The Chemical Engineering Journal and the Biochemical Engineering Journal最新文献

We have proposed the model of a 2-D fractal objects exhibiting an important contour length within a finite area. This structure offers a large internal interface can be used as a catalytic support. In the case of a single first-order reaction A → R at the interface, numerical simulations show evidence for a new diffusional regime due to the fractality of the support. In this regime, the rate of formation of product R no longer depends on the kinetic rate constant of the reaction.

It has been suggested that rising bubbles in dense fluids resemble an inverted dripping faucet and that they undergo analogues period-doubling bifurcations to chaos. We present experimental results that demonstrate that this analogy is weak because the dominant source of instability in the bubble train is inherently different — mutual interactions between spatially separated bubbles as opposed to nozzle dynamics. Unlike the dripping faucet, the initial instability in a bubble train develops at a location far from the injection nozzle and progresses toward the nozzle with increasing gas flow. From qualitative and rigorous quantitative observations, we conclude that rising-bubble dynamics are best described as ‘small-box spatio-temporal chaos’ with a flow instability. Such dynamics can superficially appear to be simple temporal chaos when considering spatially localized measurements. We show similarity between our experimental results and a bubble-interaction model that accounts for drag and coalescence effects without considering any nozzle dynamics.

A kinetic model of gasification of porous carbon particles characterized by broad pore size distributions is developed. The interaction between the intrinsic kinetics of surface oxidation and intraparticle diffusion of reactants is modelled, taking into account the wide variation of local diffusivities within the pore space as the length scale of pores charges. In particular, the model considers the configuration diffusion mechanism, which dominates transport in pores whose size is of the order of the diffusing molecule size. The model is based on the iterated application of Thiele analysis to branching pore sequences of different topology. Computation are directed to investigate the sensitivity of the model to the pore space topology, to the parameters of the pore structure and to variables determining the rate of surface reaction and of intraparticle diffusion.

Chemical reactions in time-periodic 2D chaotic flows are examined by solving numerically the convection-diffusion-reaction equation. Three flow conditions are considered: a predominantly regular system, a predominantly chaotic system with a few regular islands, and a globally chaotic system devoid of noticeable islands. Chaotic mixing has a strong impact on systems undergoing a single bimolecular reaction A + B → C. Maximum concentration of C occurs in well-mixed chaotic regions; in comparison, little reaction takes place inside poorly mixed non-chaotic islands. Chaotic mixing also has a significant impact on competitive-consecutive reactions A + B → P, B + P → W. The relative amounts of P and W generated by the reactions are strongly affected by the presence of islands. While the desired product P predominates in chaotic regions, most of the waste W is generated inside islands.

Starting from the analysis of correlated percolation lattices, we develop a new predictive model for the permeability of porous media. The model proposed introduces a new characteristic length scale parameter related to the pore-pore correlation function of the digitalized image of the porous structure. The model predicts with good accuracy the permeability of complex pore structures such as correlated percolation lattices, deterministic fractals, fractal percolation lattices and correlated porous media in general.

In this article we apply input/output (I/O) renormalization to linear transport phenomena on fractals. We focus mainly on first-order reaction kinetics, on sorption dynamics and on renormalization of integral quantities in the case of finitely ramified structure. Moreover, care is taken to show how the theory can be extended to thes tudy of infinitely ramified fractals and non-linear model and to the case of an unbounded number of input sites.

Driven by economic pressures and government emission regulations, the electric power industry is moving toward tighter control of boilers to improve plant efficiency and reduce emissions. Tighter control depends on better boiler diagnostic tools, especially for discriminating dynamic patterns and correlating those patterns with overall performance. Our research indicated that improved discrimination of dynamic pattern in boilers can be achieved by combining traditional data analysis techniques and chaotic time series analysis. Suggested analysis tools and data acquisition procedures are described, along with example results for measurements from a pressurized fluidized bed and a low_x pulverized coal boiler.

We discuss recent developments in the application of fractal concepts and percolation theory to transport processes in heterogeneous media. The phenomena that we discuss include several types of nonlinear transport processes in disordered systems, which are relevant to the flow of non-Newtonian fluids in porous media, to electrical current in composites and doped polycrystalline semiconductors, to fracture and breakdown in disordered materials and natural rock, to elastic and viscoelastic properties of solids, polymers and gels, to flow in geological formations, and to several other problems. We emphasize the universal aspects of such phenomena, i.e., those that are independent of the microscopic or small-scale features of the systems in which they occur.

The Langmuir-Freundlich isotherm, generalized for mixed-gas adsorption on solids, is probably the most frequently applied equation in tecnological applications. A theoretical analysis of its origin suggests that this isotherm equation may be related to the situation when no correlations exist between the adsorption energies of various components. Some further modifications and improvements of this equation are proposed and tested.