Cool-down Process Research Articles

Towards the conceptual design of the cryogenic system of the Future Circular Collider (FCC)

Following the update of the European strategy in particle physics, CERN has undertaken an international study of possible future circular colliders beyond the LHC. The study considers several options for very high-energy hadron-hadron, electron-positron and hadron-electron colliders. From the cryogenics point of view, the most challenging option is the hadron-hadron collider (FCC-hh) for which the conceptual design of the cryogenic system is progressing. The FCC-hh cryogenic system will have to produce up to 120 kW at 1.8 K for the superconducting magnet cooling, 6 MW between 40 and 60 K for the beam-screen and thermal-shield cooling as well as 850 g/s between 40 and 290 K for the HTS current-lead cooling. The corresponding total entropic load represents about 1 MW equivalent at 4.5 K and this cryogenic system will be by far the largest ever designed. In addition, the total mass to be cooled down is about 250’000 t and an innovative cool-down process must be proposed. This paper will present the proposed cryogenic layout and architecture, the cooling principles of the main components, the corresponding cooling schemes, as well as the cryogenic plant arrangement and proposed process cycles. The corresponding required development plan for such challenging cryogenic system will be highlighted.

Influence of collector heat capacity and internal conditions of heat exchanger on cool-down process of small gas liquefier

Joule-Thomson cooling systems are commonly used in gas liquefaction. In small gas liquefiers, transient cool-down time is high. Selecting suitable conditions for cooling down process leads to decrease in time and cost. In the present work, transient thermal behavior of Joule-Thomson cooling system including counter current helically coiled tube in tube heat exchanger, expansion valve, and collector was studied using experimental tests and simulations. The experiments were performed using small gas liquefier and nitrogen gas as working fluid. The heat exchanger was thermally studied by experimental data obtained from a small gas liquefier. In addition, the simulations were performed using experimental data as variable boundary conditions. A comparison was done between presented and conventional methods. The effect of collector heat capacity and convection heat transfer coefficient inside the tubes on system performance was studied using temperature profiles along the heat exchanger.

Development of a New Method for Residual Stress Analysis on Fiber Reinforced Plastics with Use of Digital Image Correlation

In scope of the investigation of residual stresses the hole drilling method is an accepted method. The method is though not applicable for materials with high anisotropic behavior. Therefore a new algorithm is derived which allows the calculation of residual stresses in laminates made of unidirectional layers. Also the strain gauges deliver only strains on the areas where the strain gauges are applied. With the use of a high resolution imaging system and digital image correlation this area and the informational output can be widely improved. First, the derivation of the residual stress analysis algorithm is presented. For this an adequate finite element model, which is modeling the cooldown process as well as the drilling process, is set up and the surface strains are extracted. Based on this information an algorithm is derived and presented. Within the derivation a change of the layup, a possible change of the cooldown process and a variation of the drilling steps can be investigated. In consequence the input parameters of the algorithm can vary dependent on these factors. Second, the new optical testing setup with refinements to be able to measure the small deformations within micro-strains on the specimen’s surface is prepared and the concept presented. To solve the problem of casting shadows of the drill a special camera setup is being used.

Electrical and Mechanical Characteristics of HTS Twisted Stacked-Tape Cable Conductor

Electrical and mechanical characteristics of a twisted stacked-tape cable (TSTC) made of REBCO tapes are presented for both power transmission and magnet applications. It was found that the twist-pitch length and bending diameter that results in 2% degradation in the critical current are approximately proportional to the tape width. The critical twist-pitch length and bending diameter are roughly 22 times and 150 times the tape width, respectively. The cable critical-current of a square cross-section TSTC conductor is proportional to the square of the tape width, while the critical engineering-current-density is independent of the width. Both the current and current density are inversely proportional to the tape thickness. Finally, a method to mitigate the thermal contraction of a conductor during cooldown for power transmission applications is also discussed. Using a helically twisted conductor, the thermal contraction can be minimized by designing a cable for which the twisted-cable-diameter is reduced during the cooldown process while maintaining the conductor overall length constant.

Cross-stacked carbon nanotubes assisted self-separation of free-standing GaN substrates by hydride vapor phase epitaxy.

