Reaction Coefficient Research Articles

Numerical Investigation of the Influence of the Degree of Reaction in an Axial Compressor Stage With Tandem Vanes

Abstract Many investigations have defined Smith-type diagrams to guide the preliminary designs of conventional axial compressor stages on the choice of loading, flow coefficient, and degree of reaction. However, the recent development of unconventional axial compressor stages with tandem vanes has not been accompanied by similar studies aimed at tailoring existing correlations to the new type of vanes. While it is clear that axial compressor stages with tandem vanes operate in higher working ranges than conventional stages, it is less clear how the choice of reaction affects the aerodynamic behavior of such setups. For this purpose, this paper numerically investigates a low-speed axial compressor stage with different degrees of reaction for increasing loading levels. The metal angles of the unshrouded rotor and the shrouded stator are modified to ensure that the other design parameters of the stage, namely the work and flow coefficients, are kept constant, and that the influence of the degree of reaction is isolated. The investigation begins with Q2D simulations of the reference midspan aerofoils. It then extends to a 3D configuration, while maintaining the radial distribution of the aerofoil parameters from the reference 3D blades. New correlations are presented, aiming to show how the performance of the stage in terms of efficiency, total pressure losses, and loading coefficients of the vanes are influenced by the different degrees of reaction investigated. This paper, therefore, provides insight into the preliminary choices of parameters for the design of axial compressor stages with tandem vanes.

Substrate-related factors and kinetic studies of Carbohydrate-Rich food wastes on enzymatic saccharification

Food waste biorefinery is a sustainable approach to producing green chemicals, however the essential substrate-related factors hindering the efficacy of enzymatic hydrolysis have never been clarified. This study explored the key rate-limiting parameters and mechanisms of carbohydrate-rich food after different cooking and storing methods, i.e., impacts of compositions, structural diversities, and hornification. Shake-flask enzymatic kinetics determined the optimal dosages (0.5 wt% glucoamylase, 3 wt% cellulase) for food waste hydrolysis. First order kinetics and simulation results determined that reaction coefficient (K) of cooked starchy food was ∼ 3.63 h−1 (92 % amylum digestibility) within 2 h, while those for cooked cellulosic vegetables were 0.25–0.5 h−1 after 12 h of hydrolysis. Drying and frying reduced ∼ 71–89 % hydrolysis rates for rice, while hydrothermal pretreatment increased the hydrolysis rate by 82 % on vegetable wastes. This study provided insights into advanced control strategy and reduced the operational costs by optimized enzyme doses for food waste valorization.

Analysis of longitudinal stress and deformation characteristics of shield tunnel under faulting dislocation

Fault dislocation seriously threatens the structural security of cross-fault tunnels during operation. Regarding the mechanical response of the tunnel across faults, the tunnel was equated as the Timoshenko beam on the Vlasov foundation in the present study, and the mechanical analytical model of the cross-fault tunnel was established and solved by the finite difference method. Published cases were utilized to validate the reasonableness of the analytical model. The influence law of critical parameters of the model on the response of the tunnel was investigated by parameter sensitivity analysis. Finally, the mechanical properties of the tunnel under the non-homogeneous foundation conditions were discussed. The calculation results of the proposed analytical model were similar to the existing model test monitoring data, and the trend was the same, demonstrating the correctness of the analytical model. The tunnel-fault distance, foundation reaction coefficient, foundation shear stiffness, and effective factor of bending stiffness changed the maximum tunnel bending moment, while the fault inclination changed the position where the maximum bending moment occurred. For the non-homogeneous foundation, the difference of adjacent foundation parameters significantly affected the response law of tunnel longitudinal internal forces, and the maximum tunnel bending moment presented a particular nonlinearity with the change of foundation parameters.

