Influence of the gas mixture temperature on the efficiency of synthesis gas production from ethanol in a nonequilibrium plasma

The mechanism behind the plasma conversion of a mixture of ethanol vapor, water vapor, air, and carbon dioxide CO₂ in the nonequilibrium plasma of a tornado discharge is studied. The influence of the CO₂ flow rate, the current through the discharge, and the gas temperature in the discharge on the concentrations of molecular hydrogen and carbon monoxide CO is studied. Comparison between the concentrations of the gaseous mixture’s main components at the output from the reactor obtained experimentally and by numerical simulation shows that the adopted kinetic mechanism adequately describes the plasma kinetics in the mixture.     

Pulsed modes of the formation of multilayer char structures on the surface of fire-retardant intumescent paints

A mathematical model of the propagation of the front of decomposition of active fire-retardant intumescent paints in pulsed mode is developed. A hypothesis explaining the mechanism of the experimen-tally observed pulsed modes of decomposition front propagation by the existence of an exothermic step in the decomposition reaction, leading to the self-acceleration of the reaction and rapid burnout of the reacting substance layer, is suggested. A theory of the propagation of the decomposition front in the pulsed mode based on a minimum number of empirical parameters obtainable from experiment is developed. Based on numerical simulation results, formulas are derived for predicting the time history of the thickness of the char structure and the time during which the fire-retardant composition can protect the object from fire. These formulas can be used to calculate the desired thickness of the fire-retardant coating that would withstand a fire or a thermal agent of given intensity for a desired time.     

Gasification of porous carbon particle by steam

Diffusive-kinetic model of porous carbon particle gasification by steam is developed. The model considers the processes of heat and mass transfer both inside the porous particle and above it. Heat losses by radiation to the particle from furnace wall are taken into account. Heterogeneous reactions of carbon with steam and carbon with carbon dioxide and homogeneous reaction of carbon monoxide with steam are considered. Pressure variation caused by gas mass increasing inside the particle is considered too. The analysis of the model inside the porous particle made possible determining the correlation between the reaction rate of carbon with steam and the reaction rate of carbon with carbon dioxide. The homogeneous reaction is supposed to be equilibrium. It is considered that the kinetics of heterogeneous reactions is known, than the equations of the model may be solved; and consequently the dependences of the particle gasification rate and the composition of the gasification products vs. composition, pressure and temperature of ambient gas and the internal surface of the porous particle are determined.     

Numerical investigation of hydrodynamics behaviour of melt layer during laser cutting of steel

Understanding of the melt layer hydrodynamic behaviour during laser-cutting process under gas jet assistance is of high importance for cut quality control. In the present work, a numerical model is developed to calculate the three-dimensional behaviour of the melt flow on the kerf front, while an inert gas jet interacts with the melt film. Fluent CFD code is used to solve the governing hydrodynamic equations by finite volume method. The results show that the melt flow on the kerf front reveals a strong instability, which depends on the cutting speed and on the gas jet velocity. Global flow behaviour (gas and molten metal flows) computed using a laminar model, reveals oscillations of the gas–metal liquid interface, which is assimilated to Kelvin–Helmholtz instability. The origin of this instability is discussed in terms of instabilities in thermal dynamics and hydrodynamics. Instability in thermal dynamics is related to the localized melting, while the instability in hydrodynamics is governed by forces balance between gas and resistant surface tension.     

