Hasil untuk "Low temperature engineering. Cryogenic engineering. Refrigeration"

Y. Ye, Q. Wang, Jian Lu et al.

High-entropy alloys (HEAs) are presently of great research interest in materials science and engineering. Unlike conventional alloys, which contain one and rarely two base elements, HEAs comprise multiple principal elements, with the possible number of HEA compositions extending considerably more than conventional alloys. With the advent of HEAs, fundamental issues that challenge the proposed theories, models, and methods for conventional alloys also emerge. Here, we provide a critical review of the recent studies aiming to address the fundamental issues related to phase formation in HEAs. In addition, novel properties of HEAs are also discussed, such as their excellent specific strength, superior mechanical performance at high temperatures, exceptional ductility and fracture toughness at cryogenic temperatures, superparamagnetism, and superconductivity. Due to their considerable structural and functional potential as well as richness of design, HEAs are promising candidates for new applications, which warrants further studies.

E. Ezugwu

Yonghao Zhao, Xiaozhou Liao, Sheng-wei Cheng et al.

S. Y. F. Zhao, X. Cui, P. Volkov et al.

Twisted interfaces between stacked van der Waals (vdW) cuprate crystals present a platform for engineering superconducting order parameters by adjusting stacking angles. Using a cryogenic assembly technique, we construct twisted vdW Josephson junctions (JJs) at atomically sharp interfaces between Bi2Sr2CaCu2O8+x crystals, with quality approaching the limit set by intrinsic JJs. Near 45° twist angle, we observe fractional Shapiro steps and Fraunhofer patterns, consistent with the existence of two degenerate Josephson ground states related by time-reversal symmetry (TRS). By programming the JJ current bias sequence, we controllably break TRS to place the JJ into either of the two ground states, realizing reversible Josephson diodes without external magnetic fields. Our results open a path to engineering topological devices at higher temperatures. Editor’s summary Twisted two-dimensional (2D) structures exhibit a wealth of interesting behaviors. Recently, the 2D materials used in such superlattices have largely been graphene and various transition metal dichalcogenides. However, cuprate superconductors can also be thought of as 2D materials, with the copper-oxide planes coupled to each other through Josephson coupling. Zhao et al. created high-quality twisted structures of a bismuth-based cuprate by cleaving a single exfoliated crystal and placing the two halves on top of each other at various angles. Near the twist angle of 45°, Josephson coupling was suppressed by the d-wave superconducting order parameter of the material. The researchers also observed a Josephson diode effect caused by the breaking of time reversal symmetry. —Jelena Stajic Transport measurements were used to characterize twisted cuprate Josephson junctions at various twist angles.

José Peixoto, Alexis Gonzalez, Janki Bhimani et al.

Programmable caching engines like CacheLib are widely used in production systems to support diverse workloads in multi-tenant environments. CacheLib's design focuses on performance, portability, and configurability, allowing applications to inherit caching improvements with minimal implementation effort. However, its behavior under dynamic and evolving workloads remains largely unexplored. This paper presents an empirical study of CacheLib with multi-tenant settings under dynamic and volatile environments. Our evaluation across multiple CacheLib configurations reveals several limitations that hinder its effectiveness under such environments, including rigid configurations, limited runtime adaptability, lack of quality-of-service support and coordination, which lead to suboptimal performance, inefficient memory usage, and tenant starvation. Based on these findings, we outline future research directions to improve the adaptability, fairness, and programmability of future caching engines.

Ivoni Carlos Acunha Jr.

Energy efficiency in industrial refrigeration systems should be an object of study, especially large ones used for producing and storing food and beverage products. This is because this system requires large electricity consumption and, consequently, carries out environmental impacts. Some strategies and technologies can be used to increase the coefficient of performance (COP) of refrigeration units, such as intelligent operation through variable speed drives (VSDs) in pumps and fans, floating head pressure work, optimization of ice and chilled water production, intelligent controls in condensers and compressors, use of mathematical modeling and computer simulations, among others. Therefore, this work aims to highlight the impact of strategy and technology employment on energy efficiency improvements at industrial refrigeration systems by bringing studies of cases about refrigeration units used in food refrigeration of dairy, pork, and poultry products.

Zhai Rui, Li Zhijun, Yang Zhao et al.

