Scaling AI Data Centers: Overcoming Cooling Challenges

AI data centers are scaling rapidly to meet the intense compute demands of generative models and large language model inference. These workloads, often accelerated by NVIDIA’s latest GPU architectures, drive greater compute intensity, contributing to higher energy use, and thermal complexity. As racks grow denser and hotter, maintaining efficiency and uptime becomes both more challenging and more critical. 

Boyd solves these challenges with innovative cooling solutions that improve efficiency, enhance sustainability, and reduce water and energy consumption at both system and facility levels. Our holistic approach, engineered for the extreme heat flux and scale of AI infrastructure, enables smarter thermal design decisions that lower total cost of ownership and strengthen long-term data center resilience. 

AI Workloads Drive Data Center Efficiency Challenges

AI workloads demand massive computational throughput, pushing data center designs beyond traditional power and thermal limits. Operators managing NVIDIA accelerated GPU clusters, like those using the NVIDIA GB200 NVL72, confront higher rack power densities, liquid cooling requirements, and need to manage environmental impacts. 

While these high-performance GPUs deliver exceptional processing power, they generate significant thermal loads. Conventional air-cooling systems often fall short, requiring data center operators to rethink thermal management architectures. Efficient energy planning must address kilowatts per rack, thermal uniformity, and hotspot prevention. At hyperscale, even minor inefficiencies compound into major operating expenses, driving the need for innovative cooling strategies that maximize performance per watt and conserve resources. 

Boyd’s System-Level Cooling Approach

Boyd tackles AI data center cooling challenges comprehensively, from chip to facility. Our precision-engineered liquid cooling components, including cold plates, heat exchangers, and coolant distribution units, optimize thermal management for high power densities found in GPUs like the NVIDIA GB200 NVL72. By employing smart flow control and minimizing pressure drops, our liquid cooling solutions efficiently dissipate heat while reducing water and energy consumption. 

Beyond individual components, Boyd partners with NVIDIA accelerated system integrators and data center operators to deliver fully customized closed-loop cooling systems. These systems provide precise coolant temperature control and optimized flow paths, significantly lowering water use and boosting energy efficiency by reducing reliance on energy-intensive air-cooling methods. This holistic approach ensures robust operation and resilience for demanding next-generation AI workloads. 

Sustainable Cooling Solutions for AI Data Centers

Boyd enables more sustainable data center operations by enhancing thermal performance and reducing dependence on water-intensive cooling towers. Our high-efficiency liquid cold plates and low-approach-temperature CDUs minimize the temperature difference between the chip and ambient air, allowing operators to use alternative cooling methods like free air cooling, even in warmer climates. 

These system-level improvements lower energy consumption and reduce water waste while maintaining reliable chip temperatures. With closed-loop cooling designs and high thermal efficiency, Boyd helps data centers meet sustainability goals, cut operational costs, and stay compliant with evolving environmental standards. 

Boyd: Beyond Cooling, Powering Performance

Boyd delivers more than advanced cooling components. For NVIDIA accelerated AI data centers, we provide extensive service and support that maximize uptime and system reliability. Our customized service plans and rapid-response maintenance help operators prevent costly downtime and maintain optimal thermal performance. 

By collaborating closely with data center operators and system integrators, Boyd enables proactive troubleshooting, continuous system monitoring, and preventive maintenance. This partnership approach ensures consistent reliability and long-term resilience, supporting the intensive demands of next-generation AI applications. 

Future-Proof Your AI Data Center with Boyd

Boyd enables NVIDIA accelerated AI data centers to optimize energy efficiency, conserve water, and deliver dependable uptime through advanced cooling solutions. Our system-level strategy addresses the unique challenges of high-density AI workloads, combining precision-engineered components, complete cooling systems, and expert support. Optimize energy efficiency, conserve water, and deliver dependable uptime through advanced cooling solutions. Our system-level strategy addresses the unique challenges of high-density AI workloads, combining precision-engineered components, complete cooling systems, and expert support. 

By partnering with Boyd, data center operators minimize operating costs, achieve sustainable performance, and future-proof their infrastructure for evolving AI demands. Contact our experts today to discover how Boyd can enhance your AI data center’s resilience and efficiency. 

The Future of AI: Powered by Efficient Cooling

Artificial intelligence large language models are now surpassing 1 trillion parameters, making next-generation technology essential. This new era of AI-driven computing prioritizes power efficiency, acceleration, networking, and storage. NVIDIA’s GB200 NVL72 addresses these challenges, but unlocking its full potential requires reliable and efficient cooling that is easy to deploy. Liquid-cooled GB200 NVL72 racks significantly lower a data center’s carbon footprint and energy use. These systems boost compute density, optimize floor space, and support high-bandwidth, low-latency GPU communication within expansive NVLink domain architectures. The GB200 delivers 25x more performance at the same power level compared to H100 air-cooled infrastructure, while also conserving water. Boyd’s modular innovative cooling solutions ensure AI-driven data centers operate at peak performance and energy efficiency, making them essential to harness the full capabilities of NVIDIA’s GB200 in an easy-to-deploy way.