Interrelation of anode and cathode processes in electrochemical carbon oxidation in a fuel cell with molten carbonate electrolyte

The object to be investigated is a fuel cell with a free molten carbonate electrolyte, which ensures direct electrochemical oxidation of solid hydrocarbons. The polarization characteristics of anode and cathode fuel cell assemblies, and also composition and gas release rate of gaseous products of anode reactions are studied. It is shown that the maximum voltages in the open cell circuit are obtained when the oxygen-carbon dioxide ratio in the cathode gas mixture corresponds to stoichiometric reaction coefficients that ensure replenishment of ions in electrolyte. However, the maximum current density values were obtained with a low carbon dioxide content. It is found that at high current values, anode potential fluctuations are observed. It is shown that carbon monoxide is the product of anode processes, along with carbon dioxide. The carbon monoxide content grows with temperature. The carbon dioxide content grows with increasing current in the fuel cell and with growing carbon dioxide content in cathode gases. The release rate of carbon oxidation products nonlinearly depends on the current value in the fuel cell. It is concluded that there is interrelation between the mass-exchange processes in the fuel cell, which is determined by the balance between cathode gas incoming into the reaction zone, the number of molecules generated during fuel oxidation, molecule dissolution and diffusion into the cathode region, and also the amount of gas released in the form of bubbles.     

Comportement thermique d'un générateur à sorption solide

The thermal behaviour of a solid sorption generator of active carbon/alcohol machine, is studied during heating and cooling phases with a preheated air flow. A bicylindrical walls generator that contains 0.9 kg of a granular adsorbent in the presence of residual gas is tested during a cycle of an average duration of 3 hours; the grains of active carbon are rod-shaped of 0.003 m diameter and 0.008 m average length. The thermal contact conductance of adsorbent to the wall has an important influence on the rate of heat transfer between the generator and the external source of heat. In the absence of alcohol, heat transfer occuring without mass transfer in active carbon is essentially due to the conduction. A numerical bidimensional model allows one to justify experimentally the observed evolution and proposes thermal contact conductance between active carbon pellets and the generator wall. A parametric study of the thermal contact conductance gives 6.5 W·m⁻²·K⁻¹ as the best value. A simulation of heating and cooling phases with average conductance values between 5 and 30 W·m⁻²·K⁻¹ gives model estimated heating and cooling phases duration.     

Experimental investigation on the flame front resistance of gas channel growth with melt formation in iron ore sinter beds

The resistance of the flame front within the solid bed constitutes a fundamental and crucial area in porous bed combustion as the flame front propagation is highly related to the productivity and product quality. This paper focuses on the iron ore sintering, a thermal agglomeration process in steel mills. The results from a detailed experimental study of the pilot-scale pot tests under the conditions of a wide range of fuel rate are presented. The primary objective is to provide better understanding of the growth of gas channels relating to melt formation in the flame front and its resistance to flow. The sintering bed was divided into several zones based on the temperature profile and component distribution. Even though there is a continuous one-to-one replacement of humidified zone with porous sintered zone, a constant air flow rate during sintering could be obtained, indicating the ～100?mm high-temperature zone has a controlling effect on sintering bed permeability. The specific pressure drop value in high-temperature zone increases from ～3?kPa in upper bed to ～7?kPa in bottom bed, which varies with the bed temperature and structure properties. Both the green bed and sintered bed were scanned by X-ray computed tomography, the reconstruction and image analysis showed that the sintered bed has large gas channels and many more closed pores due to solid-melt-gas coalescence. More melt is generated when the heat is accumulated along the bed or input higher coke content, showing a propensity to suppress the gas channel growth and amplify the mismatch of gas transportation along the bed. Higher coke rate leads to a higher resistance in flame front, resulting in a slower flame front speed. These results are aimed to provide quantitative validation for improvements of a numerical sintering model in a future work.     

Hybrid cellular automata method. Application to research on mechanical response of contrast media

In the work, a hybrid cellular automata method was developed to study behavioral peculiarities of heterogeneous materials and contrast media. The method is a combination of two approaches: classical and movable cellular automata methods. The method was verified through comparing simulation data on sorption of carbon dioxide in lignite and corresponding experimental data provided by researchers from Velenje Lignite Mine (Slovenia). The obtained estimates of model parameters were used in numerical simulation of the gas phase on the strength and fracture of lignite samples. It is shown that the presence of the gaseous atmosphere even of pressure 0.1 MPa changes the effective strength of the lignite sample and the character of their fracture. The developed method can be used to study behavioral peculiarities of complex multicomponent media such as coal beds in mine zones.     

