Liquid Nitrogen Bath Research Articles

Machining-Induced Damage and Corrosion Behavior of Monel-400 Alloy Under Cryogenic Cooling Conditions: A Sustainable Initiative

AbstractMonel-400 is a nickel-based heat-resistant superalloy (HRSA) that is primarily used in oil and marine applications. Machining Monel-400 alloy for marine applications usually involves drilling and milling operations for assembly purposes, which should meet the requirements to withstand use in salt-water environments (i.e. lower surface finish to reduce corrosion and lack of burrs for tight sealing between mating parts). However, drilling of Monel-400 alloy can be challenging due to its high strength and density, which induces thermal effects that can influence the surface and geometrical integrity of the holes. Consequently, the use of environmentally friendly cooling technologies, such as cryogenics, is an excellent alternative to mitigate these effects, something which has not been widely investigated in the open literature when drilling Monel-400 alloy. Therefore, the current study aims to investigate the machinability of Monel-400 alloy under dry and cryogenic cooling conditions. The effects of cutting parameters and the use of a cryogenic liquid nitrogen bath on the surface integrity and corrosion resistance of holes were evaluated. Additionally, cutting forces, chip formation, and corrosion performance were analyzed. The results showed that the cutting forces increased by up to 8% under cryogenic cooling. Under cryogenic conditions, reduced elastic deformation resulted in a smaller chip size. Both cutting conditions produced a smooth surface finish with a roughness value of less than 0.2 µm. Corrosion resistance was reduced under cryogenic conditions at spindle speed of 5000 rpm. The current work showcases that cryogenic cooling is recommended for drilling Monel-400 alloy used in marine applications, but care should be taken in employing optimal cutting parameters to mitigate any effects on corrosion resistance.

Calculation of AC loss using 2D homogenization method for HTS synchronous condenser rotor and validation

Compared with low-temperature superconductors, second-generation high-temperature superconducting materials offer higher current densities and temperature margins, which provide a boost to the development of superconducting condenser towards large capacity and light weight. In this paper, a 3D-to-2D dimensionality reduction and simplification method is proposed to address the problem of massive computation of 3D finite element model during the optimization of superconducting condenser rotor performance parameters. This method splits the pole based on the geometric characteristics of the rotor pole, establishes a 2D simplified model of each part of the pole after splitting, and uses the simplified model to calculate the key physical quantities such as the magnetic field, AC loss, temperature change, etc., during the excitation process of the superconducting condenser rotor. This method effectively reduces the computational complexity of the model and improves the efficiency of the calculation and iterative optimization of the magnet pole parameters. In order to verify the correctness of the electromagnetic calculation results of the simplified model, the rotor magnet model was assembled to carry out experiments in liquid nitrogen bath, and the experimental results were in good agreement with the calculation results.

The effect of low temperatures on monitoring structural health using acoustic-ultrasonic piezoelectric transducers on composite structures.

Composite materials have proven to be one of the ideal choices when it comes to structural applications requiring high performance working at extreme low temperatures, such as hydrogen tanks or space structures. One of the main challenges of using them is that they are susceptible to impact and fatigue, which may lead to different damages. Implementing structural health monitoring (SHM) systems is one strategy to enhancing their reliability, with guided waves (GW) being one of the most promising techniques. For the effective implementation of GW-based SHM in these applications, an in-depth comprehension of its behavior up to cryogenic temperatures is required for accurate monitoring. In this regard, the objective of the present work is to preliminary investigate the effect of low temperatures on wave propagation and transducer integration. By progressively removing a composite panel from a liquid nitrogen (LN2) bath with an integrated GW-SHM network based on co-bonded DuraActTM transducers, the GW and temperature are continuously monitored from LN2 CT to room temperature. The results show that the behavior of the GW by decreasing the temperature does not follow a monotonic pattern, having at least local maxima in terms of amplitude, and nonlinear behavior for the time-of-flight. Electromechanical impedance and C-Scans ensured the quality of the bonding of the co-bonded DuraActTM transducers.

