Cool-down Procedure Research Articles

Assignment of polar nanoregions influence from relaxor/ergodic states on the rare-earth optical emissions

Polar state transitions are one of the most intriguing phenomena in relaxor ferroelectric research, motivating many phenomenological models and experimental analyses. In addition to many electrical techniques that permit the evaluation of characteristic temperatures, this manuscript shows that the changes in rare-earth luminescence properties can act as an alternative probe. Here, we explore the luminescence properties of erbium-doped PLMN–13PT (lanthanum-modified lead magnesium niobate–lead titanate) under temperature and electric field-induced polar state transitions. In analogy to the magnetism setups, four electric field conditions were carried out during the cooldown and heating procedures: no-field, poled, zero-field-cooled (ZFC), and field-cooled (FC). The intensities of visible Er3+ emissions 4S3/2 → 4I15/2 and 2H11/2 → 4I15/2 exhibit peculiar behavior at the freezing temperature (TF) for the no-field condition, as nonlinear to linear transition, and a maximization. In an external electric field, these features shift to higher temperatures for the poled condition, and the amplitude evolves with a higher slope below TF for ZFC. However, in the FC condition, the emissions behave similarly to the no-field case, indicating competition between the modes of depolarization. Our results show that rare-earth ion emissions correlate with the polar nanoregion dynamics and probe the ergodic, non-ergodic, and paraelectric transitions.

On Residual Stresses and Reference Temperatures in Thermomechanical Simulations of Photovoltaic Modules Using the Finite Element Method

Thermomechanical simulation of photovoltaic (PV) modules using the finite element method (FEM) is a useful tool to evaluate module design features in terms of structural integrity, reliability, and durability. One of the main challenges in the numerical modeling of a PV module is the incorporation of residual stresses induced by the manufacturing process. Modeling assumptions and abstractions are necessary to limit the model complexity and reduce the computational time. However, oversimplifications and incorrect assumptions can lead to erroneous numerical results. Unfortunately, much simulation work still neglects process-induced stresses. This can lead to incorrect predictions of the stress–strain history and erroneous conclusions during the design process. Here, we review current modeling practices for incorporating process-induced stresses, and contrast numerical models that consider residual stresses with those that neglect them. We find that the simulation objective and available material properties dictate which process steps need to be modeled, and explore in depth the modeling of residual stresses induced by the lamination process. We demonstrate that a simplified cooldown procedure at the beginning of the simulation can increase the model accuracy and discuss appropriate choices for starting and reference temperatures in the finite element model.

Performance analysis of high-speed cryogenic turbo-expander at cooling process based on numerical and experimental study

Abstract In order to make a detailed understanding of the cryogenic turbo-expander off-design performance at cool-down procedure, an extensive experimental and numerical program have been carried out on a mixed and inward flow radial turbine. According to the design and cooling process condition, just like pressure at stator inlet or brake power of the turbo-expander, a series of CFD simulations were carried out in order to guide design and off-design iterations towards achieving a matched flow capacity for each situation. The analyses also include the study of the effect of different gas models on the CFD calculations. Through the results analysis it was concluded that the direct use of the Hepak database for the real gas properties in the CFD solver improve the prediction of the thermodynamic properties and so the performance of the turbo-expander. With experimental comparison, the cryogenic turbo-expander off-design performance at cooling process can be better known.