Boyd: Cooling AI with Precision and Efficiency

Streamlined GB200 Integration with Boyd’s Cooling

Precision Cooling for Peak GB200 Performance

Boyd precisely tunes cooling solutions to maximize the performance of NVIDIA’s GB200. We engineer cold plates, liquid cooling loops, rack manifolds, and CDU systems to enhance the GB200 ecosystem. By optimizing performance, we ensure your data center runs at peak efficiency.

Expanding AI Capabilities: Efficient Cooling for Higher Density

Boyd’s innovative cooling solutions increase compute density without expanding a data center’s footprint. Scale up operations while minimizing space and power consumption with our energy-efficient cooling systems to boost your AI capabilities without compromising sustainability.

Pioneering AI Cooling with Boyd

Boyd and NVIDIA lead the charge in making the new era of computing cooler and more efficient. Our partnership demonstrates the commitment to deliver sustainable, high-performance cooling for next generation computing applications. Collaborate with us to leverage our rich heritage, expertise, and capabilities in developing cutting-edge systems that deliver energy-efficient and high-performance cooling solutions tailored to your needs. To learn more about our innovative cooling solutions or to discuss your project needs, schedule a consultation with our experts to see how our expertise can elevate your data center’s efficiency and performance.

Power Surge: AI Pushes Data Center Cooling to the Limit

A Multi-Pronged Approach: Cooling Solutions for Every Component

The COOLERCHIPS concept addresses all deployment levels and program objectives with innovative cold plate technology using a green refrigerant. Two-phase flow visualization techniques optimize cold plate architecture and operating conditions. CFD simulation refines flow and temperature distribution inside the immersion tray. At the rack level, an in-rack distributed pumping and flow separation system replaces the conventional cooling distribution Units (CDU). This system separates vapor from liquid and directs spent vapor back to the condensing unit to improve efficiency. Immersion manifolds connect directly to the heat rejection unit. Multiple identical racks connect to emulate an IT cluster, all linked to external heat rejection units with cool array coolers, potentially reducing the cooling tower footprint by four times. This integration reduces total power consumption to only 5% of the IT load.

Green & Efficient: Next-Gen Data Centers with Zero Water

Beyond the Benchmark: Cooler Tech Chases Evolving Needs

The program continues to advance data center cooling technology as AI-driven computing and high-performance computing (HPC) evolve, which increases the demand for more efficient cooling solutions. It refines advanced cooling technologies to optimize efficiency and responsiveness, leveraging achievements in high power density, low PUE, and environmental sustainability. This ongoing refinement ensures that the program remains at the forefront of innovation in data center cooling, meeting evolving industry needs and setting new benchmarks for efficiency and environmental responsibility.

Boyd Powers COOLERCHIPS: Cold Plate Tech Drives Efficiency

Boyd’s extensive expertise in two-phase cooling and liquid cooling systems is fundamental to the success of the COOLERCHIPS program. Our advanced cold plate technology plays a pivotal role in achieving the program’s ambitious objectives, effectively managing the substantial thermal demands of next generation data centers. Boyd’s cold plates, engineered for optimal efficiency and performance, are essential components in this effort. By incorporating Boyd’s innovative cooling solutions, the COOLERCHIPS program ensures that data centers operate not only with enhanced efficiency but also with a sustainable approach, paving the path for future innovations in data center cooling.

Collaborate with us to leverage our rich heritage, expertise, and capabilities in developing innovative liquid cold plates for advanced two-phase pumping systems, enabling energy-efficient and high-performance cooling solutions for your specific applications.

Beyond Performance: Addressing Reliability Concerns in Liquid Cooling

The Boyd Difference

Understanding the Roots of Coolant Leakage in Liquid Cooling Systems

In liquid cooling systems, coolant leakage poses a significant risk and can compromise performance and reliability. Understanding why coolant leaks is crucial for effective prevention. Corrosion and fluid interconnect issues are the primary factors that cause coolant leakage.

Fluid Interconnect Issues:

Ensuring Leak-Free Reliability in Liquid Cooling System Fluid Interconnect Joints, Fittings, and Seals

Our liquid cooling systems feature diverse joint technologies to meet varying customer needs while preventing leaks. We solder or braze joints to create strong, durable metal components and assemblies, perfected over decades of manufacturing experience. For barb fittings, we enhance security by pairing them with tube clamps, ensuring a tight and leak-free connection. To protect O-ring seals, we incorporate filters during testing and within our Coolant Distribution Units (CDUs) to remove larger particles that could damage the seals’ integrity. Boyd meticulously manufactures, handles, tests, and packages liquid cooling loop joints, fittings, and seals to ensure secure fluid interconnections before they reach the customer. This rigorous process maintains joint integrity and minimizes leak risks.

Erosion corrosion occurs when increased coolant velocity erodes metal surfaces, often caused by turbulent flow or sharp turns in the coolant path. This erosion weakens materials, heightening the risk of leaks and eventual system failure. Effective design solutions minimize flow velocity changes and ensure smooth coolant pathways to prevent erosion corrosion.

