bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vibration-Free 40-80K Turbo-Brayton Cryocooler and its Very High Efficiency Recuperator for Earth Observation Instruments
Authors: Dalban-Canassy M , Rehayem E , Ungureanu A , Salquebre Q , Berindei J 
Published: July 2024

Abstract
Several studies have demonstrated that Reverse Turbo-Brayton cryocoolers could be the next space cryogenic revolution, thanks to their capability to provide vibration-free remote cooling in the temperature range of 4 to 150K and for medium to high cooling powers. With this motivation, Absolut System developed a very low vibration 40-80K Reversed Turbo-Brayton cooler, work performed under the ESA Technical Program Technical Research Program - 4000113495/15/NL/KML. The cooler is based on two turbo-compressor stages, a high efficiency recuperator and a cryogenic turbo-expander, for operation between 300 and 40K. Following the fabrication of the cooler, we performed tests on both individual components, compressors, expander and recuperator as well as on the complete cooler. The turbomachines use aerodynamic bearings, i.e. contactless bearings, generate very little vibrations and exhibit no wear over time. The characterizations performed during the project concern exported micro-vibration behaviors of the compressors and the expander, operating respectively up to 250,000RPM and 150,000RPM, and thermodynamic performance of the different elements. The cooler was tested down to its minimum temperature and required the development of specific operating procedures for the conditioning of the circuit. We report here in a first part the main results and observations stemming from the test campaigns carried out during the project. This work showed the necessity of putting additional effort into the recuperator, one of the most critical components of the cooler. Absolut System is thus also working in parallel on developing a very high efficiency and compact heat exchanger, which we report in a second part, for the specific needs of Turbo-Brayton Coolers in response to the ESA Proposal ESA-TDE-TECMTT-SOW-023649. The technology selected for this is based on the common tube and shell but using very thin tubes of small diameters (<1mm). The challenge of this exchanger is not only the manufacturing, but also the very stringent requirements. Obtaining an efficiency higher than 97.5% in a very small mass while maintaining very low pressure drops, makes for a very challenging project. We have performed the design phase, tested, and validated different aspects of the assembly. The design for the first breadboard model has been validated numerically and is in the fabrication process. Testing the exchanger will then take place to characterize the performances of the recuperator and allow for a comparison between experimental results and analytical and CFD models. This effort participates in placing the Turbo-Brayton cryocoolers at the forefront of space coolers and pushing Europe even further in State of Art advancements for space to bring us closer to fulfill future Space Explorations and Earth Observation missions.
Efficiency Improvement of Small Cryogenic Helium Turbo-expanders in TIPC
Authors: Ke Changlei , Xiong Lianyou , Peng Nan , Dong Bin , Li Kongrong , Zhang Xiaohua , Liu Liqiang 
Published: July 2024

Abstract
An experimental helium liquefier/refrigerator, using ultra high speed cryogenic turbo-expanders is designed and developed in Technical Institute of Physics and Chemistry (TIPC), and liquefaction rate of around 42 L/hr and refrigeration capacity of around 130 W @ 4.5 K is achieved. The turbo-expander constitutes the most critical component of a helium liquefier/refrigerator causing that the turbine efficiency has a great influence on the performance of the whole cryogenic process plant. Inlet Flow Radial (IFR) turbine design is dictated by criteria like velocity ratios. For small flow rate plants the size of the turbine impeller needs to be reduced. In order to reach a high efficiency, the rotational speed must be increased to complete a large specific enthalpy drop. The present article describes the latest technical developments at TIPC, including results obtained during field trials with the TIPC helium liquefier and refrigerator. The motivation of these developments is to improve the efficiency of the machines, and also to widen the range of operation.
Research on the State Equation of High-Pressure Expansion Process of Liquid Hydrogen
Authors: Wu Q , He M , Yang S Q , Xie X J , Gong L H 
Published: July 2024

Abstract
Liquid hydrogen, characterized by high purity, efficient storage and transportation, and renewable clean energy, has become a crucial component in the efficient utilization of energy. A profound understanding of the thermodynamic properties of the high-pressure expansion process of liquid hydrogen plays a significant role in the utilization of hydrogen energy, the development of liquid hydrogen booster pumps, and the implementation of liquid hydrogen-related projects. In this paper, starting from the perspective of the state equation, we conduct research on the large-scale high-pressure expansion process of liquid hydrogen. Several commonly used state equations are employed to calculate the PVT (Pressure-Volume-Temperature) values of this process, and appropriate modifications and combinations are made to improve the accuracy of the state equations. The advantages and disadvantages of the different equations of state for each pressure range and the causes of errors are further discussed based on the standard values given in the NIST database, and some suggestions are made for the improvement of the equations of state and the design of liquid hydrogen-related equipment.
The study of active gas-gap heat switch using carbon nanotubes as the adsorption material
Authors: Yu F Q , Pan T , Li K , Zhu Z Z , Wei F , Dai W 
Published: July 2024

