Overcome Thermal-Management Challenges in Rugged-System Design to Optimize SWaP-C
What you’ll learn:
- Thermal management for rugged systems with SWaP-C constraints, balancing size, weight, and heat.
- Active, passive, and hybrid cooling strategies for improved thermal performance.
- Board-level techniques, efficient enclosures, and power management to help minimize heat.
In state-of-the-art rugged system design today, SWaP-C (size, weight and power plus cost) optimization remains key to the design process, especially for defense, aerospace, and industrial applications. The demand for small-size, lightweight systems with low energy consumption is continuously growing, while relentless pressure remains on reducing production costs while meeting standards like SOSA, CMOSS, and HOST.
Among the most important variables driving SWaP-C optimization, thermal management takes center stage. Good thermal management is a must for long-term system performance and reliability—particularly if it's a ruggedized system that will be exposed to severe environments.
Poor heat dissipation causes overheating, leading to reduced performance, safety, and life expectancy of electronic components. The highest power consumption, caused by thermal inefficiency, further compromises the target SWaP-C for each application. Therefore, new thermal solutions become critical to sustain system performance and stability.
This article updates the advanced thermal-management strategies and techniques used to find the solutions for these challenges. The designers will be able to reach an optimal solution in balancing the constraints of size, weight, power, and cost with respect to thermal performance by incorporating the latest cooling methods. The following sections explore these solutions for insight into their implementation in rugged systems for SWaP-C optimization.
The Role of Thermal Management in Rugged Systems
Rugged systems are designed to operate dependably over a broad range of extreme environmental conditions: temperature, humidity, dust, shock, and vibration. Such mission-critical systems are applied in many industries, including military, aerospace, and heavy industrial sectors. Examples include communications devices, control systems, avionics, and sensor platforms that must operate in the harshest of environments while delivering optimal functionality.
Good thermal management is especially crucial for the reliability and longevity of such systems. For these “ruggedized” systems to work, temperature within them must be managed and dissipated correctly. The several active components, mainly processors, power modules, and memory devices, all emit heat during their functions.
Temperature rise degrades materials, hastens aging, and reduces the service life of electronics. In extreme cases, a system failure due to the inability to maintain the temperature may reach dangerous situations that disrupt operations and result in expensive downtime or even mission failure.
Poor thermal management thus has great implications for system efficiency and performance. In most cases, when overheating occurs, components throttle their performance to prevent further damage. This results in reduced processing power, slow response time, and inefficiency in power usage.
Furthermore, driving demands in SWaP-C have resulted in smaller-sized electronics and integrated circuits, making the challenge of heat dissipation even more difficult. This compact nature of rugged systems allows for very little room for any traditional cooling methods, therefore necessitating creative and integrated thermal management.
Thermal-Management Challenges in SWaP-C Constrained Designs
Rugged system design under SWaP-C constraints presents different challenges to thermal management. The more compact, lightweight, and power-efficient systems become, the more tightly heat-dissipation management ties to performance without a corresponding increase in costs. Every element of SWaP-C brings its set of challenges that need to be dealt with, without losing the overall system reliability or functionality.
Balancing Size and Weight
One of the fundamental challenges of any SWaP-C-constrained design is the balance of size and weight with effective thermal management. Traditional cooling solutions like liquid-cooling systems can be quite bulky by themselves. These prove to be very problematic to integrate into rugged applications, where every space and weight must be utilized very efficiently.
Systems are increasingly miniaturized to meet constraints on size and weight, ultimately increasing the density of the heat. Hence, more heat has to be managed in a very small volume. Extra strain is therefore put on the thermal-management system, which has to function more efficiently within limited space with low weight. Optimizing the design for lightweight yet highly effective thermal solutions becomes critical to avoid tradeoffs that can impact the overall system's SWaP-C goals.
Handling Power Dissipation
Another major challenge with power-dense systems is how to manage the heat without consuming more energy. Lots of heat is generated by high-performance electronics, especially in those power-dense applications like processors, power converters, or RF amplifiers.
However, this goes against the intention of minimizing overall energy usage by increasing power consumption for the thermal-management system. Efficiency in the thermal-management solution is, therefore, of prime importance to ensure that heat is dissipated effectively while keeping additional power requirements at a minimum.
Some of these innovative solutions, such as passive cooling techniques like phase-change materials, can control the heat dissipation effectively without increasing energy consumption. Equally, incorporating simulation tools such as computational fluid dynamics (CFD) in designs for modeling and optimizing thermal performance in advance without prototype creation is important. This will minimize unnecessary power consumption while ensuring the heat will be handled appropriately.
Meeting Cost Considerations
Active cooling systems, or custom-designed heat exchangers, can raise the overall cost of a system. Most of the time, the project budget will not allow it, and designers need to balance the performance provided with financial consequences.
Most rugged systems, though, have a budget that's set by mission or commercial demands in the broader system. The thermal-management solution must meet performance and reliability needs for the system, but within cost constraints. The right balance between affordability and advanced thermal performance is critical to the overall success of SWaP-C-optimized designs.