Boil-off gas balanced method of cool down for liquefied natural gas tanks at sea

Cooling down the cargo tanks of liquefied natural gas carriers (LNGC) prior to the ships arrival at discharge and loading ports follow various widely adopted operating procedures. The tank cool-down procedures typically followed cannot though be considered as best practice, because they consume considerable boil-off gas while reducing tank temperatures. An alternative tested method, described here, consumes considerably less liquefied natural gas (LNG) during the tank cool-down process, which is beneficial, particularly during the ballast voyages. In certain circumstances, LNGC consume liquid marine fuels so that they are able to preserve enough LNG heel to complete tank cool down at sea to required low temperatures before reloading can be commenced. The novel method devised for cooling down LNGC, particularly those fitted with membrane cargo tanks, at sea prior to arrival at a loading terminal involves much lower LNG heel consumption than conventional methods. The boil-off gas (BOG)-balanced tank-cool-down method applies continuous spraying, at very low rates, of the tanks with LNG extracted from the heel. This procedure enables the ship’s engines to consume all excess BOG without the need to pass some of it as waste for combustion in the gas combustion unit or steam dump. It also ensures that the LNG cargo tanks are maintained at stable and constant pressure and reduces the coolant LNG quantity consumed. The BOG-balanced tank-cool-down is straightforward to implement and monitor, simplifying tank pressure control. Test results demonstrate that tank cool-down rates of 4 to 5 ◦C/per hour can be maintained such that tank temperatures can be reduced from +30 to -130 ◦C within 37 hours. The method could work on LNGC with Moss-type tanks but is likely to be less effective as they are typically fitted with fewer tank spraying nozzles. Cited as : Kulitsa, M., Wood, D.A. Boil-off gas balanced method of cool down for liquefied natural gas tanks at sea. Advances in Geo-Energy Research, 2020, 4(2): 199-206, doi: 10.26804/ager.2020.02.08

The CUORE cryostat

The CUORE experiment (Cryogenic Underground Observatory for Rare Events) is a ton-scale detector, operating at a cryogenic temperature around 10 mK, searching for neutrinoless double-beta decay in 130Te and other rare events. The experiment cryogenic infrastructure, its subsystems and the cool-down procedure that allowed CUORE to obtained the first physics results will be presented.

Experimental investigation of PWR accident scenarios at the PKL test facility

PKL is the only test facility in Europe that replicates the entire primary side and the most important parts of the secondary side of western-type Pressurized Water Reactors (PWR) in the scale of 1:1 in heights. It is also worldwide the only test facility with 4 identical reactor coolant loops arranged symmetrically around the Reactor Pressure Vessel (RPV) for simulation of nonsymmetrical boundary conditions between the reactor loops. Thermal-hydraulic phenomena observed in PWRs are simulated in the PKL test facility for over 40 years. The analyses carried out in these years encompass a large spectrum of accident scenario simulations and corresponding cool-down procedures. The overall goal of the PKL experiments is to show that under accident conditions - even for extreme and highly unlikely assumptions as additional loss of safety systems - the core cooling can be maintained or re-established by automatic or operator- performed procedures and that a severe accident e.g. a core melt-down can be avoided under all circumstances. Another goal of the tests performed in the PKL facility is the provision of data for validation of thermal-hydraulic system codes. This paper presents recent modifications of the PKL facility, applied in order to adapt the facility to the latest western-type designs currently built in the world. The paper discusses also important results obtained in the last years.

Investigation of Non-cooldown SG Secondary Condition on the Natural Circulation Cooling Procedure

In typical pressurized water reactor (PWR), in case that one steam generator (SG) cannot be credited for the primary cooldown, it is necessary to homogenize primary coolant temperature among loops using at least one reactor coolant pump (RCP) for the plant cooldown. If the natural circulation condition is established due to unavailability of all the RCPs, the continuous cooldown using intact SGs causes to disturb the smooth depressurization because it leads to void generation in the top of the non-cooldown SG tube where the high temperature coolant is remained. For this purpose, W.Sakuma, et al.[1] suggested the outline of asymmetric cooldown procedure without any RCPs restart. Since the suggested procedure is based on only one secondary condition (SG dry-out) of non-cooldown SG, and hence the impact of difference of the secondary condition should be investigated. In this paper, the sensitivity analyses were performed to confirm the impact on the asymmetric cooldown procedure, and consequently, it was confirmed that the coolable range used in the procedure was expanded if the water inventory exists in non-cooldown SG. Therefore it was concluded that the coolable range which was defined with the SG dry-out condition in non-cooldown SG can be conservatively applied for the operating procedure.

