The Flight Path to Zero Emissions Aviation's transition to zero-emission propulsion is one of the greatest engineering challenges of our time. While battery technology lags behind the power needs of large aircraft, superconducting electric propulsion systems cooled by liquid hydrogen (LH2) offer a viable, scalable solution. At the heart of this innovation lies a crucial component: the cryogenic heat exchanger.

Why Cryogenic Cooling is Key Superconducting motors can achieve extraordinary power densities (>20 kW/kg) and efficiencies (>98%) but only if maintained at ultra-low temperatures (around 20 K). LH2, already on board as fuel, serves as an ideal coolant, turning heat exchangers into mission-critical enablers for efficient and lightweight thermal management.

Design Drivers and Performance Demands For a 3MW superconducting motor, the heat exchanger must:

  • Operate near 20K to maintain superconductivity
  • Withstand heat loads of 2-4 kW, mainly from stator AC losses
  • Maintain effectiveness above 95%, ideally 98%
  • Survive pressures from 1-15 bar
  • Meet stringent aerospace certification (EASA CS-25)
  • Minimise weight to support a powertrain target of >20 kW/kg

The Manufacturing Frontier: Traditional vs Additive Traditional methods like brazed plate-fin and diffusion-bonded exchangers struggle with weight, hydrogen compatibility, and design flexibility. Additive Manufacturing (AM) presents a breakthrough:

  • Laser Powder Bed Fusion (L-PBF) enables fine features and complex internal geometries like TPMS lattices for high thermal performance.
  • Materials like Scalmalloy® CX, developed for cryogenic and hydrogen use, combine strength, thermal conductivity, and embrittlement resistance.

Challenges in Additive Manufacturing Realising these benefits isn’t trivial:

  • Porosity and residual stress must be managed via process control and post-treatments like HIP.
  • Wall thickness optimization must balance strength, thermal transfer, and leak-tightness.
  • Certification under CS-25 requires rigorous testing: CFD, FEA, cryogenic hydrogen testing, and NDT techniques like CT scanning and ultrasonic testing.

Smart Design: Topology and System Integration Advanced computational tools support multi-objective optimization (thermal performance, pressure drop, weight). Using generative design and TPMS structures, engineers can:

  • Maximise heat transfer per unit mass
  • Reduce pressure drops
  • Integrate ports, sensors, and mounts into a single printed part

Material Matters: Scalmalloy® Leads the Pack Scalmalloy® CX stands out as a strong candidate:

  • High strength-to-weight ratio
  • Proven ductility and toughness at 20 K
  • Designed for AM and compatible with hydrogen exposure

Conclusion: Engineering the Future of Flight Cryogenic heat exchangers are the unsung heroes in the journey to net-zero aviation. By combining superconducting motors with advanced additive manufacturing and smart design, we can unlock efficient, scalable, and certifiable propulsion systems for the next generation of aircraft.

As we move from theory to test and from prototype to flight, collaboration across materials science, thermal engineering, and aerospace certification will be vital.

The sky is no longer the limit—it's the proving ground.

‍