Realisation of the triple-point of Argon: comparison between two devices

A new cryostat for the realization of the triple-point of the argon (83.8058 K), a defining fixed point of the International Temperature Scale of 1990 (ITS-90), was acquired at Italian National Metrological Institute (INRiM). The new system, manufactured by Fluke, is intended to substitute the current National reference, a model developed at BNM-INM in the 1975. The main difference between the two system is in the way to control the temperature. In the BNM-INM device the temperature is controlled adjusting the pressure of liquid nitrogen bath, in the Fluke system instead, an electrical heater wrapped around the argon cell is used, following cryogenic practice. This paper describes the result of the direct comparison and shows typical phase transitions obtained with the two argon systems. Then, a complete uncertainty budget is evaluated for the new Fluke system and compared with the National standard.

DarkSide-20k Veto Photon-Detector Units: construction and characterization

DarkSide-20k is a global direct dark matter search experiment situated underground at LNGS (Italy), designed to reach a total exposure of 200 tonne-years nearly free from instrumental backgrounds. The core of the detector is a dual-phase Time Projection Chamber (TPC) filled with 50 tonne of low-radioactivity liquid argon.The entire TPC wall is surrounded by a gadolinium-loaded polymethylmethacrylate (Gd-PMMA), which acts as a neutron veto, immersed in a second low-radioactivity liquid argon bath enclosed in a stainless steel vessel. The neutron veto is equipped with large-area Silicon PhotoMultiplier (SiPM) array detectors, placed on the outside of the TPC wall. SiPMs are arranged in a compact design meant to minimize the material used for PCBs, cables and connectors: the so-called Veto Photon-Detector Units (vPDUs).A vPDU comprises 16 vTiles, each containing 24 SIPMs, together with front-end electronics, and amotherboard, which distributes voltage and control signals, sums vTiles channels, and drives theelectrical signal transmission. The neutron veto will be equipped with 120 vPDUs. The paper willfocus on the production of the first vPDUs, describing the assembly chain in the U.K. institutes, inorder to underline the rigorous QA/QC procedures, up to the final characterization of the firstcompleted prototypes. Tests will be extensively performed in liquid nitrogen baths either for thesingle vTiles and for the assembled vPDUs, with the purpose of assigning a “quality passport” toeach component.

Development of the first non-planar REBCO stellarator coil using VIPER cable

The benefits of operating fusion devices, such as tokamaks and stellarators, at high fields make high-temperature superconducting magnets necessary to realize a compact fusion power system. Superconducting stellarators, such as W7-X, have used standard low-temperature superconductor technology niobium-titanium. ARPA-E has recently funded a two-year project led by the startup Type One Energy and involving the Fusion Technology Institute at the University of Wisconsin-Madison, the Plasma Science to design and fabricate the first non-planar high-temperature superconductor (HTS) rare-earth barium copper oxide (REBCO) coil for a high-field stellarator based on the SPARC tokamak’s VIPER cable concept. The design consists of a 1.5-turn non-planar REBCO coil supported by a pair of 3D printed stainless steel radial plates. The ultimate goals of the project are to determine if commercial REBCO tapes and additive manufacturing can be used to fabricate high field () non-planar coils with tight bending radii () and with a degradation of the critical current smaller than 20% with respect to the expected performance. In this work we present numerical analysis for non-planar coils (critical current, magnetic field map, Lorentz forces and quench aspects) at the operating conditions of 77 K and 20 K and the fabrication and testing in liquid nitrogen (77 K) of the first two non-planar demonstrators for stellarators based on a VIPER cable. The first demonstrator is a short NOn-planar VIPER cabLe (cable demonstrator at which we will refer to as NOVEL) equipped with 100 HTS REBCO tapes and with a critical current of 5700 A at 77 K (self-field); the second is a MultIple turns (1.5-turns) NOn-plANar coil (coil demonstrator at which we will refer to as MINOAN) equipped with 30 HTS tapes and with a critical current of 2100 A at 77 K (self-field). Both demonstrators were tested at 77 K (liquid nitrogen bath) and the results showed that—even after being bent into non-planar shapes with bend radii —the degradation of the critical current was within 15%, meeting the expected goals of the project.