Cooldown procedure success criteria map for the full break size spectrum of SBLOCA

A success criteria map defining successful implementation of a cooldown procedure to mitigate small-break loss of coolant accident (SBLOCA) with failed high pressure safety injection system for the OPR1000 is generated for the full break size spectrum from 0.5 in to 2.5 in diameter breaks. The success criteria map is a multi-dimensional response surface that gives the expected peak clad temperature (PCT) as a function of break size and operator action time to start the 55.6 °C/hr reactor coolant system cooldown and depressurization involving secondary side steam dump through manual manipulation of the atmospheric dump valves (ADV). The PCT response surface is constructed through a regression analysis using a Gaussian process model (GPM) coupled to an adaptive sampling procedure that greatly reduces the computational cost and analysis time by limiting the number of required best estimate simulations of the SBLOCA with the MARS code to approximately 100. Break flow rates and times to core heat up each span several orders of magnitude when considering the full break size spectrum so an innovative solution of transforming the break size and ADV actuation time input variables using exponential and logarithm functions was implemented such that the regression could be performed on the scaled and transformed input space.

Impact of Remanent Magnetic Field on the Heat Load of Original CEBAF Cryomodule

The heat load of the original cryomodules for the continuous electron beam accelerator facility is ~50% higher than the target value of 100 W at 2.07 K for refurbished cavities operating at an accelerating gradient of 12.5 MV/m. This issue is due to the quality factor of the cavities being ~50% lower in the cryomodule than when tested in a vertical cryostat, even at low RF field. Previous studies were not conclusive about the origin of the additional losses. We present the results of a systematic study of the additional losses in a five-cell cavity from a decommissioned cryomodule after attaching components, which are part of the cryomodule, such as the cold tuner, the He tank, and the cold magnetic shield, prior to cryogenic testing in a vertical cryostat. Flux-gate magnetometers and temperature sensors are used as diagnostic elements. Different cool-down procedures and tests in different residual magnetic fields were investigated during the study. Three flux-gate magnetometers attached to one of the cavities installed in the refurbished cryomodule C50-12 confirmed the hypothesis of high residual magnetic field as a major cause for the increased RF losses.

Low Temperature Test of HWR Cryomodule

Low temperature test for half-wave resonator (HWR) cryomodule is performed at the superfluid helium temperature of 2 K. The effective temperature is defined for non-uniform temperature distribution. Helium leak detection techniques are introduced for cryogenic system. Experimental set up is shown to make the low temperature test for the HWR cryomodule. The cooldown procedure of the HWR cryomodule is shown from room temperature to 2 K. The cryomodules is precooled with liquid nitrogen and then liquid helium is supplied to the helium reservoirs and cavities. The pressure of cavity and chamber are monitored as a function of time. The vacuum pressure of the cryomodule is not increased at 2 K, which shows leak-tight in the superfluid helium environment. Static heat load is also measured for the cryomodule at 2.5 K.

Experimental and Analytical Assessment of Natural Circulation Interruption Phenomenon in the LSTF and PKL Test Facilities

Following an accidental event in a nuclear pressurized water reactor, involving the loss of primary-side forced coolant flow, the core decay heat is generally removed through a natural circulation convection process. The cooldown of the reactor coolant system is carried out through the secondary-side heat sink following prescribed guidelines. However, under asymmetric primary-side cooling conditions, natural circulation interruption (NCI) in the loops with an inactive steam generator may take place. Under such conditions, the cooldown of the primary side may be hindered and the transient may evolve toward a degraded state. The NCI issue was recently addressed within the thermal-hydraulic experimental projects ROSA-2 and PKL-2 of the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development. The objective was to identify the conditions that may lead to the occurrence of NCI, to develop cooldown procedures that prevent the occurrence of NCI, and to assess the thermal-hydraulic code capabilities in predicting this phenomenon. In the current study, NCI experimental tests carried out in the LSTF (Large Scale Test Facility) and PKL (Primaer-KreisLauf) facilities are assessed using the best-estimate thermal-hydraulic system codes CATHARE and ATHLET. The simulation results are presented and conclusions are derived accordingly.