Study on Stability of Elastic Compression Bending Bar in Viscoelastic Medium

In the southeastern coastal regions of China, thick layers of marine soft soil are widely distributed, exhibiting characteristics such as high compressibility, high porosity, low strength, high sensitivity, and easy thixotropy, and these viscoelastic behaviors of foundation soil have significant implications for elastic compression bending bar, as evidenced by issues such as post-construction settlement of roadbeds and long-term operation deviation of bridge pile foundations. In this study, a mechanical model of an elastic bar embedded in an elastic and viscoelastic medium, fixed at the base and free at the top, is established based on the Winkler foundation assumption. The deflection function of a bar subjected to both axial force and locally distributed horizontal load is derived using the Rayleigh-Ritz method. Utilizing the elastic-viscoelastic correspondence principle, the viscoelastic medium surrounding the bar is modeled as an elastic medium in which the ground reaction coefficient varies within phase space formulation. This study provides a robust theoretical foundation for soft soil foundation engineering projects and fills a significant gap in the literature by offering a comprehensive framework for understanding displacement in elastic bars within viscoelastic media. Drawing upon the derivation of the deformation function for elastic rods within a viscoelastic medium, the findings of this research hold significant applicability across a range of domains. These include, but are not limited to, the expansion of roadways in regions characterized by coastal soft soil, as well as the monitoring of deformation and lifespan in bridge pile foundations.

Combined model for 15N, 13C, and spin-state chemistry in molecular clouds

We present a new gas-grain chemical model for the combined isotopic fractionation of carbon and nitrogen in molecular clouds. To this end, we have developed gas-phase and grain-surface chemical networks where the isotope chemistry of carbon and nitrogen is coupled with a time-dependent description of spin-state chemistry, which is important for nitrogen chemistry at low temperatures. We updated the rate coefficients of some isotopic exchange reactions considered previously in the literature, and here we present a set of new exchange reactions involving molecules substituted in 13C and 15N simultaneously. We applied the model to a series of zero-dimensional simulations representing a set of physical conditions across a prototypical prestellar core, exploring the deviations of the isotopic abundance ratios in the various molecules from the elemental isotopic ratios as a function of physical conditions and time. We find that the 12C/13C ratio can deviate from the elemental ratio to a high factor depending on the molecule, and that there are highly time-dependent variations in the ratios. The HCN/H13CN ratio, for example, can obtain values of less than ten depending on the simulation time. The 14N/15N ratios tend to remain close to the assumed elemental ratio within approximately 10%, with no clearly discernible trends for the various species as a function of the physical conditions. Abundance ratios between 13C-containing molecules and 13C+15N-containing molecules however show somewhat increased levels of fractionation as a result of the newly included exchange reactions, though they still remain within a few tens of percent of the elemental 14N/15N ratio. Our results imply the existence of gradients in isotopic abundance ratios across prestellar cores, suggesting that detailed simulations are required to interpret observations of isotopically substituted molecules correctly, especially given that the various isotopic forms of a given molecule do not necessarily trace the same gas layers.

Deformation Analysis of a New Subway Transfer Channel Closely Undercrossing an Existing Station

Disturbances that occur due to the construction of new subway transfer channels in cities pose a significant threat to the safe operation and structural stability of existing subway stations. Due to the construction of the new Jin-Fu Station of Chengdu Rail Transit Line 27, the transfer channel of the new Jin-Fu Station closely underpasses the station of the existing Metro Line 6. First, based on the random medium theory, the curved integral boundaries of the rectangular section are improved and simplified by the numerical simulation. Second, the mechanical response of the underpass construction to the existing subway station is analyzed by Pasternak foundation model theory. Finally, the accuracy of the theoretical calculation is verified by the three-dimensional numerical calculation and the measured data, and the sensitivity of its parameters is analyzed. The results show that maintaining a certain net distance d (that is, increasing the thickness of the interlayer soil) is conducive to forming the soil arch effect and reducing the deformation of the existing station above. The settlement of the existing station can be reduced by increasing the height-to-width ratio of the excavated section, but the maximum bending moment of the floor will increase slightly. With the increase in the foundation reaction coefficient k, the interaction between the soil mass and the existing station is enhanced, and the deformation, bending moment, and shear force on the floor of the existing station increase significantly. When the foundation reaction coefficient increases to 10k, there is an obvious uplift phenomenon outside the settlement trough of the existing station floor.

