Cryogenic Cycle Research Articles

Comparison of random forest, support vector regression, and long short term memory for performance prediction and optimization of a cryogenic organic rankine cycle (ORC)

In this paper, three machine learning algorithms (Random Forest (RF), Support Vector Regression (SVR), and Long Short Term Memory (LSTM)) were used to predict and compare the thermodynamic performance of a 1 kW Organic Rankine Cycle (ORC) system under cryogenic operating conditions (i.e., cold source temperature < −160 °C). The cryogenic ORC system uses liquid nitrogen as the cold source, hot water as the heat source, and propane as the working fluid. Ten key operating parameters were selected as input parameters through Variable Importance Measures, and the output work of the expander, the cold exergy efficiency, and the system exergy destruction were used as output parameters. Moreover, the multi-objective optimization of this experimental system was conducted by applying the Non-dominated Sorting Genetic Algorithm III. The results showed that the RF algorithm was the most suitable algorithm among the three machine learning algorithms. According to the optimal results of the prediction model, the maximum error was 5.0251%, which was relatively small compared to the optimal results under experimental conditions. The related results demonstrate the feasibility of machine learning for cryogenic ORC data prediction, which can guide the design and improvement of ORC systems under low-temperature cold source conditions.

Effects of rejuvenation modes on the microstructures and mechanical properties of metallic glasses

This study systematically investigates the effects of three rejuvenation modes, namely biaxial loading, thermal pressure loading, and cryogenic thermal cycling, on the microstructures and mechanical properties of Cu64Zr36 metallic glasses (MGs) using molecular dynamics (MD) simulations. The simulation results demonstrate that biaxial tension application during loading results in a rejuvenated glassy state with high strength. Specifically, we find that the yield stress, Young's modulus, and shear modulus of the rejuvenated glass obtained by biaxial tensile loading decreased by 2.8%, 2.1%, and 2.7%, respectively, compared to an as-cast MG reference. We also find that MGs achieve the greatest degree of rejuvenation, at the expense of strength, with the use of thermal pressure loading. Interestingly, the application of cryogenic thermal cycling results in a rejuvenated state with a lower strength drop compared to thermal pressure loading. Furthermore, analysis of the potential energy and medium-range-order (MRO) size indicates that the microstructures of MGs achieves a high-energy ordered glass state after thermal pressure loading, but a high-energy disordered glass state after biaxial tensile loading and cryogenic thermal cycling. These findings provide meaningful insights into the effect of rejuvenation modes on the microstructures and mechanical properties of MGs, as well as useful guidelines for designing MGs with high strength and superior plasticity for prospective applications in industry.

Optimal design of direct expansion systems for electricity production by LNG cold energy recovery

The aim of this paper is the investigation of cold energy recovery of liquefied natural gas (LNG) in regasification terminals achievable through direct expansion techniques. After an overview of the state of the art related to the LNG system and the technologies proposed for power recovery, multi-pressure direct expansion solutions with internal heat recovery (multi-pressure DE) are analysed. The purpose is to identify the highest level of recoverable energy and the optimal design parameters, considering technological constraints such as pressure and minimum end-expansion temperature. The multi-pressure DE solutions prove to be innovative power recovery methods because, with a relatively low use of seawater, it is possible to save regasified LNG and generate electrical power, valorising the energy invested in liquefaction. An estimate of recoverable power in operating terminals is carried out. Configurations with cryogenic or non-cryogenic turboexpanders are discussed. Using the proposed solution with non-cryogenic turboexpander and distribution pressure of 3.5 MPa, 56 kJ for each kg of LNG can be produced, which can become more than 150 kJ/kg with cryogenic turboexpanders. For long-distance distribution, cryogenic multi-pressure DE cycles can recover around 100–120 kJ per kg of LNG. The presented techniques can allow recovery of up to and over 30% of the maximum specific work available in LNG regasification.

