickel plating and can be costly, making it unsuitable for large heatsinks. Brazing does not require nickel plating, but the welding costs remain high.

l Riveting: The fins are inserted into grooves in the substrate, which are then pressed together with a mold to tightly hold the fins in place. The advantage of riveting is good thermal conductivity, but there is a risk of gaps and loosening after repeated use. Improving the riveting process can enhance reliability, but costs will also increase, so riveted heatsinks are often used in applications where reliability requirements are not high.

l Bonding: This generally involves using thermally conductive epoxy resin to tightly bond the fins and substrate together, facilitating heat transfer. While bonding uses thermally conductive epoxy resin, its thermal conductivity is significantly lower than that of welding, making it suitable for heatsinks with higher fins and small spacing. It can be used in scenarios where thermal performance requirements are not high.

We will regularly update you on technologies and information related to thermal design and lightweighting, sharing them for your reference.

Thank you for your attention to Walmate. 

The battery storage housing plays a crucial role in energy storage systems, serving essential functions such as load protection, thermal uniformity, electrical installation, and waterproof sealing. With the increasing demands for battery energy density, aluminum alloy materials have become an effective solution to enhance battery system performance due to their higher thermal conductivity and lower density.

The integrated design of flow channels with the housing sidewalls can save welding work in critical load-bearing areas, thereby improving overall structural strength. This design ensures structural safety and stability under various conditions, including static loads, lifting, and random vibrations, while also improving the airtight performance of the housing to some extent. Furthermore, the integrated design helps reduce the number of parts and lower the weight of the housing. Made through extrusion molding, this process has low mold costs, is easy to process, and can be easily modified to meet flexible production needs.

1-Main Types of Aluminum Extruded and Welded Energy Storage Lower Housing

The liquid-cooled lower housing for energy storage typically has a width of 790-810 mm and a height ranging from 40-240 mm, divided into flat and flange types (see below). The length of the liquid-cooled lower housing is related to the capacity of the energy storage product, with common specifications including 48s, 52s, and 104s.

flat tray liquid-cooled lower housing

flanged battery tray liquid-cooled lower housing

2-Structural Form of Aluminum Extruded and Welded Energy Storage Lower Housing

The liquid-cooled lower housing serves as the foundational structure of the entire battery pack, consisting of a bottom plate with flow channels, sealing strips, water nozzles, frames, beams, brackets, and lifting ears, all welded together to form a rectangular frame structure made entirely of aluminum alloy.

Explosive view of the battery lower tray

The liquid-cooled lower housing must possess sufficient load-bearing capacity and structural strength, which imposes high requirements on welding quality, including welding processes, weld grade control, and welder skills, to ensure safety and reliability in actual applications. Liquid cooling technology demands high airtightness for the liquid-cooled housing, including the airtightness of the lower housing and the liquid cooling flow channels. Additionally, the liquid cooling flow channels must withstand the pressure of the coolant flow, necessitating even higher airtightness requirements.

3-Welding Quality Requirements

Generally, the liquid-cooled bottom plate is welded using friction stir welding, and the end caps of the flat liquid-cooled lower housing also employ friction stir welding. Typically, the weld depression for friction stir welding should be ≤0.5 mm, and there should be no detachment or metallic foreign objects that could fall off under vibration conditions.

Liquid cooling flow channels, frames, water nozzles, lifting ears, beams, and accessories are often welded using TIG or CMT welding. Considering the performance requirements of different components, full welding is used for liquid cooling flow channels, frames, water nozzles, and lifting ears, while segment welding is applied to beams and accessories. The flatness of the front and rear battery module beam areas should be <1.5 mm for a single module and <2 mm overall, with frame flatness allowing ±0.5 mm for every additional 500 mm of frame length.

Weld surfaces must be free from defects such as cracks, incomplete penetration, lack of fusion, surface porosity, exposed slag inclusions, and incomplete filling. Generally, the height of the water nozzle weld should be ≤6 mm, and other welds should not extend beyond the lower surface of the housing. The internal welds of the front and rear module beams must not protrude from the inner surface.

The weld penetration must meet relevant standard requirements. For arc-welded joints, the tensile strength should not be less than 60% of the minimum tensile strength of the base material; for laser and friction stir welded joints, the tensile strength should not be less than 70% of the minimum tensile strength of the base material.

Additionally, the welding of the lower housing must meet the airtightness standard of IP67. Therefore, post-welding treatment generally requires the weld slag and seams in the front and rear module beam areas to be ground flat. External welding on the tray should not be ground, and the sealing surfaces at the welds need to be smooth, with no significant height differences from the frame.