Boyd addresses these corrosion risks by implementing advanced seals, corrosion-resistant materials, precise manufacturing techniques, and rigorous testing in liquid cooling systems. These proactive measures not only mitigate fluid interconnect issues but also ensure reliable and efficient operation. They safeguard the integrity of high-value electronics, reduce downtime, and lower maintenance costs over the system’s lifespan.

Optimizing Leak Containment: Beyond System Shutdown

Optimizing Performance, Eliminating Leaks: The Boyd Advantage in Liquid Cooling

Boyd pioneers’ innovation through the design of leak-free solutions, advanced sealing techniques, and corrosion-resistant materials. Our engineering and material science expertise enables us to develop robust solutions that ensure the integrity and reliability of liquid cooling systems. Boyd tackles challenges such as fluid interconnect issues and corrosion risks through rigorous testing and precision manufacturing capabilities. Schedule a consultation with our experts to explore our comprehensive range of leak-free solutions tailored to meet your specific project needs and optimize system performance.

EV Battery Module Types

Pouch Cells

Pouch cells are flat, rectangular batteries enclosed in flexible, pouch-like packaging, engineered for seamless integration into irregular or confined spaces within a vehicle’s design. Their uniform distribution throughout the vehicle effectively balances weight and enhances stability, making them an ideal choice for custom designed EVs.

Prismatic Cells

Boyd’s Innovative Solutions for EV Battery Modules

Thermal Management

Boyd’s cutting-edge cooling technologies efficiently dissipate heat and prevent thermal runaway, without adding excessive weight or size to the EV. Our advanced liquid cooling systems and customized cold plates efficiently manage battery heat to prolong battery lifespan and enhance overall performance.

Seal and Protect

Innovate with Boyd

Boyd has decades of experience and expertise delivering thermal, insulation and shielding, and sealing and protection solutions for the eMobility industry. We have a track record of shipping over a billion eMobility components and installed our technologies in over 2 million eMobility vehicles. Leverage our 60+ years of automotive heritage for proven reliability and quality. Boyd’s rapid prototyping and design iterations accelerates time to market.

Our advanced liquid cooling and material science expertise enable us to incorporate multiple capabilities into vertically integrated eMobility solutions. To learn more about our EV Battery solutions or to discuss your project needs, schedule a consultation with our experts.

Generative AI and EV Batteries: Why Liquid Cooling?

Advancing technologies like high performance artificial intelligence (AI) and electric vehicle (EV) batteries use more power. More power generates more waste heat, so much that generative AI and EV battery innovators are shifting to liquid cooling. We’ll explore why liquid cooling is a fundamental part of this conversation.

Cp air = 1.0035 J/gK

Cp water = 4.1813 J/gK

Cp ethylene glycol = 2.36 J/gK

Cp propylene glycol = 2.5 J/gK

Higher heat capacity = more efficient, higher capacity cooling.

Density Air = 0.001204 g/cm³

Density Water = 0.9982067 g/cm³

Higher Heat Capacity and Density Work Together

Liquid cooling’s edge doesn’t come from its high heat capacity or density independently. Combining these two properties make liquid a powerful cooling solution.

Most applications are restricted by how much space is available for cooling. Here’s an example:
We’ll hold the volume constant to compare; Assume we have 100cm³ for simplicity.

• In 100cm³, we can have either 0.12g of air or 99.8 g of water.
• 0.12g of air can absorb 0.12 Joules of energy before it increases 1 degree Celsius
• 99.8g of water can absorb 417 Joules of energy before it increases 1 degree Celsius

That’s over 3000 times more heat absorbed in the same volume.

Why isn’t Liquid Cooling used for Everything?

Liquid cooling can cool more and faster than air but it comes with its own challenges. Air is easily available. Air only requires fans, blowers, ducting, or air baffling to control flow. Liquid is not readily and abundantly available everywhere. Liquid cooling requires tubes, manifolds, pumps, and fittings to circulate liquid. Liquid presents leak and water damage risk that is preventable with smart sensors, software, and system redundancies, but this adds to infrastructure complexity. High density also means liquid is more difficult to move compared to air. Liquid systems either move slower or require more powerful pumping systems.

Innovators in generative AI and EV batteries turn to liquid cooling when thermal demands surpass what is feasible with air cooling. The need for higher performance outweighs liquid’s additional system and infrastructure complexities.

Picking the Right Cooling System for your Application with Boyd

Boyd has decades of high reliability liquid cooling system field performance in regulated and high safety critical markets. We have dependably cooled high power loads by refining liquid system design to mitigate liquid cooling system challenges while maximizing its high cooling capacity benefits. Innovators in generative AI and EV batteries who are pushing their performance boundaries, and by default their thermal management system boundaries, are turning to Boyd for liquid cooling concepts, advanced component and system design, thermal simulation and modeling, cooling innovation, global manufacturing at scale, and 100% in-line leak testing.

