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

Siyu Zhong, Pengfei Sui, Peter Holtappels et al.

Excellent energy efficiency and system stability are critical factors guiding the practical application of carbon dioxide reduction reaction (CO 2 RR) systems. This work promotes reduction reaction kinetics in a modified zero-gap electrolyzer by regulating the operation temperature and pressure. The energy efficiency of the CO 2 RR system is enhanced, such as 52.6 % at a current of 1.2 A under alkaline conditions and 49.4 % under neutral conditions, with the characteristics of low voltage and high Faradaic efficiency. In addition, the optimization of the reaction microenvironment effectively alleviates the precipitation issue, enabling the system to operate stably for more than 100 h, with a Faradaic efficiency of more than 90 % for CO generation. Engineering-integrated electrochemistry inspires the future development of CO 2 RR technology.

Mingyu Shan, Lei Zhang, C. Xing et al.

ABSTRACT The hardened crystallization of asphalt binder due to thermoreversible aging in cold regions directly impacts its resistance to low-temperature cracking. The thermoreversible aging mechanism of a polymer-modified asphalt binder (PMA, including styrene-butadiene-styrene-modified asphalt binder (SBSMA) and crumb rubber-modified asphalt binder (CRMA)) was investigated using molecular dynamics (MD) methods. The fracture characteristics and crystallization properties of the PMAs were analyzed through single-edge notched beam (SENB) tests and crystallization kinetics. The results show that in the process of thermoreversible aging of PMA, the mobility of the asphalt molecular segment gradually decreases, the free volume of PMA continuously decreases, and the molecules gradually gather. Asphaltene plays a crucial role in the thermoreversible aging of PMA. It is suggested to evaluate the low-temperature properties of the PMA by measuring the fracture energy from the SENB tests after a 24-hour conditioning time. The relative crystallinity of PMA follows an exponential distribution pattern over time and a normal distribution trend with decreasing temperature. The crystal nucleation and growth modes of PMA exhibit one-dimensional rod-shaped instantaneous growth, characterized by high restriction and disorder. CRMA is recommended as the preferred asphalt binder for highway engineering projects in cold regions.

Chen Yiqun, Wu Jianghong, Yang Huaiyu

An electric vertical take-off and landing flying vehicle (eVTOL) is a potential technology for future urban air mobility. A major challenge for thermal management systems is the high cooling requirement and the variable application scenarios. To overcome this challenge, a multi-scene eVTOL-integrated thermal management system was developed. In this study, an eVTOL thermal management simulation platform based on Amesim simulation software was developed to investigate the effects of flight conditions on thermal management and range. The simulation results show that increasing the cruise altitude can reduce the thermal management energy consumption when the ground temperature is high. The maximum reduction of energy consumption for thermal management energy is 4 kW when the cruising temperature ranges from 10 ℃ to 26 ℃. When the hovering rescue duration is more than 150 s during the emergency rescue operation, the temperature difference inside the battery becomes too pronounced. A reduced payload improves the range, with the unloaded range being 1.33 times greater than the fully loaded range.

E. Blagin, Dmitry A. Uglanov, V. Urlapkin et al.

BACKGROUND: The global transition to low-carbon energy requires the development of efficient technologies for utilizing the cold energy of liquefied gases. However, existing solutions are expensive and have low efficiency. Gaps in the improvement of working fluids and Rankine cycle parameters limit the profitability of such systems. This study is aimed at selecting the optimal working fluid and operating conditions ensuring the least payback period and the highest energy efficiency. AIM: To develop of a method for selecting the optimal working fluid and parameters of a closed Rankine cycle for regasification of cryogenic products, ensuring the highest energy efficiency and the least plant payback period. METHODS: 1) Thermodynamic analysis, i.e. simulation of the Rankine cycle using the equations of energy, entropy, and exergy to estimate efficiency and energy losses; 2) Exergetic analysis to determine irreversible losses in system components (heat exchangers, turbine, and pump) and assess their influence on the overall efficiency; 3) Economic modeling to calculate the cost of equipment and operating costs based on empirical dependencies, followed by optimization based on the least payback period; 4) Multi-criteria optimization (Pareto method) to search for trade-off solutions between the plant capacity and capital costs for various working fluids; 5) Comparative analysis to assess the effectiveness of alternative working fluids (methane, oxygen, and organic refrigerants) based on thermodynamic and economic indicators. RESULTS: The study allows to determine the optimal operating parameters of the system, including the choice of the working fluid, temperature conditions, and design features of heat exchangers, contributing to the development of more effective and profitable cryogenic power engineering solutions. CONCLUSION: Methane used as a working fluid in a closed Rankine cycle provides the best performance in terms of power, efficiency, and payback. Further improvement of the system requires optimization of heat exchangers to reduce exergy losses.