Below：Extrusion+FSW battery tray for ESS

We will regularly update you on technologies and information related to thermal design and lightweighting, sharing them for your reference.

Thank you for your attention to Walmate. 

As the power density and heat generation of various electronic and power products continue to rise, heat dissipation faces increasingly severe challenges. Liquid cooling solutions are gradually becoming the mainstream option due to their efficient heat dissipation, low energy consumption, low noise, and high reliability. 

Liquid cooling systems work by attaching cooling plates to battery packs (or other heat sources) and using circulating coolant to carry away the heat generated during operation. This heat is then transferred through one or more cooling circuit heat exchangers, ultimately dissipating the thermal energy of the energy storage system into the external environment.

                    Flanged style battery tray in BESS                                 Cold plate in Solar inverter

As a core component of liquid cooling solutions, the liquid-cooled plate is an efficient heat dissipation component. Its primary function is to remove heat generated by the battery (or other heat sources) through the circulation of coolant, keeping the equipment operating within a safe temperature range. If the channels of the liquid-cooled plate are not clean, it can affect the uniformity of coolant flow. Larger foreign particles can block or impede coolant flow, leading to ineffective heat transfer and consequently impacting the heat dissipation efficiency and overall performance of electronic devices.

Moreover, if impurities remain in the channels, they may damage the oxidation protective film on the metal surfaces, causing corrosion or erosion of the liquid-cooled plate. Additionally, impurities in the channels can lead to poor component contact, potentially causing seal aging or damage, which increases the risk of leakage and affects the long-term stable operation of the system.

1-Cleanliness Requirements for Liquid-Cooled Plate Channels

Current energy storage liquid cooling solutions generally require that no foreign objects, aluminum chips, oil, or liquids are present in the channels. In some cases, specific quality requirements regarding the size of hard and soft particles may be defined.

2-High-Risk Contamination Phases in Liquid-Cooled Plate Manufacturing

During the processing and manufacturing of cold plates, the internal channels and cooling interfaces are particularly vulnerable. The manufacturing processes, including cutting and channel removal, can easily introduce foreign objects such as oil, cutting coolant, and machining chips into the channels. The machining operations occur at the channel entrances, making protection difficult, and once chips enter, they are hard to remove.

(Processing of Liquid-Cooled Plate Components: Channel Removal and Deburring）

After the processing of the cold plate channel, components such as plugs and water nozzles are welded to form closed channels. The channel structure is typically non-linear, which creates blind spots for flushing. After welding, the machining process requires a large amount of cutting coolant for the tools and workpieces, generating significant metal chips. This step is particularly prone to contamination from coolant, chips, and other pollutants, which are difficult to completely remove once they enter.

3-Cleaning and Protection of Liquid-Cooled Plate Channels

To ensure the reliability and performance of liquid-cooled plate components, strict cleaning operations are typically performed. High-pressure water jets are used to flush the internal channels of the liquid-cooled plate to remove any residues, particles, or other impurities. After flushing, the liquid-cooled plate components need to be dried to ensure no moisture remains in the channels.

(Processing of Liquid-Cooled Plate Components:flushing and degreasing）

If the cold plates and other liquid-cooled components are not adequately protected during manufacturing, they are susceptible to contamination from metal chips, oil, cutting coolant, etc., especially during the machining process. The handling process of the cold plates also easily allows foreign objects to enter. Generally, protective measures at the channel entrances are considered in advance, such as dust covers and rubber sleeves for water nozzles.

Thus, cleaning the internal channels of cold plates becomes a necessary measure to eliminate channel contamination and enhance channel cleanliness. In production practice, comprehensive preventive controls should be implemented throughout the process. Based on this, specific contamination control measures should be proposed for particular components and processes to effectively manage the contamination inside the cold plate channels.

Abstract：Hydrogen fuel cells, also known as proton exchange membrane fuel cells (PEMFCs), are widely used in electric vehicle charging stations, automobiles, and other power generation facilities due to their advantages of high efficiency, zero emissions, and zero pollution. Hydrogen fuel cell vehicles emit 3-5 times more heat during operation than traditional fuel vehicles. This article briefly describes the current technology related to hydrogen fuel cell heat dissipation.

1-Working Principle of Hydrogen Fuel Cells

Hydrogen fuel cells release a large amount of heat during operation, among which electrochemical reaction heat accounts for about 55%, irreversible electrochemical reaction heat accounts for about 35%, Joule heat accounts for about 10%, condensation heat and various heat losses account for about 5%. The heat generated by hydrogen fuel cells is approximately equal to the electrical energy they generate. If not dissipated in a timely manner, the temperature inside the battery will significantly increase, thereby affecting its service life.

