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Phase changes associated with the boiling of cryogenic liquids are interesting phenomena. In the present study, liquid nitrogen, which has applications in microelectronics, semiconductors, and the space sector, has been considered as a representative cryogenic fluid. The boiling of liquid nitrogen was investigated at different lengths and time scales. At the micro level, classical molecular dynamics (MD) based simulations were performed to understand various facets of boiling, considering a film of liquid nitrogen on a solid surface. For macroscale study, the route of computational fluid dynamics (CFD) has been adopted. For accurately tracking the dynamic interface, coupled level set volume of fluid approach (CLSVOF) has been implemented. CFD results show the formation of vapour bubbles in liquid nitrogen at different degrees of wall superheats. Temporal variation of heat flux has been evaluated. Finally, the results obtained from MD and CFD simulations have been compared. [ABSTRACT FROM AUTHOR]

The present work emphasizes the development of a generic methodology that addresses the core issue of any running chemical plant, i.e., how to maintain a delicate balance between profit and environmental impact. Here, an ethylene oxide (EO) production plant has been taken as a case study. The production of EO takes place in a multiphase catalytic reactor, the reliable first principle-based model of which is still not available in the literature. Artificial neural network (ANN) was therefore applied to develop a data-driven model of the complex reactor with the help of actual industrial data. The model successfully built up a correlation between the catalyst selectivity and temperature with other operational parameters. A hybrid multi-objective metaheuristic optimization technique, namely ANN-multi-objective genetic algorithm (MOGA) algorithm was used to develop a Pareto diagram of selectivity versus reactor temperature. The Pareto diagram will help the plant engineers to make a strategy on what operating conditions to be maintained to make a delicate balance between profit and environmental impact. It was also found that by applying this hybrid ANN-MOGA modeling and optimization technique, for a 720 KTA ethylene glycol plant, approximately 32,345 ton/year of carbon-di-oxide emission into the atmosphere can be reduced. Along with the reduction of environmental impact, this hybrid approach enables the plant to reduce raw material cost of nine million USD per annum simultaneously. [ABSTRACT FROM AUTHOR]

The present study conducts a comparative analysis between selective catalytic reduction (SCR) using a Cu-zeolite catalyst and selective non-catalytic reduction (SNCR) for the removal of NO x from industrial waste gas. The primary objective of this investigation is to computationally explore the removal of NO x using NH3 at various reactor conditions, along with the study of different hydrodynamic aspects. The study revealed the impact of different porosity of the catalyst (in SCR) and the number of baffles (in SNCR) on the reaction and fluid flow profile. Distinct geometries were employed to model each process, incorporating a turbulent model and kinetic parameters with an eddy-dissipation model (EDM) for simulations. Analyzing the effect of the NH3/NO ratio on NO conversion efficiency is a crucial component of the study. With diminishing efficiency at higher ratios, the SCR process demonstrated nearly complete NO conversion at a certain NH3/NO ratio, and this value changes with the inlet gas temperature. In contrast, SNCR produced less favorable conversion rates than SCR, indicating that the amount of NH3 supply affects conversion efficiency. At the SCR system’s optimum NH3/NO ratio, SNCR achieved an 83 % conversion, and the conversion rate remained relatively constant as the ratio was increased. The results highlight the various possibilities for optimization of the reactor systems in terms of efficiency and economic feasibility. [ABSTRACT FROM AUTHOR]

Evaporation of a sessile droplet on a hot solid substrate is an important problem in fluid mechanics. It is relevant to theoretical issues in heat transfer as well as several practical applications. This study investigates the spreading and evaporation of a nanoscale water droplet on a solid platinum surface. The major objective was to analyze the effect of an external electric field on these phenomena. Varying the intensity and direction of the external electric field, a series of molecular dynamics simulations were carried out to understand these phenomena at a molecular level. The results reveal that a horizontal electric field assists in droplet spreading, whereas a vertical electric field enhances the rate of evaporation for a certain range of field intensities. It also shows that the substrate temperature plays an important role in such processes. It is seen that the effect of an external electric field on droplet evaporation becomes significant at an intermediate range of surface temperatures and this effect is not clearly visible for either very high or very low range of surface temperatures. [ABSTRACT FROM AUTHOR]

Grand-canonical transition-matrix Monte Carlo and histogram reweighting techniques are used herein to study the vapor-liquid coexistence properties of two-dimensional (2D) flexible oligomers with varying chain lengths (m = 1-8). The phase diagrams of the various 2D oligomers follow the correspondence state (CS) principle, akin to the behavior observed for bulk oligomers. The 2D critical density is not influenced by the oligomer chain length, which contrasts with the observation for the bulk oligomers. Line tension, calculated using Binder's formalism, in the reduced plot is found to be independent of chain length in contrast to the 3D behavior. The dynamical properties of 2D fluids are evaluated using molecular dynamics simulations, and the velocity and pressure autocorrelation functions are investigated using Green-Kubo (GK) relations to yield the diffusion and viscosity. The viscosity determined from 2D non-equilibrium molecular dynamics simulation is compared with the viscosity estimated from the GK relations. The GK relations prove to be reliable and efficient for the calculation of 2D transport properties. Normal diffusive regions are identified in dense oligomeric fluid systems. The influence of molecular size on the diffusivity and viscosity is found to be diminished at specific CS points for the 2D oligomers considered herein. In contrast, the viscosity and diffusion of the 3D bulk fluid, at a reduced temperature and density, are strongly dependent on the molecular size at the same CS points. Furthermore, the viscosity increases and the diffusion decreases multifold in the 2D system relative to those in the 3D system, at the CS points. [ABSTRACT FROM AUTHOR]

A new method is reported for fabrication of polymeric micro- and nanoparticles from an intermediate patterned surface originated by dewetting of a polymeric thin film. Poly ( d , l -lactide- co -glycolide) or PLGA, a biocompatible polymer is used to develop a thin film over a clean glass substrate which dewets spontaneously in the micro-/nano-patterned surface of size range 50 nm to 3.5 µm. Since another water-soluble polymer, poly vinyl alcohol (PVA) is coated on the same glass substrate before PLGA thin film formation, developed micro-/nano-patterns are easily extracted in water in the form of micro- and nanoparticle mixture of size range 50 nm to 3.0 µm. This simplified method is also used to effectively encapsulate a dye molecule, rhodamine B inside the PLGA micro-/nanoparticles. The developed dye-encapsulated nanoparticles, PLGA-rhodamine are separated from the mixture and tested for in-vitro delivery application of external molecules inside human lung cancer cells. For the first time, the use of thin film dewetting technique is reported as a potential route for the synthesis of polymeric micro-/nanoparticles and effective encapsulation of external species therein. [ABSTRACT FROM AUTHOR]