An Experimental Study on Manipulation of Individual Coil Current in Parallel-Connected HTS Pancake Coils

This paper reports experimental results of individual coil current manipulation by heater operation in parallel-connected three no-insulation (NI) high-temperature superconductor (HTS) pancake coils. The resistive heater was installed at the coil terminal of the lowermost pancake coil. During magnet operation with a power supply current held constant in a bath of liquid nitrogen at 77 K, the heater was operated to reduce the coil current of the lowermost pancake coil. Due to the heater operation, the coil currents of the uppermost and the middle pancake coil increased as a result of the coil-to-coil current sharing mechanism. The result demonstrates the potential of handling the unstable magnet operation in a parallel-connected magnet by taking action to each coil individually such as coil current reduction without significant degradation of the magnetic field intensity.

Analysis of Nonuniform Contact Resistivity Distribution on No-Insulation HTS Racetrack Coil

This paper presents a numerical analysis and experiment to investigate a contact resistivity distribution of a no-insulation (NI) high-temperature superconductor (HTS) racetrack coil. Since the racetrack coil consists of straight and curved sections with continuously varing curvatures, the local inhomogeneity of contact resistivity can occur. We adopt a partial element equivalent circuit (PEEC) method to investigate this inhomogeneity. A 50-turn NI HTS single pancake test coil is fabricated to figure out the discrepancy of contact resistivity, and the coil is charged up to 100 A in a liquid nitrogen bath. Voltage profiles between inserted voltage taps and the magnetic fields at the coil center are measured and compared with two simulation cases: 1) uniform contact resistivity; 2) nonuniform contact resistivity distribution. The results indicated that nonuniform distribution of contact resistivity may exist. Lastly, the current and Joule heat distribution during the ramping process is analyzed by the PEEC model.

Limitation of Current Transport in Coated Conductors: Statistical Fluctuations or Weak Spots?

Traditionally, the critical current, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> , of a superconducting wire, considered as the limit of DC operation, is experimentally verified on a sample few centimeters long. This approach could fail in case of high-temperature superconductor wires, where significant changes of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> along the conductor length, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , are commonly observed. Then, the quantity that could replace the uniform critical current as the entry data in designing of a superconducting device is to be found. We have analysed the properties of 6 coated conductor tapes provided by 4 different manufacturers. First, the overall critical current of the full tape length, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> , has been evaluated from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c(x</i> ) data. However, the dissipation in a non-uniform conductor with fluctuating critical current concentrates in the “weak spots” with the lowest <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> values. Then, depending on the conditions of heat removal, thermal runaway in some location could happen before reaching <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> during conductor testing or operation. Taking into account the conductor architectures and assuming the cooling in liquid nitrogen bath, we computed the thermal runaway current, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_tr</i> , at which the weakest location in each of the analysed conductors would convert to a “hot spot” with rapid increase of temperature. Then, comparing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_tr</i> to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> one can identify which of these two values is lower, i.e., represents the upper limit of transportable current. We discuss how the result of such analysis would be influenced by a metallic stabilisation that exhibits significant impact on cooling.

