Compared with air cooling, an efficient cooling system is crucial for ensuring battery performance and safety in the development of EV vehicles. Known as a core cooling component within the thermal management system, the cold plate plays a vital role in the EV vehicle's cooling system. This article delves into enhancing the thermal conductivity of cold plates through design optimization, which explores strategies like optimizing the layout and number of cooling channels, selecting materials with high thermal conductivity, applying advanced surface treatment technologies, optimizing thermal interface materials (TIM), and using simulation and model analysis for predictive optimization. These approaches boost the cooling efficiency of new energy vehicles and extend battery life, enhancing vehicle safety and reliability. The detailed exploration of these strategies offers deep technical insights into designing and optimizing cooling systems for EV vehicles.
Part 1: Key Technologies of Liquid Cooling Plate for Heat Dissipation
Part1 A: Multi-channel Design Optimization
Channel Layout Optimization
In the quest for enhanced thermal management systems in EV vehicles, optimizing the layout of cooling channels within heat sinks or liquid cooling plates stands as a pivotal strategy. The layout of cooling channels directly influences the thermal conduction path, subsequently affecting the thermal resistance and overall heat exchange efficiency of the cooling system. Among the various channel geometries-straight, spiral, and branched-each presents unique advantages and considerations in terms of heat distribution, manufacturing complexity, and fluid dynamics behavior.
-Straight Channel Cold Plates:
With its simple design and ease of manufacturing, The straight channel layout is widely used. This layout provides a direct cooling path, allowing the cooling fluid to pass quickly through the battery package, making it suitable for battery packs that require uniform heat dissipation and have relatively low thermal loads. In new energy vehicles, the straight channel layout is particularly well-suited for compact and simple battery packs, such as those in small electric vehicles or hybrid cars, where efficient heat dissipation is needed but space and cost are limited.
For example, the Chevrolet Volt classified as a Plug-in Hybrid Electric Vehicle (PHEV), is the Chevrolet Volt's battery pack design that incorporates an efficient cooling mechanism to maintain the battery in its optimal working condition. Its cooling system may utilize straight channels to simplify the cooling process and minimize space occupancy to upgrade its thermal performance.
-Spiral channels Cold Plates:
Spiral channels enhance thermal exchange efficiency by extending the coolant's flow path and increasing the contact time between the fluid and the channel walls. This design is particularly suitable for applications with high thermal loads or those requiring efficient thermal conduction. For example, spiral channel cold plates also achieve a more uniform heat transfer, reducing high heat loads for EV vehicle heat dissipation. However, this design may lead to higher flow resistance, necessitating stronger pumps to maintain flow. Therefore, opting for spiral channels is appropriate when the system can tolerate higher energy consumption and has high requirements for cooling efficiency.
-Branched Channel Cold Plates:
The layout of branched channel liquid cooling plates divides the main channel into multiple branches, allowing the coolant to be distributed more evenly across different parts of the battery packs. This design suits battery packs with irregular shapes or uneven heat load distribution. It optimizes the flow of the coolant, ensuring that even areas within the battery packs with higher heat loads receive adequate cooling. The branched channel layout is applicable for applications that require high uniformity in temperature, such as in large electric vehicles and high-end electric sports cars. These battery packs need precise temperature control for each battery cell to ensure optimal performance and safety.
For example, The Porsche Taycan is a high-performance electric sports car, known for its exceptional driving performance and fast charging capabilities. To maintain battery performance and extend its lifespan, the Taycan may employ a complex cooling system design, including a branched channel layout, to achieve uniform temperature distribution within the battery packs.
The most significant advantage of this approach is that it isolates the coolant from the battery cells/modules, eliminating a potential safety hazard. The Taycan's module layout is divided into upper and lower layers, so its water cooling system is also divided into upper and lower layers, totaling 13 cooling branches. Each tubed cold plates branch has two parallel water cooling pipes featuring 10 parallel flow channels, and the size of each channel is 3mm*2mm; the entire cooling pipe has a thickness of about 4mm and a width of about 35mm.
Channel Size and Distribution Strategy
The choice of channel size plays a crucial role in the design of liquid cold plates for EV vehicles, also affecting the overall performance of the secondary cooling system. Both large and small holes in cold plate has their applications based on the specific needs and design of the EV vehicles.
-Large Channel Cold Plates:
Large channel cold plates refer to those with a wider inner diameter, ranging from 5 - 10 millimeters which are considered an effective choice for improving the flow performance of the liquid coolant due to their low pressure in flow rate. This design allows the use of a pump without high power, thereby reducing the system's energy consumption. Large channel layouts are suitable for new energy vehicles with relatively uniform heat load distribution and higher energy efficiency requirements. For example, EV vehicles intended for city commuting might prefer large channel designs to achieve reasonable cooling efficiency and lower energy consumption toward high power electronics.
In those EV vehicles where the heat load is relatively uniformly distributed and there is a high demand for energy efficiency, large-channel cold plates are particularly suitable for EV components. For example, some city buses tend to use large-channel designs to achieve reasonable cooling efficiency and lower energy consumption. But, more space is needed when using a large channel liquid cold plate. This is the reason why we rarely see large-channel liquid cold plate in private EV vehicles because EV cars often focus more on space utilization and the overall compactness of the vehicle during design to meet consumers' needs for driving experience.
