Constrained Efficient Global Optimization for Pultrusion Process

Composite materials, as the name indicates, are composed of different materials that yield superior performance as compared to individual components. Pultrusion is one of the most cost-effective manufacturing techniques for producing fiber-reinforced composites with constant cross-sectional profiles. This obviously makes it more attractive for both researchers and practitioners to investigate the optimum process parameters. Validated computer simulations cost less as compared to physical experiments, therefore this makes them an efficient tool for numerical optimization. However, the complexity of the numerical models can still be “expensive” and forces us to use them sparingly. These relatively more complex models can be replaced with “surrogates,” which are less complex and are therefore faster to evaluate representative models. In this article, a previously validated thermochemical simulation of the pultrusion process has shortly been presented. Following this, a new constrained optimization methodology based on a well-known surrogate method, i.e., Kriging, is introduced. Next, a validation case is presented to clarify the working principles of the implementation, which also supports the upcoming main optimization test cases. This design problem involves the design of the heating die with one, two, and three heaters together with the pulling speed. The results show that the proposed methodology is very efficient in finding the optimal process and design parameters.     

Characterization of a thermochemical reactor for thermal solar energy

The main purpose of this work is to elucidate the thermochemical characteristics of a fluidized bed reactor to be used as a solar reactor in thermal energy storage. Zinc sulfate dissociation was studied over the temperature range from 973 to 1123 K. During the reaction problems such as non isothermisity of the bed and pressure drop changes with the reaction, were detected. It was shown that the fluidity increased with temperature and degree of dissociation, but the pressure drop amplitude increased exponentially with gas velocity and particle size when slugging is present in the bed.     

Effect of inclusions on the solidification structures of ferritic stainless steel: Computational and experimental study of inclusion evolution

The effect of oxide and nitride inclusions in a steel melt on the formation of the equiaxed grain structure during solidification of ferritic stainless steel has been investigated. The solidified grain size decreased with an increasing content of titanium. In steel samples with large solidified grains, the inclusions were generally a two-phase system in which the titanium oxide was precipitated in the liquid TiO_x–Cr₂O₃–SiO₂ matrix during cooling. Alternatively, in steel samples with fine equiaxed grains, single TiN and MgAl₂O₄–TiN complex particles were observed. MgO–Al₂O₃–TiO_x ternary compounds formed in molten steel, and the spinel crystals grew at the expense of the liquid phase as the temperature decreased. Concurrently, the TiN nucleated on the surface of the MgAl₂O₄ particles because the lattice disregistry between MgAl₂O₄ and TiN was low. The formation behaviors of non-metallic compounds were successively predicted via thermochemical computation. Single mode log-normal distributions with mode particle diameters (d_mode) were observed in many samples, whereas a bimodal distribution was obtained in solidified samples with a fine-grained equiaxed structure. The grain sizes of the solidified samples decreased when the mean diameter of the inclusions increased. Consequently, the solidification structure can be interpreted based on the effectiveness of TiN and MgAl₂O₄–TiN complex inclusions as inoculants for the nucleation of δ-Fe.     

Particle Technology in the Formulation and Fabrication of Thermal Energy Storage Materials

This article reviews the state of the art of the formulation and fabrication of sensible, latent, and thermochemical thermal energy storage (TES) materials with special focus on the role of particle technology in enhancing the performance of these materials. Molten salt-based sensible TES materials have been intensively studied, particularly the use of doped nanoparticles for enhancing specific heat capacity and thermal conductivity. For latent TES, the inclusion of property enhancers is among the most effective approaches to address the low thermal conductivity and supercooling issues of phase change materials (PCMs), whereas the encapsulation of PCMs and structurally stabilized composite PCMs are the favorable methods to address leakage and chemical incompatibility challenges. Thermochemical TES materials are often incorporated with an inert or an active host matrix for structural stabilization.     

Thermochemical liquefaction characteristics of microalgae in sub- and supercritical ethanol

Thermochemical liquefaction characteristics of Spirulina, a kind of high-protein microalgae, were investigated with the sub- and supercritical ethanol as solvent in a 1000 mL autoclave. The influences of various liquefaction parameters on the yields of products (bio-oil and residue) from the liquefaction of Spirulina were studied, such as the reaction temperature (T), the S/L ratio (R₁, solid: Spirulina, liquid: ethanol), the solvent filling ratio (R₂) and the type and dosage of catalyst. Without catalyst, the bio-oil yields were in the range of 35.4 wt.% and 45.3 wt.% depending on the changes of T, R₁ and R₂. And the bio-oil yields increased generally with increasing T and R₂, while the bio-oil yields reduced with increasing R₁. The FeS catalyst was certified to be an ideal catalyst for the liquefaction of Spirulina microalgae for its advantages on promoting bio-oil production and suppressing the formation of residue. The optimal dosage of catalyst (FeS) was ranging from 5-7 wt.%. The elemental analyses and FT-IR and GC-MS measurements for the bio-oils revealed that the liquid products have much higher heating values than the crude Spirulina sample and fatty acid ethyl ester compounds were dominant in the bio-oils, irrespective of whether catalyst was used.     

