Energy Minimization Method Research Articles

Thermodynamic Study of One-step Production from Isobutene to Methyl Methacrylate

Methyl methacrylate (MMA) has emerged as an essential industrial monomer. However, the toxic by-production and shortage supply of MMA in the global market has gained great attention. Herein, a one-step synthesis to produce MMA from isobutene via a direct oxidative esterification process has been demonstrated to curb the aforementioned downsides. Thermodynamic analysis via Gibbs free energy minimization method proved the feasibility of this route via the equilibrium constant. Despite tert-butanol and isobutane showed higher equilibrium constant than isobutene, they should be avoided. Isobutane is highly flammable while the precursor of tert-butanol is exorbitant. Thus, isobutene was selected for the equilibrium compositions screening. Isobutene conversion was 90% and 15% MMA yield at 700 °C and IBN: O2: MeOH ratio with 1:7:1. This route is mainly limited by the generation of side reactions from the reaction of CH3OH and O2. By varying the feedstock ratio at 1:2:1, the MMA yield increased to ~25%. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Vibration–impact study on the functionally graded graphene nanoplatelets reinforced composite curved open-type shell

This paper investigates the stability of the curved system reinforced by graphene nanoplatelets (GPLs) under low-velocity impact. Hertz contact theory is employed in order to model the contact force between the shell and the impactor. In order to acquire the displacement domains, higher-order shear deformation theory (HSDT) with twelve parameters is used. The governing equations, in addition to end conditions, are attained by the Minimum potential energy method. Then the formulations are solved through the Galerkin method as well as the Newmark method. By coupling Galerkin and Newmark methods, we solved the governing equations of the curved system under external excitation for attaining the dynamic and low-velocity impact responses. The results section shows the influence of boundary conditions, velocity, mass, and radius of the impactor, and the weight fraction of GPLs on indenter velocity, contact force, and the indentation of the GPLs reinforced open-type shell under low-velocity impact.

Study on Thermal Plasma Combined Treatment for Medical Waste

A thermal plasma combined treatment of medical waste proposed here combines the advantages of pyrolysis and gasification technologies, which provides an option for the harmless, reduction and recycling treatment of medical waste. In addition, a simulation model based on the Gibbs free energy minimization method was developed to explore the characteristics of plasma pyrolysis, gasification, and combined treatment methods. Compared with the plasma pyrolysis method, the plasma combined treatment method can not only produce more syngas with high calorific value but also achieve higher process efficiency. Different from the plasma gasification method, the combined treatment method uses nonoxidizing gas as the working gas for plasma torches, which helps slow down the ablation of plasma torch cathode. Besides, three main components of medical waste were analyzed through the plasma combined treatment model. Simulation results show that materials with high carbon and hydrogen content, such as plastic and rubber, can not only help to increase syngas output and calorific value but also improve system efficiency to a certain extent.

Simple phase unwrapping method with continuous convex minimization.

Phase unwrapping is a problem to reconstruct true phase values from modulo 2π phase values measured using various phase imaging techniques. This procedure is essentially formulated as a discrete optimization problem. However, most energy minimization methods using continuous optimization techniques have ignored the discrete nature and solved it as a continuous minimization problem directly, leading to losing exactness of the algorithms. We propose a new minimum norm method that can yield the optimal solution of the discrete problem by minimizing a continuous energy function. In contrast to the graph-cuts method, which is state of the art in this field, the proposed method requires much less memory space and a very simple implementation. Therefore, it can be simply extended to 3D or 4D phase unwrapping problems.

