Cryo, Volume 1, Issue 1 (March 2025) – 5 articles

The integration of more-electric technologies into aero-engines has revolutionized their multi-power architectures, substantially improving system maintainability and operational reliability. This advancement has established more-electric systems as a cornerstone of modern aerospace electrification research. Concurrently, liquid hydrogen (LH₂) emerges as a transformative solution for next-generation power generation systems, particularly in enabling the transition from 100 kW to megawatt-class propulsion systems. Beyond its superior energy density, LH₂ demonstrates dual functionality in thermal management: it serves as both an efficient coolant for power electronics (e.g., controllers) and a cryogenic source for superconducting motor applications. This study systematically investigates the electrification pathway for LH₂-fueled aero-engine multi-electric systems. First, we delineate the technical framework, elucidating its architectural characteristics and associated challenges. Subsequently, we conduct a comprehensive analysis of three critical subsystems including LH₂ storage and delivery systems, cryogenic cooling systems for superconducting motors, and Thermal management systems for high-power electronics. Finally, we synthesize current research progress and propose strategic directions to accelerate the development of LH₂-powered more-electric aero-engines, addressing both technical bottlenecks and future implementation scenarios. Full article

Reciprocating liquid hydrogen pumps are essential equipment for hydrogen refueling stations with liquid hydrogen stored. The valves play a crucial role in facilitating unidirectional flow and the pressurization of liquid hydrogen within the pump. This paper establishes a comprehensive numerical model to simulate the whole working cycle of a reciprocating liquid hydrogen pump. The influence of valve parameters and pump operating conditions on the motion characteristics of valves, including lift, closing lag angle, and impact velocity, is investigated. The results indicate that with the maximum lift of the suction valve at 10 mm and the discharge valve at 5 mm, the closing lag angle is minimal, and the impact velocity of the valve falls within an acceptable range. The optimal rotation speed range is between 200 and 300 rpm, within which both the closing lag angle and impact velocity of valves are minimized. Excessive maximum lift and low rotational speed lead to significant oscillations and high impact velocity in valve movement with the effects being more pronounced in the suction valve. The effects of the subcooling degree of inflow liquid hydrogen on the valve motion are further analyzed. The findings suggest that the subcooling degree of inflow liquid hydrogen helps inhibit the vaporization in the pump operation and ensures the valves work correctly. This work would contribute to pump optimization and valve collision failure analysis in reciprocating liquid hydrogen pumps. Full article

A balanced flowmeter not only inherits the advantages of orifice plate flowmeters but also stabilizes the flow field, reduces permanent pressure loss, and effectively increases the cavitation threshold. To perform an in-depth analysis of flow characteristics through the perforated plate and achieve performance optimization for the liquid hydrogen (LH₂) measurement, a numerical calculation framework is established based on the mixture model, realizable turbulence closure, and Schnerr–Sauer cavitation model. The model is first evaluated through comparison with the liquid nitrogen (LN₂) experimental results of a self-developed balanced flowmeter as well as the measuring setup. The flow coefficient and pressure loss coefficient are especially considered, and a comparison is made with the orifice plane considering cavitation and non-cavitation conditions. The cavitation cloud and temperature contours are also presented to illustrate the difference in the upper limit of the Re between water, LN₂, and LH₂ flow. The results show that compared to LN₂ and water, LH₂ has a larger cavitation threshold, indicating a wider range of Re number measurements. Full article

Despite the numerous benefits of high-temperature superconducting (HTS) power transformers, they are highly sensitive and vulnerable from a thermal perspective, particularly under fault current conditions due to their fault current tolerance properties. Ensuring the proper operation of the cooling system can enhance the transformer’s performance during fault and overload conditions. To improve the thermal management of this transformer in both convective heat transfer and nucleate boiling conditions, utilizing liquid nitrogen (LN₂) nanofluid instead of conventional LN₂ is a promising solution. In this study, a two-phase Eulerian model using ANSYS Fluent software is employed to analyze the impact of different volume fractions (VFs) of Al₂O₃ nanoparticles with a 40 nm diameter on the cooling performance of a power HTS transformer. The numerical simulations are conducted using the Ranz–Marshal method for heat transfer and the finite element method for solving the governing equations. Nanoparticle concentrations ranging from 0 to 1% are evaluated under various fault conditions. Additionally, the influence of nanoparticles on bubble behavior is examined, partially mitigating the blockage of cooler microchannels. The simulation reveals that adding nanoparticles to the fluid reduces the temperature of the hotspot by 29% in steady state and by 34–52% under different fault currents as a result of 0–46% enhancement of nucleate boiling heat transfer, thereby improving the cooling efficiency of the transformer. Full article