A new approach for evaluating photosynthetic bio-hydrogen production: The dissipation rate method

A dissipative rate model is established by using the non-equilibrium thermodynamics method to evaluate photosynthetic bio-hydrogen production process. The mass transfer dissipation rate, chemical reaction dissipation rate and total dissipation rate for the bio-hydrogen production processes with glucose and acetic acid are calculated and analyzed respectively by using the proposed dissipation rate model. When substrate concentration is taken as variable (15 g/L,20 g/L and25 g/L), the total dissipation rate and mass transfer phenomenological coefficient of hydrogen production process with 20 g/L are the lowest, and the maximum dissipation rate is 7.7288J/h. The phenomenological coefficient of chemical reaction is larger at high concentration. When the temperature is variable (298.15 K,303.15Kand308.15 K), the dissipation rate is lowest at 303.15 K and the chemical reaction coefficient is largest and the maximum dissipation rate is 6.0596J/h. In addition, the mass transfer phenomenological coefficient is larger at high temperature. With the initial pH as variable (6.5,7.0,7.5), the maximum dissipation rate of 11.2271J/h is obtained at pH 7.5. At high pH, the mass transfer phenomenological coefficient is large and the chemical reaction coefficient is exactly the opposite. This model can predict the energy dissipation law in the process of photosynthetic biohydrogen production, and provide a theoretical basis for the subsequent process optimization.

Identifying key pipe attributes and locations to best determine chlorine decay coefficients within a water distribution system

Abstract Water distribution system (WDS) characteristics can impact drinking water quality. Kinetic reaction coefficients of residual disinfectant associated with bulk water (kb) and pipe wall (kw) during water distribution can lead to water quality degradation. Determining these coefficients can be expensive and time-consuming. The main objective of this study is to determine the most relevant pipe characteristics and locations to best determine chlorine decay coefficients in a WDS. This article aims to evaluate various scenarios of kb and kw values and compare them to measured data in a full-scale WDS. The most accurate scenario is also compared with the lowest-cost scenario to identify the most effective information needed to determine these coefficients, in terms of location within the WDS and pipe characteristics (age, diameter, and material). Results showed that the scenario with the highest kw and kb values corresponds best to the field-measured data. Moreover, determining specific kinetic coefficients was shown to be more accurate for gray cast iron pipes, pipes installed in a period before 1960, and vulnerable zones for residual chlorine decay.

Pointwise error estimate of the compact difference methods for the fourth‐order parabolic equations with the third Neumann boundary conditions

Various boundary value conditions have been endowed for the fourth‐order differential equations. In the current work, a class of the fourth‐order parabolic equations with the third Neumann boundary conditions is concerned, where the values of the second and third spatial derivatives of the unknown function are given at the boundary. A novel average is defined to get the compact approximation near the boundary. Then a compact difference scheme is derived by using the weighted average and the method of order reduction. Due to the special and highly accurate discretization at the boundary, the related terms have to be handled skillfully during the analysis. By the energy method, the unique solvability, unconditional stability, and convergence of the derived compact difference scheme are strictly proved. The analytical difficulties caused by the boundary approximation are successfully overcome. As far as we know, this is the first time that the global pointwise fourth‐order convergence in space of the difference approach for this problem is achieved. In addition, the generalization to solve the case with a space‐dependent reaction coefficient is discussed. Finally, two numerical examples are computed to verify the accuracy of proposed numerical schemes.