R&D of on-board metal-insulation REBCO superconducting magnet for electrodynamic suspension system

Metal-insulation (MI) REBCO high-temperature superconducting (HTS) magnet has the advantages of short charging delay, low contact losses, and self-protection abilities, which shows important application prospects in many fields. Recently, Institute of Electrical Engineering, Chinese Academy of Sciences developed a prototype on-board MI HTS coil used for electrodynamic suspension (EDS) system working with an acceleration of beyond 8 g. To design a reliable engineering on-board magnet, specific Ic angle dependence data of short sample under different fields were fully considered to estimate the operating margin and losses accurately of the on-board magnet. A semi-analytical method, combination of the dynamic circuit method and finite element method, was used to analyze the dynamic electromagnetic force distribution inside the on-board magnet under motion state, in which the effect of the propulsion coils and the figure-eight-shaped coils were taken into considerations. Finally, a full-size MI double pancake racetrack coil was fabricated and tested in a liquid nitrogen bath. The test results meet the design requirements and verify the feasibility of the design, which provides an important reference for the experiment of on-board EDS with high acceleration in the future.

Subzero Temperature Storage to Preserve the Quality Attributes of Veiled Virgin Olive Oil

Unfiltered olive oils (UO) have gained popularity in the global market, but they lose their quality characteristics faster than filtered oils (FO). In this work, refrigeration and freezing temperatures were explored to maintain UO quality features during storage. A full factorial design was applied to an UO and to the same oil after filtration to evaluate the effect of storage temperature (room temperature, 4 °C and -20 °C) and freezing speed (slow-freezing, in the freezer at -20 °C and fast-freezing, in a bath of liquid nitrogen). Official quality parameters, polar and nonpolar phenolic compounds, oxidative stability index, volatile compounds and descriptive sensory profile were measured periodically over 24 months of storage in the dark. Storage temperature influenced the quality of both UO and FO, but in different ways. At non-freezing temperature, UO experienced a severe decrease in its sensory quality compared to FO, mainly due to the hydrolysis of secoiridoids and degradation of the volatile fraction, but storage at -20 °C allowed to effectively preserve UO quality traits, thus resulting as a suitable strategy to increase the shelf-life of UO to satisfy the demand of consumers for this particular product. The results showed that slow-freezing was the most appropriate method for freezing.

Numerical modeling of radiation-induced reactions: Fricke dosimeter at 298 K, 198 K, and 77 K

The Fricke dosimeter is a widely used gamma radiation dosimetry system. The system is based on the detection of Fe2+ to Fe3+ oxidation in an aqueous solution of ferrous sulfate in sulfuric acid, exposed to ionizing radiation in the presence of oxygen. The system is formed by a series of highly dependent chemical reactions. We developed a numerical model of coupled differential equations based on the mass balance; each equation incorporates information about the formation and breakdown of each molecule, as well as a term that represents an external source of radiation. The numerical model can reproduce the behavior of the experimental data at room temperature. We proposed a correction factor to simulate the behavior of the dosimeter at temperatures of 198 K and 77 K, respectively, when the system is in a thermal bath of dry ice or liquid nitrogen. This model could support a variety of experimental challenges for radiation at low temperatures in different fields of industry and could have relevance for astrobiology problems by offering the possibility of simulating reactions in comets and other exoplanetary bodies.

Effect of the Storage Conditions and Freezing Speed on the Color and Chlorophyll Profile of Premium Extra Virgin Olive Oils

Premium extra virgin olive oils (PEVOO) are oils of exceptional quality and retail at high prices. The green color of recently extracted olive oils is lost during storage at room temperature, mainly because of the pheophytinization of chlorophylls. Since a green color is perceived as a mark of high-quality oils by consumers, it is especially important for PEVOO to maintain their initial green color. This study assessed the effect of applying low temperatures (refrigeration and freezing) and modified atmospheres on the color of four PEVOO for 24 months. Also, the effect of two freezing methods (slow freezing by placing the oil at -20 °C and fast freezing by immersing the oil in a bath of liquid nitrogen) was studied. Results showed that the green color was better preserved in oils frozen and stored at -20 °C whereas in oils frozen with liquid nitrogen the green color was lost much faster during frozen storage. An in-depth study of this unexpected phenomenon showed that this loss of green color was mainly due to a pheophytinization of chlorophylls. This phenomenon did not happen at the moment of freezing with liquid nitrogen, but over the first 100 days of storage at -20 °C. In addition, correlations between single chlorophyll and pheophytin contents and chromatic coordinates were established.