Feasibility analysis of water gas shift reaction for the removal of trace CO in hydrogen

The thermodynamic simulation analysis of carbon monoxide water gas shift in rich hydrogen was researched by using the method of Gibbs free energy minimization with Aspen plus software. For the purpose of purifying trace amount of CO in hydrogen, two raw gas compositions, 1%CO–99%H2 and 1%CO–24%CO2–75%H2, were purposely selected, and the influences of water to gas molar ratio (1–7) and transformation temperature (40–280 °C) were investigated. The results showed similar variation law as compared with the water gas shift of a pure CO gas. When the transformation temperature increased, the chemical equilibrium shifted toward the reverse direction, resulting in decreased CO equilibrium conversion; when the water to gas molar ratio increased, the CO conversion increased. The results also showed that CO2 had great negative effects on CO conversion compared with H2. For the CO/H2 feed gas, it was concluded that it was possible to reduce the 1% CO content to 100 ppm at 120 °C with the use of the best low-temperature catalyst reported in literature. If we want to further reduce the trace amount of CO in hydrogen to 10 ppm, it is necessary to develop ultra-low temperature catalysts that are highly active below 70 °C.

Thermochemical recuperation by steam methane reforming as an efficient alternative to steam injection in the gas turbines

Improving the energy efficiency of gas turbines is an extremely important task of the world energy industry. This paper presents the results of thermodynamic analysis of a gas turbine unit with thermochemical exhaust heat recuperation by steam methane reforming (chemically recuperated gas turbine — CRGT). The thermochemical exhaust heat recuperation systems consist of a reformer, a steam–methane mixture preheater, and a steam generator. The main goal of this paper is comparing CRGT efficiency with the efficiency of a gas turbine unit with steam injection (STIG). To calculate the recuperated heat in a reformer, the thermodynamic analysis of steam methane reforming was performed via Gibbs free energy minimization method. Both thermodynamic cycle and reforming analysis were performed via Aspen HYSYS. The analysis was performed in the temperature range of working fluid at a turbine inlet (Tin) of 800–1300 °C and the steam-to-methane ratio of 1, 2, 3 (mol-to-mol). The results showed that thermochemical exhaust heat recuperation can be considered as an alternative to steam injection in gas turbines. The efficiency of CRGT is higher than the efficiency of STIG for the same steam-to-methane ratio. With increasing in Tin the efficiency of CRGT is increasing. The efficiency of STIG and CRGT at Tin=1300 °C for a steam-to-methane ratio of 3 is 37.4% and 47.3%, respectively.

The effect of oxidation of Al(1 1 1) surface on the catalytic efficiency of decomposition of ammonium perchlorate: A density functional theory study

The study of the decomposition behavior of ammonium perchlorate (AP) on Al surface is of crucial significance to the rational design of aluminum-based solid propellants containing AP. It is of interest to understand the underlying reaction pathways and primary reaction mechanism. Herein, the decomposition reactions of perchloric acid and ammonia molecules on oxidized Al(1 1 1) surface are investigated using density functional theory (DFT) to gain insight into the reaction mechanisms at the molecular-level. The co-adsorption configurations of perchloric acid and ammonia on Al(1 1 1) surface are obtained by energy minimization method, and the activation energy barriers of all elementary reactions are calculated through transition state searching method. In the co-adsorption configurations, perchloric acid decomposes and generates OH group and atomic oxygen and chlorine, whereas the ammonia molecule retains its integrity and forms a hydrogen bond with hydroxyl. When these molecules are adsorbed on oxidized Al(1 1 1) surface in isolation, the activity of HClOx(x = 1–4) is reduced by the formation of hydrogen bond between the 3-fold-coordinated oxygen atom and hydroxyl of HClOx. Furthermore, larger coverage by oxygen atoms adsorbed on Al surface leads to higher energy barriers of the decomposition reactions of HClO4. However, for NH3 the energy barriers of the dehydrogenation reactions are less affected by the degree of oxygen coverage of the Al surface, except for the completely oxidized Al substrate. A series of elementary decomposition reaction steps of AP is proposed to explain the decomposition mechanism of AP on Al(1 1 1) surface.