Magnetic flux studies in horizontally cooled elliptical superconducting cavities

Previous studies on magnetic flux expulsion as a function of cooldown procedures for elliptical superconducting radio frequency (SRF) niobium cavities showed that when the cavity beam axis is placed parallel to the helium cooling flow and sufficiently large thermal gradients are achieved, all magnetic flux could be expelled and very low residual resistance could be achieved. In this paper, we investigate flux trapping for the case of resonators positioned perpendicularly to the helium cooling flow, which is more representative of how SRF cavities are cooled in accelerators and for different directions of the applied magnetic field surrounding the resonator. We show that different field components have a different impact on the surface resistance, and several parameters have to be considered to fully understand the flux dynamics. A newly discovered phenomenon of concentration of flux lines at the cavity top leading to temperature rise at the cavity equator is presented.

Reduction of helium loss from a superconducting accelerating cavity during initial cool-down and cryostat exchange by pre-cooling the re-condensing cryostat

A Zero-Boil-Off (ZBO) cryostat is designed to realize a compact, stand-alone cryogenic system for the AIST superconducting accelerator (SCA). Under normal operation there is no evaporative helium loss from the cryomodule and therefore operating costs associated with the supply of liquid helium can be eliminated. The only significant loss of helium from the module occurs during the initial cavity cool-down procedure or when the re-condensing cryostat is replaced. It takes about 3h to cool down the cryostat head from room temperature (300K) to 4K. During this time around 100L of liquid helium is lost due to evaporation. By pre-cooling the cryostat inside a low heat load vacuum tube before transfer to the cryomodule, this evaporative loss could be essentially eliminated, significantly reducing the volume of liquid helium required for the initial cryomodule cool-down. The pre-cooling system also provides an efficient method to test the cryostat prior to use.

Training Profiles and Motivation of Male and Female Youth Soccer Players

The objective of this study was to investigate training profiles and motivation of male and female youth soccer players in different age groups and levels of play. A total of 1075 youth soccer players (U15-U19) from the Bavarian Football Association (BFV) in Germany completed a survey which investigated the total hours of training per week, and hours of training spent in endurance, sprint, technical/tactical, strength and other training and warm-up and cool-down procedures. Significant differences (p<0.05) between male high- and low-level players were seen in the amount of hours in sprint, technical/tactical and strength training. These differences were also found on motivation of the players. The total amount of training increased significantly with age in female players, but the only difference between high- and low-level players was in the amount of endurance training in the U19-group and game-related motivation in the U17-group. This study provides guidelines for training load and content in youth soccer players by gender, age and skill levels.

Effect of Competition on Nitric Oxide, Carbon Monoxide, and Cyclic Guanosine Monophosphate Levels in Training Horses

The aim of this study was to compare the effect of exercise on nitric oxide (NO), carbon monoxide (CO), and cyclic guanosyl monophosphate (cGMP) levels in jumping and dressage horses involved in competition. Blood samples were collected from the jugular vein of 100 horses involved in jumping or dressage competition at three time points: baseline at rest, on reaching the schooling but before exercise, and over a jump or dressage course. Fourteen healthy horses not involved in competition were used as control group. Exercise increased plasma CO concentration in both jumping and dressage horses, and this effect was more apparent in dressage horses. Exercise also increased NO plasma concentration in jumping horses, whereas it did not significantly modify NO plasma concentration in dressage horses. After exercise, plasma cGMP concentration was higher in both groups. Our results show that different signaling pathways are initially activated by exercise and that this activation is specific to the different modes of exercise. This information can be used to optimize warm-up and cool-down procedures for sport horses or to optimize training programs for equine athletes.

