Novel Segmental Model for Predicting Bed-to-Tube Heat Transfer Coefficient in Gas–Solid Fluidized Beds

Accurate prediction of the bed-to-tube heat transfer coefficient (HTC) is the foundation of developing efficient fluidized bed heat exchangers, but there is still a lack of an effective prediction method. In this paper, the heat transfer mechanism around the immersed tube is revealed through the correlation analysis method. A computational fluid dynamics simulation was conducted to provide various flow field data for a gas–solid fluidized bed with an immersed tube. A correlation analysis was conducted to characterize the relationship between the local HTC and various factors. The results show that Kendall’s rank correlation coefficient (rk) between the solid phase volume fraction and HTC is less than 0.5 on the top of the tube, while the rk on the bottom side exceeds 0.9. According to the distribution characteristics of rk and the emulsion phase contacting time fraction (δe) around the tube, a theoretical model containing three different heat transfer mechanisms was developed. The threshold value for defining the dynamically changing boundaries of each heat transfer mechanism is obtained (δe = 0.88 and rk = 0.82). A comparison analysis demonstrates that the proposed model can predict the average HTC with a deviation of less than ±25% within a wide range of particle sizes (100–1000 μm)

Anchoring Tailored Low-Index Faceted BiOBr Nanoplates onto TiO₂ Nanorods to Enhance the Stability and Visible-Light-Driven Catalytic Activity

In this work, a fantastic one-dimensional (1D) BiOBr/TiO₂ nanorod (NR) heterojunction composite was rationally proposed and designed from the perspective of molecular and interface engineering. The fabricated intimately connected interfacial heterojunction between two-dimensional BiOBr nanoplates and 1D TiO₂ NRs acts as an interfacial nanochannel to promote efficient interfacial charge migration and separation of photogenerated electron–hole pairs. As a result, 1D BiOBr/TiO₂ NR heterojunctions exhibited outstanding visible-light photocatalytic activities and sustained cycling performance. Under visible-light irradiation for 120 min, the reduction efficiency of Cr­(VI) over the TB-2 sample (molar ratio: <i>n</i>(Ti)/<i>n</i>(Bi) = 2:1) is as high as 95.4% without adding any scavengers. Furthermore, the sample also shows excellent photodegradation activity of RhB with a much higher apparent rate constant of 0.49 min^–1 and 88.5% total organic carbon removal ratio. Furthermore, the corresponding mechanism of enhanced photocatalytic activity is proposed according to comprehensively investigated results from photoluminescence spectroscopy, photoelectrochemical measurement analysis, and radical trapping experiments. This study provides an attractive avenue to design and fabricate highly efficient 1D NR heterojunction photocatalysts, which possessed a high application value in the field of environmental remediation, especially for wastewater purification

Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

Surfactant molecules can form micellar network structures that can be applied for turbulent drag reduction through their breakage and recombination behaviors. One of the mechanisms of turbulent drag reduction by surfactants is the “viscoelastic theory” as proposed by DeGennes. However, evaluating the rupture and coalescence properties of network micelles is challenging. Here, we study the breakage and recombination behaviors of an individual rodlike micelle using Martini coarse-grained force field molecular dynamics simulations. The flexibility of an individual micelle can be measured by its breakage energy. Micelle recombination behaviors can be attributed to three mechanisms: the coalescence energy, zeta potential, or hydrophobic driving effect of the surfactant micelles. Thus, an excellent micelle that is beneficial for turbulent drag reduction is difficult to rupture but easy to recombine. The breakage behavior should be considered prior to the recombination behavior, because the breakage energy of an individual micelle is approximately 1–2 magnitudes greater than its coalescence energy under various conditions. Organic counterion salts, such as salicylate sodium, favor micelle recombination because of their electrostatic screen effect and uneven distribution on the surfactant micelle surface. Furthermore, this work brings a novel approach to understanding the breakage and recombination behaviors of surfactant micelles, providing an essential and scientific guidance to the effective use of surfactants in turbulent drag reduction. It also provides direct evidence to support the viscoelastic theory

Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

Surfactant molecules can form micellar network structures that can be applied for turbulent drag reduction through their breakage and recombination behaviors. One of the mechanisms of turbulent drag reduction by surfactants is the “viscoelastic theory” as proposed by DeGennes. However, evaluating the rupture and coalescence properties of network micelles is challenging. Here, we study the breakage and recombination behaviors of an individual rodlike micelle using Martini coarse-grained force field molecular dynamics simulations. The flexibility of an individual micelle can be measured by its breakage energy. Micelle recombination behaviors can be attributed to three mechanisms: the coalescence energy, zeta potential, or hydrophobic driving effect of the surfactant micelles. Thus, an excellent micelle that is beneficial for turbulent drag reduction is difficult to rupture but easy to recombine. The breakage behavior should be considered prior to the recombination behavior, because the breakage energy of an individual micelle is approximately 1–2 magnitudes greater than its coalescence energy under various conditions. Organic counterion salts, such as salicylate sodium, favor micelle recombination because of their electrostatic screen effect and uneven distribution on the surfactant micelle surface. Furthermore, this work brings a novel approach to understanding the breakage and recombination behaviors of surfactant micelles, providing an essential and scientific guidance to the effective use of surfactants in turbulent drag reduction. It also provides direct evidence to support the viscoelastic theory

Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

Surfactant molecules can form micellar network structures that can be applied for turbulent drag reduction through their breakage and recombination behaviors. One of the mechanisms of turbulent drag reduction by surfactants is the “viscoelastic theory” as proposed by DeGennes. However, evaluating the rupture and coalescence properties of network micelles is challenging. Here, we study the breakage and recombination behaviors of an individual rodlike micelle using Martini coarse-grained force field molecular dynamics simulations. The flexibility of an individual micelle can be measured by its breakage energy. Micelle recombination behaviors can be attributed to three mechanisms: the coalescence energy, zeta potential, or hydrophobic driving effect of the surfactant micelles. Thus, an excellent micelle that is beneficial for turbulent drag reduction is difficult to rupture but easy to recombine. The breakage behavior should be considered prior to the recombination behavior, because the breakage energy of an individual micelle is approximately 1–2 magnitudes greater than its coalescence energy under various conditions. Organic counterion salts, such as salicylate sodium, favor micelle recombination because of their electrostatic screen effect and uneven distribution on the surfactant micelle surface. Furthermore, this work brings a novel approach to understanding the breakage and recombination behaviors of surfactant micelles, providing an essential and scientific guidance to the effective use of surfactants in turbulent drag reduction. It also provides direct evidence to support the viscoelastic theory

Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

Surfactant molecules can form micellar network structures that can be applied for turbulent drag reduction through their breakage and recombination behaviors. One of the mechanisms of turbulent drag reduction by surfactants is the “viscoelastic theory” as proposed by DeGennes. However, evaluating the rupture and coalescence properties of network micelles is challenging. Here, we study the breakage and recombination behaviors of an individual rodlike micelle using Martini coarse-grained force field molecular dynamics simulations. The flexibility of an individual micelle can be measured by its breakage energy. Micelle recombination behaviors can be attributed to three mechanisms: the coalescence energy, zeta potential, or hydrophobic driving effect of the surfactant micelles. Thus, an excellent micelle that is beneficial for turbulent drag reduction is difficult to rupture but easy to recombine. The breakage behavior should be considered prior to the recombination behavior, because the breakage energy of an individual micelle is approximately 1–2 magnitudes greater than its coalescence energy under various conditions. Organic counterion salts, such as salicylate sodium, favor micelle recombination because of their electrostatic screen effect and uneven distribution on the surfactant micelle surface. Furthermore, this work brings a novel approach to understanding the breakage and recombination behaviors of surfactant micelles, providing an essential and scientific guidance to the effective use of surfactants in turbulent drag reduction. It also provides direct evidence to support the viscoelastic theory

NiSx Quantum Dots Accelerate Electron Transfer in Cd_0.8Zn_0.2S Photocatalytic System via an rGO Nanosheet “Bridge” toward Visible-Light-Driven Hydrogen Evolution

Minimizing the charge transfer barrier to realize fast spatial separation of photoexcited electron–hole pairs is of crucial importance for strongly enhancing the photocatalytic H₂ generation activity of photocatalysts. Herein, we propose an electron transfer strategy by reasonable design and fabrication of high-density NiSx quantum dots (QDs) as a highly efficient cocatalyst on the surface of Cd_0.8Zn_0.2S/rGO nanosheet composites. Under visible-light irradiation, the formation of a two-dimensional (2D) Cd_0.8Zn_0.2S/rGO nanohybrid system with 2 wt % NiSx loading gave a prominent apparent quantum efficiency (QE) of 20.88% (435 nm) and H₂ evolution rate of 7.84 mmol g^–1 h^–1, which is 1.4 times higher than that of Pt/Cd_0.8Zn_0.2S/rGO. It is believe that the introduced rGO nanosheets and NiSx QDs obviously improved the interfacial conductivity and altered the spatial distribution of electrons in this nanoarchitecture. Thus, the synergistic effects of interfacial junctions result in a regulated electron transportation pathway along the basal planes and ultrafast transfer and spatial separation of photoexcited carriers, which are responsible for the enhanced photocatalytic performance. This work gives a facile and effective strategy to understand and realize rationally designed advanced photocatalysts for high-efficiency, stable, and cost-efficient solar hydrogen evolution applications

Mechanistic Study of Pd–Cu Bimetallic Catalysts for Methanol Synthesis from CO₂ Hydrogenation

Density functional theory (DFT) calculations were carried out to explore the adsorptions of reactive species and the reaction mechanisms on Pd–Cu bimetallic catalysts during CO₂ hydrogenation to methanol. All the possible preferred adsorption sites, geometries, and adsorption energies of the relative intermediates on pure Cu(111) and three PdCu(111) surfaces were determined, revealing that both the adsorption configuration and corresponding adsorption energy are changed by doping with Pd atoms. The strengthened COOH* adsorption and the greatly weakened OH* adsorption change the rate-limiting step from CO₂ hydrogenation forming <i>trans</i>-COOH* on Cu(111), Pd₃Cu₆(111), and Pd₆Cu₃(111) surfaces to <i>cis</i>-COOH* decomposition forming CO* and OH* on Pd ML surface. Additionally, the highest activation barriers for the overall reaction pathway are reduced in the following trend: Cu(111) > Pd₆Cu₃(111) > Pd₃Cu₆(111) > Pd ML (monolayer). Compared to the reaction on clean Cu(111) surface, the complete reaction pathways for CH₃OH synthesis on PdCu(111) surfaces, especially on Pd ML, were facilitated and the yields of byproducts CO and CH₄ are suppressed, which corroborates well with experimental reports showing that Pd–Cu bimetallic catalysts have a strong synergistic effect on CO₂ hydrogenation to methanol. The present insights are helpful for the design and optimization of highly efficient Pd–Cu bimetallic catalysts used in CH₃OH formation from CO₂ hydrogenation