Screening of Potential Additives for Alleviating Slagging and Fouling during MSW Incineration: Thermodynamic Analysis and Experimental Evaluation

The formation of slagging and fouling during municipal solid waste (MSW) incineration not only significantly affects heat transfer, but also results in shortened operating cycles. In order to solve the issues, the effect of different additives on the migration and transformation patterns of alkali/alkaline earth metals (AAEM) and chlorine during MSW incineration is screened based on the Gibbs energy minimization method. The effect of potential additives on the ash fusion temperature and combustion reactivity of MSW char is subsequently verified and evaluated by experimental methods. The thermodynamic equilibrium analysis shows that Al(NO3)3, Ca(NO3)2, and Mg(NO3)2 have great potential to increase the ash fusion temperature. The experimental investigation confirms that the addition of Al(NO3)3, Ca(NO3)2, and Mg(NO3)2 significantly increases the ash fusion temperature. The order of increasing the ash fusion temperature by different additives is Mg(NO3)2 > Ca(NO3)2 > Al(NO3)3. The addition of Mg(NO3)2 significantly increased the initial deformation temperature, softening temperature, hemispheric temperature, and flow temperature of ash from 1180, 1190, 1200, and 1240 °C to 1220, 1230, 1240, and 1260 °C, respectively. The addition of Cu(NO3)2, Fe(NO3)3, and KMnO4 significantly decreases the temperature at the maximum weight loss rate of MSW char, while increasing the maximum weight loss rate. Additionally, Cu(NO3)2 shows the best performance in improving the combustion reactivity of MSW char. The addition of Cu(NO3)2 evidently increases the maximum weight loss rate from 0.49 to 0.54% °C−1. Therefore, it is concluded that Mg(NO3)2 and Cu(NO3)2 are supposed to be the most potential candidates for efficient additives. This study presents an efficient and economical method to screen potential additives for alleviating slagging and fouling during MSW incineration.

Linear-Time Algorithms for RNA Structure Prediction.

RNA secondary structure prediction is widely used to understand RNA function. Existing dynamic programming-based algorithms, both the classical minimum free energy (MFE) methods and partition function methods, suffer from a major limitation: their runtimes scale cubically with the RNA length, and this slowness limits their use in genome-wide applications. Inspired by incremental parsing for context-free grammars in computational linguistics, we designed linear-time heuristic algorithms, LinearFold and LinearPartition, to approximate the MFE structure, partition function and base pairing probabilities. These programs are orders of magnitude faster than Vienna RNAfold and CONTRAfold on long sequences. More interestingly, LinearFold and LinearPartition lead to more accurate predictions on the longest sequence families for which the structures are well established (16S and 23S Ribosomal RNAs), as well as improved accuracies for long-range base pairs (500 + nucleotides apart). This chapter provides protocols for using LinearFold and LinearPartition for secondary structure prediction.

Free energy calculation and ghost force correction for hot‐QC

A new efficient variant of hot-QC, the finite temperature version of the quasicontinuum (QC) method, is presented. In the original formulation of hot-QC, a dynamically evolving atomistic region is coupled with either a dynamic (hot-QC-dynamic) or a static (hot-QC-static) continuum region. In the current work, a free energy minimization method is employed in which atom positions in both the atomistic and continuum regions always occupy equilibrium positions. The effect of ghost forces at the interface of the atomistic and continuum regions is discussed for all three variants of hot-QC using two examples: a perfect cubic crystal and a Lomer dislocation dipole. Errors due to ghost forces and due to mesh entropy are considered and the efficacy of their correction terms are evaluated. It is shown that the proposed free energy minimization method has comparable accuracy to the other methods with significantly higher efficiency.

Liquid organic hydrogen carriers (LOHCs) in the thermochemical waste heat recuperation systems: The energy and mass balances