Low temperature-resistant superhydrophobic and elastic cellulose aerogels derived from seaweed solid waste as efficient oil traps for oil/water separation

Aerogel has excellent application potential in adsorption, heat preservation, and other areas due to its typical advantages of low density and high porosity. However, there are several issues with the use of aerogel in oil/water separation, including weak mechanical qualities and challenges in eliminating organic contaminants at low temperature. Inspired by cellulose Iα, which has excellent performance at low temperature, this study used cellulose Iα nanofibers extracted from seaweed solid waste as the skeleton, through covalent cross-linked with ethylene imine polymer (PEI) and hydrophobic modification of 1, 4-phenyl diisocyanate (MDI), supplemented by freeze-drying technology to form three-dimensional sheet, and successfully obtained cellulose aerogels derived from seaweed solid waste (SWCA). The compression test shows that the maximum compressive stress of SWCA is 61 kPa, and the initial performance still maintains 82% after 40 cryogenic compression cycles. In addition, the contact angles of water and oil on the surface of the SWCA were 153° and 0°, respectively, and the stable hydrophobic time in simulated seawater is more than 3 h. By combining the elasticity and superhydrophobicity/superoleophilicity, the SWCA with an oil absorption capacity of up to 11–30 times its mass, might be utilized repeatedly for the separation of an oil/water mixture.

Thermal shock behavior of Fe-based amorphous coatings under cryogenic cycling treatment

Fe-based amorphous coatings were deposited on invar alloy substrates by ADM-4D detonation-gun with different spraying parameters. The cryogenic cycling treatment (CCT) from 0 to 60 cycles was performed on the coatings to investigate the effects of CCT on the thermal shock behaviors of the coatings. In combination with finite element analysis and in-situ tensile test, the study revealed that the thermal shock behaviors of the coatings are primarily influenced by porosity and interfacial oxidation. The presence of pores in the sprayed coatings helps dissipate strain energy, thereby slowing down the initiation and propagation of cracks in the CCTed Fe-based ACs. On the other hand, interfacial oxidation causes a sudden increase in the maximum thermal stress in the oxidation regions, which is the primary cause of cracks in the coatings.

Improved ductility of annealed Fe-based metallic glass with good soft magnetic property by cryogenic thermal cycling

The brittleness after annealing treatment severely restricts the subsequent processing and application of Fe-based magnetic metallic glass. Through proper annealing treatment combined with cryogenic thermal cycling, we obtained excellent comprehensive properties of Fe-based metallic glass ribbons with not only good soft magnetic properties but also high bending deformation ability. After thermal cycling, the sample rejuvenated with higher energy state and larger size of soft regions, which facilitated the initiation and branching of shear bands, leading to the improvement of bending plasticity. Although the large soft regions may act as pining sites for domain walls, the domain structure and coercivity of the sample remained nearly identical because of the reduced number of crystal-like structures. Our study indicates that the cryogenic thermal cycling is an effective method to regulate mechanical and magnetic properties, which makes it powerful means to obtain excellent performance of Fe-based magnetic metallic glasses.

Heterogeneity dependent cryogenic thermal cycling behavior of metallic glasses: A potential energy landscape perspective

Even though cryogenic thermal cycling (CTC) was well documented to be an effective and non-destructive way to plasticity and toughness of metallic glasses (MGs), non-monotonic (rejuvenation to relaxation and vice versa) and even monotonic relaxation processes were reported frequently and the underlying mechanism is remain unsolved until now. By systematically alter the heterogeneity of a La-based MG via annealing treatment, in the present study, the effect of heterogeneity on CTC induced behavior of the MG were evaluated and analyzed. A typical non-monotonic process, i.e., rejuvenation first and then relaxation, was captured and the cycling number and heterogeneity dependent relaxation enthalpy and hardness were evaluated and extended discussion. The rejuvenation-relaxation process along with other non-monotonic and monotonic processes gathered from previous studies could be interpreted by the perspective of energy potential landscape. Specifically, the location where the corresponding energy state correlated to the specific heterogeneity of the MG located in the energy landscape determined whether rejuvenation or relaxation occurs upon CTC treatment.