Boyd is an invaluable liquid cooling partner with thermal management expertise across the whole air and liquid cooling spectrum to help push the limits of air-cooled solutions like 3D vapor chambers and remote heat pipe assemblies or safely introduce liquid systems with coolant distribution units, chillers, and liquid loops and cold plates. We’re cooling the most advanced generative AI and EV battery applications in the market today with advanced, high efficiency, dependable liquid cooling systems. Contact us to discover how we can help cool your AI and EV battery systems.

A $5 Million grant from the U.S. Department of Energy (DOE) supports NVIDIA and seven partners, including Boyd, to build an advanced liquid cooling system that enables a future class of efficient power-dense data centers. The DOE program, called COOLERCHIPS, focuses on innovative technologies to reduce data center energy consumption and environmental impact. Boyd is excited to be part of this program alongside other industry leaders in a collaborative effort to develop a new generation of energy efficient cooling solutions.

Need for Change: Advanced Cooling Solutions for Data Centers

Extreme air-cooling using two-phase technologies and current liquid-cooling systems face limitations in cooling intense high-power computing environments. As data centers continue to evolve with more computing power, system architects must innovate cooling solutions to meet increasing demands. These next generation data centers require exceptional performance, reliability, and energy efficiency on top of increased heat dissipation.

Innovative Cooling Technology: Two-phase Cooling and Liquid Cooling Systems Combination

Combining two-phase cooling and liquid cooling systems into pumped two-phase systems, or evaporative liquid cooling, leverages the benefits of both cooling technologies. First, two-phase cooling utilizes cold plates to cool chips and facilitate evaporation and re-formation of the coolant. Next, entire servers, including their lower-power components, are encased in hermetically sealed containers filled with coolant to provide a comprehensive cooling solution. With an optimized pumped two-phase cooling system, data center engineers can overcome anticipated thermal challenges for future data centers.

Innovate with Boyd: Two-phase Cooling and Liquid Cooling Systems

Boyd’s strong heritage of two-phase cooling and liquid cooling systems technologies provides a solid foundation for collaborative development. Our ability to innovate with technologies like coolant distribution units, 3D vapor chambers, liquid loops and cold plates, remote heat pipe assemblies, and chillers enables us to explore new possibilities and develop advanced cooling solutions that best fit your applications. Partner with us to tap into our strong heritage, expertise, and capabilities to develop innovative liquid cold plates for advanced two-phase pumping systems, enabling energy efficient and high performance cooling for your applications.

Embedded systems are becoming more complex, processing and analyzing a growing number of sensors and signals. The result of this increased computing is often higher and more concentrated electronic heat loads.

How to Design a Liquid Cooling System for High-Performance System Thermal Management

Because excessive heat compromises the reliability of a system, air cooling is no longer adequate for some applications. Many engineers are turning to liquid cooling to remove the heat.

The complexities of designing a liquid cooling system can be intimidating for those unfamiliar with this set of technologies. Although selecting thermal components for a liquid cooling loop is relatively straightforward, there are other considerations or nuances that can be overlooked. These include materials compatibility, corrosion prevention, condensation control, the position of the liquid cooling loop, use of standard versus custom parts, joints, fittings, connectors, and maintenance and service.

A liquid cooling loop typically consists of a liquid cold plate, pump, heat exchanger, and pipes or hoses (Figure 1). The board generates waste heat, which is transferred from the board to the thermally conductive plate, and then to the liquid coolant that flows through the cold plate. Typically, the fluid path matches hot spots on the board. The heated coolant is then pumped through the heat exchanger, where heat is moved from the coolant to either ambient air, or, in the case of a liquid-to-liquid heat exchanger, to another liquid coolant. The cooled coolant then flows through pipes or hoses back to the cold plate, completing the cooling loop. Under normal operation, liquid coolant continuously flows through the liquid cooling loop to keep the board cool.

Material Compatibility

Since all materials and the fluid in the liquid cooling loop need to work together as a system, they need to be compatible with one another and should be selected together. Copper works well for most applications, since it has excellent thermal conductivity and is compatible with most non-corrosive fluids. Aluminum is compatible with fluids such as polyalphaolefin (PAO), oil, ethylene glycol and water solutions (EGW), as well as Fluorinert™, an electrically insulating inert perfluorocarbon fluid manufactured by 3M and used in many electronics cooling applications. Stainless steel is compatible with most fluids, including corrosive fluids such as deionized water. Several different fluids are compatible with various standard cold plate and heat exchanger materials (Figure 2).

Figure 2: Various fluids are compatible with a variety of standard cold plate and heat exchanger materials

Most liquid coolants also need a small percent of additives to inhibit corrosion and to lubricate the pump. However, it is important to note that corrosion inhibitors can be rendered ineffective by incompatible materials elsewhere in the system, so this must be evaluated as well. Biocides, algaecides, and pH adjustments may also be helpful in maintaining your system, depending on which liquid coolant is selected.

Corrosion Prevention

Corrosion can cause problems two different ways. Not only can material corrode away, which leads to leaks, but the corroded material can be deposited elsewhere in the system and block fluid passages or filters. This can produce a pressure drop that causes reduced coolant flow. In addition, if the deposition occurs on active heat transfer surfaces, the extra thermal resistance caused by fouling can make temperatures rise.