This paper is presented a concept of thermochemical recuperation of waste heat based on hydrogen extraction from liquid organic hydrogen carriers (LOHC), on the example of methylcyclohexane-toluene system. The advantages of this concept is described, for example, a possibility to use a moderate low temperature of waste heat for generation high-exergy “green” hydrogen fuel. To understand the effect of operating parameters on the energy and mass balance, the thermodynamic analysis was performed. The chemical system for hydrogen generation was analyzed via Gibbs free energy minimization method. The thermodynamic analysis was conducted under various operating conditions: temperature of 100–400 °C, pressure of 1–4 bar. Aspen HYSYS software was used for the energy and mass conservation analysis. Sankey diagram for the energy flows is depicted. The results showed that the maximum energy efficiency the thermochemical waste heat recuperation system have in the temperature range above 300–350 °C. In this temperature range, the effect of pressure on the energy balance is negligible and it is recommended for the thermochemical recuperation system to use LOHC with a pressure of 1.5–2 bar. Based on the analysis, it was concluded that the temperature potential of waste heat for about 300–350 °C is enough for the investigated concept. An analysis of a mass balance showed that the decreasing in condensation temperature leads to a significant increasing in the share of condensed toluene from toluene-hydrogen mixture after a reactor. If temperature of a hydrogen-toluene mixture of 20 °C at pressure above 2 bar about 96% of toluene can be condensed after the first condenser.

Calculation of horizontal displacement of loess fill slope supported by frame prestressed anchors based on minimum potential energy method

Combined with the deformation characteristics of flexible retaining structure, the horizontal displacement calculation method of loess fill slope supported by frame prestressed anchors is proposed. Based on the minimum potential energy method, the analytical solution of horizontal displacement of slope under self-weight and additional load is derived, and the influence of soil parameters and supporting structure parameters on displacement is analyzed. The proposed calculation method is applied to a practical engineering and compared with the numerical simulation, which shows that the method is reasonable and reliable. The minimum potential energy method is clear in concept and simple in solving the horizontal displacement of loess fill slope supported by frame prestressed anchors. The calculation method proposed in this paper can be applied to the structural optimization design of loess fill slope supported by frame prestressed anchors, and further enrich the displacement calculation theory of slope supported by flexible retaining structure.

Оцінка міцності та надійності автотранспортних засобів

At present, the issue of ensuring the strength and reliability of wheeled vehicles, the creation of which requires compliance with all modern requirements, has not been fully resolved. In this regard, improving the methodology for assessing the strength and reliability of vehicles is an urgent task, the solution of which involves finding answers to the following questions: the choice of a rational version of the bearing system and economically sound profiles; selection of materials with appropriate physical and mechanical characteristics, etc. The choice of a rational variant of the load-bearing system of frame structures of vehicles requires a comparative assessment of possible options at all stages of design work. The load-bearing structures of vehicles are statically uncertain. Therefore, the process of assessing the strength and reliability of vehicles with different types of design schemes is a complex task, which today does not have a single methodological solution. In order to solve this problem, the model of the stress-strain state of the spatially loaded frame structure of the HESSTON S 125 solid fertilizer spreader is considered by a modified method of minimum potential deformation energy of structural structures using the Heaviside function. The frame is a welded load-bearing structure consisting of three longitudinal spars connected by a front beam and crossbars. Carrying out the correct and rational analysis of the stress-strain state of such a bearing system is possible only with the use of a modified method of minimum potential deformation energy. As a result of modeling, recommendations were obtained for the rational design of components and components of wheeled vehicles with increased reliability while reducing material consumption. Ultimately, this leads to an increase in their strength and reliability while reducing material consumption.

Mathematical study on gravity effect of the liquid bridge between two rigid spheres

To better understand how gravity affects the evolution of capillary force and meniscus shape of the vertical liquid bridge between two millimeter-size spheres, an explicit mathematical model was built using Surface Evolver software. In this study, the rupture behavior of liquid bridge in the equilibrium state was studied using the energy minimization method, and the validity of the mathematical method followed was verified by comparing with existing research results. In addition, the gravity effect on the meniscus shape and geometric parameters were systematically studied. Finally, the gravity effect on the residual liquid volume after the liquid bridge ruptures was examined, and a calculation method for the residual liquid volume on the sphere was proposed, which was proven by mathematical methods and experiments. The relative error was <16% when the liquid dripping error was neglected, proving the feasibility of the calculation method.