A criterion of the critical threshold of the maximum shear stress in bulk metallic glasses with cryogenic thermal cycling by statistics in nanoindentation

The shear transformation zones of metallic glasses have been widely studied by nanoindentation. In this work, the mathematic relationship between the relevant parameters is analyzed emphatically. Bulk metallic glasses were given different activation volumes by the cryogenic thermal cycling treatment. Nanoindentation experiments were carried out in a load-controlled loading mode. The critical threshold of the maximum shear stress, (τmax)C, was obtained by the noise-reduction procedures and the statistical analysis. And the activation volume, V*, was obtained from the nonlinear slope by introducing a first-order polynomial. Based on the mean-filed theory, a criterion is successfully established, (τmax)C=V*−λ, where λ=0.30±0.10. According to lots of previous studies on (τmax)C and V* of metallic glasses, three applicable conditions of the criterion are extracted.

Effect of deep cryogenic processing cycles on surface roughness, dimensional stability and microstructure of high carbon high chromium tool steel for cutting tool and dies applications

Abstract The main objective of this investigation is to analyze the influence of DCT cycles on microstructural evolution, surface roughness, hardness and dimensional stability of AISI D2 tool steel for cutting tools and dies applications. The cryogenic quenching was done using gaseous nitrogen. The AISI D2 tool steel was subjected to two DCT cycle: DCT-I (Hardening + DCT + tempering) and DCT-II (Hardening + tempering + DCT). The dimensional stability of AISI D2 tool steel was evaluated using standard Navy C-ring test. The coordinate measuring machine (CMM) was employed for the precise measurement of Navy C-ring subjected to different DCT cycle. The surface roughness was evaluated with R a (arithmetic mean roughness) and R t (total height of roughness profile) values using surface roughness tester. The microstructural features were analyzed using optical (OM) and scanning electron microscopy (SEM). The electrical resistivity and hardness of treated samples were measured using micro-Ohm meter and Vickers microhardness tester. Results showed that AISI D2 tool steel treated with DCT-I cycle exhibited greater surface finish, hardness and dimensional stability compared to DCT-II cycle. It is mainly attributed to the greater precipitation of finer carbides and balancing of tensile-compressive residual stresses.

Energy, conventional exergy and advanced exergy analysis of cryogenic recuperative organic rankine cycle

Energy, conventional exergy and advanced exergy analysis of cryogenic recuperative organic rankine cycle

Correlation between Mechanical and Morphological Properties of Polyphenol-Laden Xanthan Gum/Poly(vinyl alcohol) Composite Cryogels

This study aimed to evaluate the effect of the synthesis parameters and the incorporation of natural polyphenolic extract within hydrogel networks on the mechanical and morphological properties of physically cross-linked xanthan gum/poly(vinyl alcohol) (XG/PVA) composite hydrogels prepared by multiple cryo-structuration steps. In this context, the toughness, compressive strength, and viscoelasticity of polyphenol-loaded XG/PVA composite hydrogels in comparison with those of the neat polymer networks were investigated by uniaxial compression tests and steady and oscillatory measurements under small deformation conditions. The swelling behavior, the contact angle values, and the morphological features revealed by SEM and AFM analyses were well correlated with the uniaxial compression and rheological results. The compressive tests revealed an enhancement of the network rigidity by increasing the number of cryogenic cycles. On the other hand, tough and flexible polyphenol-loaded composite films were obtained for a weight ratio between XG and PVA of 1:1 and 10 v/v% polyphenol. The gel behavior was confirmed for all composite hydrogels, as the elastic modulus (G') was significantly greater than the viscous modulus (G″) for the entire frequency range.

