Characterization of the temperature and oxygen concentration field in a decentralized solid‑waste incinerator for villages and towns

Decentralized solid-waste incinerators(DSWIs)have certain advantages for waste disposal from villages and towns.However,the incineration condition is always affected by the distribution of temperature and oxygen concentration,which causes difficulties in operation and maintenance.In this study,the temperature and oxygen concentration distribution of DSWI were characterized using different air flow rates and bottom ash volumes.The results showed that the adjustment of air flow has no significant influence on the heating process of the DSWI,while the retention of bottom ash did affect the temperature and oxygen concentration fields in the furnace.When the air flow rate was increased without the retention of bottom ash,99%of the furnace volume temperature was observed between 780℃ and 800℃.However,once the bottom ash was retained,the whole furnace temperature was steadily maintained between 800℃ and 850℃.When the air flow rate was increased without bottom ash,the highest furnace volume percentage of oxygen concentrations higher than 3%maxed out at 11%volume,while it could reach 100%when bottom ash remained.The distribution of the temperature and oxygen concentration in the DSWI characterized by this research provides strong support for the operation and management of such systems.

Numerical simulation of low-concentration CO_(2) adsorption on fixed bed using finite element analysis

Accurately predicting distributions of concentration and temperature field in fixed-bed column is essential for designing adsorption processes.In this study,a two-dimensional(2D),axisymmetric,nonisothermal,dynamic adsorption model was established by coupling equations of mass,momentum and energy balance,and solved by finite element analysis.The simulation breakthrough curves fit well with the low-concentration CO_(2) adsorption experimental data,indicating the reliability of the established model.The distributions of concentration and temperature field in the column for CO_(2) adsorption and separation from CO_(2)/N_(2) were obtained.The sensitivity analysis of the adsorption conditions shows that the operation parameters such as feed flow rate,feed concentration,pellet size,and column height-to-diameter ratio produce a significant effect on the dynamic adsorption performance.The multi-physics coupled 2D axisymmetric model could provide a theoretical foundation and guidance for designing CO_(2) fixed-bed adsorption and separation processes,which could be extended to other mixed gases as well.

Unusual local electric field concentration in multilayer ceramic capacitors

Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element simulation to understand the effect of pores on the electric reliability of MLCCs.Electricfield is found to be concentrated significantly in the vicinity of these pores and the strength of the local electric-field is 1.5e5.0 times of the nominal strength.Unexpectedly,the concentration degree of the pores in the inner electrode is much higher than that in the dielectrics and dielectric-electrode interfaces.Meanwhile,geometry orientations are found to have a remarkable influence on the local electric field strength.The pores act as an insulation degradation precursor via local electric,thermal center,and oxygen vacancies accumulation center.Such unusual local electric field concentration of multitype pores can provide new insights into the understanding of insulation degradation evolution,processing tailoring and design optimization for MLCCs.

A NUMERICAL MODEL OF FAR-FIELD COD CONCENTRATION DISTRIBUTION FOR NATURAL RIVER

A far field numerical model is developed to simulate jet pollution into natural rivers. Its character is to compute the velocity and pollution concentration separately. The velocity is computed by SIMPLEC algorithm in boundary fitted coordinate systems. The pollution concentration distribution is computed by developed QUAL IIm and QAIIL 2D program. The present model was applied to the Xiantao section of the Hanjiang River a tributary of Yangtze River, and Xiangjiang River. The flow field and COD distribution are in good agreement with field data.

Numerical model of flow and pollutant transportation in non-orthogonal curvilinear coordinates

The planar 2D k-ε double equations' turbulence model was adopted and transformed into non-orthogonal curvilinear coordinates. The concentration convection-diffusion was introduced to planar 2D SIMPLEC algorithm of flow in non-orthogonal curvilinear coordinates. The numerical model of pollutant transportation in non-orthogonal curvilinear coordinates was constructed. The model was applied to simulate the flow and pollutant concentration fields. In the testing concentration field, two optimal operations of contamination discharging both along bank and in the centerline at the first bend of the meandering channel were adopted. Comparison with available data showed the model developed was successful, was valuable to engineering application.

