Study on the Formation of Complex Chemical Waveforms by Different Computational Methods

Chemical wave is a special phenomenon that presents periodic patterns in space-time domain, and the Belousov–Zhabotinsky (B-Z) reaction is the first well-known reaction-diffusion system that exhibits organized patterns out of a homogeneous environment. In this paper, the B-Z reaction kinetics is described by the Oregonator model, and formation and evolution of chemical waves are simulated based on this model. Two different simulation methods, partial differential equations (PDEs) and cellular automata (CA) are implemented to simulate the formation of chemical waveform patterns, i.e., target wave and spiral wave on a two-dimensional plane. For the PDEs method, reaction caused changes of molecules at different location are considered, as well as diffusion driven by local concentration difference. Specifically, a PDE model of the B-Z reaction is first established based on the B-Z reaction kinetics and mass transfer theory, and it is solved by a nine-point finite difference (FD) method to simulate the formation of chemical waves. The CA method is based on system theory, and interaction relations with the cells nearest neighbors are mainly concerned. By comparing these two different simulation strategies, mechanisms that cause the formation of complex chemical waves are explored, which provides a reference for the subsequent research on complex systems.

A nonlinear prediction model, incorporating mass transfer theory and expert rules, for refining low-carbon ferrochrome

SYNOPSIS We present an optimal oxygen-blowing system with expert rules to improve the efficiency of refining low-carbon ferrochrome. A nonlinear model based on mass transfer theory, the principles of heat transfer, and the principles of high-temperature chemical reactions for refining low-carbon ferrochrome are established. The model is mainly used to control the oxygen supply rate during argon-oxygen top-bottom double-blown refining, thereby controlling the refining temperature and reducing the carbon content. Twenty production tests using a 5 t argon-oxygen refining furnace demonstrate the effectiveness of the system and reliability of the nonlinear model. A comparison of the model data with the experimental data shows that although the model fails to predict the silicon content in the final refined product, it can predict the contents of the main components at the refining end-point and the refining temperature accurately. Keywords: prediction model, end-point control, mass transfer theory, expert rules.

A microscopic experimental study of nanoparticle motion for the enhancement of oxygen absorption in nanofluids

The behavior of nanoparticle motion has a great influence on gas-liquid mass transfer. However, it has been very difficult to characterize the motion of nanoparticles from a micro view in mass transfer experiments. In this study, a novel method was proposed to investigate nanoparticle Brownian motion through the application of the total internal reflection fluorescence microscope in a self-designed sample (a quasi-static liquid micro-groove) and the mass transfer enhancement of nanoparticles. Nanoparticle movement behavior was photographed using an electron-multiplying charge coupled device, and 100 consecutive images were recorded using Micro-Manager software at a rate of 20 fps. The images were processed through the particle tracking velocimetry algorithm to calculate two-dimensional motion rates of nanoparticles caused by Brownian movement. It showed that nanoparticle loadings influenced the motion rates significantly, and the motion rates were larger with smaller particle sizes under the same operating condition. The mass transfer coefficients in the quasi-static gas-liquid mass transfer system were calculated and analyzed through microscopic measurement. Based on the above thought, three important non-dimensional numbers [Sherwood (Shp), Reynolds (Rep), and Schmidt (Scp) numbers] for mass transfer theory were studied.

Turbulence simultaneously stimulates small- and large-scale CO2 sequestration by chain-forming diatoms in the sea

Chain-forming diatoms are key CO2-fixing organisms in the ocean. Under turbulent conditions they form fast-sinking aggregates that are exported from the upper sunlit ocean to the ocean interior. A decade-old paradigm states that primary production in chain-forming diatoms is stimulated by turbulence. Yet, direct measurements of cell-specific primary production in individual field populations of chain-forming diatoms are poorly documented. Here we measured cell-specific carbon, nitrate and ammonium assimilation in two field populations of chain-forming diatoms (Skeletonema and Chaetoceros) at low-nutrient concentrations under still conditions and turbulent shear using secondary ion mass spectrometry combined with stable isotopic tracers and compared our data with those predicted by mass transfer theory. Turbulent shear significantly increases cell-specific C assimilation compared to still conditions in the cells/chains that also form fast-sinking, aggregates rich in carbon and ammonium. Thus, turbulence simultaneously stimulates small-scale biological CO2 assimilation and large-scale biogeochemical C and N cycles in the ocean.

INVERSE PROBLEMS IN THE HEAT AND MASS TRANSFER THEORY

This article is a survey of the recent results obtained preferably by the author and its coauthors and devoted to the study of inverse problem for some mathematical models, in particular those describing heat and mass transfer and convection-diffusion processes. They are defined by second and higher order parabolic equations and systems. We examine the following two types of overdetermination conditions: a solution is specified on some collection of spatial manifolds (or at separate points) or some collection of integrals of a solution with weight is prescribed. We study an inverse problem of recovering a right-hand side (the source function) or the coefficients of equations characterizing the medium. The unknowns (coefficients and the right-hand side) depend on time and a part of the space variables. We expose existence and uniqueness theorems, stability estimates for solutions. The main results in the linear case, i.e., we recover the source function, are global in time while they are local in time in the general case. The main function spaces used are the Sobolev spaces.

Prediction of Blunting Area of Abrasive Grains on a Grinding Wheel

The article presents the results of calculating the blunting area of abrasive grains of grinding wheels, determined in accordance with the previously developed model. The mathematic model of the size of the blunting area of an abrasive grain considers the main mechanisms of its wear—mechanical and physicochemical. These mechanisms are taken into account in the model. For the first time, the kinetic theory of strength was used for determining the mechanical wear of abrasive grain. The mass transfer theory was used to study the physicochemical wear: coefficients of chemical affinity with the abrasive material are experimentally defined for the assortment of workpiece materials. The developed mathematic model is a multiple-factor one and this will allow to predict the size of wear of the abrasive wheel for different technological conditions. Also, the article presents the experimental method for determining the blunting area of abrasive grains of grinding wheels, which allows making a direct measurement of wear parameters of grinding wheels. The main parameter of grinding wheel wear is the length of the blunting area of the grain, which was measured out in the direction of the cutting speed vector. The grinding wheels of different graininess were studied—F60 and F46. The grinding wheel working surface was studied by numerical photos and microscope. The results of these experiments have confirmed the adequacy of the design model.

Experimental Study of Mobile Solar Reverse Osmosis for Remote Areas

Reverse osmosis (RO) technique is one of most efficient methods to desalinate the salt water. An accurate and detailed experimental method was established to analyze the performance of the unpotable water RO process, which is the solution-diffusion and mass transfer theory. The RO is going to be operated using an alternative energy source, solar energy. The solar cells are utilized to run the RO unit with a single vertical membrane. DC current is produced by a solar panel which produces 18 maximum volt and 4.25 maximum DC current. The solar panel was utilized to run out the DC booster pump without using an inverter. The production of freshwater is the major studied parameter in this project with other parameters, such as the efficiency of the RO unit and the salt rejection percentage (610 max PPM). The experimental work provides a more detailed understanding of solar RO unit in order to be utilized in the remote areas.