中红外二氧化碳传感器的研制及在农业中的应用

利用二氧化碳气体分子在4.25μm处的基频吸收带,研制了一种差分式中红外二氧化碳检测系统.系统的光路部分由热辐射红外光源、双通道热释电探测器和球面反射镜构成,电路部分主要包括信号处理、光源驱动及主控模块.采用Tracepro软件对气室结构进行仿真和优化设计,使气体吸收光程达到30cm,改善了系统的性能.实验研究了系统对不同浓度二氧化碳气体样品的传感特性.实验结果表明,由拟合曲线得到的浓度与实际浓度误差较小,在0~5 000ppm范围内,测得二氧化碳浓度的标准差小于45ppm,而在500ppm以下,测量浓度的标准差小于5ppm;对浓度为0ppm的二氧化碳气体样品连续测量2h,测量结果的标准差约为2.8ppm;根据Allan方差分析得到系统的1σ检测下限为2.5ppm.在每个二氧化碳传感器上增加无线模块nRF24L01,构成传感器节点,在选定的日光温室大棚中构建了无线传感器网络,采集了温室大棚中的二氧化碳浓度信息,验证了所研制的传感器性能.     

Numerical simulation on the influence of water spray in thermal plasma treatment of CF4 gas

Nitrogen thermal plasma generated by a non-transferred DC arc plasma torch was used to decompose tetrafluoromethane (CF₄). In the thermal decomposition process, water was used as a chemical reactant source. Two kinds of water spray methods were compared: water spray directly to the arc plasma flame and indirectly to the reactor tube wall. Although the same operating conditions of input power, waste gas, and sprayed water flow rate were employed for each water spray methods, a relatively higher decomposition rate was achieved in the case of water spray to the reactor wall. In order to investigate the effects of water spraying direction on the thermal decomposition process, a numerical simulation on the thermal plasma flow characteristics was carried out considering water injection in the reactor. The simulation was performed using commercial fluid dynamics software of the FLUENT, which is suitable for calculating a complex flow. From the results, it was revealed that water spray to the reactor wall and use of a relatively small quantity of water are more effective methods for decomposition of CF₄, because a sufficiently high temperature area and long reaction time can be maintained over large area.     

钾基CO2吸收剂再生反应特性

通过热重分析试验研究了钾基 CO2 吸收剂的再生反应特性.深入分析了气氛、分解终温和升温速率对再生转化率和分解反应速率的影响.通过热分析方法求取了反应动力学参数.研究发现,其分解终温最佳值为 200℃;CO2 和H2O 在分解终温较低时对反应过程的影响较大;升温速率对反应的影响程度在其高于 10℃/min 后明显减弱;KHCO3分解反应的表观活化能为 90～120 kJ/mol.本文为干法 K2CO3/KHCO3 循环脱除 CO2 的研究提供了一定的基础数据.     

Droplet-Laden Mist Film Cooling Effectiveness of Cylindrical Holes Embedded in a Transverse Trench

A three-dimensional numerical model of calculating in the Euler approach is developed to calculate a two-phase turbulent near-wall flow; simulation of thermal efficiency of a gas-droplet shielding injected into a transverse trench through inclined cylindrical holes is fulfilled. The influence of the main thermo-gas-dynamic characteristics of the two-phase flow on thermal efficiency is analyzed. Significant increase in thermal efficiency was obtained by adding droplets in the nearwall coolant flow (up to 2 times in comparison with a single-phase flow). A particular advantage of this method of coolant injection is achieved at high injection parameters. It is shown that the use of two-phase gas-droplet near-wall shielding is promising for protection of surfaces against thermal influence of the heated gas flows.     

