As the aviation industry accelerates its transition toward electric, hybrid, and fuel cell-based propulsion, new thermal management challenges are emerging. Energy must be managed extremely efficiently in order to maximize aircraft range. These next-generation aircraft systems demand cooling solutions that are lightweight, efficient, and reliable, and the systems typically used today are not up to the task. The Challenge: Managing Heat in Next-Gen Aviation

Modern aircraft propulsion systems generate high power, leading to excessive waste heat that must be dissipated effectively. The challenges extend beyond heat dissipation:

• Limited space and weight constraints
• High levels of vibration in flight environments
• Safety and reliability concerns
• Excess electrical energy consumed by cooling systems reduces range

As per the description from the Therma4HERA project, next generation of hybrid-electric aircraft will generate up to 20 times more waste heat than today’s jets, highlighting the growing challenge of thermal management in electrified aviation. Current thermal management systems handle only 35-50 kW, while future aircraft will need to dissipate 300-1,000 kW from batteries, fuel cells, and power storage systems.

Without advanced cooling innovations, the viability of electrified aviation remains uncertain. Research from institutions such as NASA and the European Union Aviation Safety Agency (EASA) has consistently highlighted the need for more efficient thermal management strategies to ensure the safety and efficiency of next-generation aircraft.

NASA’s High-Efficiency Electrified Aircraft Thermal Research (HEATheR) program emphasizes the necessity of novel cooling strategies to handle the extreme thermal loads in electric propulsion systems. This includes the development of high-performance heat exchangers, optimized thermal architectures, and advanced materials to improve heat dissipation while maintaining lightweight and compact designs. These efforts are crucial to preventing overheating, reducing energy consumption, and ensuring operational safety in future electrified aviation systems.

EASA’s Hybrid-Electric Propulsion System (EHPS) Progress and Roadmap also outlines Europe's strategic approach to addressing thermal management challenges, with a strong emphasis on thermal runaway prevention. As battery energy densities increase, the risk of thermal runaway, a chain reaction that can lead to overheating and catastrophic failure, becomes a critical safety concern. The EU is focusing on the integration of advanced thermal insulation materials, early detection systems, and improved passive and active cooling mechanisms to mitigate these risks and ensure the safe operation of hybrid-electric aircraft.

The Potential of Two-Phase Cooling

Two-phase cooling is emerging as a promising alternative to conventional air and liquid cooling. By utilizing phase-change heat transfer mechanisms, this technology offers:

• Superior heat dissipation due to vaporization with minimal weight impact (no pumps).
• Resilience to acceleration and vibration, making it ideal for aircraft applications.
• Scalability, allowing integration into various aircraft architectures, to cool various components.
• Zero-maintenance, due to ultra reliable systems with no moving parts

This potential is reflected both in historic use of these technologies and continuing research within the field. Here are a few highlights I found during my research for this article:

• NASA Goddard Thermal Branch - Two-Phase Cooling Systems
• National Aerospace Laboratory (NLR) - Benefits and Drawbacks of Using Two-Phase Cooling Technologies in Military Platforms
• Military Embedded Systems - Two-phase cooling meets the challenges of modern radar applications

Remember, most two-phase early applications were in the space sector, and while aviation is different, many of the same factors still apply.

Calyos' Research and Development Contributions

At Calyos, we have been actively contributing to research and development efforts through several key EU-funded projects and technical studies.  This includes:

• The TheMa4HERA project, which is developing and testing innovative thermal management technologies for hybrid electric aircraft, addressing the challenge of dissipating heat in the range of 300 to 1,000 kW. The project includes the development of a full digital twin to simulate and optimize component-level requirements, as well as validation in a full-scale test facility to ensure real-world applicability.
• The HE-ART project, which will demonstrate the viability of a hybrid electric turboprop within a dedicated full-scale ground test demonstrator. By integrating an electric drive train with an ultra-efficient thermal turboprop engine and 100% sustainable aviation fuel compatibility, the project aims to improve efficiency and reduce greenhouse gas emissions by up to 30%. The initiative will incorporate cutting-edge technologies, including core thermal engine advancements, an electric drive train, electrical distribution systems, a gearbox, a propeller, a nacelle, and a heat exchanger.
• The JOIN-EM project, focused on solving the challenges of manufacturing lighter, safer, and more efficient thermal management systems for next-generation aircraft through electromagnetic pulse welding (EMW) of copper-aluminium hybrid components.
• The BISANCE project, making green aviation even greener with an autonomous biphasic system to simultaneously cool engine oil and provide ice protection.

Image Source: Calyos

These projects, supported by the European Union’s Horizon program, highlight the growing recognition of two-phase cooling as a crucial enabler of future aerospace technologies.

Calyos also recently presented two papers at the Joint 22nd International Heat Pipe Conference and the 16th International Heat Pipe Symposium in Thailand:

• Experimental investigation of the effect of the vibration on the operation of the direct contact condensation “box” component of a Capillary Jet Loop
• Heat Transfer Performance of a Six-turn Pulsating Heat Pipe for Aeronautical Application under Vibration Environment

Shaping the future of aircraft cooling

By combining our research events, and our proven expertise together with aviation clients we believe we can continue the development of innovative two-phase solutions that will help support the future of sustainable aviation.

Our two-phase cooling solutions offer a compelling combination of efficiency, reliability, and scalability that will appeal to engineers as they look to solve new thermal challenges.

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