The current greenhouse effect and the "dual-carbon" goal have set off a new wave of refrigerant substitution, requiring new refrigerants to achieve a comprehensive balance between environmental protection, safety and thermal properties. However, there are currently no ideal substitutes for these refrigerants. Most environmentally friendly refrigerants, such as R290, R32, and R1234yf, which have low ozone depletion potential (ODP) and Global Warming Potential (GWP), are flammable and pose safety risks. Identifying suitable flame retardants for environmentally friendly flammable refrigerants has emerged as a crucial focus of current research on refrigerant alternatives. This article provides a recent overview of research progress on the compatibility of flame retardants with flammable refrigerants. The main focus was categorizing the various flame retardants and assessing their efficacy across different flammable substances. It also discusses their performance, effects, mechanisms, and environmental impacts. Furthermore, the article analyzes their potential applications and development trends and recommends flame retardants compatible with flammable substances.

Geng Yi, Shi Junye, Chen Jiangping et al.

The heat pump system， as a core component of the thermal management system in new energy commercial vehicles， plays a critical role in improving vehicle range and economic efficiency through energy efficiency optimization and multi-mode cooperative control. This study employed R134a as the refrigerant and developed a multivariate cooperative control framework based on a proportional-integral （PI） control algorithm. The dynamic performance characteristics of the heat pump system under diverse environmental conditions were systematically investigated using advanced modeling environment for simulations （AMESim）. Focusing on two typical operating scenarios： high-temperature cooling at 40 ℃ and wide-range low-temperature heating （-15 to 0 ℃）， a hierarchical control strategy integrating air-， water-， and dual-source coupled heat pump modes was proposed， along with a cascaded waste heat utilization model for motors. The results show that in the dual-target cooling mode， the system achieves simultaneous temperature control for the battery pack and cabin within 200 s， with the compressor power stabilized at approximately 7 000 W and a coefficient of performance （COP） ranging from 2.5 to 3.0. Under low-temperature heating conditions， the dual-source heat pump mode achieved a heating COP of 2.1， representing 60% energy savings over traditional PTC heating systems.

LAI Xiaocheng, YAO Yuanlin, CHEN Kai et al.

R290 is an environmentally friendly Refrigerant, but it has flammable characteristics, making it difficult to be widely used. From the perspective of product development, aiming at the safety problem of refrigerant leakage of split-type air-conditioner using R290, the distribution law of refrigerant leakage was explored by building an experimental platform for detecting concentration distribution of refrigerant after leakage and a refrigerant leakage response system was built to determine the optimal detection location of the Sensor. The experimental results show that when the refrigerant leaks rapidly, the refrigerant will quickly form explosive clouds above the air conditioner. The explosive clouds can be effectively eliminated by starting the fan and controlling the Air outlet angle, but when the Air volume is less than 55% of the standard minimum Air volume, the leaked refrigerant cannot be evenly diffused. The selection conditions of the optimal detection position were determined by experiments, and effective explosion-proof measures were formulated, which can achieve rapid response within 17s, and there is no explosion risk area. This study provides guidance for the application of R290 and the development of products.

Pierre-Emmanuel Goffi, Raphaël Tremblay, Bentley Oakes

Successfully engineering interactive industrial DTs is a complex task, especially when implementing services beyond passive monitoring. We present here an experience report on engineering a safety-critical digital twin (DT) for beer fermentation monitoring, which provides continual sampling and reduces manual sampling time by 91%. We document our systematic methodology and practical solutions for implementing bidirectional DTs in industrial environments. This includes our three-phase engineering approach that transforms a passive monitoring system into an interactive Type 2 DT with real-time control capabilities for pressurized systems operating at seven bar. We contribute details of multi-layered safety protocols, hardware-software integration strategies across Arduino controllers and Unity visualization, and real-time synchronization solutions. We document specific engineering challenges and solutions spanning interdisciplinary integration, demonstrating how our use of the constellation reporting framework facilitates cross-domain collaboration. Key findings include the critical importance of safety-first design, simulation-driven development, and progressive implementation strategies. Our work thus provides actionable guidance for practitioners developing DTs requiring bidirectional control in safety-critical applications.