Both galvanic corrosion and erosion-corrosion should be minimized in the liquid cooling loop. Galvanic corrosion occurs when dissimilar metals are in electrical contact with each other in the presence of an electrolyte such as a conductive liquid. Most water-based coolants are electrolytic to some degree. To prevent galvanic corrosion, either the loop should be designed with similar materials throughout the system, ideally with just one metal, or a non-conductive fluid should be used. The galvanic potentials of all materials in the system should be considered. This includes not only the primary thermal components, but also all connectors, fittings, valves, and junctions in the fluid path.

Erosion-corrosion is the acceleration in the rate of corrosion in metal due to the relative motion of a fluid and a metal surface. It is most often found in pipe bends & elbows, tube constrictions, and other structures that alter flow direction or velocity. Erosion-corrosion is most prevalent in soft alloys, such as copper and aluminum.

Some methods for minimizing erosion-corrosion include allowing bends to have larger angles, changing pipe diameters gradually rather than abruptly, and improving flow lines within the pipe by deburring, i.e., smoothing out irregularities. Other methods include reducing the amount of dissolved oxygen, changing the pH, and switching the pipe material to a different metal or alloy. See our application notes “Erosion-Corrosion in Cooling Systems” and “Avoiding Galvanic Corrosion” for more information on corrosion.

Condensation and Liquid Cooling Loop Design

In addition to minimizing corrosion, it’s important to minimize or prevent condensation. One of the risks of using coolants below ambient temperatures is that condensation may form on cool surfaces. This condensation can drip onto electronics or collect in the bottom of the system and cause corrosion. To avoid condensation, surface temperature can be maintained above the ambient dew point by either insulating these surfaces or using higher fluid temperatures. Boyd offers a variety of insulating materials like SOLIMIDE® Foam to maintain line temperatures and prevent condensation and potential damage.

In a properly designed and maintained liquid cooling loop, leaks are very unlikely. However, to minimize the effect of any potential leaks, the reservoir and liquid loop can be located below electronics that would short out if coolant or condensate dripped or sprayed on them. Other options include installing a liquid shield or barrier over the high-voltage portions of the electrical system.

When designing the liquid cooling loop, there is also the option of using standard or custom parts. There are advantages and disadvantages to each. Standards are readily available if replacements are needed. Custom parts, on the other hand, are optimized for the application’s size, performance, and device requirements. However, they will have longer lead times and may have a higher cost.

Joints, Fittings, and Connectors

The number of joints in the cold plate or heat exchanger is important. When there are more joints that must be brazed, there is a higher risk of leaks. It is important to ensure that the manufacturer is highly skilled at brazing, has proper test procedures in place, and eliminates any unnecessary braze points within a custom component.

To prevent leaks, the right fittings must be selected and properly used. For a leak-free joint, a beaded tube fitting mates with a hose that is secured with a clamp. Hard plumbing is generally preferable to hoses, but hoses may be used in environments where systems are exposed to shock or vibration. A unit with a straight tube fitting can be welded into the system or used with a self-locking, torque-free fitting. With a quick-disconnect coupler that isn’t drip-free, you’ll need to expect the occasional drop of fluid when connecting or disconnecting the fittings. For more information, please review our application note on “Choosing a Quick Disconnect Coupler”.

Another option is to use O-rings fittings that are manufactured to Society of Automotive Engineers (SAE) material specifications or those manufactured to military specifications. These fittings are available in various materials and sizes and provide a reliable leak-free seal. Boyd’s O-Ring portfolio and expertise can help ensure you select the right material, certifications, and size quickly to help prevent leaks within your system.

Maintenance and Service

Although maintenance and service may be the last thing engineers consider when designing a liquid cooling loop, including this consideration in the design process will help to reduce problems over the long term. Several different types of questions must be answered.

For example:

• Will the pump need lubrication over its life or is the coolant going to perform that function?
• Will the fluid reservoir need topping off?
• Which components are field-replaceable?
• What is the maintenance schedule?
• What is the required pump life?
• If pump replacement is needed, how does one charge the system and start the system up?

Other questions concern what the user must do to get the system working again.

• Does this require removing the electronics and cold plate, or just the electronics, and can both be easily removed and replaced merely by snapping in a new one?
• If the cold plate is replaced, will it be shipped with cooling fluid?
• Does the OEM ship the system or field-replaceable unit filled with fluid?
• If so, freezing of the fluid may be a concern, such as in aircraft cargo holds that get very cold.

These questions must be considered by members of both design, operations and maintenance teams. Involving all affected individuals in the decision will help to ensure smooth operations in the future.

Materials compatibility, corrosion prevention, condensation control, the position of the liquid cooling loop, standard versus custom parts, joints, fittings, connectors, hoses, and maintenance and service requirements all must be considered when designing either a modified standard or custom liquid cooling loop. When properly integrated into a system, liquid cooling can provide highly effective heat removal with low risk. Today, tens of thousands of cold plates and heat exchangers are liquid cooling electronics in some of the most demanding and high-performance applications.