We report a novel method to fabricate high quality 2-inch freestanding GaN substrate grown on cross-stacked carbon nanotubes (CSCNTs) coated sapphire by hydride vapor phase epitaxy (HVPE). As nanoscale masks, these CSCNTs can help weaken the interface connection and release the compressive stress by forming voids during fast coalescence and also block the propagation of threading dislocations (TDs). During the cool-down process, thermal stress-induced cracks are initiated at the CSCNTs interface with the help of air voids and propagated all over the films which leads to full self-separation of FS-GaN substrate. Raman and photoluminescence spectra further reveal the stress relief and crystalline improvement of GaN with CSCNTs. It is expected that the efficient, low cost and mass-producible technique may enable new applications for CNTs in nitride optoelectronic fields.

In-situ surface contamination removal and cool-down process of the DEAP-3600 experiment

The DEAP-3600 experiment is a single-phase detector that uses 3600 Kg of liquid argon to search for Dark Matter at SNOLAB, Sudbury, Canada, 6800 ft. underground. The projected sensitivity to the spin-independent WIMP-nucleon cross-section is 10-46 cm2 for a WIMP mass of 100 GeV.A key experimental requirement is the reduction of any possible source of background that would mimic a Dark Matter signal This document will review how radiogenic surface backgrounds were reduced in-situ by removing 500 microns of acrylic from the innermost part of the detector with a resurfacing robot. Furthermore it will review the transient cool-down process of the experiment, necessary to reach cryogenic operating temperature.

Experimental and modeling investigation of an ICE (internal combustion engine) based micro-cogeneration device considering overheat protection controls

A dynamic simulation model for the micro-cogeneration unit based on ICE (internal combustion engine) is built as a new component on TRNSYS. This model considers dynamic processes including start-up, cool-down, and overheat protection controls. Through an experiment study, the steady and dynamic performances of the unit are presented and analyzed for calibrating the parameters of the dynamic model. Then the model is validated by the experiment data during steady and dynamic processes. The improvement of prediction accuracy of the model by considering dynamic processes is analyzed. The validation results show that the dynamic model can well predict the characteristics of the unit during start-up, cool-down, and overheat protection control processes. The cumulative prediction errors of the dynamic model decrease with the increase of the start–stop interval. By considering the dynamic processes, 5.18% and 3.2% of Qth and ηtotal cumulative prediction errors are decreased respectively when the start–stop interval is 0.5 h. The primary energy saving ratio and CO2 emission reduction ratio increases with the increase of the start–stop interval. The start–stop interval for the unit in this paper should be longer than 0.5 h, or the energy consumption of micro-cogeneration unit would be larger than that of conventional system.

Probabilistic Fracture Mechanics Analysis of Boling Water Reactor Vessel for Cool-Down and Low Temperature Over-Pressurization Transients

Abstract The failure probabilities of the reactor pressure vessel (RPV) for low temperature over-pressurization (LTOP) and cool-down transients are calculated in this study. For the cool-down transient, a pressure–temperature limit curve is generated in accordance with Section XI, Appendix G of the American Society of Mechanical Engineers (ASME) code, from which safety margin factors are deliberately removed for the probabilistic fracture mechanics analysis. Then, sensitivity analyses are conducted to understand the effects of some input parameters. For the LTOP transient, the failure of the RPV mostly occurs during the period of the abrupt pressure rise. For the cool-down transient, the decrease of the fracture toughness with temperature and time plays a main role in RPV failure at the end of the cool-down process. As expected, the failure probability increases with increasing fluence, Cu and Ni contents, and initial reference temperature-nil ductility transition ( RT NDT ). The effect of warm prestressing on the vessel failure probability for LTOP is not significant because most of the failures happen before the stress intensity factor reaches the peak value while its effect reduces the failure probability by more than one order of magnitude for the cool-down transient.