Quasilinear problems with nonlinear boundary conditions in higher-dimensional thin domains with corrugated boundaries

AbstractIn this work, we analyze the asymptotic behavior of a class of quasilinear elliptic equations defined in oscillating(N+1)\left(N+1)-dimensional thin domains (i.e., a family of bounded open sets fromRN+1{{\mathbb{R}}}^{N+1}, with corrugated bounder, which degenerates to an open bounded set inRN{{\mathbb{R}}}^{N}). We also allow monotone nonlinear boundary conditions on the rough border whose magnitude depends on the squeezing of the domain. According to the intensity of the roughness and a reaction coefficient term on the nonlinear boundary condition, we obtain different regimes establishing effective homogenized limits inNN-dimensional open bounded sets. In order to do that, we combine monotone operator analysis techniques and the unfolding method used to deal with asymptotic analysis and homogenization problems.

Modelling of Deep Street Canyon Air Pollution Chemistry and Transport: A Wintertime Naples Case Study

The impact of urban morphology on air quality, particularly within deep canyons with longer residence times for complex chemical processes, remains insufficiently addressed. A flexible multi-box framework was used to simulate air quality at different canyon heights (3 m and 12 m). This approach incorporated essential parameters, including ventilation rates, background concentrations, photochemical schemes, and reaction coefficients. A field campaign within a deep canyon with an aspect ratio of 3.7, in Naples, Italy was conducted and used for the model evaluation. The model performance demonstrated good agreement, especially at the street level, when employing a realistic light intensity profile and incorporating volatile organic compound (VOC) chemistry. Our findings indicate that peroxyl radical production affects NO2 and O3 levels by up to 9.5% in deep canyons and underscore the significance of vertical distribution (approximately 5% variance) in health assessments and urban air quality strategy development. The model response was sensitive to changes in emissions as expected, but also, somewhat more surprisingly, to background conditions, emphasizing that policies to remove pollution hotspots must include local and broader citywide action. This work advances the understanding of air quality dynamics in deep urban canyons and presents a valuable tool for effective air quality management in intricate urban environments.

Stochastic Simulation of Continuous Time Random Walks: Minimizing Error in Time-Dependent Rate Coefficients for Diffusion-Limited Reactions

Stochastic Simulation of Continuous Time Random Walks: Minimizing Error in Time-Dependent Rate Coefficients for Diffusion-Limited Reactions

Event-Triggered Adaptive Control of a Parabolic PDE–ODE Cascade With Piecewise-Constant Inputs and Identification

We present an adaptive event-triggered boundary control scheme for a parabolic PDE-ODE system, where the reaction coefficient of the parabolic PDE, and the system parameter of a scalar ODE, are unknown. In the proposed controller, the parameter estimates, which are built by batch least-square identification, are recomputed and the plant states are resampled simultaneously. As a result, both the parameter estimates and the control input employ piecewise-constant values. In the closed-loop system, the following results are proved: 1) the absence of a Zeno phenomenon; 2) finite-time exact identification of the unknown parameters under most initial conditions of the plant (all initial conditions except a set of measure zero); 3) exponential regulation of the plant states to zero. A simulation example is presented to validate the theoretical result.

Displacement-based seismic performance of RC bridge pier

To correctly manage the road infrastructure before and after an earthquake, it is necessary to estimate and even predict the seismic performance of the bridge. The quantification of the bridge's seismic performance response was present in terms of displacement and also based on previous research of reinforced concrete bridge pier models. The displacement did define from a force lateral-displacement response diagram corresponding to the capacity curve, calculated through a non-linear static pushover analysis of the reinforced concrete bridge pier model for each limit state, from intact state to collapse. Thus, six defined displacements correspond to the cracking displacement, the yielding displacement, the spalling displacement, the crushing displacement, the buckling displacement, and the fracturing displacement. The six defined limit states correspond to the cracking limit state, the yielding limit state, the spalling limit state, the crushing limit state, the buckling limit state, and the fracturing limit state. Also, parametric analysis did carry out to evaluate the influence, relative importance, and trend of the input parameters in response to the seismic performance of the reinforced concrete bridge pier model. Eleven input parameters did analyze as the concrete compressive strength, the yield stress of reinforcing steel, the concrete cover thickness, the pier aspect ratio, the configuration of the transverse reinforcement, the spacing of the transverse reinforcing steel, the transversal diameter of the transverse reinforcing steel, the longitudinal reinforcement ratio, the transversal diameter of the longitudinal reinforcing steel, the axial load ratio, and coefficient of subgrade reaction.