High-order shock-fitting methods for direct numerical simulation of hypersonic flow with chemical and thermal nonequilibrium

In recent years, much progress has been made in the direct numerical simulation of laminar-turbulent transition of hypersonic boundary layer flow. However, most of the efforts at the direct numerical simulation of transition previously have been focused on the idealized perfect gas flow or “cold” hypersonic flows. For practical problems in hypersonic flows, high-temperature effects of thermal and chemical nonequilibrium are important and cannot be modeled by a perfect gas model. Therefore, it is necessary to include the real gas models in the numerical simulation of hypersonic boundary layer transition in order to accurately predict flow field parameters. Currently most numerical methods for hypersonic flow with thermo-chemical nonequilibrium are based on shock-capturing approach at relatively low order of accuracy. Shock capturing schemes reduce to first-order accuracy near the shock and have been shown to produce spurious oscillations behind curved strong shocks. There is a need to develop new methods capable of simulating nonequilibrium hypersonic flow fields with uniformly high-order accuracy and avoid spurious oscillations near the shock. This paper presents a fifth-order shock-fitting method for numerical simulation of thermal and chemical nonequilibrium in hypersonic flows. The method is developed based on the state-of-the-art real gas models for thermo-chemical nonequilibrium and transport phenomena. Shock-fitting approach is used because it has the advantage of capturing the entire flow field with high-order accuracy and without any oscillations near the shock. The new method has been tested and validated for a number of test cases over a wide span of free stream conditions. The developed method is applied for the study of receptivity of free stream acoustic waves over a blunt cone for hypervelocity flow. Some preliminary results of the computations of the high order shock fitting method for the above mentioned study have also been presented.     

液氮中单管加注二氧化碳气体的实验研究

向饱和液氮中加注常温二氧化碳气体时,为形成细小而分散的固体二氧化碳颗粒以及充分且均匀的固液混合物,通过实验分别采用不锈钢盘管、大管径塑料管以及金属毛细管往液氮中加注一定流量下的常温二氧化碳气体,研究固液混合过程、凝固颗粒大小以及管路的堵塞状况。结果表明,不管是否经过预冷,大直径管道加注时,经过一段时间后管道必定发生堵塞;而毛细管加注则不会堵塞,但是气体流量会发生脉冲性变化。     

Estimating cutting front temperature difference in disk and CO2 laser beam fusion cutting

A three-dimensional, semi-stationary, simplified thermal numerical model was developed. The average cutting front temperature difference in disk and CO₂ laser beam fusion cutting of 90MnCrV8 was estimated by computing the conductive power loss. Basing on heat affected zone extension experimentally measured and using an inverse methodology approach, the unknown thermal load on the cutting front during laser cutting was calculated. The accuracy of the numerical power loss estimation was evaluated comparing the results from simulation with the ones from analytical models. A good agreement was found for all the test cases considered in this study. The conduction losses estimation was used for justifying the lower quality of disk laser cuts due to the lower average cut front temperature. This results in the increase of viscosity of molten material and in the subsequent more difficult ejection of the melted material from the cut kerf.     

Delay time for fine particle ignition within gas with fluctuating temperature

The Pontryagin equation was applied to calculating the average time for the random process escaping the assign interval: this gives the average delay time for waiting of particle ignition moment in a turbulent flow of gas. A direct numerical simulation method was developed for gas temperature fluctuations with assigned autocorrelation function and particle temperature fluctuations due to exothermal chemical reaction. The method was based on numerical solution of a system of stochastic differential equations. Results of direct simulation were validated through comparing with the analytical solution available for particles without exothermal reaction. Analytical calculations and results of direct numerical simulation for the delay time of particle ignition are in agreement.     