Numerical Study on the Gas Leakage and Dispersion at the Street Intersection of a Building Group

Accidents involving natural gas leakage and dispersion pose a significant threat to human life and property.This threat is especially relevant at the street intersection at which dense buildings,heavy traffic flow,and complex underground pipe networks meet.Scholars have conducted numerous studies on gas leakage and dispersion,but investigations of natural gas leakage and dispersion at the street intersection of a building group are not in-depth.In this paper,we presented a three-dimensional(3D)physical model based on the Computational Fluid Dynamic(CFD)methodology to study the natural gas leakage and dispersion at the street intersection of a building group.We validated the CFD methodology applied in the research based on the data from the field tests and wind tunnel experiments.Then,we simulated and analyzed the pressure,wind,and concentration of natural gas dispersion at the street intersection.The simulation results showed that vortex regions,low-pressure zones,and a building group effect could cause a build-up of natural gas concentration under perpendicular wind direction conditions.In addition,the area of hazardous region tended to increase first and then drop with the dispersion height.In the case of this study,the maximum area of hazardous region is 200 m2 located in the height of 55 m,which is the middle plane in the computational domain.The results in the paper can provide scientific references for the safe operation and emergency-management decisions of municipal gas.

A semi-analytical solution for electric double layers near an elliptical cylinder

A theoretical analysis on the electric double layer formed near the surface of an infinite cylinder with an elliptical cross section and a prescribed electric potential in an ionic conductor was performed using the linearized Gouy–Chapman theory. A semi-analytical solution in terms of the Mathieu functions was obtained. The distributions of the electric potential, cations, anions, and electric field were calculated. The effects of various physical and geometric parameters were examined. The fields vary rapidly near the elliptical boundary and are nearly uniform at far field. Electric field concentrations were found at the ends of the semi-major and semi-minor axes of the ellipse. These concentrations are sensitive to the physical and geometric parameters.

Singular Functions and Characterizations of Field Concentrations:a Survey

In the presence of closely located inclusions of the extreme material property,the physical fields,such as the electric field and the stress tensor,may be concentrated and arbitrarily large in the narrow region between two inclusions.Recently there has been significant progress on the quantitative characterization of the field concentration in the contexts of electrostatics(Laplace equation),linear elasticity(Lam´e system),and viscous flow(Stokes system).This paper is to review such progress in a coherent way.

Pollutant Concentration Distribution Behind Peninsular Models

Planar laser-induced fluorescence (PLIF) was used to study the characteristics of pollutant mixing and transport in wakes behind peninsula-type bodies. Fluorescein sodium was introduced 40 cm upstream of the peninsula as a tracer. The concentration field was measured behind semicircula-shape and sinusoid-shape peninsulas for steady inlet flows for a distance of seven radii downstream of the bodies. Analysis of the mean concentration and root mean square concentration fields showed that two factors mainly affected the concentration field in the near wake, the convection of pollutants with the main flow and the entrainment in the mixing shear layer. The impact of the shape on the concentration distribution is complex because of these two factors. In the present experiments, the semicircular peninsula caused better pollutant mixing, while the sinusoidal peninsula resulted in higher concentrations in the near wake region.

A feasible approach to field concentrators of arbitrary shapes

We propose a simple method to design field concentrators of arbitrary shapes based on Fabry-Perot resonances. The material parameters are feasible in terms of metallic layered structures and gradient index dielectrics. The functionalities are well confirmed by numerical simulations.

Effects of elevated atmospheric CO_2 concentration and temperature on the soil profile methane distribution and diffusion in rice–wheat rotation system

The aim of this experiment was to determine the impacts of climate change on soil profile concentrations and diffusion effluxes of methane in a rice-wheat annual rotation ecosystem in Southeastern China. We initiated a field experiment with four treatments：ambient conditions（CKs）, CO2 concentration elevated to - 500 μmol/mol（FACE）,temperature elevated by ca. 2°C（T） and combined elevation of CO2 concentration and temperature（FACE ＋ T）. A multilevel sampling probe was designed to collect the soil gas at four different depths, namely, 7 cm, 15 cm, 30 cm and 50 cm. Methane concentrations were higher during the rice season and decreased with depth, while lower during the wheat season and increased with depth. Compared to CK, mean methane concentration was increased by 42%, 57% and 71% under the FACE, FACE ＋ T and T treatments, respectively, at the 7 cm depth during the rice season（p 〈 0.05）. Mean methane diffusion effluxes to the 7 cm depth were positive in the rice season and negative in the wheat season, resulting in the paddy field being a source and weak sink, respectively. Moreover, mean methane diffusion effluxes in the rice season were 0.94, 1.19 and 1.42 mg C/（m^2·hr） in the FACE,FACE ＋ T and T treatments, respectively, being clearly higher than that in the CK. The results indicated that elevated atmospheric CO2 concentration and temperature could significantly increase soil profile methane concentrations and their effluxes from a rice-wheat field annual rotation ecosystem（p 〈 0.05）.