铝锆炭滑板的热化学侵蚀机理

分析了宝钢３００ｔ钢包滑板使用后的损毁情况。研究了滑板的氧化,铁、锰的氧化物及钙对滑板的化学侵蚀,提出了铝锆炭滑板的热化学侵蚀机理,并指出了滑板的发展方向。     

Technoeconomics of large-scale clean hydrogen production – A review

Hydrogen is widely used in many industries, yet its role in the clean energy transition goes beyond being an element of these industries. Near-term practical large-scale clean hydrogen production can be made available by involving nuclear, solar, and other renewable energy sources in the process of hydrogen production, and coupling their energy systems to sustainable carbon-free hydrogen technologies. This requires further investigation and assessment of the different alternatives to achieve clean hydrogen using these pathways. This paper assesses the technoeconomics of promising hydrogen technologies that can be coupled to nuclear and solar energy systems for large-scale hydrogen production. It also provides an overview of the design, status and advances of these technologies.     

Exergy analysis of Cobalt–Chlorine thermochemical hydrogen production cycle: A kinetic approach

Increasing energy needs and reducing greenhouse gas emissions require immediate studies on carbon-free energy solutions, namely hydrogen. There are numerous methods among the production methods of hydrogen in a green manner. Hydrogen, which is then primarily obtained as a result of the separation of water with thermochemical cycles, is an environmentally friendly and sustainable hydrogen production method. In this study, the Cobalt–Chlorine (Co–Cl) cycle, which is one of the new thermochemical cycles, is examined in detail in terms of thermodynamics. There are four reactions in the Co–Cl thermochemical cycle. These are listed as the hydrolysis reaction in which hydrogen is obtained, the thermolysis reaction in which oxygen is obtained, the reduction reaction and finally the hydrochlorination reaction. According to the results of the analysis performed kinetically with the Aspen Plus software, the exergy efficiency of the cycle is calculated as 33%. When the exergy destruction of all reactions is compared, it is seen that the greatest exergy destruction occurs in the hydrolysis reaction, and the lowest exergy destruction occurs in the hydrochlorination reaction. The fact that the exergy efficiency is high when evaluated in terms of kinetics shows that the cycle is feasible in terms of thermodynamics. In addition, the costs of the cycle are to be considered in the future studies as it is an important criterion.     

The oxygen-releasing step in the water splitting cycle by MnFe2O4–Na2CO3 system

Investigation of the feasibility of the thermochemical two-step water splitting cycle based on MnFe₂O₄/Na₂CO₃ system is reported. Influence of temperature and carbon dioxide pressure on the oxygen-releasing step was investigated. XRD analysis was applied to obtain phase identification of reacted powders at investigated experimental conditions. Different sodium sub-stoichiometric Na_1−δ(Mn_1/3Fe_2/3)O_2−δ/2 compounds were observed and their structure determined by using Rietveld analysis. Selected experimental conditions permitted to define a T/pCO2$T/p_{{\text{CO}}_{\text{2}}}$ phase diagram, showing different solid phases coexistence regions. Experimental conditions that permit complete regeneration of the initial MnFe₂O₄/Na₂CO₃ mixture were identified (field I in the reported diagram), demonstrating the possibility of full chemical cyclical operation of the system.     

Monoclinic zirconia-supported Fe3O4 for the two-step water-splitting thermochemical cycle at high thermal reduction temperatures of 1400–1600 °C

Two-step thermochemical water-splitting using monoclinic ZrO₂-supported Fe₃O₄ (Fe₃O₄/m-ZrO₂) for hydrogen production was examined at high thermal reduction temperatures of 1400–1600 °C. After thermal reduction of Fe₃O₄/m-ZrO₂, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 °C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe₃O₄ on a m-ZrO₂ support and the conversion of Fe₃O₄ to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe₃O₄-to-FeO conversion reached 60% when the Fe₃O₄/m-ZrO₂ was thermally reduced at 1600 °C. The phase transition of m-ZrO₂ support to tetragonal ZrO₂ (t-ZrO₂) did not occur during the thermal reduction at 1400–1500 °C, but it did proceed slightly at 1600 °C. Fe ions from Fe₃O₄ did not enter the ZrO₂ lattice during high-temperature thermal reduction. Thus, the Fe₃O₄ loaded on a m-ZrO₂ support can continuously contribute as a Fe₃O₄–FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400–1600 °C.