Kinematic Chain Equivalent Method for Tube Model and Elastodynamic Optimization for Parallel Mechanism Based on Matrix Structural Analysis

The platforms of parallel mechanisms usually suffer vibration loads. In these cases, structure elastodynamic analysis and elastodynamic optimization of parallel mechanisms are important. A tube structure is very common for parallel mechanisms. This work establishes the model of a tube structure based on matrix structural analysis. The kinematic pair equivalent method is used to simulate the surface contact between the inner and outer tubes. The corresponding mass and stiffness matrices are derived through the strain energy minimization method. The reconfigurable legged lunar lander has been used as an example to verify the effectiveness of this method. By adding the mechanism configuration to the optimization process, the equivalent static load method and the desirability approach are combined and modified. A procedure for the multi-objective elastodynamic optimization of parallel mechanisms is proposed. The optimization procedure is implemented on the lander and the results show a reduction in mass and an increase in natural frequency.

Efficiency of chemically recuperated gas turbine fired with methane: Effect of operating parameters

Previously, a set of optimistic studies have been published to show the efficiency of chemically recuperated gas turbines (CRGT) based on steam methane reforming. The thermodynamic efficiency of such turbines is depending not only on temperature and pressure in a cycle but also on temperature, pressure and steam-to-methane ratio in a recuperation system. In this paper, the effect of operational parameters (temperature, pressure, steam-to-methane ratio) on the efficiency of CRGT was determined. Exhaust heat recuperation in CRGT is taking place due to methane reforming, steam-methane mixture heating, and steam generation. A thermodynamic enthalpy of steam methane reforming process was determined via Gibbs free energy minimization method. The thermodynamic analysis of CRGT was performed in Aspen HYSYS. The efficiency of CRGT was determined for a wide range of operational parameters (gas turbine inlet temperature of 800–1500 °C, pressure of 5–25 bar, steam-to-methane ratio of 1...3). Based on the analysis it was confirmed that the efficiency of CRGT and thermochemical exhaust heat recuperation system is increasing with an increase in temperature. An increase in temperature and steam-to-methane ratio leads to an increase in a share of recuperated heat in a reformer. The heat recuperation rate is up to 0.63 for a high-temperature gas turbine and a steam-to-methane ratio of 3. The efficiency of CRGT is up to 49% for gas turbines with inlet gas temperature of 1500 °C which is an available level in modern gas turbines from Mitsubishi, Siemens, Alstom, etc.

Modeling and analysis of soft robotic surfaces actuated by pneumatic network bending actuators

Soft robots are a nascent field that aims to provide a safe interaction with humans and better adaptability to unstructured environments. Many tentacle-like one-dimensional soft robots that can mimic the basic motion in nature are developed owing to ease of design and fabrication. To expand the spectrum of soft robots, this paper gives a detailed introduction of a new type of sheet-like two-dimensional soft robot. This soft robot is called soft robotic surface (SRS), which is actuated by pneumatic network bending actuators. An analytical model of the SRS is constructed based on the minimum potential energy method, which considers both its geometry complexity and material nonlinearity. The comparisons among the analytical, experimental, and numerical results demonstrate that the analytical model can accurately predict the SRS deformation. The maximum root mean squared error for the surface morphing is 3.429 mm, which is less than 5% of the maximum displacement for the free end. The effects of the actuating pressure and structural parameter on the SRS deformation are also investigated. The results reveal that the deformation shape of the SRS can be reconfigured by controlling the applied pressure. And the bending angle of the two actuators both decreases with the increase of the width and thickness of the soft surface. The SRS extends the research on soft robots and the developed analytical model also solves the fundamental problem of how to programme the surface morphing of soft robot surfaces. Finally, we fabricate a soft gripper that can grasp object objects with different sizes, shapes, and stiffness, which demonstrates the application of the SRS.