Considering the Operating Environment
Besides size, weight, power, and cost limits, many rugged systems must operate in extreme environmental conditions, further complicating thermal management. Environments with extreme ranges of temperatures, rates of temperature change, shock, and vibration will impact performance of the thermal-management solution itself, but also the reliability of the electronics being managed.
Such factors include very extreme ambient temperatures, such as in desert or high-altitude applications, which drive systems to the edge of their thermal operating envelope and, therefore, make cooling even more difficult. In such applications, thermal solutions must be not only efficient, but also ruggedized against environmental stresses, creating more complexity in the design process. In these challenging environments, solutions that incorporate vibration damping with heat dissipation or utilize shock-resistant designs are often required.
Innovative Thermal-Management Strategies
Designers overcome thermal-management challenges in SWaP-C-constrained rugged systems by using innovative cooling strategies that strike a good balance between efficiency, compactness, and cost-effectiveness. Some of the key innovations in thermal management are reviewed below.
Why Choose Active Cooling Solutions?
Active cooling solutions include liquid cooling and pumped two-phase systems, in addition to fans, which generally are an effective method of heat management in rugged systems with high thermal loads.
Fans are the most prevalent means of active cooling, operating via forced convection to pass air over heat-generating components. Their mechanical nature also makes them vulnerable to failure when operating in environments featuring large-sized dust and sand, or with extreme levels of vibration as present in military and industrial applications. Depending on environmental conditions, IP-rated fans can be selected to prevent dust and water ingress in harsh conditions.
Liquid-cooling systems circulate coolant through a network of channels or cold plates (Fig. 1) and provide a more efficient method for high-power systems. Several cold plates can oftentimes be manifolded to provide liquid cooling to multiple components or systems.
Liquid cooling is especially helpful in systems that are densely packed and where airflow may not be substantial. The addition of liquid cooling adds some amount of complexity: pumps, reservoirs, and leak management.
Pumped two-phase systems represent an advanced form of liquid cooling. These systems leverage the phase change of a working fluid for highly effective heat transfer. The working fluid, while evaporating, absorbs significant amounts of heat while enabling very compact cooling solutions. Though highly effective, such systems are more costly and challenging to implement and may require custom design for the specific needs of a rugged system.
Why Use Passive Cooling Techniques?
When there are limitations on power consumption and space, passive cooling techniques become potential alternatives: heat pipes, thermosyphons, and vapor chambers to name a few. These solutions depend on natural heat transfer mechanisms to eliminate components that may consume power, like fans and pumps.
Heat pipes are extremely effective heat conductors that leverage phase change to transport heat away from a hot component to a cooler area. By its nature, the heat pipes are lightweight and compact, which again makes them ideal in cases of SWaP-C-constrained designs. However, designs can be limited depending on operating temperatures and environmental conditions.
Thermosyphons are very similar in operation to heat pipes, but they depend on gravity for the fluid circulation and, hence, are strictly applied in vertical systems where the heat-generating components (evaporator) are below the cooling region (condenser). They’re simple, reliable, and require no external power, though their orientation dependence can limit applicability in certain designs (Fig. 2).
Phase-change materials (PCMs) absorb and store thermal energy as they change phase from solid to liquid. Considering their properties, PCMs are suited for applications where short bursts of heat must be managed; for example, systems experiencing intermittent spikes in power. They help prevent overheating by temporarily absorbing excess heat, which can later be dissipated over time.
Mixing Active and Passive Cooling with Hybrid Approaches
In some cases, optimal SWaP-C is achieved using a hybrid solution involving both active and passive techniques. Common solutions might include heat pipes to spread or move the heat while fans or liquid-cooling systems are the primary heat-rejection technologies (Fig. 3). Consequently, this approach may give room for more critical cooling of components, with a smaller size and less power consumption for the overall cooling system.
Simulation and Testing Tools for Thermal Optimization
Modern simulation and test tools assist designers in predicting thermal behavior and making design optimizations early, thus reducing costly revisions later in development. These tools smooth the way and lighten the load of thermal design, mitigating overheating and other thermal-related failures in SWaP-C-constrained systems.
Thermal simulation software at the very early design phase in systems provides the designer with a virtual platform to model and predict the heat distribution and cooling performance. Detailed CFD and thermal analysis enable designers to simulate the dissipating heat in a number of operating conditions prior to prototyping.
Simulation software lets engineers play with various design parameters, such as heatsink placement, airflow paths, and material selections, which will show the thermal bottlenecks inhibiting heat transfer and generally optimize cooling mechanisms within SWaP-C constraints. Early-stage simulation enables fast and easy modifications to system layouts, making it easier to meet goals for size, weight, and power with cost before freezing a design.
Simulation results provide a major source of insight into component behavior and allow the designer to predict thermal issues that might otherwise not be considered. These tools also let engineers investigate a range of different scenarios, such as thermal performance during extreme environmental conditions, where they can learn to anticipate and design out many issues with rugged-system designs.
Importance of Iterative Testing and Validation Under Real-World Conditions
While simulation tests are invaluable during the design phase, physical validation of theoretical models is crucial to make sure that the system operates correctly under real conditions. Real-world testing is critical for rugged systems that undergo extreme conditions that are impossible to simulate comprehensively.