Written by Richard Goldman and Tracey Barber
Original Published in RTC magazine, July 2006

Visit our Liquid Heat Exchanger Section or Liquid Cooling System Section to learn more about Boyd’s full liquid loop solutions.

The performance of high-powered lasers depends on effective cooling. High-powered lasers generate a significant amount of heat that must be removed from the laser system to avoid overheating critical components.

Optimizing a Laser by improving Liquid Cooling System

Carbon dioxide (CO2) lasers, excimer lasers, ion lasers, solid-state lasers, and dye lasers all use liquid cooling to remove excess heat. Laser liquid cooling helps accomplish three goals: maintaining a precise laser wavelength and higher output efficiency, achieving desired beam quality, and reducing thermal stress on a laser system. Recirculating chillers, liquid-to-liquid cooling systems, ambient cooling systems, cold plates, and heat exchangers are a few of the cooling technologies used in laser systems’ liquid cooling loops.

Low-powered lasers, such as small helium-neon or argon-ion lasers, may not require cooling or may come with their own cooling fan, which is generally sufficient. Some smaller gas lasers and many solid-state lasers contain their own built-in cooling system, usually a closed-loop heat exchanger. Larger gas lasers or other high-powered lasers, such as industrial CO2, large-frame argon- and krypton-ion lasers, and excimer lasers, however, typically require an external source of water flowing through the light-generating section of the laser system.

According to Coherent, Inc, manufacturer of lasers and laser systems, their ion lasers produce between 5kW and 55kW of waste heat as a by-product of the laser action. In order to avoid overheating critical components, Coherent notes the importance of efficiently removing this heat from the laser system and recommends the use of cooling water. Other laser systems may have more or less heat to remove, but the need for cooling remains.

Precise Wavelength, Optical Conversion Efficiency, & Beam Quality

One reason it’s important to remove excess heat from a laser system is that an increase in temperature will result in an increase in wavelength. This wavelength increase can compromise a laser system’s performance. Since diode laser wavelength increases with an increase in temperature, temperature must be uniform throughout the diode arrays in order to have high overall optical conversion efficiency in a pumping application. For example, the wavelength of light emitted from GaAs diode laser bars shifts at a rate of approximately 0.3nm/°C due to temperature related changes in bandgap energy and refractive index. To have a high overall optical conversion efficiency of light from GaAs diode bars in pumping some solid-state lasers, it is critical for the wavelength of light energy from each emitter to be within a very narrow wavelength band or within 1-2°C of each other. Cooling can help to keep the beam aligned in front of the emitter (± 5 microns).

Beam quality is also important in some laser applications. For example, with laser material processing, printing, marking, cutting, and drilling, strong beam focus is required. In high power lasers, the heating of the gain medium, such as the laser crystal, can cause thermal lensing. These thermal effects in the gain medium can affect laser wavefronts and therefore beam quality. With diode-pumped solid-state (DPSS) lasers, the crystal must be cooled and the temperature should be controlled to 0.5°C. (See Figures 1 and 2.)

Reduction of Thermal Stress

Lower operating temperatures can also increase the lifetime of a laser system’s components and reduce maintenance. This is especially true for DPSS lasers, since the mean time between failures (MTBF) is affected significantly by excess heat. It therefore makes sense for laser designers and manufacturers to integrate a cooling system within their laser. This helps ensure that the MTBF is extended and downtime is reduced, saving on operation and maintenance. By integrating a cooling system, it also helps the laser manufacturer ensure optimal laser system performance.

For low heat loads, recirculating chillers are usually the simplest solution as installation is so easy. At high heat loads, liquid-to-liquid cooling systems are more cost effective. However, their use is restricted to situations where chilled facility water is available. The necessity to plumb them into facility water may affect the locations they can be used in and the portability of the equipment.

If you have high heat loads and need to reject the heat to facility water, the choice between an LCS and a recirculating chiller with a water-cooled condenser depends on your set-point temperature. If your set-point temperature is higher than your maximum facility water temperature, an LCS is more cost-effective. However, if you need to cool close to or below the facility water temperature, you will need a refrigerant based chiller with a water-cooled condenser.

Recirculating Chillers

Commercially available recirculating chillers provide convenient cooling for a laser cooling. Compressor-based recirculating chiller coolant temperature can be set to between -5.0°C and 35.0°C and maintain ±0.1°C temperature stability, ensuring that the laser system is operating at the optimal wavelength and as efficiently as possible.

Recirculating chillers are also more environmentally friendly and cost-effective than using tap water. Chillers are closed-loop systems that use active refrigeration. They are used for cooling laser systems when there is a high heat flux, high ambient temperatures, or when a laser system requires a chilled environment, such as with excimer lasers. Typically they have cooling capacities ranging from 800W-6kW, a PID controller, large thermal mass tank, and advanced refrigeration control circuits to ensure that they maintain the tight temperature stability needed for laser system pointing stability and beam quality. In addition, recirculating chillers can provide consistent flow and pressure to the system while maintaining control of the quality of the coolant. It’s important to ensure that appropriate cooling system pressure is maintained, since excessive water pressure can create vibrations in the laser head.

