Subcritical Process Research Articles

Thermodynamic, Economic and Maturity Analysis of a Carnot Battery with a Two-Zone Water Thermal Energy Storage for Different Working Fluids

The rising share of renewable energies leads to increased fluctuations in electrical power supply. One possibility to shift the surplus energy based on demand is a Carnot battery (CB). A CB uses a heat pump or resistance heater to convert and store thermal energy into electrical energy. Later, the stored thermal energy is converted back into electrical energy using a heat engine. This study investigates a CB with a two-zone tank for thermal energy storage. A transcritical process with CO2 is applied for charging, while discharging employs a transcritical process with CO2 and six refrigerants operating in a subcritical process. The transcritical process with CO2 and the four most promising subcritical processes are compared regarding round trip efficiency and levelized cost of electricity (LCOE) depending on the pinch points 5 K and 1 K in the heat exchangers. Additionally, the technology readiness level (TRL) is determined for these configurations. The results show round-trip efficiencies between 11.3% and 33.5% and LCOEs ranging from EUR 0.95 (kWh)−1 to EUR 2.09 (kWh)−1 for the considered concepts with TRLs of up to six.

Assisted percolation of slow-spreading mutants in heterogeneous environments.

Environmental heterogeneity can drive genetic heterogeneity in expanding populations; mutant strains may emerge that trade overall growth rate for an improved ability to survive in patches that are hostile to the wild type. This evolutionary dynamic is of practical importance when seeking to prevent the emergence of damaging traits. We show that a subcritical slow-spreading mutant can attain dominance even when the density of patches is below their percolation threshold and predict this transition using geometrical arguments. This work demonstrates a phenomenon of "assisted percolation", where one subcritical process assists another to achieve supercriticality.

Uniqueness and absence of percolation of classical gases

We reconsider Mürmann’s theorem, i.e., the 1-1 correspondence between Poisson exclusion finite-cluster processes and subcritical stable Gibbs processes of finite range. Subcritical processes realize configurations that decompose into only finite clusters. Existence or uniqueness of Poisson exclusion cluster processes then imply the corresponding statement for subcritical, stable Gibbs processes of finite range. Applications to continuum Potts models are given.

Design and numerical analysis of supersonic radial-inflow turbines for transcritical ORC processes

Radial inflow turbine design was investigated for ORC systems having transcritical and close to critical point expansion. The analysis was carried out by combining the turbine design and turbine loss analysis with a thermodynamic cycle analysis. Six fluids were investigated, including three hydrocarbons and three fluorocarbons. The objective is to investigate in detail the design and efficiency of ORC turbines designed for transcritical cycles and close to the critical point expansions, where the real gas effects and the density changes along the expansion are significant. The results of the efficiency predictions gained by using the existing enthalpy loss correlations were compared against computational fluid dynamics simulations. It was revealed that using supercritical inlet state leads to more compact turbine wheel dimensions, increased turbine power, as well as increased rotational speed, when compared to subcritical processes. On the other hand, higher turbine efficiencies were reached with subcritical turbine inlet conditions. This is mainly because of the increased stator outlet Mach number, increased expansion ratio, and lower blade height at the rotor inlet with supercritical turbine inlet conditions, resulting into higher losses along the expansion.

The stationary and quasi-stationary properties of neutral multi-type branching process diffusions

The stationary asymptotic properties of the diffusion limit of a multi-type branching process with neutral mutations are studied. For the critical and subcritical processes the interesting limits are those of quasi-stationary distributions conditioned on non-extinction. Pedagogical derivations are given for known results that the limiting distributions for supercritical and critical processes are found to collapse onto rays aligned with stationary eigenvectors of the mutation rate matrix, in agreement with discrete multi-type branching processes. For the sub-critical process the previously unsolved quasi-stationary distribution is obtained to first order in the overall mutation rate, which is assumed to be small. The sampling distribution over allele types for a sample of given finite size is found to agree to first order in mutation rates with the analogous sampling distribution for a Wright-Fisher diffusion with constant population size.