STRENUOUS EXERCISE DURING PREGNANCY

New knowledge is urgently needed in order to advise fit women in physically-active occupations (military service, police work, fire-fighting, competitive athletics) on safe intensities, durations and frequencies of physical exertion during a healthy pregnancy Recent studies from Dr. Wolfe's laboratory have examined cardiac autonomic function and acid-base regulation in fit, healthy women at rest and during exercise above and below the ventilatory anaerobic threshold (Tvent) in late gestation. Oxygen uptake kinetics in response to a step increase in work rate (80% Tvent) were also examined. Cardiac autonomic studies demonstrated that vagal/parasympathetic modulation is reduced at rest and sympatho-adrenal responses are attenuated during strenuous exercise above Tvent, resulting in a reduction in maximal heart rate reserve. Acid-base studies showed that pregnant women were able to maintain arterial pH values higher than those of non-pregnant controls at rest and during exercise at work rates above and below Tvent. Finally, the time constant for oxygen uptake kinetics was significantly slower in pregnant subjects compared to non-pregnant controls. Parallel studies from Dr. Mottola's lab have examined metabolic and cardiorespiratory responses to prolonged steady-state treadmill exercise in late gestation. Results showed that healthy, fit pregnant women exhibit transient post-exercise reductions in blood glucose, suggesting a temporary reduction in fetal glucose availability. Another study involving a case control design reported that exercise of 5 times or more per week increases the odds ratio of giving birth to a low birth weight baby, whereas an exercise frequency of 3–4 times per week does not affect birth outcome. In summary, information presented in this mini-symposium supports the hypothesis that healthy, fit pregnant women are well-adapted to perform acute bouts of high-intensity, short duration as well as prolonged exercise at moderate intensities. However, the use of proper warm-up and cool-down procedures and nutritional measures to prevent post-exercise in blood glucose levels are both recommended. Further study is needed to formulate evidence-based guidelines for prenatal exercise in this population.

Planar SQUID gradiometers fabricated on 24° and 30° SrTiO/sub 3/ bicrystals

HTS dc SQUID gradiometers have been fabricated on 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/ bicrystal substrates with slots and flux dams in the SQUID washers. The spatial response of such devices has been measured experimentally and compared with modelled results. Single layer devices, in terms of gradient sensitivity, have characteristics that deviate only slightly from idealized first order gradiometers. The low frequency flux noise of these devices is discussed with particular emphasis on both the unshielded properties and the effect of various cooldown procedures on the noise.

High-temperature superconducting YBCO dc SQUID gradiometers fabricated on STO bicrystal substrates

HTS dc gradiometers have been fabricated with slots and flux dams in their SQUID washers. Using a single layer of YBCO, the gradient sensitivity is limited by the sensing magnetometer in the centre of the structure. The spatial response of such devices has been measured experimentally indicating that single layer devices, in terms of gradient sensitivity, have characteristics that deviate slightly from idealized first order gradiometers. The flux noise of these devices is discussed with particular emphasis on their unshielded low frequency noise properties. We also discuss the effect of different cooldown procedures on the flux noise.

Grain size-dependence of the spezific heat of YBa 2Cu 3O 7-sinters

The low temperature specific heat of YBa2Cu3O7 sinters is measured as a function of their average grain size. The latter is controlled by the sintering time at 940°C, the cool-down procedure in the oxygen atmosphere being kept the same for all samples. Contrary to earlier observations /l/ we now find an extra contribution to the specific heat which is largest for the smallest grain sizes.

Analysis of time-varying characteristics of signals from borssele reactor

A method of random data analysis, based on least squares autoregressive (AR) modeling, was applied to signals from Borssele reactor. In this method, the model parameters are determined directly from the data without estimating correlation functions, enabling to avoid the modeling errors often encountered when the number of samples is small. From the estimated AR model, auto power spectral density (APSD) and secondary noise signatures are derived easily. The following secondary signatures were used to quantify the time-variation of statistical properties of the signals: • - sample variance of the signal, • - sample variance of the residual, • - resonance frequencies of peaks in the APSD, • - amplitudes of the peaks, • - magnitude of the APSD at the lowest frequency. The purpose of this paper is to demonstrate the usefulness of the method as a practical tool for surveillance and diagnostics of a nuclear power plant. The method was implemented into the PDP-11 system of the physics department o ECN, where signals are available taking the advantage of on-line link with Borssele reactor instrumentation. The method was applied to several sets of data in which non-stationary was recognized. Typical examples of them are: the signals obtained while the reactor was undergoing a power level change, the response of vibration sensors to artificial disturbance imposed under cold shut-down conditions and pressure standing wave phenomena observed during the cool-down procedure. Through the analysis, it was confirmed that the method is highly efficient in detecting changes of the statistical properties of the signals. In addition to the detection, information relevant to the cause and extent of the changes was also extractable. Development of diagnosis systems covering not only stationary but also time-varying operation modes of nuclear reactors can be accomplished by proper use of the present method.