Performance of Sunflower Oil as a sensible heat storage medium for domestic applications

Experimental results evaluating the thermal performance of edible Sunflower Oil as a heat storage medium for domestic cooking applications are presented. The thermal performance of Sunflower Oil is evaluated during charging, 24h heat retention and discharging cycles. Results of charging reveal that high temperature charging is the most viable option. This is because it results in higher energy, higher exergy, higher exergy factor and higher stratification number values. The charging efficiency is found to only represent the rate of heat transfer and it indicates nothing about the quality of the stored energy. The optimal charging time proposes that charging be continued until a point when the stratification number drops to 80% of its peak value. Heat retention results during 24h show that high temperatures result in more heat losses during the cool-down heat retention processes. An optimal heat retention temperature is also suggested by the results. An optimal discharging flow-rate is also suggested by the discharging results. This is a compromise between obtaining a high rate of heat transfer and using the stored energy more effectively. The stratification number profiles show initial rises during the discharging cycles since the top temperatures drop at slower rates as compared to the bottom temperatures which results in larger thermal gradients as compared to the initial thermal gradients.

Investigation of Temperature Dependence of Raman Shift of Diamond-Like Carbon Coatings Used in Heat-Assisted Magnetic Recording

Heat assisted magnetic recording (HAMR) can overcome the super-paramagnetic limit and increase areal density beyond 1 Tb/in2 in hard disk drives [1]. In HAMR, a pulsed laser beam is first used to heat the magnetic medium beyond its Curie temperature and then data is magnetically recorded during the cool-down process while the coercivity of the medium is still low. High temperatures at the head disk interface are caused by the laser heating process which leads to lubricant depletion, magnetic degradation, and carbon overcoat damage of the head/disk interface [2]. The carbon overcoat can also be graphitized or oxidized leading to poor corrosion protection and inferior tribological performance [2]. The heated spot size achieved by the pulsed laser is very small, approximately 25nm in diameter. In addition, the duration of a typical laser heating cycle, including the cooling process, is very short, on the order of one ns. The measurement of the temperatures in the heated laser spot is of great interest for HAMR technology since reliability is strongly affected by the temperature rise in the heated laser spot. It is very difficult, if not impossible, to measure the temperature rise in the laser heated spot using conventional methods such as thermocouple measurements. To simulate and investigate the near field effects in heat assisted magnetic recording, tip enhanced Raman spectroscopy can be used (Fig. 1). Tip Enhanced Raman Spectroscopy (TERS) combines an atomic force microscope (AFM) and a Raman spectrometer to investigate the near field effects between the tip of an AFM and the adjacent surface. In TERS, a laser is focused on the tip of a metallized AFM tip, mounted in a scanning probing microscope. The laser illumination causes localized heating of the probe tip and the disk surface. Plasmon interactions at the interface between the probe tip and the surface enhance Raman scattering from the laser illumination. The scattered light is measured with a spectrometer and then analyzed in order to quantify the temperature rise in the disk due to the near-field heating by the AFM tip.

Dynamics of liquid nitrogen cooling process of solid surface at wetting contact coefficient

Liquid cryogens cooling by direct contact is very often used as a method for decreasing the temperature of electronic devices or equipment i.e. HTS cables. Somehow, cooldown process conducted in that way could not be optimized, because of cryogen pool boiling characteristic and low value of the heat transfer coefficient. One of the possibilities to increase the efficiency of heat transfer, as well as the efficiency of cooling itself, it is to use a spray cooling method. The paper shows dynamics analysis of liquid nitrogen cooling solid surface process. The model of heat transfer for the single droplet of liquid nitrogen, which hits on a flat and smooth surface with respect to the different Weber numbers, is shown. Temperature profiles in calculation domains are presented, as well as the required cooling time. The numerical calculations are performed for different initial and boundary conditions, to study how the wetting contact coefficient is changing, and how it contributed to heat transfer between solid and liquid cryogen.

Experimental study on the mixed refrigerant heat transfer performance in a plate-fin heat exchanger during a single-stage cryogenic cycle

Plate-fin heat exchangers (PFHEs) are mostly employed in small- and medium-sized LNG plants. However, studies on the heat transfer performance of mixed refrigerant in a PFHE under low-quality have rarely been conducted. In this paper, an experimental setup that utilized a single-stage cryogenic cycle with commercial compressors and a customized PFHE was established to study the heat transfer performance of the PFHE throughout the cool-down process. The components of the mixed refrigerant included nitrogen, methane, ethylene, propane and isobutane. Several experiments were conducted to obtain a refrigeration temperature as low as −160 °C. The characteristics of the cool-down process and the temperature difference change in the RHE were discussed. Meanwhile, five sets of condensation correlations and 13 sets of flow boiling correlations were selected to predict the HTC in the PFHE. The experimental overall HTC of the PFHE based on the hot sides was approximately between 11.88 and 37.74 W m−2 K−1. However, most of the existing correlations were not able to correctly predict the HTC of the PFHE in this work. Meanwhile, some suggestions regarding the PFHE design in a mixed refrigerant cryogenic system were proposed.

