Cryogenics最新文献

High-temperature superconducting (HTS) pinning maglev has achieved rapid development in recent decades. The levitation system of the HTS pinning maglev is mainly composed of Dewar with built-in HTS bulks and permanent magnet guideway (PMG). For a maglev transportation system, damping is important for vibration attenuation, and the inherent damping characteristics of the HTS pinning maglev system have not been evaluated clearly. In this paper, the damping characteristics of the HTS pinning maglev system are analyzed through experiments and simulations. Experiments are conducted to measure the dynamic responses of the system under free and forced vibrations. The logarithmic envelope method is used to evaluate the system damping under free vibration. The cross-correlation function is utilized to obtain the phase difference between the system vibration signal and excitation signal, and then calculate the system damping under forced vibration conditions. In addition, a two-dimensional finite element model including HTS bulks, PMG, and Dewar conductive shells is established to evaluate the damping force generated by each component during system vibrations. The additional eddy current damping of the conductive Dewar shell is considered and analyzed. Finally, from the perspective of system damping and thermal stability of HTS bulks, suggestions for selecting Dewar shell materials are proposed.

This paper presents a novel design of a low-speed and high-torque cryogenic direct-drive PMSM. A new simplified model is proposed to address the inaccuracy of the electro-thermal coupling model of the common cryogenic PMSM design. The coupling model focuses on the influence of the winding copper loss on the resistance, which improves the accuracy of calculating the temperature distribution and resistance value. Compared with FEM, the error of the calculation results is 4.8%. A new design method is proposed to address the problem that the common low-temperature PMSM designs lead to a rise in the copper loss. Measuring the improvement of the magnet performance in low temperature, the method reduces the turns of the coil, which significantly reduces the amount of copper loss. Compared with common methods, the amount of copper loss reduces 29.5%. Furthermore, a prototype is fabricated and tested, the results of which verifies the rationality of the design.

Cryogenic distillation is widely acknowledged as the primary industrial method for producing liquid nitrogen of high purity. However, the distillation process is highly sensitive to tilting and swinging, which limits the application of cryogenic air separation in offshore infrastructures. This paper proposes a small-scale air separation process that incorporates a dual-column distillation to enhance distillation performance under offshore conditions. Experiments were conducted under standard (no-tilting and stationary), tilting, and swinging conditions. The results indicate that the proposed distillation plant can maintain nitrogen purity to a certain extent under offshore conditions. The product impurity (oxygen content) increased significantly as the tilting angles increased beyond 4° for horizontal titling and 3° for longitudinal titling, respectively. The distillation performance was less affected by the swing than the tilting. High-purity nitrogen could be produced when swing amplitude was within ±10° and swing period was between 6 s and 11 s. The results can provide engineering guidance for the design and installation of the columns of air-separation plants.

In the context of the High Luminosity upgrade of the Large Hadron Collider at CERN, a framework implementing experimental techniques and numerical analysis has been developed to systematically assess the temperature distribution in complex He II-cooled composite magnet geometries. The experiments are designed to measure the heat transfer coefficients in the magnet coil layers using coil samples in a stagnant superfluid helium bath. A numerical tool-kit has been developed to facilitate intensive parametric studies, in addition to estimation of helium content via a phenomenological model. The workflow of the tool-kit is built to handle complex geometries composed of different materials each with their temperature-dependent properties, at low computational cost. This framework has been validated with experimental data obtained from laboratory-scale experiments on impregnated coil samples, reported and discussed here. Three use cases for the developed numerical tool, with increasing levels of complexity, are presented and its results discussed.

The heat transfer performance of nitrogen PHPs with different heat transmission distances (100 mm and 500 mm) and tube configurations (single-loop and complex-loop) were experimentally investigated. Experiments were conducted in the vertical bottom heat mode with different filling ratios (15 %–70 %). The results showed that the maximum effective thermal conductivity increased proportionally with the heat transmission distance whereas the thermal resistance remained constant (0.2 K/W at a filling ratio of 31.8 %). This verified the outstanding long-distance heat transfer advantage of the nitrogen PHP. Experiments at different filling ratios showed that the maximum thermal conductivity decreased as the filling ratios increased. A filling ratio of 31.8 % was recommended. Under this operating condition, the PHP can load the maximum heat input while exhibiting relatively high effective thermal conductivity. Compared to the single-loop configuration, the complex-loop exhibited higher effective thermal conductivity, and this enhancement in thermal performance was more pronounced for the longer PHP.