Gurkirat Singh, K. N. Pandey

In a variety of high temperature engineering applications including aerospace, marine, power plants etc. Nimonic-90 because of its ability to withstand high temperatures, Nimonic-90 is a preferred engineering material in various high-temperature applications, such as aerospace, marine, and power plants, due to its exceptional ability to withstand elevated temperatures. In such a high-temperature application, Nimonic-90 experiences oxidation and hot corrosion after a period of time. It has been observed that Deep Cryogenic treatment (DCT) appreciably improved the mechanical properties of the materials but its effect on hot corrosion and oxidation at high temperatures has still not been thoroughly investigated. Therefore, this study investigates the effect of Deep Cryogenic Treatment on hot corrosion and oxidation of Nimonic-90 superalloy at 9000C. The samples were subjected to Deep Cryogenic Treatment cycle at −1960C and then oxidation and hot corrosion environment was provided in a thermal cyclic furnace. At 900°C, new phases, such as oxides of nickel, chromium, and titanium, formed. These phases acted as protective layers, improving Nimonic-90′s corrosion resistance and preventing further oxidation. Deep Cryogenic Treatment has shown significant improvement in corrosion behaviour of Nimonic-90 superalloy. The findings demonstrated that the weight gain resulted from hot corrosion products was greater than the weight gain in an oxidation environment. The most corrosion-resistant sample in hot corrosion had an average scale thickness of 70.97 µm which was 31.96% smaller xthan the untreated sample whereas in oxidation samples, the most corrosion resistant sample had average scale thickness of 23.97 µm which was 52.06% smaller than the oxidized untreated sample.

R. Bao, Wentao Sun, Chuanjun Huang et al.

Carbon fiber reinforced polymer (CFRP) composites are widely used in cryogenic engineering due to their lightweight, high strength and corrosion resistance. Practical applications are often involved in processing CFRP structural components with holes. However, the presence of these holes has an important effect on the overall mechanical properties of the CFRP structural components. In the present work, we introduce the acoustic emission (AE) technique to characterize the mechanical response of the CFRP upon tensile stress within the temperature range of 20 K to 300 K. Through the application of the AE technology, we monitored the damage process in real time under quasistatic axial tensile stress of the CFRP laminates containing hole in a cryogenic environment and analyzed the damage mechanism of the perforated CFRP laminates at different temperatures.

K. Parto, S. Azzam, K. Banerjee et al.

In recent years, quantum-dot-like single-photon emitters in atomically thin van der Waals materials have become a promising platform for future on-chip scalable quantum light sources with unique advantages over existing technologies, notably the potential for site-specific engineering. However, the required cryogenic temperatures for the functionality of these sources has been an inhibitor of their full potential. Existing methods to create emitters in 2D materials face fundamental challenges in extending the working temperature while maintaining the emitter’s fabrication yield and purity. In this work, we demonstrate a method of creating site-controlled single-photon emitters in atomically thin WSe2 with high yield utilizing independent and simultaneous strain engineering via nanoscale stressors and defect engineering via electron-beam irradiation. Many of the emitters exhibit biexciton cascaded emission, single-photon purities above 95%, and working temperatures up to 150 K. This methodology, coupled with possible plasmonic or optical micro-cavity integration, furthers the realization of scalable, room-temperature, and high-quality 2D single- and entangled-photon sources. Quantum defects in 2D semiconductors are promising quantum light sources, but the required cryogenic temperatures limit their applicability. Here, the authors report a method to create single-photon emitters in monolayer WSe2 operating at temperatures up to 150 K without plasmonic or optical cavities.

Jian Liu, Laigui Wang, Hewan Li et al.

Hui Wei, Jue Li, B. Hu et al.