Multi objective ecological optimization of an irreversible Stirling cryogenic refrigerator cycle

The primary objective of the current study is to demonstrate the multi-objective, ecological optimization of an irreversible Stirling cycle-based cryogenic refrigerator. The novelty of the work lies in the ecological optimization of the system, where irreversibilities are considered during the study and the thermal reservoirs have finite energy. The heat source and heat sink exchange energy with the working fluid and respective thermodynamic processes are carried out. The aim is to maximize the ecological objective function and the ecological coefficient of performance, and the effect of design variables on the objective function is investigated. The heat sink capacitance rate, temperature ratio, heat source, and sink capacitance rates, and effectiveness of the hot and cold side heat exchangers are regarded as the design variables. A heat transfer search algorithm is used to optimize the objective functions, and multiple optimal solutions are presented using the Pareto optimal curve. The multi-criteria decision technique TOPSIS is employed to select the ideal solution. For an ideal point selected through TOPSIS, the system works at an optimum ECF and ECOP of 787 W and 5.9, respectively. The ECOP of the system for the current study is 1.81 times and 4.03 times higher than the existing literature. However, the maximum ECF of 1797 W or maximum ECOP of 17.2 can be obtained for the given constraints of design variables.

The effect of thermal and cryogenic environments on the impact performance of aluminum-glass fibers/epoxy laminated composites

In this research work, the effect of various environments on the impact properties of fiber metal laminates was investigated. To do so, in the first step, the 2024 aluminum layers were surface modified with the etching method. Then, the various glass fibers/epoxy composites with the configurations of (0°/0°/0°/0°, 90°/90°/90°/90°, +45°/−45°/−45°/+45° and 0°/90°/90°/0°) were sandwiched between two aluminum sheets. In the following, these samples were aged under thermal cycling (between 25 and 100 °C), isothermal aging at the temperature of 100°C, cryogenic cycling (between −196 and 25 °C), and cryogenic isothermal aging at the temperature of −196°C. To understand the effect of various aging methods on the mechanical features of these structures, the Charpy impact test was performed. Also, the failure mechanisms and related phenomena were assessed by visual observations and microstructural investigations. In the first steps of thermal aging, the impact strength of FMLs was improved, which the highest of that being 46.9%. In the higher cycles or exposing times, the impact strength showed reducing trends, due to thermal degradations of the epoxy matrix. The cryogenic cycling in the high cycles reduced the impact strength of FMLs. But in the cryogenic isothermal condition, in some cases, the improvement in the impact strength was seen, which the highest of that being about 43.4%.

Effect of cryogenic cycling and above-Tg annealing on the corrosion behavior of Zr-Cu-Ti-Be metallic glass

This work investigates the electrochemical properties of Zr-based Zr35Ti30Cu8.25Be26.75 metallic glass after cryogenic treatment and isothermal annealing above glass transition temperature. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments are used to understand the effect of structural state on the corrosion behavior of Zr-based metallic glass. The metallic glass samples are cycled between liquid nitrogen to room temperature and isothermally held at liquid nitrogen to unravel the effect of cryogenic treatments on the electrochemical properties. The corrosion of cryogenically treated and high temperature annealed samples is compared with the as-cast samples. The results show that holding at liquid nitrogen temperature improves the corrosion resistance of metallic glass compared to cryogenic cycling and the high temperature annealing. These findings are explained based on the changes in structural state of metallic glass.