2-Hydrogen Fuel Cell Heat Dissipations

Compared to fuel powered vehicles, hydrogen fuel cell vehicles have a higher heat generation and a more complex system. At the same time, due to the limitation of the working temperature of hydrogen fuel cells, the temperature difference between hydrogen fuel cells and the outside world is smaller, making it more difficult for the heat dissipation system to dissipate heat. The working temperature of hydrogen fuel cells has a significant impact on fluid flow resistance, catalyst activity, stack efficiency, and stability, thus requiring an efficient heat dissipation system.

Liquid cooling technology is currently the mainstream technology in the application of hydrogen fuel cells in vehicles. It aims to reduce water pump power consumption by reducing system pressure drop, eliminate excess heat in hydrogen fuel cells with the lowest power consumption, and optimize the distribution of circulating working fluid flow channels to reduce internal temperature differences and improve the uniformity of battery temperature distribution.

90% of the heat generated in hydrogen fuel cells is eliminated by the heat dissipation system through thermal conduction and convection, while 10% of the heat is dispersed to the external environment through radiation heat dissipation. Traditional heat dissipation methods include air cooling, liquid cooling, and phase change heat dissipation.

3-Heat Transfer of PEMFC System

3.1 Stack Heat Transfer

After heat is generated inside the PEMFC, it will be transferred between the various components inside the PEMFC and the external environment. The heat transfer inside the fuel cell stack mainly depends on the thermal resistance of each component and the contact thermal resistance between different components. As the gas diffusion layer is the "bridge" connecting the main heat generation component (membrane electrode) and the main heat dissipation component (bipolar plate), its thermal resistance and the size of the contact thermal resistance with other components have a significant impact on the heat transfer performance inside the PEMFC. In addition, the contact thermal resistance between different components can have a significant impact on the internal heat transfer of the fuel cell stack.

3.2 Cooling Liquid Heat Transfer

The cooling methods of fuel cells include air cooling, liquid cooling, and phase change cooling.

The factors that affect coolant heat transfer include the PEMFC stack end, the coolant itself, and the radiator end. The coolant comes into direct contact with the bipolar plate at the end of the PEMFC stack, so the coolant flow channel structure has a significant impact on its heat transfer. In addition, the properties of the coolant itself can also affect the related heat transfer process. Considering the insufficient available space, choosing a coolant with a larger heat capacity can reduce the size of the radiator and improve the thermal management performance of PEMFC. Therefore, the demand for new high-efficiency coolants is becoming increasingly evident.

       The trend towards miniaturization of electronic devices is increasing, while the demand for more functions and higher performance further drives the reduction of external dimensions at various packaging levels, resulting in a rapid increase in power density.

       The miniaturization of equipment originally stems from cost reduction considerations. Cooling solutions directly increase the weight, volume, and cost of the product without any functional benefits, but they provide product reliability.

      Controlling component temperature within a specified range is a common standard for determining the acceptable level of a design, and effective heat dissipation is crucial for the stable operation and long-term reliability of electronic products.

      On the one hand, the result of device miniaturization is a decreasing design margin and a lower tolerance for over design. On the other hand, the overall trend of miniaturization has given rise to increasingly messy and complex geometric models, deepening the close integration of mechanical and electronic components in products. As a result, the flow space is greatly compressed, limiting the range of convective heat dissipation and making the structure of the core material of thermal design - the radiator - more complex.

       Heat sink is the most commonly used heat dissipation strengthening component in electronic device thermal design. Its strengthening principle is to increase the heat exchange area. When designing, it is generally necessary to consider the heat flux density of the heat source, the temperature requirements of the heating components, the internal space size of the product, the installation and appearance design of the heat sink, and other requirements.

     The performance of a heasink is influenced by many factors such as material, geometric dimensions, bottom flatness, thermal resistance, surface treatment, installation and fastening methods, and working environment temperature and humidity.

1.  Heatsink material

      The materials used for heatsinks mainly include aluminum, aluminum alloy, copper, iron, etc. Aluminum is the most abundant metal element stored in nature, with light weight, strong corrosion resistance, and high thermal conductivity, making it very suitable as a raw material for radiators. Adding some metals to aluminum to form aluminum alloys can significantly improve the hardness of the material. Graphite has the conductivity and thermal conductivity of metallic materials, as well as the plasticity similar to organic plastics, and is further applied in fields such as electronics,

communication, and lighting.

2.  Heatsink manufacturing process

The processing technology of radiators mainly includes CNC, aluminum extrusion, shovel teeth, slotting teeth, etc.

       Aluminum extrusion: The aluminum extrusion heat sink heats the aluminum ingot to around 460 ℃, and under high pressure, allows semi-solid aluminum to flow through an extrusion mold with grooves, extruding the initial shape of the heat sink, and then cutting and further processing. The aluminum extrusion process cannot accurately ensure the flatness and other dimensional requirements of the radiator, so further processing is usually required in the later stage.