High-Speed Measurement of Complex Shaped Parts at Elevated Temperature by Laser Triangulation

The increasing quality expectations and the global competition push manufacturing industry to adopt strategies of lean manufacturing and precision engineering. In order to reach these aims it is necessary that the measuring process is integrated in the production chain to provide timely feedback for process control. Nowadays, however, forged products are typically measured after the cool-down process, which can take several hours. The advantages obtainable if forgings would be measured online are clear: deviations in the production process would be recognized earlier and the production process could be promptly adjusted. On-line measurement capabilities have the potential to reduce overall production costs and consequently are of interest to many forging industries, including those producing complex products such as turbine blades. Under these circumstances, the HOTGAUGE project was initiated: an international EUROSTARS project with the goal to develop a measuring system, capable of measuring freeform shaped parts at elevated temperature (approx. 800°C) directly after the forging step. The output of the measuring system is a 3D model of the hot part including temperature information. The 3D coordinate measuring system is composed by two main subsystems: a 2D laser-triangulation system capable to scan a complete section of the part, and a moving platform, which moves the part through the measuring plane. The architecture and the components of the measurement system as well as measurement results are presented in this paper.

Micromechanical measurement of beating patterns in the quantum oscillatory chemical potential of InGaAs quantum wells due to spin-orbit coupling

The quantum oscillatory magnetization M(B) and chemical potential μ(B) of a two-dimensional (2D) electron system provide important and complementary information about its ground state energy at low temperature T. We developed a technique that provides both quantities in the same cool-down process via a decoupled static operation and resonant excitation of a micromechanical cantilever. On InGaAs/InP heterostructures, we observed beating patterns in both M(B) and μ(B) attributed to spin-orbit interaction. A significantly enhanced sensitivity in μ enabled us to extract Rashba and Dresselhaus parameters with high accuracy. The technique is powerful for detailed investigations on the electronic properties of 2D materials.

The effect of hydrogen and oxygen contents on hydride reorientations of zirconium alloy cladding tubes

Abstract To investigate the effect of hydrogen and oxygen contents on hydride reorientations during cool-down processes, zirconium–niobium cladding tube specimens were hydrogen-charged before some specimens were oxidized, resulting in 250 ppm and 500 ppm hydrogen-charged specimens containing no oxide and an oxide thickness of 3.8 μm at each surface. The nonoxidized and oxidized hydrogen-charged specimens were heated up to 400°C and then cooled down to room temperature at cooling rates of 0.3°C/min and 8.0°C/min under a tensile hoop stress of 150 MPa. The lower hydrogen contents and the slower cooling rate generated a larger fraction of radial hydrides, a longer radial hydride length, and a lower ultimate tensile strength and plastic elongation. In addition, the oxidized specimens generated a smaller fraction of radial hydrides and a lower ultimate tensile strength and plastic elongation than the nonoxidized specimens. This may be due to: a solubility difference between room temperature and 400°C; an oxygen-induced increase in hydrogen solubility and radial hydride nucleation energy; high temperature residence time during the cool-down; or undissolved circumferential hydrides at 400°C.

Frequency pre-tuning of the niobium-sputtered quarter-wave resonator for HIE-ISOLDE project at CERN