High lithiophilic nitrogen-doped carbon nanotube arrays prepared by in-situ catalyze for lithium metal anode

Lithium metal has a very outstanding theoretical capacity(3860 mAh/g)and is one of the most superior anode materials for high energy density batteries.However,the uncontrollable dendrite growth and the fo rmation of"dead lithium"are the important hidden dangers of short cycle life and low safety.However,the uncontrollable dendrite growth and the fo rmation of dead lithium leads to short cycle life and hidden dange r,which hinder its practical application.Controlling the nucleation and growth process of lithium is an effective strategy to inhibit lithium dendrite.Herein,a simple in situ self-catalytic method is used to construct nitrogen doped carbon nanotube arrays on stainless steel mesh(N-CNT@SS)as a lithium composite anode.The N-doped CNTs provide a great number of N-functional groups,which enhance the lithiophilic of anode and provide a large number of uniform nucleation sites,hence it has excellent structural stability for cycles.The arrays provide neat lithium-ion transport channels to uniform lithiumion flux and inhibits dendrite generation,revealed by the COMSOL multi-physics concentration field simulation.The N-CNT@SS composite anode sustain stable at 98.9%over 300 cycles at 1 mA/cm2.NCNT@SS as the anode is coupled LiFePO_(4)(LFP)as the cathode construct a full battery,demonstrating excellent cycling stability with a capacity of 152.33 mAh/g and capacity retaining ratio of 95.4%after 100 cycles at 0.5 C.

Safety design analysis of a vent mast on a LNG powered ship during a low-temperature combustible gas leakage accident

Liquefied natural gas(LNG)is a kind of clean energy,and many LNG-powered vessels have been de-signed and built around the world.However,LNG introduces the potential risk of leakage and explosion accidents;thus,it is necessary to conduct safety assessments on the layout of typical facilities during the initial design stage.In this paper,an on-deck LNG fuel area model is established by employing the computational fluid dynamics(CFD)method according to an LNG-powered Aframax oil tanker.The distri-bution of potential dangerous areas on the concentration field and temperature field is presented under leakage and diffusion accident conditions with vent masts of different heights.The results show the fol-lowing:the gas concentration rises rapidly at the initial stage of leakage and tends to stabilize after a certain period;the leakage and diffusion trend of light gas is basically the same as that of heavy gas,and the lowest heavy gas and light gas temperature on the deck between the storage tank and the upper building is-7.9 C and 4.7°C,respectively,when the venting mast leakage point is at the height of 6 m;and the higher the mast leakage point is,the more safe the ship design.For safety considerations,the height of the venting mast designed in this paper should not be lower than the height of the LNG storage tank,which is 10 m.

NUMERICAL SIMULATION OF 3-D REAERATION IN BODY-FITTED COORDINATE SYSTEM

A three-dimensional numerical model was developed to simulate reaerationusing a body-fitted coordinate system. The model was designed to calculate the velocity and oxygenconcentration separately, called, 'no pairing resolution'. The velocity was calculated by SIMPLECalgorithm in the body-fitted coordinate system. The considerably proposed model was checked by areaeration experiment couducted in an open channel. The computed results agree considerably wellwith the experimental data. The model was also used to predict the reaeration in an S-shapedchannel, and the numerical results are discussed.

Prediction for the Mineralization of the Water Quality of Lake Bostan

In this paper, a non-uniform, mixed type model for predicting the water quality of Lake Bostan (Bositeng) is presented. With corresponding boundry conditions, three modes of prediction are made for the developmental tendency of mineralization.