As an example, a simulation might illustrate that there’s sufficient heat dissipation for nominal conditions. However, in real life, dust accumulation, component aging, or shifting temperatures of the surrounding ambiance could deteriorate performance.
Physical testing includes functional testing and environmental stress tests of thermal cycling, vibration, and shock that measure the effectiveness and robustness of cooling mechanisms. These tests ensure the thermal-management solution developed for the system is robust enough to handle the operational stresses it will encounter in the field.
Design Techniques for Minimizing Heat in SWaP-C Designs
The ultimate goals for all systems constrained in SWaP-C are minimizing heat generation and optimizing the dissipation of heat. With the incorporation of thoughtful design techniques on boards, packaging, and power management, engineers can stay within their design margins while keeping thermal loads as low as possible.
Board-Level Techniques for Heat Management
Among the basic approaches to heat management at a circuit-board level, proper component placement and thermal vias stand out, as does integration of heat spreaders.
- Component placement: The location of heat-generating components is critical for appropriate heat spreading and prevention of thermal hotspots. The high-power components, like processors and power converters, need to be kept away from other sensitive heat-sensitive elements in the circuitry.
- Thermal vias: These are vertical heat-transferring avenues drilled through a printed circuit board (PCB) to transfer heat from one layer of the board to another or to any heatsinks. By offering a route for heat to move away from hot components, thermal vias help lower the localized heat concentration and spread heat more evenly across the PCB. They’re most helpful in multilayer boards where space is minimal to effectively transfer heat from the surface-mounted components either to cooler internal layers or to a heatsink.
- Heat spreaders: Thin metal plates or layers of material that are highly thermally conductive, such as copper or graphite, may be provided in the PCB as heat spreaders. Spreaders help distribute the heat over a larger area to avoid localized heat buildup around the critical components.
Enclosure and Packaging Considerations
Enclosure and packaging design is also critical for heat-dissipation management in compact systems. The enclosures of rugged systems must strike a balance between internally protecting components against extreme environmental conditions and allowing for effective heat transfer.
Enclosure design can have tremendous influence on the thermal performance of a system. In SWaP-C-bound designs, for example, enclosures must often be small and light, with limited room for large heatsinks or large and robust fans. Instead, designers must concentrate their efforts on selecting the materials and shapes of an enclosure that will maximize the dissipation of heat.
Enclosures could utilize aluminum alloys to make the enclosure act as a passive heatsink to conduct heat away from the internal components and dissipate it to the external environment. In this respect, the shape and surface area of the enclosure may be optimized—for instance, by adding fins or ribs, which increase the surface area—to reinforce natural convection and radiation-based cooling without implication for an increased overall size of the enclosure.
If the environment is more extreme, then sealed enclosures may be required to protect against dust, moisture, and chemical exposure. In such circumstances, one enclosure cooling method utilizes heat pipes to transfer the heat between the enclosure and the environment while utilizing fans to actively cool the enclosure using ambient air (Fig. 4).
Power-Management Strategies
In any electronic system, the amount of power consumed is directly proportional to the amount of heat generated. By making power management more efficient both at component and system levels, the engineer can reduce the heat output. This can be as simple as choosing power-efficient-rated components. At the system level, minimizing the losses due to resistance within the paths of power delivery means less power will be wasted as heat, which further contributes to a better system thermal profile.
Real-World Examples of Successful Thermal Management in Rugged Systems
Advanced Cooling Technologies (ACT) combined HiK heat spreaders and liquid cold plates to manage 2,880 W of heat in a ruggedized electronics chassis. The design uses heat pipes to isolate sensitive electronics from potential liquid-cooling loop failures, enhancing durability and minimizing risks in demanding environments. Rigorous testing confirmed the system's effectiveness, with predicted and actual performance closely aligned.
This hybrid solution provides reliable thermal management for high-power electronics, ensuring robust performance even in rugged, high-stress conditions. For more details, check out ACT's case study.
Thermal Management: Today and Tomorrow
Typically, the most difficult area in the design of rugged systems—thermal management—often represents an optimal balance of SWaP-C. Systems have become smaller, lighter, and more power-efficient; however, ways of managing heat effectively to maintain system reliability are getting increasingly difficult.
Military, aerospace, and industrial systems all have one thing in common: Finding the perfect thermal solution that will ensure the longevity of a system, as well as operational performance and mission success.
These issues can only be addressed if thermal planning is integrated early in the design process. Advanced simulation tools utilize innovative cooling strategies and efficient design techniques at both board and enclosure levels to optimize thermal performance well before physical prototyping even begins. This proactive approach minimizes the probability of thermal bottlenecks, saves huge amounts in development cost, and makes for systems with no compromise in performance or durability to meet the SWaP-C goals.
The future of thermal management in rugged systems will be aided by further advances in materials, cooling technologies, and simulation tools. The potential for innovation in hybrid cooling solutions, passive heat-management techniques, and the use of advanced materials like PCM will be pushed by the demand to make systems more compact, lighter, and energy-efficient. As system complexity grows, thermal management will remain at the center of providing high-performance rugged systems reliably.