Cooperative game-based anchor process allocation within sustainable palm oil based complex for environment-food-energy-water nexus evaluation

The challenge in clean palm oil production falls on the management of palm oil mill effluent which is a notable source of greenhouse gas emissions and water pollution. To address these critics against edible palm oil, an integrated palm oil-based complex (POBC) considering effluent elimination and refinery integration is suitable for environmental-food-energy-water (EFEW) nexus development. Optimal retrofit of palm oil mill into EFEW nexus-integrated POBC requires multi-objective considerations to balance the trade-offs between profitability, energy contribution, greenhouse gas, water and land footprints via fuzzy optimisation. With limited practical knowledge, potential flowsheet modifications should be investigated for flexible POBC design. In a cooperative game context, interconnecting processes act as multiple players cooperating to achieve the goal of the game, i.e., POBC performance, where each player has a distinctive impact on the outcome. In this work, such process performance was suggested to be distributed using cooperative game model, to target the EFEW-based anchor process, i.e., the process stage of greatest contribution in the weighted EFEW nexus, for desired flowsheet advancement. Considering these aspects, an integrated fuzzy and cooperative game optimisation framework was developed to identify the anchor process of an EFEW nexus-integrated POBC. EFEW objective-based process performance allocation in the fuzzy optimal POBC was weighted by the decision-maker to allocate the anchor process using developed models and Excel tools. Nut/kernel separation and cogeneration stage is the EFEW-based anchor process in the fuzzy optimal POBC with EFEW nexus score of 41% in this work. A comparative analysis between the proposed method with other approach was done. The favourability of EFEW contributions by POBC in terms of benefit-drawback ratio increased with the percentage of boiler efficiency increment within the targeted anchor process. Targeting anchor process aids planning for process maintenance and advancement to avoid resource wastage on sub-critical processes.

Improvement of paperboard moisture resistance by coating with lignin using the rapid expansion of subcritical solutions process

Improvement of paperboard moisture resistance by coating with lignin using the rapid expansion of subcritical solutions process

The Survival Probability for a Class of Multitype Subcritical Branching Processes in Random Environment

The asymptotic behavior of the survival probability for multi-type branching processes in a random environment is studied. In the case where all particles are of one type, the class of processes under consideration corresponds to intermediately subcritical processes. Under fairly general assumptions on the form of the generating functions of the laws of reproduction of particles, it is proved that the survival probability at a remote instant n of time for a process that started at the zero instant of time from one particle of any type is of the order of λnn−1/2, where λ ∈ (0, 1) is a constant defined in terms of the Lyapunov exponent for products of the mean-value matrices of the laws of reproduction of particles.

A first study of the potential of integrating an ejector in hydrogen fuelling stations for fuelling high pressure hydrogen vehicles

This present study evaluates the potential of entraining the low-pressure hydrogen to fuel cell vehicles during fuelling processes, which is expected to promote the development of the hydrogen fuel automotive industry. A computational fluid dynamics model is developed to evaluate the potential of the proposed hydrogen fuelling process. A flow behaviour analysis is performed to show the detailed flow structure in the critical and sub-critical processes for the hydrogen ejector. The critical suction pressure and critical back pressure are assessed under various inlet pressures of the primary nozzle. The results show that the high-pressure hydrogen accelerates in the primary nozzle, leading to the decrease of the static pressure, which generates the suction effect in the downstream of the nozzle exit to entrain the hydrogen from the low-pressure tank. The entrainment ratio declines along with the increasing back pressure or decreasing inlet pressure of the suction chamber. This study suggests that the integration of an ejector instead of a reduction valve into the hydrogen fuelling station improves the energy efficiency by utilizing less hydrogen from the high-pressurized hydrogen storage during vehicle fuelling.

SOLUTION OF THE PROBLEM OF STABILITY OF 40X STEEL SHELL

Discusses the solution of the problem of a circular elastic-plastic bifurcation of thin-walled cylindrical shell under the proportional subcritical processes loading shell axial compressive force and torque in deviatoric space of deformations of A. A. Ilyushin. The solution is based on the theory of stability of inelastic systems under complex loading V. G. Zubchaninov. The incompressibility condition of the material and the homogeneity condition of the stress state in the shell up to the moment of loss of stability are used. The problem is solved in a geometrically linear formulation [1-7].

Fracture, Fatigue, and Structural Integrity of Metallic Materials

Fracture, fatigue, and other subcritical processes, such as creep crack growth or stress corrosion cracking, present numerous open issues from both scientific and industrial points of view [...]

Moderate deviations for the total population arising from a nearly unstable sub-critical Galton-Watson process with immigration

In this paper, we consider the moderate deviation of the nearly unstable sub-critical Galton-Waston process with immigration for the centered total population arising. We discuss the main influence factors for the form of moderate deviation in different stochastic processes. Moreover, we compute the exact rate function in every different situation of MDP.