Superconducting quarter-wave resonators (QWRs) will be used in the superconducting linac upgrade in the frame of the HIE-ISOLDE project at CERN. The QWRs are made of bulk copper and have their inner surface covered with sputtered niobium. Their resonant frequency is 101.28MHz at 4.5K. Each cavity will be equipped with a tuning system to both minimize the forward power and compensate the frequency variations during production and beam operation. After a careful examination of all contributors to the frequency variation, we decomposed them into two components: frequency shift and its uncertainties. A pre-tuning step was subsequently added to the production sequence prior to niobium sputtering to accommodate the frequency shift mainly due to mechanical tolerances during substrate production, substrate surface treatment, niobium sputtering and cooldown process. To this end, the length of the QWR was chosen as a free parameter for the pre-tuning. Consequently the tuning system needs only to compensate the frequency uncertainties and Lorentz force detuning, thus its design has been largely simplified and its production cost was reduced by 80% comparing to its previous version. We have successfully applied this tuning scheme to five HIE-ISOLDE QWRs and the measured tuning error was 2.4±1.9kHz. This is well consistent with our calculations and well recoverable by the current simplified tuning system. It is worth noticing that the pre-tuning method only involves one-time measurement of the cavity׳s resonant frequency and its outer conductor length. This paper focuses on HIE-ISOLDE high-β QWR, but the method can be applied to HIE-ISOLDE low-β QWRs and other variants of QWR-like cavities.

Tensile hoop stress-, hydrogen content- and cooling rate-dependent hydride reorientation behaviors of Zr alloy cladding tubes

250ppm hydrogen-charged (250ppm-H) and 500ppm-H Zr alloy cladding tubes oxidized to 2.5μm at their inner and outer surfaces were employed to examine the effect of tensile hoop stress, hydrogen content, cooling rate and oxygen content on the radial hydride precipitation behaviors during cool-down processes. The oxidized cladding tube specimens were heated up to 400°C and then cooled down to room temperature at cooling rates of 0.3, 2.0 or 8.0°C/min under tensile hoop stresses of 80, 100 or 150MPa. The amount of the radial hydrides precipitated and their growth during the cool-down processes were found to be strongly dependent upon the hydrogen content, tensile hoop stress, cooling rate and oxygen content. The lower hydrogen content, the higher tensile hoop stress, the slower cooling rate and the lower oxygen content generated the larger fraction of radial hydrides and the longer radial hydride length. These phenomena may be explained by the solubility difference between room temperature and 400°C, the effect of tensile hoop stress on the radial hydride nucleation energy, cooling-rate-dependent hydrogen super-saturation and high temperature residence time, and the effect of undissolved circumferential hydrides on the radial hydride precipitation.

Thermal Analysis of the ITER TF Feeder CFT and ICF

There are many cryogenic components in the Feeder working at 4.5–80 K, cooled by the supercritical helium and helium gas, in order to reduce the heat load to the cooling system, a thermal model of the TF Feeder is built in ANSYS, including both conduction and radiation effects. The analysis considers the cool-down process and the working status, to find out the thermal performance of the Feeder.

Cooldown-induced hydride reorientation of hydrogen-charged zirconium alloy cladding tubes

Radial hydride precipitation behaviors of Zr-Nb alloy cladding tubes were investigated using 250 and 500 ppm hydrogen-charged Zr-Nb alloy cladding tubes, cooldown processes from 400 to 300, 200°C and room temperature with five kinds of cooling rates of 0.3, 2.0, 4.0, 7.0 15.0 °C/min under a tensile hoop stress of 150 MPa, which can simulate various cooldown processes during an interim dry storage of PWR nuclear fuel. The slower cooling rate and the lower terminal cooldown temperature generated the more hydrides precipitated during the cooldown as well as the larger fraction and the longer length of radial hydrides. These phenomena can be explained by the difference in the terminal solid solubility of hydrogen for dissolution and precipitation occurring during the heatup and cooldown processes and the cooling rate-dependent hydride nucleation and growth rates. In addition, a drastic decrease in ultimate tensile strength and plastic strain of the tensile tested specimens experiencing the cool-down processes appear to be correlated with the amount of the radial hydrides precipitated during the cooldown.

Modeling and Dynamic Simulation of a Large Scale Helium Refrigerator

In order to simulate the transient behaviors of a newly developed 2kW helium refrigerator, a numerical model of the critical equipment including a screw compressor with variable-frequency drive, plate-fin heat exchangers, a turbine expander, and pneumatic valves wasdeveloped. In the simulation,the calculation of the helium thermodynamic properties arebased on 32-parameter modified Benedict-Webb-Rubin (MBWR) state equation.The start-up process of the warm compressor station with gas management subsystem, and the cool-down process of cold box in an actual operation, were dynamically simulated. The developed model was verified by comparing the simulated results with the experimental data.Besides, system responses of increasing heat load were simulated. This model can also be used to design and optimize other large scale helium refrigerators.