Detailed simulation of primary atomization mechanisms in Diesel jet sprays (isolated identification of liquid jet tip effects)

In this study, the atomization characteristics of Diesel jet front tip have been investigated to elucidate the physical mechanisms by detailed numerical simulation. The computations are carried out with the finest grid resolutions ever that can resolve the final droplet generation by surface tension. The numerical methods are based on level-set interface tracking. The methods were validated by test cases and the grid resolution survey shows that the resolutions for the present study are sufficient. The present flow setup excludes nozzle disturbances to investigate how the disturbances from the liquid jet front would lead to atomization where the liquid jet impacts against the quiescent gas. The liquid jet front becomes an umbrella-like shape. From the front umbrella tip edge, ligament breakup first occurs. Ligament breakup is strongly correlated with the gas motion in the vicinity. The gas region behind the front is highly disturbed by atomization. By the gas recirculation motion here, air and some droplets are entrained and mixed. Also, the disturbances are fed back to the front umbrella by this motion and become synchronized with the breakup. Droplet pinch-off is mainly in the short-wave mode, but some ligaments are elongated by local gas stretch to finally have a long-wave mode shape, namely a mode shift occurs. The above findings of liquid jet front umbrella formation, atomization at the umbrella edge, mixing and atomization loop in the recirculation flow region and droplet generation mode give an insight to the modeling of droplet generation in actual sprays.     

A chemical kinetic model for chemical vapor deposition of carbon nanotubes

Carbon nanotubes (CNTs) are classified among the most promising novel materials due to their exceptional physical properties. Still, optimal fabrication of carbon nanotubes involves a number of challenges. Whatever be the fabrication method, a process optimization can be evolved only on the basis of a good theoretical model to predict the parametric influences on the final product. The work reported here investigates the dependence of the deposition parameters on the controllable parameters for carbon nanotube growth during Chemical vapor deposition (CVD), through a chemical kinetic model. The theoretical model consisted of the design equations and the energy balance equations, based on the reaction kinetics, for the plug flow and the batch reactor, which simulate the CVD system. The numerical simulation code was developed in-house in a g++ environment. The results predicted the growth conditions for CNT: the deposition temperature, pressure and number of atoms, which were found to be influenced substantially by the initial controllable parameters namely the temperature, volumetric flow rate of the carbon precursor, and the reaction time. An experimental study was also conducted on a CVD system developed in the laboratory, to benchmark the computational results. The experimental results were found to agree well with the theoretical predictions obtained from the model.     

Non-Equilibrium Heating of Molecular Gases

The results of non-equilibrium heating of air, carbon dioxide, nitrogen in a plasmatron with porous arc channel at intense gas blow are presented. The investigations are performed in the current range 100–500 A, at the gas pressure being higher than atmospheric. The deviation from the equilibrium conditions in the flow behind the plasmatron for air and carbon dioxide is evaluated by reaction products of nitrogen oxides synthesis and carbon dioxide conversion outputs. It is shown that these processes have non-equilibrium mode and it can explained by an increased products output. For nitrogen the excess of the vibrational temperature T_v over the translational T is defined by the laser probe method (at T = 1500 K T_v = 3000 K).     

Plasma polymerization of styrene with carbon dioxide under glow discharge conditions

Plasma polymerization gains increasing interest for the deposition of films with functional properties suitable for a wide range of modern applications on account of its advantageous features. In this study, carbon dioxide (CO₂) was chosen as carrier gas at flow rates of 30 and 60 sccm, respectively and styrene vapor was used as the monomer to prepare polystyrene films on glass substrates. The structure and composition of the plasma polymerized films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and compared with the film prepared by conventional thermal polymerization. The morphology information of the films was provided by optical microscopy. XPS and FT-IR results reveal that chemical composition of the plasma polymerized films is different from that of the thermal polymerized film and that oxygen content in the plasma polymerized films increases with the flow rate of CO₂. Furthermore, the presence of oxygen-containing groups on the surface of plasma polymerized polystyrene films is confirmed. It is also found that the composition and morphology of the plasma polymerized films are controlled by the flow rate of CO₂.