Characterization and evaluation of antioxidation of lignin from bamboo powder using a formic acid-catalyzed ethanol organosolv process

The antioxidant activity of lignin for producing biochemicals has attracted attention. In this paper, a separation method for lignin is proposed, with high-yield and high-antioxidant activity by using a formic acid-catalyzed subcritical ethanol process. The formic acid-catalyzed ethanol lignin (EOL/FA) and ethanol organosolv lignin (EOL) were first prepared using a high-pressure autoclave at different formic acid dosages. Then, the antioxidant activity and the structural and thermal properties of EOL/FA, EOL, alkali lignin, and sodium lignosulfonate were analyzed using antioxidant analysis, Fourier transform infrared (FTIR) spectroscopy analysis, and thermogravimetric analysis (TGA). The phenolic hydroxyl content of the four lignins was also determined by the Folin–Ciocalteau colorimetric method. Results showed EOL/FA had a higher radical scavenging ability and higher total phenolic hydroxyl content than industrial lignin. It indicated that the formic acid-catalyzed subcritical ethanol process was effective for enhancing the antioxidant activity of lignin.

The Inspection of Spheroidized Annealing on SCM435 Cold-Forging Quality Steel Wires with Protective Atmosphere

A cold-forging quality steel rod is usually applied for manufacturing wire which is generally produced by drawing wire coil into wire, followed by spheroidized annealing treatment to achieve the necessary formability for cold forging. The subcritical and intercritical processes are usually used to spheroidize the steel wires. The cold-forging quality SCM435 alloy medium carbon steel wires are widely used to manufacture high tension bolts for mechanical and heavy industry. In this study, the spheroidized annealing experiments on SCM435 alloy steel wires are conducted in a commercial bell furnace with a protective atmosphere of nitrogen or hydrogen. The mechanical properties of annealed steel wires are measured by tensile and Rockwell hardness tests and the process capability is evaluated. It is experimentally revealed that, for SCM435 alloy medium carbon steel wires, the wire quality with intercritical annealing is much better than that with subcritical annealing and is markedly affected by furnace atmospheres. The intercritical annealing quality on SCM435 alloy steel wire in hydrogen atmosphere furnace is better than in nitrogen atmosphere furnace. A comparison between the results obtained using the intercritical annealing with hydrogen atmosphere and the measures using the subcritical annealing shows that the intercritical annealing effectively improves the performance measures of low strength and high ductility over their values at the subcritical annealing. The results presented in this study could be a reference for fasters wire manufacturers.

Breaking rocks made easy. Blending stress control concepts to advance geomorphology

AbstractAll landscapes are subject to stress fields, conditioned by their formation and ongoing tectonic and geomorphic changes. With this ESEX Commentary we wish to stimulate a debate on this invisible but persistent stress control on landforms, processes and materials in geomorphology. We address the legacy of active and passive stress fields, which translates into the concept of ‘tectonic predesign’, in conjunction with a perspective of geomorphic processes being driven by subcritical stresses. These concepts complement each other as ‘subcritical processes’ are controlled by tectonic predesign and in turn modulate the stress fields. This offers new theoretical and practical perspectives on how landscapes evolve, processes form materials and how rocks break easily. © 2018 John Wiley & Sons, Ltd.

Estimation of the mean in partially observed branching processes with general immigration

In the paper we investigate asymptotic properties of the branching process with non-stationary immigration which are sufficient for a natural estimator of the offspring mean based on partial observations to be strongly consistent and asymptotically normal. The estimator uses only a binomially distributed subset of the population of each generation. This approach allows us to obtain results without conditions on the criticality of the process which makes possible to develop a unified estimation procedure without knowledge of the range of the offspring mean. These results are to be contrasted with the existing literature related to i.i.d. immigration case where the asymptotic normality depends on the criticality of the process and are new for the fully observed processes as well. Examples of applications in the process with immigration with regularly varying mean and variance and subcritical processes with i.i.d. immigration are also considered.