Novel Theories for Modeling the Surface Stabilization and Dendrite Suppression for Lithium-Metal Anode Based on Piezoelectric Effect

During electrodeposition, a small perturbation can cause the metal surface to lose its stability and form dendrite. Lithium dendrite is a key barrier that has impeded the commercialization of lithium metal batteries as well as fast charging. We find a piezoelectric mechanism to suppress dendrites, whose effect measured by over-potential can easily be 106 stronger than mechanically blocking dendrite with a stiff film. We first expanded the classical electrochemical reaction kinetics by incorporating the effect of stress and thin film piezoelectricity. We then developed a novel theory that couples the fields of electrochemistry, piezoelectricity and thin film mechanics. We then developed a rigorous stability analysis approach to reveal the effect of surface tension, mechanical blocking and piezoelectric mechanism on the stability of electrodeposition. We finally developed a theoretical expression of the critical wavelength, which provides useful guidance on achieving stable electrodeposition for various systems [1].We further developed a theory for a bulk porous piezoelectric medium which couples electrochemistry, piezoelectricity, and mechanics. Specifically, we derived a piezoelectric overpotential, which reveals a fundamental relation to surface charge density, dielectric property of the medium, electrolyte concentration and diffusivity, and the reaction coefficient. Our simulation results show that piezoelectric medium can effectively suppresses electrodeposition on any protrusion, leading to a flat, dendrite-free surface [2].

Modeling the Coulombic Efficiency of the Aqueous Iron Electrode

The aqueous iron electrode is attractive for large-scale energy storage because of its long life and low materials cost. The redox potential of the Fe ↔ Fe2+ reaction is approximately 50 mV negative of that of the hydrogen evolution reaction. Hydrogen evolution therefore causes self discharge of the iron electrode during rest and competes with the iron reaction during charge. Here we model the effect of electrode design and cell operation on the coulombic efficiency of charging the iron electrode at modest charging rates (<C/20). Kinetic parameters (exchange current density and transfer coefficients) for the iron dissolution-precipitation reaction and for the hydrogen evolution reaction are estimated from experimental measurements of electrode overpotential and hydrogen generation rate. The volume change from Fe(OH)2 to Fe metal results in a significant increase in porosity during charge and results in change in electrochemically active surface area. The porous-electrode model includes transport in the electrolyte, Butler-Volmer kinetics, and change in volume and surface area.The model provides a theoretical explanation for experimental observations that coulombic efficiency decreases with decreasing charge rate, and that coulombic efficiency is lower in thicker electrodes. We then use the model to explore the impact for large-format cells of electrode size and design on coulombic efficiency.