Litz wire loss performance and optimization for cryogenic windings

AbstractLitz wires operating in a cryogenic environment can potentially improve both the efficiency and power density of electrical machines and passive components. However, due to the low resistivity and high magnetic fields, eddy‐current losses may become significant in cryogenically cooled windings, especially in airgap winding arrangements or in the case of significant slot leakage fields, unless the litz wire parameters are carefully chosen. A framework for litz wire loss performance optimization and experimental characterisation at cryogenic temperatures is provided. An optimum operating temperature for minimum loss is derived based on analytical expressions, which highlights the role of litz wire parameters, current density and external field. The proximity loss model, used to calculate the optimum operating temperature, is validated experimentally. Two test rigs with different magnetic cores were designed and built. Copper and aluminium litz wires with a strand diameter down to 0.1 mm were tested in a liquid nitrogen bath with a uniform harmonic external magnetic field up to 0.5 T peak and a frequency up to 1 kHz. Measurements show good agreement with the theoretical results and confirm that the proposed model can be confidently used during the preliminary design of cryogenic windings.

Design and development of LN2 cooled cryopump for application in high heat flux test facility

• A liquid nitrogen cooled sorption cryopump is developed for the High Heat Flux Test Facility at IPR. • Design details, fabrication details, operational concept and thermo-structural analysis results are described. • The pump geometrical concept is novel because it provides ease of assembly, integration and trouble free operation in horizontal and vertical direction mounting. • The pump has 250 mm opening and offers pumping speed of ∼5106.6 l/s for water vapour and ∼1197 l/s for nitrogen using liquid nitrogen as coolant. • The pump integration and operation with High Heat Flux Test Facility is discussed. High Heat Flux Test Facility (HHFTF) at Institute for Plasma Research is established for testing thermal performance of Plasma Facing Components (PFC) and Plasma Facing Materials (PFM) that are expected to withstand steady-state and transient heat flux of the order of 10 MW/m 2 and 20 MW/m 2 , respectively, expected in plasma fusion devices. During high heat flux testing of PFCs and PFMs, water vapour and other trapped gases are released. For the pumping need, a cryocooler based commercial cryopump and a turbo-pump is used. In addition to that, an indigenously developed liquid nitrogen cooled cryopump is mounted to the High Heat Flux (HHF) test facility. The developed cryopump has 250CF inlet flange and mounted vertically downward to an angle port (50°) to the D-shaped vacuum chamber of the HHF facility. The pump has integrated liquid nitrogen bath to provide stable cooling to the cryopanels and radiation shield. Cryopanels are made of copper and coated with micro-porous activated charcoal. The pump's geometrical concept is novel because it provides ease of assembly, integration and trouble free operation in horizontal and vertical direction mounting. The pump offers pumping speed of ∼5106.6 l/s for water vapour and ∼1197 l/s for nitrogen using liquid nitrogen as coolant. The pump geometry, thermal and structural analysis, fabrication and experimental details are discussed in this paper. After integrating the cryopump to the HHF test facility, performance studies were carried out and initial test results are also discussed.

Improving the induction motor power density by its operation at liquid nitrogen bath

This work presents a study of an induction motor at two different operating temperature conditions: room temperature and 77 K. The goal is to analyze its performance and obtain its most relevant features. Experimental tests were carried out in the laboratory under room temperature and liquid nitrogen (LN2) bath. The authors designed a prototype bench with a controlled load to measure magnitudes like torque, speed, current, power, power factor, efficiency, and others. The results show a considerable increase in the torque and efficiency, but in contrast, the starting torque is drastically reduced at cryogenic temperature. Besides, at 77 K, the slip is much lower than at room temperature. The experiments show a substantial rise in the motor’s power density, indicating that cooled induction motors can be applied in applications where volume and weight are restricted.

