Mathematical Modeling of Multicomponent Mass Diffusion in Porous Pellets: Mass and Molar Formulations

AbstractHeterogeneous catalysis is of outermost significance in many fields of gas conversion and processing in chemical industries. Accurate modeling of intra-particle heat and mass transport is a prerequisite for the design of many industrial processes and the interpretation of experiments. In recent literature, deviations are noticed between simulation results of mole and mass formulated pellet model equations. Further investigations are thus required to reveal the reason for this deviation. In this study, a survey is given discussing the different assumptions commonly adopted within the pellet modeling framework. The modeling framework outlined both on mass and molar basis may provide as a basis for further investigations on model simulation comparisons of mole and mass based pellet equations

Modelling of high pressure binary droplet collisions

AbstractDroplet collision efficiency is a rather uncharted area for real hydrocarbon systems under non-atmospheric conditions. It is also of great interest in many industrial applications. In this work binary head-on droplet collisions at high pressure have been simulated using the lattice Boltzmann method. A model that captures the physics of the coalescence process is used where no external criterion for coalescence is needed. The collision process is described in terms of hydrodynamic variables and through a quantitative study of energy loss. At high pressures, low inertia collisions are the most frequent. Distinguishing between bouncing and coalescence under these conditions is needed in order to provide closure conditions for macroscopic CFD models. A limit of Re<170ρlg is found to predict coalescence in all the cases simulated. In addition this paper explains the stochastic behaviour of low inertia coalescence at high pressure. This has major implications both when building macroscopic models for predicting industrial process efficiencies and in the optimization of equipment internals working with droplets at high pressure as is the case for combustion chambers and gas–liquid separators

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Chemical reactor modeling: multiphase reactive flows

Chemical Reactor Modeling closes the gap between Chemical Reaction Engineering and Fluid Mechanics.  The second edition consists of two volumes: Volume 1: Fundamentals. Volume 2: Chemical Engineering Applications In volume 1 most of the fundamental theory is presented. A few numerical model simulation application examples are given to elucidate the link between theory and applications. In volume 2 the chemical reactor equipment to be modeled are described. Several engineering models are introduced and discussed. A survey of the frequently used numerical methods, algorithms and schemes is provided. A few practical engineering applications of the modeling tools are presented and discussed. The working principles of several experimental techniques employed in order to get data for model validation are outlined. The monograph is based on lectures regularly taught in the fourth and fifth years graduate courses in transport phenomena and chemical reactor modeling, and in a post graduate course in modern reactor modeling at the Norwegian University of Science and Technology, Department of Chemical Engineering, Trondheim, Norway. The objective of the book is to present the fundamentals of the single-fluid and multi-fluid models for the analysis of single- and multiphase reactive flows in chemical reactors with a chemical reactor engineering rather than mathematical bias. Organized into 13 chapters, it combines theoretical aspects and practical applications and covers some of the recent research in several areas of chemical reactor engineering. This book contains a survey of the modern literature in the field of chemical reactor modeling

Modeling the Chemical Looping Reforming Process Operated in a Circulating Fluidized Bed Reactor Consisting of Two Bubbling Bed Units: Model Validation

A transient one-dimensional model is developed for simulation of the chemical looping reforming process in a circulating fluidized bed (CFB). A CFB reactor model consisting of two connected bubbling bed units, namely the fuel reactor (FR) and the air reactor (AR), is proposed, and the simulated results are validated by comparison with experimental data available in the literature. Three cases with different oxygen-carrier-to-fuel ratios are simulated until the equilibrium concentrations are established in the solid phase. The hydrogen conversion and oxygen carrier conversion results from the simulations are then compared with experimental data from the literature, showing that the numerical results are in fair agreement with the experimental results. Model validation against experimental data of the process performance is of paramount importance for future process design and optimization of chemical looping systems via numerical modeling and simulation

Simulation of chemical looping combustion process in a double looping fluidized bed reactor with cu‐based oxygen carriers

Chemical looping combustion (CLC) is an attractive technology that produces a pure CO2 stream and therefore the CO2 can be readily recovered by condensing water vapour. In order to understand the physical phenomena and to explore the chemical process performance of the CLC process, a CFD model has been developed. The model is implemented numerically in an in-house code including the kinetic theory of granular flow and reaction models. Methane is used as fuel and CuO is chosen as oxygen carrier. This process is configured with an air reactor and a fuel reactor. The two reactors are simulated by a sequential approach. The connection between the two reactors is realized through time-dependent inlet and outlet boundary conditions. The widely used drag models were selected to examine their effects on the flow behaviour. The results indicating that the cluster effect in the FR is higher than in the AR. The frequency factor in the reaction model was varied to fit with the experimental measurements. The predicted result with the frequency factor of 1:35 X 10 m3 gives a reasonable prediction in comparison to the experimental data.publishedVersio