Abstract
Heat switches are widely used in cryogenic systems and play an important role in controlling thermodynamic cycles and accelerating the cooling of cryogenic components, etc. Among them, the active gas-gap heat switch, as one of the mainstream heat switches, mostly uses activated carbon as the adsorbent. It desorbs/adsorbs helium by heating/cooling the activated carbon to realize the ON/OFF state. Normally, a short response time, which is related to the adsorption properties of the materials and the heating method of the adsorption bed, is desired. In order to further shorten the response time and improve the performance of the heat switch, a 3He active gas-gap heat switch using carbon nanotubes as the adsorption material was investigated. About 0.06 mW/K OFF-state conductance and 60 mW/K ON-state conductance were obtained at 4 K. The heat switch switched on within 35 s when 1.6 mW heating power was applied to the adsorption bed, and it took about 400 s at 4 K to reduce thermal conductance to 1/10 of ON-state conductance when the heating of the adsorption bed was stopped.
Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF
Authors: Subedi J , Hansen B , White M , Patel V , Makara J , Atassi O , Johnson G 
Published: July 2024

Abstract
Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.
Thermal performance and stability experiments of a 1.75-meter-long helium pulsating heat pipe
Authors: Kossel L , Pfotenhauer J , Miller F 
Published: July 2024

Abstract
Experimental studies of the performance and thermal stability of extended-length helium pulsating heat pipes (PHPs) were performed at the University of Wisconsin – Madison. Multiple distinct testing procedures were carried out on helium PHPs with an adiabatic length of 1.75 meters, such as progressively increasing evaporator heat load, randomized heat load, and extended period tests. The results of these tests show that despite the stochastic nature of the fluid flow and persisting non-equilibrium conditions, long-distance helium PHPs can maintain stable and steady operation with excellent thermal performance. The progressively increasing heat load tests serve as a baseline for the 1.75-meter PHP’s performance, where the maximum effective conductivity observed was 443.4 kW/m-K at 570 mW heat load and a fill ratio of 56.42%. Furthermore, the randomized heat load test show that, with an optimized fill ratio, PHP performance is not strongly dependent on previous operating conditions and that normal operation can be swiftly recovered from a dry-out condition. The extended period test shows a stable, pseudo-steady operation for over 50 hours with no performance degradation or temperature deviations observed. The impact of PHP build quality is also discussed.
Neon pulsating heat pipe with innovative flexible evaporator to facilitate cryocooling of superconducting devices
Authors: Dixit T , Authelet G , Mailleret C , Gouit F , Stepanov V , Baudouy B 
Published: July 2024

Abstract
Cryogenic pulsating heat pipes (PHP), also termed oscillating heat pipes, are passive thermal links that transfer heat by oscillatory motion of two-phase cryogen confined in serpentine-shaped capillary tubes. It is composed of three sections, namely, the condenser (cold sink), the evaporator (heat source) and the adiabatic part that can range from several centimetres to few metres. In spite of longer lengths, PHPs hold an advantage that their weight does not radically increase in comparison to counterparts like metallic thermal straps. The aim is to present cryogenic PHPs as one of the potential thermal links aiding in distant cooling of superconducting devices from active cryocoolers. A 0.4 m long neon PHP with 1 mm capillary tube diameter has been recently developed characterized by one of the highest thermal conductance reported till date both in vertical and horizontal orientation. An innovative modification in the construction of PHP evaporator is showcased in this article. This would considerably enhance the flexibility of PHPs in terms of their employment geometrically within the targeted application. Pilot experimental results for neon PHP coupled with the altered evaporator is presented for heat load up to 18 W.
Initiation and suppression of Taconis oscillations in tubes with junctions and variable-diameter tube segments
Authors: Shenton M P , Matveev K I , Leachman J W 
Published: July 2024