Large deviations of branching processes with immigration in random environment

Abstract We consider branching process Zn in random environment such that the associated random walk Sn has increments ξi with mean μ and satisfy the Cramér condition E e hξi < ∞, 0 < h < h +. Let χi be the number of particles immigrating into the i th generation of the process, E χ i h $\begin{array}{} \mathbf{E}\chi_i^h \end{array} $ < ∞, 0 < h < h +. We suppose that the number of offsprings of one particle conditioned on the environment has the geometric distribution. It is shown that the supplement of immigration to critical or supercritical processes results only in the change of multiplicative constant in the asymptotics of large deviation probabilities P{Zn ≥ exp(θ n)}, θ > μ. In the case of subcritical processes analogous result is obtained for θ > γ, where γ > 0 is some constant. For all constants explicit formulas are given.

Using 2D NMR to characterize the structure of the low and high molecular weight fractions of bio-oil obtained from LignoBoost™ kraft lignin depolymerized in subcritical water

In this work a multilevel analysis approach have been used for characterization of LignoBoost™ kraft lignin and bio-oil produced from LignoBoost™ kraft lignin using a process based on subcritical water (350 °C, 25 MPa). LignoBoost™ kraft lignin and the different fractions of the bio-oil (light oil, heavy oil and suspended solids) was characterized with high field NMR (18.8 T, 2D13C, 1H-HSQC NMR and 13C-NMR), GPC, GC-MS and elemental composition to improve understanding of the subcritical process. By using high resolution 2D HSQC NMR it was possible determine the chemical structures both on low and high molecular weight fractions of the bio-oil. It was confirmed that the signals from the aliphatic lignin inter-unit linkages, i.e. β-O-4′, β-β′, β-1′ and β-5′, had disappeared from all of the bio-oil fractions studied. This means that both the aliphatic carbon-oxygen (CO) and to some extent carbon-carbon (CC) bonds in LignoBoost™ kraft lignin have been cleaved and an effective depolymerization has occurred. However, re-polymerization into higher molecular weight (Mw) fractions takes place simultaneously. These higher Mw fractions (heavy oil and suspended solids) were found to be re-polymerized macromolecules, with new structural networks based on guaiacol/disubstituted aromatic ethers and polyaromatic hydrocarbon structures bound tightly together.

Improvement of the Mechanical Properties of 1022 Carbon Steel Coil by Using the Taguchi Method to Optimize Spheroidized Annealing Conditions.

Cold forging is often applied in the fastener industry. Wires in coil form are used as semi-finished products for the production of billets. This process usually requires preliminarily drawing wire coil in order to reduce the diameter of products. The wire usually has to be annealed to improve its cold formability. The quality of spheroidizing annealed wire affects the forming quality of screws. In the fastener industry, most companies use a subcritical process for spheroidized annealing. Various parameters affect the spheroidized annealing quality of steel wire, such as the spheroidized annealing temperature, prolonged heating time, furnace cooling time and flow rate of nitrogen (protective atmosphere). The effects of the spheroidized annealing parameters affect the quality characteristics of steel wire, such as the tensile strength and hardness. A series of experimental tests on AISI 1022 low carbon steel wire are carried out and the Taguchi method is used to obtain optimum spheroidized annealing conditions to improve the mechanical properties of steel wires for cold forming. The results show that the spheroidized annealing temperature and prolonged heating time have the greatest effect on the mechanical properties of steel wires. A comparison between the results obtained using the optimum spheroidizing conditions and the measures using the original settings shows the new spheroidizing parameter settings effectively improve the performance measures over their value at the original settings. The results presented in this paper could be used as a reference for wire manufacturers.

Effect of Subcritical Annealing Temperature on Microstructure and Mechanical Properties of SCM435 Steel

The effect of subcritical annealing temperature on microstructure and mechanical properties of SCM435 steel was investigated through changing the heating and soaking temperature as 660 °C, 680 °C, 700 °C, 720 °C and 745 °C. The microstructure and mechanical properties of intercritically annealed specimens were analyzed. With increasing the subcritical annealing temperature from 660 °C to 720 °C, the spheroidization ratio gradually increased, and the mechanical properties, formability and Vickers hardness were improved. According to the comprehensive comparison of mechanical properties and formability, the subcritical process at soaking temperature of 680–720 °C could achieve similar annealing effect as that of intercritical process. Therefore, the subcritical annealing temperature could be set as 700 °C in practice, with the Ac1 temperature fluctuation within ±20 °C, and the applicability and stability of subcritical annealing were guaranteed in industrial application. The plant results of the cold heading showed that the subcritical annealing could replace original intercritical annealing successfully with significantly saving time and energy.