Another benefit of recirculating chillers is that most of them are compatible with a variety of fluids. For example, many recirculating chillers are compatible with ethylene glycol (EGW) or propylene glycol (PGW) solutions, which offer corrosion and freeze protection. A recirculating chiller can also be fitted for compatibility with deionized (DI) water, including a DI cartridge to maintain a system’s required resistivity. (DI water is electrically inert.)

Liquid-to-Liquid Cooling Systems

Like a recirculating chiller, a liquid-to-liquid cooling system (LCS) offers precise temperature control of process water (fluid temperature to within ±0.5°C). However, it transfers heat to facility water via a liquid-to-liquid heat exchanger. An LCS is a solution for high heat-load or high ambient temperature applications where chilled facility water is available, as an LCS often has cooling capacities up to 20kW. For laboratories with several large lasers, an economical option may be the installation of a cooling tower on the roof of the facility to provide a common source of cooled water to all systems within the building. The cooling tower will exhaust heat outside of the building, helping to maintain a comfortable work environment. With an LCS, the facility water never comes in contact with laser system water. The heat is transferred from the cooling system fluid to facility water via the liquid-to-liquid heat exchanger. This is important because the water that circulates from facility cooling towers is often treated with fungicides, algaecides, and/or antifreeze, which may be too harsh for some laser components.

Ambient Cooling Systems

Ambient cooling systems, which have cooling capacities up to 3.5 kW, are a reliable alternative to refrigerated chillers and LCS for laser applications where precise temperature control and cooling below ambient temperature are not required. An ambient cooling system consists of a high performance heat exchanger, a fan, a pump, and a reservoir. Heat is moved from water circulating through the laser system into ambient air by a liquid-to-air heat exchanger and fan, hence the term “ambient cooling system”. Ambient cooling systems do not provide temperature stability, but they are a cost-effective means for heat dissipation.

Cold Plates & Heat Exchangers

Cold plates and heat exchangers are key components in liquid cooling loops for laser cooling. Cold plates are often used in conjunction with a recirculating chiller. Many lasers use tubed cold plates. However, aluminum vacuum-brazed cold plates that have liquid flow through channels are one type of cold plate more and more laser manufacturers are selecting. Manufacturers and end-users also use flat tube cold plate technologies. A cold plate may be mounted to the component requiring cooling, such as a thermoelectric, and will receive cold fluid from the chiller and transfer hot fluid back to the chiller. (See Figure 3.) Cold plates can also be designed as the electrodes of the laser system.

Heat exchangers are often found within cooling systems, such as chillers, LCS, and ambient cooling systems. Some laser manufacturers prefer to purchase a heat exchanger separately and integrate it themselves, connecting it to their own pump and reservoir.

Cooling Lasers with Liquid

High-powered laser systems require cooling for optimal performance and longevity. If maintaining a precise laser wavelength, beam quality, high output efficiency, and up-time are important, liquid cooling may be the answer. Recirculating chillers, LCS, ambient cooling systems, cold plates, and heat exchangers are becoming critical components in laser systems.

References

To determine outgoing temperature of the air, we use the ‘Air Flow’ chart using parameters 250 CFM and 2400 W.

Coherent®, “Laser Cooling Water Guidelines for Innova® Ion Laser Systems” p. 1.

Huddle, J.J., Chow, L.C., Lei, S., Marcos, A., Rini, D.P., Lindauer, S.J., II, Bass, M., and Delfyett, P.J., “Thermal Management of Diode Laser Arrays”, Semiconductor Thermal Measurement and Management Symposium, Sixteenth Annual IEEE, pp. 154-160, 2000.

Paschotta, R., “Thermal Lensing“, Encyclopedia of Laser Physics & Technology 2007.

This simple step-by-step guide explains the different types of cooling systems available and highlights how to select the right product for your application.

Considerations to Picking a System for Your Application

The first consideration is whether you need precise temperature control or need to cool below ambient (air) temperature. If you can answer ‘no’ to both of these, you are looking for a cooling system that will simply remove bulk heat. The most cost effective solution is an ambient cooling system.

The biggest cost drivers for aluminum cold plates, after those mentioned above, are machining time and additional processing steps. Cold plate manufacturers typically have a cost associated with machining time which covers depreciation costs of the machine, power, supplies, and maintenance. Therefore, the longer the cold plate sits in the machine the more costly it is. Each additional processing step continues to drive the cost up.

Ambient Cooling Systems

There is no temperature control circuit, so an ambient cooling system does not maintain a pre-set temperature. Since the ambient air provides the cooling, the ambient temperature is the lower limit for the fluid exit temperature.