      Shovel teeth: Shovel teeth are used to cut and straighten long strip shaped metal sheets (usually aluminum or copper alloys) at a certain angle using a shovel tooth machine, and repeat cutting to form a consistently arranged fin structure. Compared to extrusion technology, the advantage of shovel teeth is that they can process heat sinks with higher fin density and higher tooth height ratio.

      Splitting: The processing of slotting heat sink involves inserting the teeth into the heat sink substrate, and connecting the teeth to the substrate through methods such as adhesive welding, brazing, or extrusion; The connection between the teeth and the base of the toothed radiator is very important. If not handled properly, it may form a certain contact thermal resistance, which affects the heat dissipation performance of the toothed radiator.

3. Surface treatment of heatsinks

       Aluminum alloys are prone to oxidation in the air (forming an alumina film), but this natural oxide layer is not dense, has weak corrosion resistance, and is prone to contamination; Based on the requirements of aesthetics, corrosion resistance, and improved heat dissipation performance, metal radiators need to undergo surface treatment. Common surface treatment processes include anodizing, sandblasting, chemical nickel plating, and baking paint.

      Anodization：The principle of anodizing is essentially water electrolysis, which involves placing aluminum or aluminum alloy as the anode in a dielectric solution and using electrolysis to form an aluminum oxide film on its surface. This process is called anodizing treatment of aluminum or aluminum alloy; After anodizing, the surface emissivity of the radiator will increase, and the heat dissipation ability of the thermal radiation will be enhanced; Anodizing can maintain or change the color of aluminum & aluminum alloys, and black anodizing is commonly used for heat sinks.

       Sandblasting：Sandblasting refers to the process of using compressed air as the power and utilizing the impact of high-speed sand flow to clean and roughen the surface of a radiator; By impacting and cutting the surface, this process can not only remove all dirt such as rust on the surface of the radiator, but also exhibit a uniform and consistent metallic luster on the product surface.

       Electroless nickel plating：Chemical nickel plating is a process of depositing nickel alloys from aqueous solutions onto the surface of objects; Its characteristics include high surface hardness, good wear resistance, uniform and beautiful coating, and strong corrosion resistance; Due to the inability of copper and aluminum to be directly soldered, both require chemical nickel plating before using processes such as soldering.

      Baking paint：Baking paint is a high-performance special coating called Teflon added to the surface of a heat sink at high temperatures (280 ℃~400 ℃), which has the characteristics of non adhesion, heat resistance, moisture resistance, wear resistance, corrosion resistance, etc.

       Compared to traditional spray painting techniques, baking paint has advantages in both aesthetics and thermal conductivity. However, heat pipe assembly heat sinks are prone to expansion and deformation due to high temperatures, so low-temperature baking paint is particularly needed during baking.

       As the power to be processed continues to increase, heat sinks begin to be combined with heat pipes, fins and other devices to form higher performance heat dissipation modules, and water-cooled heat sinks with higher heat dissipation efficiency have emerged.

      Abstract：The main heating device in the electronic control system of new energy vehicles is the inverter, which converts the direct current of the battery into alternating current that can drive the motor. During this process, the IBGT in the inverter will generate a large amount of heat. To solve the heat dissipation problem of these devices, this article will introduce the working principle of inverters and advanced liquid cooling heat dissipation technology.

1-The Application of IGBT in the Electronic Control System of New Energy Vehicles

The electronic control system, as the energy conversion unit connecting the battery and the driving motor in new energy vehicles, is the core of motor drive and control. As a device that connects high-voltage batteries and motor power, inverters are responsible for converting direct current energy (batteries, storage batteries) into fixed frequency and voltage or frequency and voltage regulated alternating current (usually 220V, 50Hz sine wave), ensuring the electrical energy conversion of new energy vehicles.

The IGBT power module in the inverter plays a very important role in this process. During the energy conversion process, IBGT will generate a large amount of heat. However, when the temperature of IGBT exceeds 150℃, IGBT cannot function, so air-cooled or water-cooled heat dissipation equipment should be used. The thermal stability of IGBT operation becomes the key to evaluating the performance of electric drive systems.

In addition to the electronic control system, IGBT is also widely used in the onboard air conditioning control system and charging station system of new energy vehicles:

As the core technical component of electric vehicles and charging stations. The IGBT module accounts for nearly 10% of the cost of electric vehicles and about 20% of the cost of charging stations, and its thermal stability becomes the key to evaluating the performance of electric drive systems.

2-IGBT liquid cooling technology