Miguel Goulão, Vasco Amaral, Marjan Mernik

Model-driven engineering (MDE) is believed to have a significant impact in software quality. However, researchers and practitioners may have a hard time locating consolidated evidence on this impact, as the available information is scattered in several different publications. Our goal is to aggregate consolidated findings on quality in MDE, facilitating the work of researchers and practitioners in learning about the coverage and main findings of existing work as well as identifying relatively unexplored niches of research that need further attention. We performed a tertiary study on quality in MDE, in order to gain a better understanding of its most prominent findings and existing challenges, as reported in the literature. We identified 22 systematic literature reviews and mapping studies and the most relevant quality attributes addressed by each of those studies, in the context of MDE. Maintainability is clearly the most often studied and reported quality attribute impacted by MDE. Eighty out of 83 research questions in the selected secondary studies have a structure that is more often associated with mapping existing research than with answering more concrete research questions (e.g., comparing two alternative MDE approaches with respect to their impact on a specific quality attribute). We briefly outline the main contributions of each of the selected literature reviews. In the collected studies, we observed a broad coverage of software product quality, although frequently accompanied by notes on how much more empirical research is needed to further validate existing claims. Relatively, little attention seems to be devoted to the impact of MDE on the quality in use of products developed using MDE.

Saba Sanami, Amir G. Aghdam

Reliable aero-engine anomaly detection is crucial for ensuring aircraft safety and operational efficiency. This research explores the application of the Fisher autoencoder as an unsupervised deep learning method for detecting anomalies in aero-engine multivariate sensor data, using a Gaussian mixture as the prior distribution of the latent space. The proposed method aims to minimize the Fisher divergence between the true and the modeled data distribution in order to train an autoencoder that can capture the normal patterns of aero-engine behavior. The Fisher divergence is robust to model uncertainty, meaning it can handle noisy or incomplete data. The Fisher autoencoder also has well-defined latent space regions, which makes it more generalizable and regularized for various types of aero-engines as well as facilitates diagnostic purposes. The proposed approach improves the accuracy of anomaly detection and reduces false alarms. Simulations using the CMAPSS dataset demonstrate the model's efficacy in achieving timely anomaly detection, even in the case of an unbalanced dataset.

Cheng Yan, Jianlu Zhu, Q. Lu et al.

Yong Yu, Xiao Xu, Michel Bosman et al.

M. S. Aydin, Nora Marek, T. Luciani et al.

Despite the potential of extrusion-based printing of thermoplastic polymers in bone tissue engineering, the inherent nonporous stiff nature of the printed filaments may elicit immune responses that influence bone regeneration. In this study, bone scaffolds made of polycaprolactone (PCL) filaments with different internal microporosity and stiffness was 3D-printed. It was achieved by combining three fabrication techniques, salt leaching and 3D printing at either low or high temperatures (LT/HT) with or without nonsolvent induced phase separation (NIPS). Printing PCL at HT resulted in stiff scaffolds (modulus of elasticity (E): 403 ± 19 MPa and strain: 6.6 ± 0.1%), while NIPS-based printing at LT produced less stiff and highly flexible scaffolds (E: 53 ± 10 MPa and strain: 435 ± 105%). Moreover, the introduction of porosity by salt leaching in the printed filaments significantly changed the mechanical properties and degradation rate of the scaffolds. Furthermore, this study aimed to show how these variations influence proliferation and osteogenic differentiation of human bone marrow-derived mesenchymal stromal cells (hBMSC) and the maturation and activation of human monocyte-derived dendritic cells (Mo-DC). The cytocompatibility of the printed scaffolds was confirmed by live–dead imaging, metabolic activity measurement, and the continuous proliferation of hBMSC over 14 days. While all scaffolds facilitated the expression of osteogenic markers (RUNX2 and Collagen I) from hBMSC as detected through immunofluorescence staining, the variation in porosity and stiffness notably influenced the early and late mineralization. Furthermore, the flexible LT scaffolds, with porosity induced by NIPS and salt leaching, stimulated Mo-DC to adopt a pro-inflammatory phenotype marked by a significant increase in the expression of IL1B and TNF genes, alongside decreased expression of anti-inflammatory markers, IL10 and TGF1B. Altogether, the results of the current study demonstrate the importance of tailoring porosity and stiffness of PCL scaffolds to direct their biological performance toward a more immune-mediated bone healing process.

Tan Qingpeng, Liu Jinping, Chen Jianxun et al.