A Study on the Electrical Contact Resistance and Thermal Conductivity of Soldered-Metal Insulation Coil With Conduction Cooling

The no-insulation (NI) winding method has been widely used in the fabrication of superconducting coils owing to its excellent thermal stability and mechanical stiffness. In the NI coil, there is a charging delay and heat loss due to leakage current. Therefore, the metal insulated (MI) winding method was proposed to reduce the charging delay and the heat loss due to the leakage current and the increased contact resistance by the metal tape. However, it is difficult to quantify the contact resistance between the turns of the coil during the design stage. To resolve this problem, a new winding method, called soldered metal insulation (SMI), was proposed by the authors, and the electrical properties were evaluated in a bath of liquid nitrogen. As a follow-up to the previous research, experimental investigations were conducted in a conduction cooling test apparatus to investigate the electrical and thermal characteristics of the SMI coil below 77 K. The electric contact resistances were evaluated through sudden discharge experiments. Then, the thermal contact resistances were measured using a heater installed on the outer turn of the coil. It is believed that the SMI winding technique can be applied to fabricate rare-earth barium copper oxide (REBCO) coils with predictable electrical and thermal contact resistances.

A Real-Time Monitoring System for Investigating Electromagnetic Behaviors of an HTS Coil

This paper presents a system for real-time monitoring spatial and temporal electromagnetic behaviors of a high temperature superconductor (HTS) coil with the no-insulation (NI) winding technique. We implemented a real-time monitoring system that consists of Hall sensors and voltage taps to measure spatial and temporal magnetic fields, and local voltages. An NI HTS test coil was wound, and the real-time monitoring system was combined with the test coil. An experimental study was performed in a liquid nitrogen bath at 77 K, where the test coil was charged with a constant ramp rate of 0.05 As <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><inline-formula><tex-math notation="LaTeX">$-1$</tex-math></inline-formula></sup> up to its operating current of 100 A. To describe measurement results, including local voltages and magnetic fields, we propose a set of simulations for coil voltages and currents, current density including <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">screening current</i> , and field gradient including <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">screening current induced field</i> . Using this set, we successfully simulated spatial and temporal electromagnetic behaviors generated by the test coil to a reasonable extent. The discussion section will provide comparison results between calculations and measurements.

Electro-Thermal Behavior of Layer-Wound BSCCO Coils With and Without Insulation

In this work, the electro-thermal behavior of two layer-wound High Temperature Superconducting (HTS) coils, realized with and without electrical insulation, is compared. Both coils are wound from the same BSCCO tape, and have a very similar geometry, with the same number of turns and layers. A heat input is applied to both coils, by tuning the current supplied to resistive heaters realized through stainless steel tapes wound on the mandrel at the inner surface of both coils. The heaters are in contact with one full inner turn of the winding. The coils are cooled in a liquid nitrogen bath, and the heaters are supplied with a constant current. Then, the windings are charged until the tape critical current is exceeded, and the tests are repeated for different heat loads. The signals acquired through voltage taps, suitably soldered at the same locations in both windings, are compared at the same testing conditions. Finally, the electrical characteristic of the different layers of the coils is related to the temperature of the heater and of the various turns of the coil by means of a 1-D thermal model.

Numerical and Experimental Study on Thermal Stability of BSCCO/REBCO Hybrid Tapes

This paper studies the thermal stability of BSCCO (Bi-2223) /REBCO hybrid tapes with different stacking methods under various operating currents in liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) bath. The thermal stability of single REBCO tape and BSCCO tape are also studied as the comparison. A 3D numerical model considering the anisotropic thermal conductivity is established to calculate the normal zone propagation velocity (NZPV) and minimum quench energy (MQE) of different hybrid tapes, and the temperature distributions of the tapes are obtained as well. The experiments of thermal stability of single tape and RB hybrid tape are also carried out. Results show the hybrid tape has better thermal stability than the REBCO tape and faster NZPV than the BSCCO tape.