Although they appear simple, ambient cooling systems are engineered for maximum capacity. The cooling system manufacturer’s thorough understanding of heat exchanger performance allows the liquid flow rate and air flow rate to be performance-matched to extract the most cooling capacity from the system. The plumbing is designed for high reliability and components are carefully selected to avoid any galvanic corrosion issues. An off-the-shelf ambient cooling system is extremely easy to use – simply connect the fluid inlet / outlet fittings to your equipment, fill the tank and turn it on!

But what if you need to control the temperature or cool below room temperature? Recirculating chillers and liquid-to-liquid cooling systems are both good alternatives.

Recirculating Chillers

Recirculating chillers offer precise temperature control (within 0.1°C) and cooling below ambient temperature. They are quiet, cover a wide range of cooling capacities, and are available with many different options and additional features. Recirculating chillers are compact, quiet and easy to install.

Recirculating chillers use refrigerant for cooling. They operate in a similar way to your refrigerator at home, except that they cool water instead of air. The process water circuit includes an evaporator, tank, and pump. The water is cooled by the refrigerant as it passes through the evaporator. On the other side of the evaporator the refrigerant evaporates to cool the water, then passes through a compressor and condenser, rejecting the heat to the ambient air.

When heat loads get high, chillers can cause the room’s air conditioning system to become overloaded as they reject the waste heat into the ambient environment. One option is to use a chiller with a liquid-cooled condenser. In this case, the refrigerant is cooled by facility-chilled water instead of air, making the chiller quieter and avoiding room-warming problems.

Another alternative for high heat loads is a liquid-to-liquid cooling system.

Liquid-to-liquid Cooling Systems (LCS)

The process side circuit is completely isolated from the facility water, protecting your equipment from fluctuations in temperature, flow rate of the facility water and any contaminants that may be present. Since the facility water provides the cooling, the facility water temperature is the lower limit for fluid exit temperature.

Liquid-to-liquid cooling systems are popular for high heat load applications as they are compact – approximately 1/3 the size of a refrigerant-based chiller of similar capacity. Without a compressor, they are also very quiet and energy efficient.

Recirculating chiller or liquid-to-liquid cooling system?

For low heat loads, recirculating chillers are usually the simplest solution as installation is so easy. At high heat loads, liquid-to-liquid cooling systems are more cost effective. However, their use is restricted to situations where chilled facility water is available. The necessity to plumb them into facility water may affect the locations they can be used in and the portability of the equipment.

If you have high heat loads and need to reject the heat to facility water, the choice between an LCS and a recirculating chiller with a water-cooled condenser depends on your set-point temperature. If your set-point temperature is higher than your maximum facility water temperature, an LCS is more cost-effective. However, if you need to cool close to or below the facility water temperature, you will need a refrigerant based chiller with a water-cooled condenser.

Selecting a Modular Cooling System

Calculate Which System You Need

MCS performance is shown as Q/ITD versus flow rate. Q is heat load, and ITD is the initial temperature difference, or the difference between MCS liquid inlet temperature and ambient air temperature.

To select the correct MCS system, you first need to determine Q/ITD. Then, using the MCS performance graph, draw a horizontal line at the calculated Q/ITD value. Finally, check that the pump will provide sufficient flow rate.

Example:

A laser produces 700 W of waste heat. The water temperature exiting the laser should be less than 35°C. Ambient room temperature is 20°C. The laser equipment requires a flow rate of at least 1 gpm. Which MCS system should be selected?

First, determine Q/ITD Q/ITD = 700 W/(35°C-20°C) = 46.7 W/°C

Using the thermal performance graph, you can see that at flow rates above 0.5 gpm, MCS20 will provide adequate performance. The standard BB pump offers a flow rate of 1.3 gpm so it will work well. If you are considering an alternative pump, use the pump flow rate calculation to verify that with the given pressure drop, flow rate will be sufficient.

Selecting a Liquid-to-Liquid Cooling System

How to Calculate which Liquid-to-Liquid Cooling System is Right for Your Application

In most Liquid-to-Liquid Cooling applications, we know the temperature of facility water (TF), the desired process set-point temperature (TP), the flow rate through the process ( P) and the heat load of the process, Q.

To determine the required capacity, Q/ITD, we first need to calculate the change in temperature, ΔT, through the process. We can do this either by solving the heat capacity equation:

or by using the heat capacity graphs found in our Thermal Reference Guide.

Next, we calculate Q/ITD to find the required cooling capacity. Q is the process heat load. ITD, the initial temperature difference, is the difference in temperature between warm return water, (TP+ ΔT) and cold facility water (TF).

Finally, refer to the Liquid Cooling System (LCS) performance curves to determine the facility process flow rate required to achieve calculated Q/ITD.

Example Liquid-to-Liquid Cooling System Calculation

Referencing the LCS performance graph, we can see that a facility flow rate above 2 gpm will meet required performance.

Conclusions for Selecting a Liquid System

Ultimately, the required cooling capacity, temperature stability, set-point temperature, and availability of facility cooling water will dictate which system to use. For further assistance in choosing a cooling system, contact our thermal design engineers to discuss your specific application requirements. Based on inputs such as your heat load and required flow rate, it will even recommend an appropriate product.