ABSTRACT The deformation behaviour of the asphalt concrete (AC) depends on the loading state and the temperature, accompanied by a large number of microcracks. In this study, the deformation and failure behaviour of the AC under uniaxial compression were investigated by the acoustic emission (AE). Both the stress–strain relationship and the energy dissipation were employed to analyse the macroscopic deformation of the specimen at low and medium temperatures. The AE parameters including count, energy and amplitude were measured in real-time during the loading process. The damage morphology of specimens was characterised by the failure location with the AE technology. Results show that with the rise of the temperature, the strength of AC specimens gradually decreased, which leads to a lower capacity in storing strain energy. The dissipative energy is greatly affected by the damage degree of the specimen. Both the event count and amplitude increased rapidly when the specimen failure occurred. The AE parameters are relatively sensitive to the deformation failure of asphalt mixtures influenced by the temperature. Furthermore, the results also imply that the AE method used in the present study to characterise the deformation failure in pavement engineering is more scientific and precise.

Yan-jun Shen, Jianshuai Hao, Xin Hou et al.

Xiurong Yang, An Jiang, Xinping Guo

H. Mao, Yanzhong Li, Xiaoning Huang et al.

Abstract In the present study the thermo-hydraulic characteristics of geyser in the cryogenic fuel transportation pipe of a liquid rocket is experimentally investigated using liquid nitrogen. The typical thermo-hydraulic appearances are characterized and analyzed in the geyser process to effectively recognize the occurrence of geyser in practical engineering. The effect of interfering factors such as heat flux, liquid level and tank ullage pressure on geyser are explored. Moreover, based on the new proposed dimensionless parameter of the maximum energy storage ability (Ae), the occurrence boundary of geyser is divided. It could be concluded from the results that a clear periodic pressure and temperature change accompanied by periodic plenty vapor ventilation could serve as an indication for geyser’s occurrence, and the eruption of cryogenic geyser has a similar appearance as that in the geothermal field. It is found that a higher tank ullage pressure and liquid level could reduce the geyser’s intensity, and a violent boiling will occur instead of geyser when the heat flux is extremely high. It is a feasible way to eliminate geyser in the cryogenic pipe by increasing the pressure inside the pipe via increasing the tank ullage pressure or liquid level in the tank. Moreover, it is found that a weak geyser would occur in LN2 and LO2 when Ae exceeds 2, and then as Ae being larger than 4, a strong geyser might occur with a noticeable pressure peak.

Liu Qiyuan, L, Hongbin et al.

Two categories of correction method for two-phase flow condensation heat transfer and pressure drop were compared for a distributed parameter model of a microchannel condenser with R134a as the refrigerant. The Cross-repeated-testing nonlinear correction method was demonstrated to be better than the conventional simple polynomial fitting correction. Using the former correction, the error of the estimation of heat transfer can be reduced by 64.5% and the mean square error was less than 3%. Similarly, the error of refrigerant side pressure drop decreased by 82.05% and the mean square error was controlled within 10%. Furthermore, this method not only proved the correctness and validity of the simulation model of a microchannel parallel-flow condenser, but also identified a way to accurate prediction of key parameters during heat transfer, including heat flux and pressure drop.

Zhang Guodong, Sun Huan, Zhu Kai et al.

The influence of the pressure head of evaporation on the operation of a loop heat pipe (LHP) is important to the performance of LHP. In this paper, the wick was separated from the heating surface;consequently, a steam chamber was formed. Simultaneously, the heat and mass transfer in the evaporator were separated. Consequently, the driving force (especially the pressure head of evaporation) was enhanced. Heat leakage was decreased as much as possible due to the low thermal conductivity of the wick. Experiments were conducted to investigate the effectof different partial vacuums(95.3–101.1 kPa) on the start-up performance for the new LHP. This newdesign was able to operate at different partial vacuums; the operating temperature, start-up time, and thermal resistance decreased with increasedpartial vacuum. Simultaneously, this LHP showed a lower thermal resistance (0.14oC/W) compared with that of LHP driven by capillary forces.