CH4 valorisation reactions: A comparative thermodynamic analysis and their limitations

In this study, we report on a first comparative thermodynamic analysis of various CH4 valorisation processes, taking into account the formation of byproducts through a network of side reactions. The analysis is carried out to assess the influence of a wide range of reaction parameters on the performance of each valorisation process in terms of CH4 conversion and desired selectivity metrics. The Gibbs free energy minimization method is used for the equilibrium study of nine CH4 conversion processes, including ten side reactions. The ΔG calculations revealed that the oxidative coupling of methane (OCM) and the methane dehydro-aromatization (MDA) reactions are thermodynamically the most and least feasible reactions, respectively. At P = 1 bar and T = 700 °C, the highest and lowest CH4 conversions were obtained by the dry reforming of methane (DRM) (90%) and oxidative dimerization (18%), respectively. The DRM and steam reforming of methane (SRM) were highly sensitive to changes in operation parameters, while the partial oxidation of methane (POM) and OCM were the least affected. The increasing addition of water in reforming reactions reduced the coke formation to zero at temperatures above 675 °C. From the comparison of the thermodynamic results with the documented experimental data, the carbon deposition was found to decrease both the selectivity and stability of catalysts. Investigations into the thermodynamic and kinetic limitations together with the catalyst design will help in the development of a commercial CH4 valorisation process.

Hydrogen production from steam and dry reforming of methane-ethane-glycerol: A thermodynamic comparative analysis

Glycerol is produced as a by-product waste during the biodiesel manufacturing process. In recent researches, glycerol has been extensively studied for its potential to be converted into higher value-added compounds because it is renewable and bioavailable compound to reduce the high biodiesel production cost. As a result, various methods and technologies, such as steam reforming and dry reforming, were utilized to convert glycerol to higher value added products. The straightforward route of dry and steam reforming techniques uses carbon dioxide and other greenhouse gases to create added-value products like syngas, which may be considered renewable alternatives to fossil fuels as global CO2 emission issues get higher and near-uncontrollable. Therefore, this article presents a novel thermodynamic equilibrium analysis of steam and dry reforming with methane-ethane-glycerol mixture based on the total Gibbs free energy minimization method for hydrogen generation. Equilibrium product compositions were determined as a function of molar ratio between H2O/methane-ethane-glycerol (WMEG) from 1:1 to 12:1 and CO2/methane-ethane-glycerol (CMEG) from 1:1 to 12:1 for steam and dry reforming respectively, where the molar basis of the methane-ethane-glycerol mixture is 1:1:1. The reforming temperatures are ranged from 573 K to 1273 K at atmospheric pressure of 1 bar. The production trends of H2, CO, CO2, CH4 and C were compared between both reforming of glycerol. From to the result of the study, the optimal operating parameter for the highest hydrogen production was under steam reforming with WMEG of 3:1 at 1273 K and zero carbon deposition is achieved. In comparison with CO and CO2 production, dry reforming produced higher yields than steam reforming. Furthermore, a significant increment of hydrogen production was not observed at higher ratios of WMEG and CMEG. Steam reforming inhibited the carbon formation thermodynamically better than dry reforming.

Simulation perspective of upgrading biomass producer gas through a shift-methanation reaction coupled with cyclic CO2 capture

Reducing the CO content and improving the lower heating value (LHV) of biomass producer gas are essential for transforming it into a reliable energy source. The present work strives to provide a simulation perspective for a biomass producer gas upgrading process containing integrated shift-methanation and cyclic CO2 capture, where the CO2 by product from the shift-methanation reactor is separated by cyclic mono-ethanolamine (MEA) scrubbing. Equilibrium calculations via the Gibbs energy minimization method reveal that the appropriate temperature and pressure window for the shift-methanation reaction is 300–450 °C and 1–5 bar, respectively. The simulation results show that the optimal stage number for both the absorber and stripper is 10. The desired value of absorber and stripper efficiency can be obtained by balancing the MEA flow rate and reboiler duty. The original biomass producer gas with a 44.4% CO content and LHV of 9.45 MJ/Nm3 is upgraded to a CO content below 10% and LHV over 14 MJ/Nm3, reaching the national classification standard of Grade I gas. The preliminary engineering design in this work combines the shift-methanation reaction with CO2 absorption–desorption, demonstrating much potential for industrial-scale applications.