Cryogenics最新文献

Plate-fin heat exchangers (PFHEs) are used in diverse applications because of their superior capabilities. Recently, the demand for PFHEs has increased in cryogenic industries. Therefore, evaluating the thermal and hydraulic performances of PFHEs under cryogenic conditions is crucial for effectively designing them. In this study, the thermal–hydraulic characteristics of cryogenic nitrogen gas flowing through PFHEs were investigated experimentally. Two PFHEs with different fin geometries are used in this study. The hydraulic diameters of the PFHEs were 2.13 and 1.47 mm. The experimental ranges of the Reynolds and Prandtl numbers were 345–7800 and 0.72–0.75, respectively. From the experimental results, a heat transfer correlation based on the Diani correlation was derived in both turbulent and laminar regimes, with root mean square percentage errors of 0.68 and 6.9 % for the turbulent and laminar regimes, respectively. For hydraulic performance, the calculated pressure drop demonstrated good agreement with the experimental data, with a root mean square percentage error of 13 %.

The use of the ADR to provide a sub-Kelvin temperature environment is required for many space missions. The mechanical design of the ADR, including the use of Kevlar to ensure proper suspension of the salt pill, must minimize thermal conductivity between components while optimizing structural capability. Heat leakage reduction and vibration resistance have different focuses when determining the suspension system strategy and must be compromised. A dimensionless parameter $\phi$ representing the slenderness of the suspension is developed to quantify both heat leakage and vibration characteristics. At constant $\phi$, the diameter of the Kevlar cords has the greatest influence on vibration, followed by Kevlar cords’ length and then their number. As $\phi$ increases, although the reduction in heat leakage becomes less pronounced, the vibration response remains essentially linearly increasing. Therefore, designing the suspension according to this principle enables optimal stability after conforming to the maximum allowable heat leakage dictated by ADR's thermal design constraints. Also, research revealed that increasing preload from 10 N to 110 N has a negligible impact on vibration damping, benefiting from the comparatively superior axial stiffness of Kevlar. Therefore, it is sufficient to apply a certain amount of preload at rest to ensure that the salt pills remain fixed.

Selecting suitable adsorbents and managing the thermal effect are two important aspects on the practical application of the hydrogen storage system by adsorption. In this research, three kinds of promising adsorbents, which include MOF-5, MIL-101(Cr) and activated carbon AX-21, were selected for evaluating the effect of pre-cooling of hydrogen in-charged into a 0.5 L cylindrical vessel experimentally and numerically as per the temperature fluctuation, heat generated, accumulated amount of the charge under the flow rate of hydrogen required by an on board 5 kW PEMFC power unit. The validation of the prediction accuracy of the model was performed by the experiments conducted respectively at 77.15 K and 298.15 K where the vessel was packed with MIL-101(Cr). Simulations were further performed to evaluate the performance of the vessel respectively packed with three kinds of adsorbents within the flow rate range 15–40 L min⁻¹ and temperature range 77.15–298.15 K. Results show that precooling the hydrogen in-charged is conducive to weakening the temperature fluctuation of the storage system, and heat from adsorption is the main factor affecting the accumulated amount of charge and the temperature fluctuation within the hydrogen storage system. It suggests that MOF-5 is a more suitable hydrogen storage medium than MIL-101(Cr) and AX-21, and charging the system with hydrogen precooled at 77.15 K under a smaller flow rate is beneficial to improving the performance of the storage system.

The superconducting flywheel system exploiting the magnetic coupling between the bulk high temperature superconductors (HTSs) and permanent magnets (PMs) exhibits excellent performance of self-stable levitation, and is promising for power applications. In this paper, we use the H-$\varphi$ formulation combined with moving mesh to establish a full 3D model for the thrust type and journal type bearings in the HTS flywheel system. We then proposed different Halbach schemes to enhance the magnetic flux density of the rotor and thus the coupling, and investigated the levitation force, relaxation characteristics, electromagnetic transient distribution, and temperature characteristics of the bearings. Results show that, under axial zero field-cooled (ZFC) condition, the optimized PM rotor scheme can significantly improve the maximum levitation force and stiffness by 4.0 and 2.3 times respectively for the thrust type bearing, and the maximum levitation force of journal type bearing can be improved by a factor of 5.5. Under the radial ZFC condition, the maximum levitation force and stiffness of the journal type bearing have been increased by 4.9 times and 2.9 times. For the relaxation of both bearings during operation, the optimized PM rotors lead to relatively greater attenuation of levitation force. The proximity of the optimized PM rotors intensifies the magnetic flux movement of the HTS bulks but only brings about a limited temperature rise, and the superconductors still maintain a good low-temperature working environment. This study provides an effective methodology for analyzing the HTS bearing systems and good references for the optimal design of compact HTS flywheel energy storage systems (FESSs).

The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2–40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |ΔS_m|= 17 J kg⁻¹ K⁻¹ (H||c) at 18 K and |ΔS_m|= 20 J kg⁻¹ K⁻¹ (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of ΔT_ad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH₂) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite.