Li Wang, Hongliang Zhang, Yang Gao

Low temperature negatively affects the engineering performance of cementitious materials and hinders the construction productivity. Previous studies have already demonstrated that TiO2 nanoparticles can accelerate cement hydration and enhance the strength development of cementitious materials at room temperature. However, the performance of cementitious materials containing TiO2 nanoparticles at low temperatures is still unknown. In this study, specimens were prepared through the replacement of cement with 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, and 5 wt.% TiO2 nanoparticles and cured under temperatures of 0°C, 5°C, 10°C, and 20°C for specific ages. Physical and mechanical properties of the specimens were evaluated through the setting time test, compressive strength test, flexural strength test, hydration degree test, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) analysis, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) in order to examine the performance of cementitious materials with and without TiO2 nanoparticles at various curing temperatures. It was found that low temperature delayed the process of cement hydration while TiO2 nanoparticles had a positive effect on accelerating the cement hydration and reducing the setting time in terms of the results of the setting time test, hydration degree test, and strength test, and the specimen with the addition of 2 wt.% TiO2 nanoparticles showed the superior performance. Refined pore structure in the MIP tests, more mass loss of CH in TGA, intense peak appearance associated with the hydration products in XRD analysis, and denser microstructure in SEM demonstrated that the specimen with 2 wt.% TiO2 nanoparticles exhibited preferable physical and mechanical properties compared with that without TiO2 nanoparticles under various curing temperatures.

Jie Yuan, Zhenlong Wu, S. Fei et al.

Refrigeration systems occupy a large proportion of the home energy consumption in the United States. Precise temperature management is a key point to enhance the energy utilization efficiency. Since proportional-integral-derivative (PID) controllers absolutely dominate control engineering, a large number of different control structures and theories have been developed to enhance the efficiency of PID controllers. A benchmark refrigeration system was proposed in PID2018 as a simulation platform for researchers to implement different control strategies. In this paper, a novel control strategy is designed for the benchmark refrigeration system, where the fractional-order lead-lag compensator is in consort with the baseline controllers and contributes to accelerate the system response by increasing the system bandwidth, and the feedforward compensators are utilized to compensate the disturbances in the benchmark problem. The simulation results given in the benchmark problem show the straightforward effectiven...

X. L. Liang, C. Qian

Cryogenic liquefied-gas storage tanks are more and more widely used in engineering. As a typical pressure vessel with a complicated structure and working at a low temperature, it is critical to ensure the safety underall possible loadings. In this paper, a finite element model for a cryogenic liquefied-gas storage tank was established. Stress analysis and the strength as well as stability assessment under two load cases with different combination of loadings were performed. It is found that the cryogenic liquefied-gas tank subjected to the normal design pressure, wind and seismic loads is satisfied to strength requirement according to the JB4732-1995 Steel Pressure Vessels—Design by Analysis.

U. Bhagyaraju, P. Kumar

Nattawat Threerachannarong, K. Siemanond

Energy and Exergy analysis are one of alternative techniques to analyze chemical processes in term of energy quality parameters such as enthalpy, entropy and exergetic temperature. The exergetic temperature can conduct Exergy Composite Curves diagram (ECCs) (Marmolejo-Correa, 2012) which represents exergy targets: exergy requirement, exergy rejection and exergy destruction etc. In addition, these targets can be used for improving processes. The strength points of these analysis are to design the new process and to improve the utility performance. Therefore, these analysis methods have been applied to low-temperature process that requires a large amount of energy consumption. In this work, there are two approaches of energy minimization. First model, a combination with ECCs diagram and mathematical programing (Wechsung, 2011) can synthesize a better design of process to reduce utility usage. Second model, a synthesis of cascade refrigeration systems (Colmenares, 1989) can indicate a configuration of refrigeration systems with alternative working fluids for minimizing the energy used by condenser and compressor. Besides that, these models were applied to a liquefied natural gas (LNG) production as a case study which comes from the Pro/II's tutorial (commercial engineering software). The results show that the Exergy and Energy analysis have an ability and potential to design new synthesis for cooling systems for sub-ambient processes and a combination of heat exchanger with compression and expansion processes.

S. Kharche, J. Moro, C. Baudet et al.

Due to its very low viscosity, cryogenic helium has been used for years to generate high Reynolds turbulent flows. The measurement of velocity fluctuations in such high Reynolds flows is however a challenging issue, as it is necessary to develop small size (typically micron-length), robust sensors, to measure the whole spectrum of fluctuations of the velocity, which may extend to hundreds of kHz and possibly higher. SBT has developed for years different facilities, in particular taking benefit of the refrigeration capacities available at CEA Grenoble. In this article we present the current status of developments of hot wire sensors at CEA. Different characterizations of Wollaston hot wires are shown, and measurements of velocity fluctuations in different conditions, in normal helium as well as in superfluid helium are shown.