KUMLU ZEMİN ÜZERİNDEKİ RADYE TEMELLERİN WİNKLER VE PSÜDO-EŞLENİK YÖNTEMLERİ İLE ANALİZİ

The settlements occurred in building foundations depend on many soil parameters. Thus, these parameters make the solution both difficult and complex during the calculating process. Therefore, finite element programs use the subgrade reaction coefficient to facilitate the foundation solution. Two different methods, which are Winkler method and Pseudo coupled method, are used in the basic solutions with the coefficient of subgrade reaction. While the Winkler method can be solved with a single field, the pseudo method can be solved with 2 or more fields. In this study, a 10 story building with a 36 m x 36 m square foundation was separately designed on four different sand soils. Two of these soils are classified as C and the others are classified as D according to Eurocode 8. The foundation of this building built on four different soils was divided into six different areas (one region, two regions, three regions, five regions, seven regions, 10 regions). Consequently, 24 analyzes were performed by using the ETABS program. According to the results obtained from these analyzes, while it is appropriate to use the Winkler method in weak sand soils for rigid foundation acceptance, it is more appropriate to use the Pseudo-coupled method in dense sand soils. Pseudo-coupled method should be used in flexible foundation solutions built on weak sand soils. The Winkler method should be used for flexible foundations built on dense sand soils. In the Pseudo-coupled method, the highest settlements were obtained in the two-region solutions. An optimum number of fields was found to be 7 for Pseudo-coupled method.

Modeling the fate of viruses in aquifers: Multi-kinetics reactive transport, risk assessment, and governing parameters

The transport of viruses in groundwater is a complex process controlled by both hydrodynamic and reaction parameters. Characterizing the transport of viruses in groundwater is of crucial importance for investigating health risks associated with groundwater consumption from private individual or residential pumping wells. Setback distances between septic systems, which are the source of viruses, and pumping wells must be designed to offer sufficient groundwater travel times to allow the viral load to degrade sufficiently to be acceptable for community health needs. This study consists of developing numerical simulations for the reactive transport of viruses in the subsurface. These simulations are validated using published results of laboratory and field experiments on virus transport in the subsurface and applying previously developed analytical solutions. The numerical model is then exploited to investigate the sensitivity of the fate of viruses in saturated porous media to hydraulic parameters and the coefficients of kinetic reactions. This sensitivity analysis provides valuable insights into the prevailing factors governing health risks caused by contaminated water in private wells in rural residential contexts. The simulations of virus transport are converted into health risk predictions through dose–response relationships. Risk predictions for a wide range of input parameters are compared with the international regulatory health risk target of a maximum of 10−4 infections/person/year and a 30 m setback distance to identify critical subsurface contexts that should be the focus of regulators.

A stabilized element-free Galerkin method for the advection–diffusion–reaction problem

A stabilized element-free Galerkin (EFG) method is presented and analyzed for the numerical solution of the advection–diffusion–reaction problem. Through deriving a stabilized Nitsche-type weak form for the problem, the presented EFG method is valid for small diffusivity and large reaction coefficient. Theoretical error of the method is analyzed. Numerical results verify the effectiveness of the method.

Uncertainty in phosphine photochemistry in the Venus atmosphere prevents a firm biosignature attribution

Context. The possible detection of phosphine (PH3) in the clouds of Venus has raised the question as to which processes could produce such large abundances of PH3. Previous studies suggested that abiotic processes including photochemical production cannot explain the claimed PH3 concentrations. However, the photochemistry of phosphorus-bearing species in the atmosphere of Venus is not well known. Aims. We aim to assess the abiotic production of PH3 considering the effect of uncertainties in the chemical rate coefficients of phosphorus-containing reactions. Methods. Using a photochemical column model, we simulated Venus-like conditions and varied the chemical rate coefficients with a Monte Carlo (MC) approach in order to estimate the associated error in the PH3 abundances throughout the atmosphere. Results. Current uncertainties and missing data in photochemical rate coefficients lead to a variation of about six orders of magnitude in the modelled PH3 abundance on Venus, assuming photochemical production of PH3 from tetraphosphorus hexoxide (P4O6) pathways. Our results suggest an abiotically produced upper limit of 2 ppb PH3 between 50 and 60 km. These concentrations are in the range of a recent reanalysis of Atacama Large Millimeter Array (ALMA) data, suggesting planet-averaged abundances in PH3 of 1–4 ppb above 55 km. Future observations of phosphorus monoxide (PO) on Venus would be beneficial for increasing our confidence in assessing PH3 as a biosignature. Conclusions. We conclude that due to the large uncertainties in phosphorus chemistry, even a firm detection of several ppb PH3 in the Venus atmosphere would not necessarily mean a biological origin.