In this study, physical models of six-row and four-row arrays of a low-ambient-temperature air-source heat pump with and without wall obstruction are established. A three-dimensional numerical simulation of the ambient flow field of the low-ambient-temperature air-source heat pump under nominal working conditions at 261.15 K is carried out. In this study, the inlet air temperature of the evaporator surface and the heat transfer rate of the low-ambient-temperature air-source heat pump under different horizontal wind speeds are investigated. The location of the unit under the worst conditions is determined, and the influence of cold air backflow on the heat transfer performance is analyzed. The ambient wind hindered the diffusion of cold air at the fan outlet and increased the deflection angle of the fan outlet, resulting in the accumulation of cold air in the upper part of the fan, and the cold air reflux phenomenon in the unit was more obvious inside and on the lee side the array. The results showed that when the horizontal distance between the units was 0.6 m, the horizontal wind speed increased from 0 to 5 m/s. The lowest inlet air temperature of the array unit is 2.44–3.69 K lower than the ambient temperature; the average heat transfer decreases by 1%–6.2%, and the average inlet air temperature is 0.78–1.57 K lower than the ambient temperature. When the distance between the unit and wall is 0.6 m, the horizontal wind speed increases from 0 m/s to 5 m/s, respectively; the lowest inlet air temperature of the array unit is 3.51–4.14 K lower than the ambient temperature; the average heat transfer rate decreases by 5.9%–11.5%, and the average inlet air temperature is 1.29–1.98 K lower than the ambient temperature. On this basis, an array air-source heat pump was simulated under different lateral spacings and distances from the wall. The results showed that increasing the lateral spacing or distance from the wall enhanced the heat transfer of the array low-ambient-temperature air-source heat pump unit. When the lateral spacing increases to 1.8 m, the average heat transfer rate of the array unit can reach more than 96.5% of the baseline heat transfer rate of the array unit. When the distance from the wall is increased to 1.8 m, the average heat transfer rate of the array unit can be more than 91.3% that of the baseline unit. A horizontal spacing or a spacing from the wall of 1.2 m is a better installation spacing, which provides a theoretical basis for on-site installation.

Yao Fu, Rameswar Panda, Xinyao Niu et al.

We study the continual pretraining recipe for scaling language models' context lengths to 128K, with a focus on data engineering. We hypothesize that long context modeling, in particular \textit{the ability to utilize information at arbitrary input locations}, is a capability that is mostly already acquired through large-scale pretraining, and that this capability can be readily extended to contexts substantially longer than seen during training~(e.g., 4K to 128K) through lightweight continual pretraining on appropriate data mixture. We investigate the \textit{quantity} and \textit{quality} of the data for continual pretraining: (1) for quantity, we show that 500 million to 5 billion tokens are enough to enable the model to retrieve information anywhere within the 128K context; (2) for quality, our results equally emphasize \textit{domain balance} and \textit{length upsampling}. Concretely, we find that naively upsampling longer data on certain domains like books, a common practice of existing work, gives suboptimal performance, and that a balanced domain mixture is important. We demonstrate that continual pretraining of the full model on 1B-5B tokens of such data is an effective and affordable strategy for scaling the context length of language models to 128K. Our recipe outperforms strong open-source long-context models and closes the gap to frontier models like GPT-4 128K.

В.В. Соколовська-єфименко, Лариса Ивановна Морозюк, В.О. Єрін et al.

LNG is transported over long sea and ocean distances only by tankers, called LNG carriers, in large on-board tanks at a temperature of -163ºC. Although these tanks are well insulated, some of the LNG evaporates under the external factors influence, and boil-off-gas gas (BOG) is formed. The main method of dealing with BOG is the reliquefaction of LNG. Many LNG carriers use technology based on the reverse Brighton cycle (RBC) for reliquefaction. The study has been carried out by thermodynamic analysis methods of the actual parameters and characteristics of the BOG reliquefaction plant based on the data obtained during the operation of the LNG carrier “UMM AL AMAD”. Energy and entropy-statistical methods of thermodynamic analysis have been used in the research. The reliquefaction plant operation has been evaluated based on the specific compression work consumption and the value of the effectiveness of a thermodynamic cycle. The analysis of the results showed that the investigated system operating according to the Brighton cycle has low energy efficiency values. The most energy-intensive loop is the nitrogen loop. It accounts for over 90% of the work overspending in the reliquefaction plant. The expander work partially compensates for the overexpenditure of compressor work. Irreversibility in the expander is 7.7%, and the N2 compressor is approximately 48.7% of the total irreversibility of the liquefaction process. In the BOG/LNG loop, the main contribution to the processes’ irreversibility is made by the BOG compressor (~3.7%) and the precooler (~1.55%) of the total irreversibility of the liquefaction process. The cryogenic heat exchanger is a component of both loops and its negative impact is estimated at 36.4% of the total irreversibility of the liquefaction process. The application of reliquefaction plants operating on the Brighton cycle is currently inefficient due to low energy efficiency and huge losses in the nitrogen loop, which does not meet IMO requirements for gas carriers