Rejuvenation to relaxation transition and liquid memory effect in La-based metallic glasses with different energy states

Rejuvenation of metallic glasses (MGs) under cryogenic thermal cycling (CTC) has been intensively studied due to its great theoretical and practical value. However, the relationship between energy states of MGs and rejuvenation capacity is still unclear. Here, a systematic study is performed on how the initial state of MGs affects the rejuvenation effect, and the difference in the initial state of MGs is mainly depicted by the fictive temperature Tf, as well as mechanical properties. A “rejuvenation to relaxation” transition upon Tf increasing is found among samples, and the critical energy state (Tf,c∼1.1Tg) at which the transition occurs are further determined. The transition towards relaxation above Tf,c is attributed to the first CTC intervention of the local structures that are smaller than structural units involved in slow β-relaxations. Besides, the CTC-induced recovery of MGs with a low Tf towards high temperature supercooled liquids has been found, and this behavior relates to the memory effect of MGs upon cooling process. When the liquid memory of MGs is awakened by CTC, the recovery to higher energy state (rejuvenation) occurs. This work supplements rejuvenation mechanism of MGs with different initial states, and provides a possibility to predict the evolution direction (rejuvenation or relaxation) of MGs by their energy states (or Tf).

Non-monotonic influence of cryogenic thermal cycling on rejuvenation and impact toughness of Ti-based bulk metallic glass composites

Cryogenic thermal cycling (CTC) can alter the energy states of bulk metallic glasses (BMGs) and their composites (BMGCs), but the fundamental mechanisms of CTC and their effects on mechanical properties are largely remain elusive. Herein, the effects of CTC on structural evolution and impact toughness, aK, of Ti-based BMGCs containing β-Ti dendrites are investigated. It is found that either rejuvenation or relaxation alternately dominates the structural evolution of the glass matrix, causing a non-monotonic rejuvenation. At 298 K, a more rejuvenated state causes a synergistic toughening by both of the glass matrix and dendrites, and the aK variation trend of BMGCs is the same as the non-monotonic rejuvenation. However, at 77 K, the aK variation trend of BMGCs is just opposite as the non-monotonic rejuvenation of the glass matrix. The rejuvenation/relaxation during CTC are correlated with the impact toughness, which provides a basis for improving toughness of BMGCs by CTC.

A design model for spiral wound heat exchangers which accounts for property variation, longitudinal heat conduction, and heat-in-leak

• A combined analytical-numerical design model for cryogenic SWHE is developed. • Analytical sizing module finds the optimum configuration of SWHE. • The effects of property variation, LHC, and heat-in-leak are investigated. • LHC impact is negligible compared to property variation and heat-in-leak. • A sensitivity analysis on the input constraint is performed. Spiral Wound Heat Exchangers (SWHEs) can be a good and reliable choice for serving as the main heat exchanger in the cryogenic gas liquefaction cycles using throttling process such as the Linde-Hampson cycle. In this application, a high pressure hot gas stream has to be cooled down via transferring heat to a low pressure cold gas in a high-effectiveness heat exchanger. Present research has been organized to develop a design model which is able to find the optimum SWHE configuration for gas liquefaction cycles. The model has to be capable of considering the important physical phenomena in the cryogenic temperature ranges, including variation of fluid properties with temperature, longitudinal heat conduction (LHC) through separating walls, and heat-in-leak. Therefore, a combined analytical-numerical design model has been developed in the present study. The design model is essentially composed of two stand-alone modules, i.e. an analytical sizing module and a numerical performance evaluation module. To develop the design model, first, the geometrical characteristics of SWHE are studied and primary geometrical parameters are recognized. Then, the analytical sizing module is developed which is able to determine the optimum values of primary geometrical parameters of SWHE minimizing the heat transfer surface area based on the input design requirements. Afterwards, a 1D finite difference numerical module is presented in which important physical phenomena can be considered in the evaluation of the thermo-hydraulic performance of all types of counter flow or parallel flow heat exchangers as well as SWHEs. Finally, the two modules are combined to construct a design model. Two examples in which the low pressure superheated vapor helium is intended to cool down the high pressure supercritical helium flowing inside the tubes are also provided to demonstrate the applicability of the proposed combined model, and also, to elucidate its sensitivity to the input constraints. It was concluded that while variations of fluid properties and the external heat fluxes due to the radiation and convection have significant influence on the performance of cryogenic SWHE, the LHC is of minor importance and can be neglected. Moreover, decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa, causes the heat exchanger length and its outside diameter to increase by 79% and 48%, respectively.