Abstract
Taconis oscillations represent spontaneous, usually unwanted excitations of acoustic modes in narrow pipes going from warm ambient environment into cold cryogenic space. These oscillations can drastically magnify heat leak and create vibrations undesirable for measurement instruments. In this study, modifications of a classical constant-diameter-tube Taconis setup are investigated. Specifically, variable-diameter tubes were found to strongly affect excitation, with wider tube segments in the warm environment encouraging oscillations, while additions of properly chosen pipe network configurations can supress the oscillations. The low-amplitude thermoacoustic theory, previously developed for thermoacoustic engines and refrigerators, was adapted for modelling Taconis phenomena, accounting for finite-length segments with temperature evolution where thermal-to-acoustic energy conversion takes place. Experiments were conducted using primarily hydrogen as a working fluid to validate theoretical predictions. With the rapid development of various hydrogen storage and transfer systems, it is expected that Taconis oscillations may become an issue, and this study provides an initial modelling framework to assess this phenomenon in hydrogen systems.
Cryopump concept development for the cryogenic mirror region of the Einstein Telescope – the future gravitational wave observatory
Authors: Hanke Stefan , Luo Xueli , Battes Katharina , Day Christian 
Published: July 2024

Abstract
The Einstein Telescope (ET), the planned gravitational-wave observatory for Europe, will increase the sensitivity and expand the observation band to lower frequencies. The main optics of the ET-Low Frequency (LF) interferometer will be cooled to cryogenic temperatures below 20 K and the whole system, consisting of the beam pipes, the suspension towers and the cryostat containing the mirror, requires high to ultra-high vacuum conditions.
To fulfill the vacuum related requirements the use of tailor-made in-situ cryopumps is envisaged. Simulations at KIT, performed with the in-house Test Particle Monte Carlo code ProVac3D and a simplified model of the system, considered the three main gas sources from the neighbouring systems and the sinks by pumping stations distributed along the pipe arms, the cryogenic pump sections close to the mirror and the cryogenic mirror environment. These simulations showed different needs for the pumping of hydrogen (to lower the residual pressures) or heavier species like water (to lower the frost formation on the cryogenic mirror surface) – depending on the position related to the mirror. With these findings, the development of a pump arrangement concept was worked out.
In parallel, the outgassing rates of the inner walls of the beam pipe tubes, influencing strongly the vacuum pumping demands, have been varied to investigate the potential use of mild steel as a beam pipe material of reduced costs.
This paper describes the developed pump arrangement concept, utilizing cryogenic pumps integrated into the beam pipe tubes of 1 m diameter, with their individual objectives regarding pumped species and needed temperatures.
Furthermore, the key parameter of frost formation on the cryogenic mirror, important for long operational phases without pause and maintenance, being also a design driving demand, is derived from the predicted residual pressure of sticky gases like water.
Thermal analysis of a FEL SCU cryostat
Authors: Shiroyanagi Y , Anliker E , Hasse Q , Ivanyushenkov Y , Kasa M , Fuerst J 
Published: July 2024

AbstractAn ANL-SLAC collaboration is working on the design of a planar superconducting undulator (SCU) demonstrator to be tested at the SLAC Free Electron Laser (FEL). The demonstrator cryostat is multi-segmented, and each segment includes an ∼1.5-m-long superconducting undulator as well as other magnetic components like a phase shifter and a beam position monitor (BPM). This LHe-based cryostat is cooled by two stage pulse tube cryocoolers (Cryomech PT425-RM). A detailed load map of the cryocooler was measured and benchmarked with the manufacturer’s load map. A thermal model of one segment of the cryostat, which includes all cooling circuits, has been created in ANSYS and analyzed using the measured cryocooler load map. This paper presents the calculated cooling power requirement and the temperatures in the cryostat.
Additive Manufacturing of cryogenic materials
Authors: Rehme O , Weidermann C 
Published: July 2024

Abstract
The use of pure copper and Inconel 718 as cryogenic materials has been well known in the cryogenic materials space. Despite their potential, little is known about the use of these materials in cryogenic environments regarding their ability to withstand these conditions when manufactured using Additive Manufacturing (AM) methods. AM has emerged as a promising production method due to its ability to produce complex geometries and near net-shape parts. Copper and Inconel 718 offer a wide range of uses in cryogenic applications, as Copper being highly conductive makes it ideal for electrical applications, whilst Inconel 718 serves well as an engineering material.
In this paper, we demonstrate the Coldgas Spraying (CS) of copper and the Selective Laser Melting (SLM) of Inconel 718 and Scalmalloy as the AM processes of choice for each respective material. The main distinction between both processes is that CS is useful for rapid deposition of material in the range of several kg/h whereas SLM is limited to a range of several hundred g/h. However, CS can only yield bulk structures while SLM allows the production of fine and intricate structures due to the nature of their approaches.
The work presented here was performed in the framework of a research project named AdHyBau. It is funded by the German government in which several partners from industry and academia seek to jointly develop a 500 kW output power electric drive for aviation applications which employs liquid hydrogen as a propellant for a fuel cell but also for advanced cooling to obtain very high power densities in the range of above 10 kW/kg.
Cryogenic aspects of a 20 MW class low-temperature superconducting generator for the renewables industry
Authors: Stautner W , Torrey D , Xu M , Wu A , Parizh M , Soni V 
Published: July 2024

