Chemical Engineering Science最新文献

Efficient flow field structures are crucial for improving the performance of all-vanadium redox flow batteries (VRFBs). Considering the large pressure drop and pump losses in traditional serpentine flow fields (SFF), this paper proposes a novel biomimetic flow field structure (BFF) for VRFB. A three-dimensional multiphysics model comparing SFF and BFF designs for VRFB is developed, the assessment was further enhanced by considering the impact of electrolyte flow rates on multiple performance indicators. The results show that BFF’s unique design substantially reduces pressure drop, especially at higher flow rates. For both SFF and BFF designs, at a low flow rate of 60 ml/min, the SFF has a slightly higher pump-based voltage efficiency, but as the flow rate increases to 120 ml/min and 180 ml/min, the BFF outperforms the SFF, demonstrating advantages of 2.057 % and 6.888 %, respectively. This comprehensive VRFB modeling analysis provides valuable insights into optimizing future flow battery designs.

Recently, biomass-derived porous carbon has gained popularity as a cathode material for Zn-ion hybrid supercapacitor (ZIHSs) due to its unique structure and heteroatoms. However, the understanding of how biomass part affects resulting carbon structure and ZIHSs performance is limited. This study utilizes cattail leaves (CLs), cattail wools (CWs), and cattail stems (CSs) as carbon sources, with each impacting carbon microstructure, morphology, specific surface area (SSA), and oxygen content. CLs-based porous carbon (CLPC) exhibits a distinct hollow tube structure with thinner walls, high oxygen content, and a large SSA, which are crucial for enhanced electrochemical performance. The aqueous Zn//CLPC ZIHSs demonstrate remarkable energy density (190 Wh kg⁻¹), specific capacity (253 mAh/g at 0.1 A/g), and cycle life (91% capacity retention over 10,000 cycles at 10 A/g). Electrochemical processes are studied through various techniques, shedding light on the relationship between cattail parts, carbon structure, and ZIHSs performance, aiding in more efficient biomass utilization.

This study evaluates the noise resilience of multi-objective Bayesian optimization (MOBO) algorithms in chemical synthesis, an aspect critical for processes like telescoped reactions and heterogeneous catalysis but seldom systematically assessed. Through simulation experiments on amidation, acylation, and S_NAr reactions under varying noise levels, we identify the qNEHVI acquisition function as notably proficient in handling noise. Subsequently, qNEHVI is employed to optimize a two-step heterogeneous catalysis for the continuous-flow synthesis of hexafluoroisopropanol. Remarkable optimization is achieved within just 29 experimental runs, resulting in an E-factor of 0.125 and a yield of 93.1%. The optimal conditions are established at 5.0 sccm and 120 °C for the first step, and 94.0 sccm and 170 °C for the second step. This research highlights qNEHVI’s potential in noisy multi-objective optimization and its practical utility in refining complex synthesis processes.

Hollow fiber ceramic membrane technology demonstrates a great potential for high performance oxygen separation from air. Upscaling of single hollow fiber membrane for membrane stacks and modules is necessary toward practical applications. However, experimental methods are very time-consuming and highly cost. Mathematical modeling is a cost-effective technique and very flexible to evaluate different upscaling strategies. In this research, built upon the experimental results of a proof-of-concept hollow fiber membrane stack, a computational fluid dynamics-based Multiphysics stack model is developed and validated. Comprehensive simulations are conducted to understand the behaviors of stacks under different operating conditions. Different designs strategies are also evaluated toward optimizations of stack performance.

Vibrated gas-fluidized beds are widely used industrially, and two main methods exist to simulate them computationally: (i) in a moving reference frame by oscillating gravity and (ii) in a stationary reference frame by moving the distributor. Further, it is unclear whether gas flow in the plenum chamber of a vibrated fluidized bed should be modeled as constant or oscillating. Here, we challenge the accuracy of different potential modeling methods by comparing with experimental results of structured bubbling because these results are deterministic, avoiding the need for comparing via statistically averaged quantities. Results show that modeling a moving distributor and moving sidewalls as physically accurately as possible is important, and modeling the system in the moving reference frame is less accurate than in the stationary reference frame, due to subtle differences. Further, it is more accurate to model the gas flow as constant rather than oscillatory in the plenum chamber.