Exergy analyses of two and three stage cryogenic cycles

Abstract Cryogenics has an important influence on industry and science. In this study, optimum working conditions are obtained by applying exergy analysis and local optimization methods to two- and three-stage vapor compression cascade cryogenic cycle. The first and second laws of thermodynamics, exergy analysis, and local optimization methods are applied to the two- and three-stage cascade cryogenic cycle. By considering the needs and demands, it is possible to create new cycles by adding new devices and/or new stages to these cycles. The results of the optimum operating conditions are obtained for the two- and three-stage vapor compression cascade cryogenic cycle. It is seen that to achieve high COP values and high efficiency; it is necessary to reduce the compression ratio of the compressor as much as the fluid allows. For the two-stage cycle, the minimum total work required for cryogenic cooling is around P 7 = 2,400 kPa. The COP value is 0.30 between P 7 = 2,400 and 2,800 kPa, and the maximum exergy efficiency is obtained around 0.235. It is seen operating the first-stage compressor at high pressures increases the total losses of the entire cycle from 7,500 to 18,550 kW. The increase in total exergy losses is around 247%, and operating the first-stage compressor at high pressures increases the exergy efficiency of the entire cycle. The increase in total exergy efficiency is around 160%. When the second-stage compressor is operated at low pressure, the COP value increases by 2%, the exergy efficiency increases by 20%, and the exergy losses decrease by around 40%.

Effect of cryogenic thermal cycling on the microstructure and mechanical properties of Zr-based bulk metallic glasses

This article investigates the effects of cryogenic thermal cycling (CTC) on the microstructure and plasticity of Zr60Cu20Al10Ni10 (Zr60) bulk metallic glass (BMG). The microstructure and mechanical properties of Zr60 BMGs at different energy states are assessed through room-temperature compression and nanoindentation tests. The heterogeneity of the internal structure of the CTC-treated samples causes a different response to thermal expansion resulting in a non-uniform local stress field distribution, which increases the energy state of Zr60 BMGs. At the same time, in the CTC-treated Zr60 BMGs, more free volume (or flow defects) is introduced, and the plasticity is increased. It has been found that, after CTC, the room-temperature plasticity of Zr-based BMGs can be significantly improved by 2–3 times compared to that of the as-cast samples. This introduces flow defects and the inhomogeneous distribution of the strain field causes the serration behavior during the deformation of BMGs to occur more frequently and the second peak of the relaxation spectrum to be more pronounced. This phenomenon indicates a more frequent generation of shear transition zones and shear band movement within them.

Tuning nanoscale heterogeneity by non-affine thermal strain to modulate defect activation and maximize magnetocaloric effect of metallic glass

The effects of non-affine thermal strain on the structure, defect activation and magnetocaloric effect (MCE) have been investigated in Gd55Co20Al24.5Si0.5 metallic glass (MG). Maxwell-Voigt models are utilized to analyze the impact of cryogenic thermal cycling (CTC) on the evolution of heterogeneous structure in term of the activated defects during creep deformation. Two kinds of flow defects with different relaxation times are observed from the relaxation spectrum, which show different responses to CTC. A power law between the maximum magnetic entropy change and its peak temperature is uncovered for Gd-based MGs above 85 K, which breaks down below 85 K for the low Gd content MGs including the high-entropy MGs. Through adjusting the CTC number, the maximum magnetic entropy of the present MG is improved to 10.7 JKg-1K−1 under 5 T, which is the largest among the Gd-based MGs with Curie temperature above 85 K. The enhancement of MCE is related to the increased fraction of solid-like zones in the amorphous matrix and nanocrystallization rendered by CTC treatment. This work sheds new insights into the correlation of MCE and nanoscale creep deformation with structural heterogeneity of MGs.