Р.В. Грищенко, А.В. Форсюк, Н.В. Іващенко et al.

In world of contemporary challenges involving the continual increase in demand for energy resources and corresponding environmental pollution, the necessity has arisen to develop and implement advanced technologies to reduce energy consumption. This calls for enhancing energy utilization efficiency and optimizing energy generation systems, taking into account the utilization of alternative and renewable energy sources. Specifically, thermal energy storage becomes crucial as an effective economic option. Thermal energy storage systems enable meeting heating or cooling needs during optimal periods when it is more energy-efficient. Traditional management methods rarely prove optimal due to fluctuating electricity tariffs, cooling loads, and ambient temperature. This leads to suboptimal achievement of maximum savings in the utilization of thermal energy storage systems. In this work, the advantages of Cold Thermal Energy Storage (CTES) systems based on Ice Thermal Energy Storage (ITES) were analysed alongside existing management strategies implemented in most enterprises and buildings utilizing ITES. A simplified engineering methodology for analysing the thermodynamic efficiency of CTES was proposed. It was determined that cold losses during exergy analysis during storage are caused by both losses through surfaces and internal exergy losses (i.e., exergy consumption due to irreversibility within the reservoir). For modern systems, exergy losses encompass both external and internal components. As an example, if the heat transfer at the external surface temperature of the storage reservoir equals the ambient temperature, external exergy losses would be zero, while total exergy losses would be entirely due to internal consumption. Conversely, if heat transfer occurs at the liquid's temperature for storage, a greater portion of exergy losses will be due to external losses. In all cases, the cumulative exergy losses, comprising internal and external exergy losses, remain constant. The implementation of CTES allows for shifting the use of electrical energy from peak to off-peak hours. During off-peak hours, electrical energy is used to charge the storage to fulfil (fully or partially) the peak demand for refrigeration equipment. Ice-based ITES has the potential to reduce maximum energy consumption, peak demand, and most importantly, the average cost of energy consumed

A. Beccari, Diego A. Visani, Sergey A. Fedorov et al.

In strained mechanical resonators, the concurrence of tensile stress and geometric nonlinearity dramatically reduces dissipation. This phenomenon, called dissipation dilution, is employed in mirror suspensions of gravitational-wave interferometers and at the nanoscale, where soft clamping and strain engineering have allowed extremely high quality factors. However, these techniques have so far been applied only to amorphous materials, specifically Si3N4. Crystalline materials exhibit substantially lower intrinsic damping at cryogenic temperatures. Applying dissipation dilution engineering to strained crystalline materials could, therefore, enable extremely low loss nanomechanical resonators, as they combine low internal friction, high intrinsic strain and high yield strength. This potential has not yet been fully exploited. Here we demonstrate that single-crystal strained silicon—a material developed for high-mobility transistors—can be used to realize mechanical resonators with ultralow dissipation. We fabricate strained silicon nanostrings with high aspect ratios supporting megahertz mechanical modes with quality factors exceeding 1010 at 7 K, a tenfold improvement over values reported in Si3N4. We estimate a thermal-noise-limited force sensitivity of (5 ± 2) × 10–20 N Hz–1/2 at 7 K—approaching that of carbon nanotubes—and a heating rate of only 60 quanta per second. The low mass and high quality factors of our nanomechanical resonators make them particularly promising for quantum sensing and transduction. Soft clamping reduces the dissipation of nanomechanical resonators, but this method has been limited to amorphous materials. When applied in crystalline silicon, it enables resonators with quality factors beyond ten billion.