The work presents a method of noninvasive measurement of long-stem cryogenic valve straightness, using simple and generally available means. The method does not require an access to valve exterior, what is a common requirement in practice, where such access is impossible in case of helium cryogenic valves confined in all-welded valve boxes. Valve’s deflection is computed using computer vision algorithms (Hough transform for circles), based on photographs of valve interior. Results obtained by the method have been validated using reference data from a validation test stand with a ruler for deflection measurement. The method may be applied for a more general case, namely to measure deflections of pipes ended with sleeves with diameters smaller than the pipe’s diameter.

Spacecraft commonly use multilayer insulation (MLI) for passive thermal control, however deployable structures such as telescoping booms impose the need to stow MLI preflight and extend with the structure for in flight operation. This paper investigates an octagonal origami folding pattern that allows predictable stowage and extension of multilayer insulation. Feasibility was demonstrated to fold, compress and extend a MLI blanket comprising 10 layers of aluminized Kapton, each separated by a layer of scrim cloth. Both folded and unfolded 10-layer MLI blankets were tested in thermal vacuum to characterize heat leak of deployed configurations. The 10-layer origami folded configuration increased thermal conductance and radiative heat transport relative to the unfolded configuration. Degradation factors for heat transport were empirically found to be $M_k=2.5\pm 0.3$ and $M_e=1.3\pm 0.2$ for effective thermal conductance and emittance, respectively.

A numerical study is performed with COMSOL multi-physics, to analyze the effect of axial spacing between double pancake (DP) coils on central magnetic field and field homogeneity of High temperature Superconducting (HTS) magnet. The magnet is wound in the form of DP coils having, inner winding diameter as 100 mm and is operated at 65 K. The field homogeneity is calculated over a Diameter of Spherical Volume (DSV) of 40 mm for the entire study. The analysis is carried out by considering a constant length of HTS tape of 750 m and varying the number of DP coils from 4 to 14. The number of turns in all the DP coil is equal for a given set of DP coils to maintain the length of HTS tape to be constant. The coil separation within DP coils is of constant gap from 0.5 to 2 mm, while the axial spacing between the DP coils is varied from 0 to 50 mm for all the set of DP coils. The optimum gap between DP coils was evaluated using Exhaustive search optimization techniques and decreased with the number of DP coils. The best field homogeneity of 662.5 ppm was achieved with 14 DP coils having $g_{DP}=20.3$ mm and $g_{SP}=2$ mm for the chosen solenoid configuration.

To fulfill the cooling capacity needs of cryomodule test facility for the Shanghai high repetition rate x-ray free electron laser (XFEL) and extreme light facility (SHINE), a 1 kW@2 K helium cryoplant has been implemented. The helium cryoplant comprises a warm compressor station and a cold box, where the former ensures a consistent supply of high-pressure helium to the latter. Normally, a proportional integral (PI) controller is employed to regulate both high-pressure and low-pressure levels in the compressor station, thereby ensuring stable operation of the cold box. However, under certain circumstances such as cold box turbine shutdown, both high-pressure and low-pressure can experience significant fluctuations, thereby posing a risk of severe safety accidents. Hence, it is imperative to conduct tests on pressure fluctuations in the aforementioned conditions. Due to the risks associated with conducting failure condition experiments, a dynamic simulation model of the warm compressor station was developed using EcosimPro software to perform failure testing. The simulation results of the compressor start process are compared with experimental data to validate the accuracy of the dynamic model. Subsequently, simulations of the valve fail open, turbine shutdown, and heat load shock conditions are conducted. Fuzzy PI (FPI) control is introduced to cope with fault conditions. The simulation results have verified the effectiveness of FPI control over conventional PI control, which can reduce maximum high pressure (HP) and recovery time under fault conditions.

The plate-fin heat exchanger is one of the most important components of helium liquefaction system as it recovers cold energy from helium gas in the cold box. Because of larger heat transfer surface area and compact geometrical configuration, plate-fin heat exchangers are widely used. The design of heat exchanger using helium as a cryogenic fluid needs high thermodynamic performance with minimum pressure drop which particularly requires the optimization of dimensional array and its geometrical configurations. In this regard, a parametric investigation was performed to compute the effective geometrical parameters and its effect on thermodynamic (effectiveness and log-mean temperature difference) performance has been discussed in detail. The present study aims to design optimization and thermodynamic performance evaluation of plate-fin type heat exchangers used in helium liquefaction systems. The developed helium liquefaction model has been simulated for the most critical liquefier with and without liquid nitrogen precooling, mixed mode, and refrigeration mode. Each component of the liquefaction model has been technically and thermodynamically analyzed and, in particular, four plate-fin heat exchangers have been considered and designed accurately using Aspen $ED{R}^{\circledR }$. Initially, the sensitivity analysis was carried out to characterize the most significant geometrical parameters (fin thickness, height, number and arrangement of layers, frequency, and fin type) and their effect on thermodynamic performance and pressure drop. After that, the artificial intelligence model was used to determine the optimal range of such geometrical variables in which the heat exchanger has maximum effectiveness and log mean temperature difference. Finally, the operating conditions obtained from cycle modeling and optimized geometrical datasets have been applied in commercial simulation software Aspen $ED{R}^{\circledR }$ for plate-fin heat exchangers design. Finally, a comparative thermodynamic analysis has been carried out to determine the performance of all the designed heat exchangers operating at four different modes (boundary conditions).