-Small Channels Cold Plates:
In contrast, small channel cold plates(Approximately a diameter of about 5 millimeters) can provide a high level of efficiency in transferring heat for high-performance EV cars and common private EV vehicles because they increase the surface area between the coolant and the channel walls for contacting, thereby accelerating the flow rate of the internal coolant. Moreover, small channel cold plates provide more flow paths on their mounting surface within a limited space which small ones can not make it.
Besides that, the ideal solution, flow rate, and thermal management objectives also need to be considered. You can contact our engineer for more technical consultation.
Part1 B: Material Selection and Application
-Selection of Suitable Materials:
There is no doubt that we chose an aluminum cold plate and copper heat pipe for heat dissipation when considering aluminum and copper heat conductivity and cost. As of February 2024, the price of copper per ton is $7,600.00 together with $3500-4000 aluminum alloy. So, it is a cost effective way to purchase aluminum instead of copper alloy.
Plus, the volume is also the key point for manufacturing EV liquid cold plates. As illustrated, 1 ton of aluminum alloy occupies a significantly larger volume than copper alloy due to aluminum lower density, which means aluminum is a suitable material to manufacture top surface area for its lightweight and copper to manufacture heat pipe for its good thermal performance. For example, we know that the battery packs of the Audi e-Tron weigh 5 kg and 700 kg of the lithium battery packs, which means that the liquid cooling plate only occupied 0.7% of the total weight. But if you use the copper cold plate, it takes over 2.5% of the total weight (Approximately 7.5 kg).
-Relationship Between Thermal Conductivity Performance and Material Thickness:
The thickness of a material affects the efficiency of the heat exchanger. Thick materials may result in increased thermal resistance, while thin ones may not be mechanically strong enough and then cause serious issues such as thermal penetration.
The first graph shows that It is apparent that graphene's mechanical strength is significantly higher than that of aluminum and copper, and it almost does not change with thickness. The mechanical strength of aluminum and copper slightly increases as the thickness increases. The second graph demonstrates the relationship between material thickness and thermal resistance. Graphene's thermal resistance is very low and is almost unaffected by thickness, whereas the thermal resistance of aluminum and copper increases linearly with an increase in thickness.
The third graph shown below shows the combination of mechanical strength, material thickness, and thermal resistance. We can see that the 0.08m aluminum alloy has the best tensile strength and low thermal resistance (0.36 °CW).
Part 2: Thermal Management Technology in Liquid-Cooled Cold Plates
Part2 A: Surface Treatment Technologies
-Surface Coating:
Thermal conductive coatings are specialized surface treatments designed to enhance the heat exchange efficiency of water cooling plates. These coatings work by improving the contact quality at the thermal interface or enhancing thermal radiation capabilities, typically incorporating materials with high thermal conductivity such as silver, copper, and aluminum, as well as nanomaterials like carbon nanotubes (CNTs) and graphene. Not only do these coatings improve thermal efficiency, but they also offer some degree of protection against corrosion and wear, thereby extending the lifespan of the liquid cooling plates.
-Surface Processing:
Through the surface processing of the water-cooling plate, the heat exchange area can be increased, thereby improving the heat transfer efficiency. This method enhances the heat exchange capacity between the fluid and the surface area of the base plate by increasing the surface roughness. For example, as shown in the picture, we can bend the liquid cooling plate to ensure that coolant passes through every part of the battery, thereby improving the thermal performance of cold plates. Kaixin Aluminum is dedicated to providing custom liquid cooling plates and aluminum heat sink machining as your requirement.
Kaixin Aluminum can provide several surface processings for your aluminum cold plate, for example, CNC machining, anodizing, powder coating, bending, etc... Or, please view our blog "a cost effective solution for customing aluminum heat sink and liquid cold plate" to learn how to save money in manufacturing aluminum cold plate and heat sink.
Part2 B: Thermal Interface Material (TIM) Optimization:
-Selection and Application of Thermal Interface Materials:
Thermal Interface Materials (TIMs) are substances used between two surfaces to improve thermal conduction. They are used between two surfaces to improve thermal conductance. Common types of TIMs include thermal pastes, pads, tapes, and liquid metals, each suitable for different applications based on their thermal conductivity, ease of application, and durability.
Part2 C: Simulation and Model Analysis-Application of CFD and Thermal Simulation Software:
It can effectively predict and optimize the thermal conductivity efficiency of custom cold plates by using Computational Fluid Dynamics (CFD) and thermal simulation software, which means that the designer can analyze the entire cooling system such as the circulation of the coolant, the layout of heat sources, thermal bridges or areas with high thermal resistance, allowing an improved design before mass production.
When conducting simulations with CFD, you need to provide detailed specifications of your cooling system for Kaixin Aluminum engineer. This includes the geometry data of the water cooling plate and its components, material properties (thermal conductivity, density, specific heat), boundary conditions (such as inlet and outlet temperatures, and flow rate), and heat generation data from heat sources. Additionally, specifying your specific goals or performance criteria for the simulation can be very beneficial. Contact Kaixin Aluminum technical engineers and we are pleased to provide you ideal solution for custom cold plates.