A concept and model of two critical Reynolds numbers Re_p,cr1 and Re_p,cr2 corresponding respectively to onsets of drag crisis and recovery are proposed. A drag model at limits of zero particle Mach and Knudsen numbers is constructed. On this basis, we develop a general drag coefficient model applicable for a spherical particle traveling in a gas by using a large number of available data derived from the previous experiments, direct numerical simulations and direct simulation Monte-Carlo methods. The scope of applicability of the proposed drag model covers all flow regimes relative to the particle characterized by particle Reynolds and Mach (or Knudsen) numbers and different particle-to-gas temperature ratios. Its comparison with two latest general drag models shows the significantly smaller relative error. Furthermore, quasi-one dimensional simulations against two supersonic nozzle gas-particle flow experiments are conducted with an in-house code to validate its accuracy in comparison with the two drag models.

Droplet microfluidic technology can use each microdroplet as a microreactor, which has the advantages of low reagent dosage, less cross contamination, and fast reaction time. Combining concentration gradient generation with droplet formation and capture to form a two-dimensional reaction condition screening platform (including reactant concentration and reaction time) is expected to broaden the application range of microfluidic screening. In this work, a microfluidic chip that can dynamically generate and capture microdroplets and form static microdroplet array was designed and fabricated. An optimized Christmas tree structure by adjusting the horizontal channel length ratio was used to generate a chemical concentration gradient while obtaining a uniform outlet flow rate, forming a droplet array with different concentrations. The performance of droplet array with microfluidic concentration gradient (DA-MCG) was verified using sodium fluorescein as a model reagent. The chromogenic reaction of NaOH and phenolphthalein, and luminol chemiluminescence reaction were used to verify the two-dimensional screening ability of DA-MCG. The results indicated that the DA-MCG has the potential to be applied in the field of multi-dimensional drug screening.

One of the most popular and financially feasible low-dosage hydrate inhibitors (LDHIs) for preventing gas hydrates formation in natural gas pipelines is poly n-vinyl caprolactam (PVCap). There is still disagreement over LDHIs’ thermodynamic effects, even though their better inhibition performance on gas hydrate nucleation and crystal growth has been demonstrated. For a long time, it was assumed that LDHIs do not affect natural gas hydrate dissociation conditions. Nevertheless, PVCap’s status as a thermodynamic hydrate promoter was established a few years ago. This work aims to provide a basic model that may be used to calculate the hydrate dissociation temperature when PVCap is present. For this reason, the van der Waals-Platteeuw solid solution theory is utilized to model the hydrate phase, and the Flory-Huggins (FH) model is used to calculate the water activity when PVCap is present in the aqueous phase. A straightforward correlation based on the hydrate dissociation enthalpy is introduced to obtain the hydrate dissociation temperature in the presence of PVCap. Some variables, including the hydrate dissociation pressure, PVCap molecular weight, and concentration, are included in the proposed model. The enthalpy of hydrate dissociation could be readily calculated using the model, which yields excellent results for the hydrate dissociation temperature for structures I and II when PVCap is present in the aqueous phase. The model performs well for both simple and mixed gas hydrates, and its accuracy is demonstrated by the temperature error obtained from the model for all 50 experimental data points, which is approximately 0.26 K.

Topology optimization is a powerful method for designing optimal structures within a given design domain, applicable not only to physical systems but also to systems involving chemical reactions. This study employs entropy generation analysis in nonequilibrium thermodynamics as a metric to evaluate optimization results in conjunction with topology optimization. To enhance our understanding of the relationship between topology optimization and entropy generation analysis, exact solutions were derived in a simple 0D case. Nevertheless, solving the partial differential equations associated with topology optimization can be computationally intensive and time-consuming. This study proposed an alternative approach that bypassed the need for optimization methods by introducing reasonable assumptions, thereby reducing the computational effort required. By assuming a linear distribution of species concentration, the proposed approach yielded comparable performance to that achieved by optimization methods. This research contributes to streamlining the design process of electrochemical devices and reducing the computational burden associated with optimization.

Research on dispersion and stability of nanoparticles in liquid media is one of the key subjects for nanomaterial utilization. Coarse-grained molecular dynamics simulations are carried out to research the self-assembly behaviors of the nanoparticles, PEO (polyethylene oxide) and OTAC (octadecyltrimethylammonium chloride) compound solution system, so as to explore the mechanism of nanoparticle dispersion stability with PEO and OTAC additives. It shows that nanoparticles influence and participate the self-assembly process of PEO and OTAC molecules mainly by electrostatic interactions. In the formation of nanoparticle-PEO-OTAC aggregate, the electrostatic potential plays a controlling role, while the van der Waals potential and hydration effect mainly stabilize and regulate the local connections between different individuals so as to balance the electrostatic potential. An electric triple layer (inner layer-coordinating adsorption layer-diffusion layer) structure is formed in the nanoparticle-PEO-OTAC aggregate, wherein the coordinating adsorption layer is essentially the secondary coordinating adsorption of individuals to the inner layer.