Abstract
In this paper we give a progress update on the cryogenic design for cooling a 20 MW class, partially superconducting generator with stationary field coils for offshore wind renewables industry [1-2]. This is a continuation of an earlier program on a 10 MW system dating back ten years. Whereas this new power rating increase leads to a radial diameter expansion of the superconducting field coils from 4 to > 9.5 m, it maintains the axial length. We show the design based on this scaled up with enlarged diameter. The field coil size increase asks for higher cooling power that leads to a bigger cold box size to accommodate the cryocoolers. In the design, as many as 8 cryocoolers can be accessed and serviced from the nacelle that houses the main cryogenic components. A typical thermal load balance sheet with all components is given and compared against the available cryocooler cooling power at different operating conditions. Due to the cryocoolers’ local point of contact cooling within the nacelle, the temperature gradient of the thermal shield that fully encloses the cold mass with its embedded field coils needs to be balanced out to minimize the heat burden on the field coils. This requires additional analytical efforts and implementation of further design features. The extended nacelle houses the cold box with its cryogenic infrastructure. The interface for the envisaged cryogenic pushbutton closed-loop circulating system remains invisible, requires no handling of cryogenic liquids and is hermetically closed. The field coil diameter increase also leads to a greater initial helium gas storage volume. In addition, it requires higher initial room temperature fill pressure within the toroidal helium vapor storage tanks and in cooling tubes connecting to the cryocoolers. The toroidal helium gas tanks are thermally coupled with the thermal shield so that helium convection inside the storage tank can improve heat transfer and reduce the temperature gradient of the thermal shield. Besides those heat transfer challenges, additional mechanical strain within this large structure is exerted on the torque tubes during initial cooldown and when energizing field coils. Some of those design challenges are quite unexpected, leading to novel workarounds in order to maintain the chosen cooling strategy. Finally, we assess those design limitations in view of further cryogenic scalability with emphasis on manufacturability and assembly.
Tuning hydrogen boil-off via inert gas insulation purge in a vapor cooled shielded fuel tank
Authors: Gitter Y K , Leachman J W 
Published: July 2024

Abstract
Vapor cooled polymer composite tanks for liquid hydrogen are a newopportunity for light weight power-system integration into unmanned aerial vehicles. Vapor shielding has the ancillary benefit of pre-conditioning the hydrogen for use by a fuel cell. However, the mass flow rate required by a fuel cell should be matched by the natural boil-off rate of the tank. With limited ability to vary insulation thicknesses, the challenge becomes satisfying the fuel cell consumption in UAVs at different mass flow rates when at varying stages of flight from take-off, cruise, and landing. This paper provides experimental measurements of mass flow rate of hydrogen from the tank considering batch purging with helium or argon in the vapor cool shielded insulation layer. A 5-shell vapor cooled shielded tank is used with two layers of insulation including aerogel, helium or argon, and two vapor channels. A more complete understanding of system-level thermal conductance is determined by mass flow of hydrogen leaving the tank during hypothetical flight.
Uncertainty analysis of Raman spectra for measuring ortho-parahydrogen compositions
Authors: Appel K R , Leachman J W 
Published: July 2024

Abstract
Determining ortho-parahydrogen compositions at cryogenic temperatures is an important quality control for liquid hydrogen custody exchange. High orthohydrogen compositions lead to an exothermic reaction resulting in increased boil off and increased venting losses of liquid hydrogen product by either the supplier or consumer. Traditional methods for measuring ortho-parahydrogen compositions such as hot-wire anemometry, nuclear magnetic resonance, and infrared spectroscopy are typically inconvenient at best. As the number of cryogenic hydrogen systems continue to increase, there is an increased need for flexible, standardized techniques for post processing composition measurements. A Raman spectrometer implemented in the Cryo-Catalysis Hydrogen Experimental Facility (CHEF) has demonstrated incredible flexibility for composition measurements of cryogenic hydrogen flows through a wide range of temperatures and pressures with the Raman probe in-situ at cryogenic temperatures. This article analyzes the uncertainty of Raman spectroscopy data of cryogenic hydrogen equilibrated at temperatures in IONEX catalyst. Spectra from hydrogen catalyzed to the equilibrium ortho-parahydrogen composition are processed and compared to expected statistical distributions for method verification.