Highly sub-cooled water ice, with temperatures as low as 10–20 K is not commonly utilized and, as a result, its fundamental properties remain generally unknown. Therefore, the thermal characteristics of water ice have been thoroughly reviewed in the scientific literature and compared with the performance of other solid materials, which can be potentially used as a cooling media in superconducting applications. The effectiveness of water ice as a cooling agent was demonstrated through experimental measurements of the temperature and the magnetic background field effects on the critical current of small MgB₂ solenoid immersed in water ice with temperatures ranging from 10 K to 36 K and external magnetic fields from 0 to 6 T. Increase of the solenoid’s temperature was observed when the transport current exceeded the critical threshold, which is determined by the conventional criterion of 1 µV/cm. The obtained results confirm that sub-cooled water ice is a promising, cost-effective, and safe coolant suitable for superconducting systems.

A Stirling cooler for space use must have a 5–10 year service life. The primary limitation is the degradation of cooling performance by gas contaminants, such as H₂O, CO, CO₂, O₂, and N₂. If these gas contaminants freeze in the regenerator or the displacer’s clearance seal, they can block the helium flow for heat exchange or disturb the smooth movement of the displacer. This study verified the effect of adsorbent adapted for the 20 K-class two-stage Stirling (2ST) cooler with a correlation between the cooling performance and the residual concentration of CO₂ gas contaminant. Although the 2ST cooler was stopped by a displacer stuck during initial cooling by adding CO₂ at 4990 ppm, the cooling performance was finally recovered to a reference level below 20 K when the equipped adsorbent was activated. Gas analysis showed that the residual CO₂ concentration was successfully reduced to 426 ppm, satisfying the less than 500 ppm requirement.

Epoxy resins are widely used in cryogenic applications due to their distinguished mechanical and electrical insulation properties. To avoid generating enormous amounts of waste that affect the environment and cause economic losses, covalent adaptable networks can be introduced into the epoxy structure to make the thermosetting network reversible. In this study, ester bond and hexahydro-s-triazine structure were adopted in epoxy structures. Two new degradable epoxy resins (HPBE and HPHE) with variances in the content of benzene rings were synthesized which were confirmed by FTIR and NMR. After curing, the thermal, mechanical, thermal conducting properties of the resulting materials were examined. The products exhibited tensile strength and flexural strength all above 120 MPa at 77 K, with glass transition temperature of 89.1 °C and 86.9 °C, respectively. Meanwhile, HPBE and HPHE demonstrated favorable thermal stability, with thermal conductivity comparable to that of the commonly used epoxy resin DGEBA. These resins could be degraded under mild conditions and demonstrated high hydrolysis efficiency (approximately 90 %). This investigation presented a viable method for the application of degradable thermosetting materials in cryogenic environments and the possibility for repairing of high-value equipment.¹

Hysteresis losses in the heat transfer between compressing or expanding gas and the adjacent wall is said to play an important role in Stirling machines, where it increases the amount of required p-V work. Previous studies have linked hysteresis loss with the pressure phase shift. In the context of this research, the effect of the pressure phase shift on the net p-V work in a single space is examined.

A Sage model of a single space piston-cylinder device is used to investigate the underlying mechanisms of the pressure phase shift. The Sage model is validated using an experimental piston seal rig. In addition, the time dependence of heat transfer is discussed along with how it affects the pressure phase shift, using an iterative model. The Schmidt equations were manipulated to determine the phase shift between pressure and volumetric oscillation in an ideal Stirling refrigerator.

The results of this investigation are surprising. It was found that even in the case of an idealized Stirling refrigerator, the phase shift between pressure and volume is non-zero in order to produce a refrigeration effect.

Dilution refrigerator provides continuous ultralow temperature environments as low as 10 mK. It has been widely used in a variety of important applications such as quantum computations. The silver powder heat exchanger in a dilution refrigerator plays a crucial role in realizing ultralow temperatures on the order of 10 mK by precooling the circulation of helium mixtures. To study the silver powder heat exchanger quantitatively, we have proposed an efficient numerical solution method for its thermodynamic model. This method utilizes constraint conditions cleverly to convert the initial value problem of differential equations into a boundary value problem, allowing us to solve the control equations using the existing ODE function quickly. Furthermore, we demonstrate the application of this method in the evaluation and design of silver powder heat exchanger. The research results of this paper have certain significance for the development of dilution refrigerator.