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1.
Ke Zhong Yanming Kang Youjun Wang 《Particuology》2008,6(5):362-368
A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature, and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation (DV) rooms. The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles. Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces. Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone. 相似文献
2.
A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature,and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation (DV) rooms.The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles.Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces.Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone. 相似文献
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《Particuology》2023
The ultra-low NOx emission requirement (50 mg/m3) brings great challenge to CFB boilers in China. To further tap the NOx abatement potential, full understanding the fundamentals behind CFB boilers is needed. To achieve this, a comprehensive CPFD model is established and verified; gas-solid flow, combustion, and NOx emission behavior in an industrial CFB boiler are elaborated; influences of primary air volume and coal particle size on furnace performance are evaluated. Simulation results indicate that there exists a typical core-annular flow structure in the boiler furnace. Furnace temperature is highest in the bottom dense-phase zone (about 950 °C) and decreases gradually along the furnace height. Oxygen-deficient combustion results in high CO concentration and strong reducing atmosphere in the lower furnace. NOx concentration gradually increases in the bottom furnace, reaches maximum at the elevation of secondary air inlet, and then decreases slightly in the upper furnace. Appropriate decreasing the primary air volume and coal particle size would increase the CO concentration and intensify the in-furnace reducing atmosphere, which favors for NOx reduction and low NOx emission from CFB boilers. 相似文献
5.
Hong Zhu * Patrick Phelan Tianhua Duan Gregory Raupp H. J. S. Fernando Beijing Institute of Microbiology Epidemiology Beijing P. R. China Department of Mechanical Aerospace Engineering Arizona State University Tempe Department of Chemical Materials Engineering Arizona State University Tempe *Author to whom correspondence should be addressed. Tel: -- E-mail: zhuhong@hotmail.com 《中国颗粒学报》2003,1(3):119-123
1.IntroductionBioaerosolsaremicroorganismsorparticles,gases,vapors,orfragmentsofbiologicalorigin(i.e.,aliveorreleasedfromalivingorganism)thatexistintheair.Bioaerosolsareeverywhereintheenvironment.Underfavorableconditions,bioaerosolsareabletogrowandpropagateonavarietyofbuildingmaterialsandindoorsurfaces,causingindoorairpollution.Therefore,owingtotheirubiquitouspresenceinnature,bioaerosolsasapollutionsourcearealmostinevitableinarangeofenclosedenvironmentsandincommunityair(Kodama&McGee,1986;Lig… 相似文献
6.
This study reports the results of a numerical investigation of three-dimensional turbulent buoyant recirculating flow within
rooms with heated obstruction. The study involves the solution of partial differential equations for the conservation of mass,
momentum, energy, concentration, turbulent energy and its dissipation rate. These equations were solved together with algebraic
expressions for the turbulent viscosity and heat diffusivity using k-ε turbulence model by performing simulations on FLUENT
6.3. The CFD method was validated via comparing with the available experimental data. A comparison with experimental results
shows good agreement. This means that the present computer code has a good capability to simulate 3D airflow and effect of
obstruction within room. The present study demonstrates the flow behavior, thermal distribution and CO2 concentration inside the room in the presence of heat flux obstruction. Two different configurations of ventilation system
have been studied. Mixing and Displacement ventilation system have been used in two geometries depending on location of opening
inlet. The ventilation effectiveness for heat removal (ET) is used to evaluate the indoor climate and average temperature is an important parameter in designs the ventilation systems.
Two notable points are presented; first, mixing ventilation is depending on throw of jet. CO2 concentration and temperature distribution have been effected in upper zone more than occupied zone with presence the obstruction.
Second notable points are presented; in displacement ventilation buoyancy effect is considerable. Vertical temperature gradient
above the obstruction implies that both fresh air and CO2 concentration. 相似文献
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8.
为能更好地分析砂土在剪切过程中的体积变化及力学行为,通过PFC~(3D)颗粒流程序,按照室内实际级配建立数值试样,进行了不同垂直压力下的砂土直剪试验模拟,并将模拟结果与室内试验结果进行了对比;研究了砂土在剪切过程中的体积变化,并用两种方法分析了砂土剪切带的演变过程;从细观角度对试样颗粒的速度场及力链网络的发展变化进行了分析研究。结果表明,数值模拟结果与室内试验结果基本一致,砂土的体积变化表现为先剪缩后剪胀,剪胀量与垂直压力成反比;剪切带厚度约为11~12倍d_(50),在剪切带内颗粒的位移和欧拉角变化较大;试样内部强力链的演变较为明显,力链网络对外荷载变化的敏感性很高;剪切过程中上盒颗粒速度场方向的变化能够较好地解释砂土产生的剪胀现象。 相似文献
9.
This paper investigates the effect of volatile organic compounds (VOCs) emission from a new carpet in a room. Two cases with
and without flow are modeled numerically. The commercial software Fluent 6 has been employed to solve the continuity, momentum,
turbulence and concentration equations. The equivalent air phase concentration is solved as the dependent variable in the
concentration equation. VOCs concentration in the breathing plane of an adult is carefully investigated. Numerical results
show that the concentration near the center of recirculating flow is the highest in the case with flow while the concentration
near the center of the carpet is the highest in the case without flow. The concentration in the right annex is lower than
that in the left annex when the ventilation exists. Computation shows that there still exists much VOCs in the carpet at 240 h.
Some additive ventilation is still necessary to maintain indoor air quality. 相似文献
10.
《Particuology》2017
Indoor airborne bioaerosols of outdoor origin play an important role in determining the exposure of humans to bioaerosols because people spend most of their time indoors. However, there are few studies focusing on indoor bioaerosols originating from outdoors. In this study, indoor versus outdoor size-resolved concentrations and particle asymmetry factors of airborne fluorescent bioaerosols in an office room were measured continuously for 6 days (144 h) using a fluorescent bioaerosol detector. The windows and door of this room were closed to ensure that there was only air infiltration; moreover, any human activities were ceased during sampling to inhibit effects of indoor sources. We focused on fine particles, since few coarse particles enter indoor environments, when windows and doors are closed. Both indoor and outdoor fluorescent bioaerosol size distributions were fit with two-mode lognormal distributions (indoor R2 = 0.935, outdoor R2 = 0.938). Asymmetry factor distributions were also fit with lognormal distributions (indoor R2 = 0.992, outdoor R2 = 0.992). Correlations between indoor and outdoor fluorescent bioaerosol concentrations show significant concentration-attenuation and a time lag during the study period. A two-parameter, semi-empirical model was used to predict concentrations of indoor fluorescent bioaerosols of outdoor origin. The measured and predicted concentrations had a linear relationship for the studied size fractions, with an R2 for all size fractions of larger than 0.83. 相似文献
11.
Amir Banari Yackar Mauzole Tetsu Hara Stephan T. Grilli Christian F. Janßen 《国际流体数值方法杂志》2015,79(10):491-513
We perform direct numerical simulation of three‐dimensional turbulent flows in a rectangular channel, with a lattice Boltzmann method, efficiently implemented on heavily parallel general purpose graphical processor units. After validating the method for a single fluid, for standard boundary layer problems, we study changes in mean and turbulent properties of particle‐laden flows, as a function of particle size and concentration. The problem of physical interest for this application is the effect of water droplets on the turbulent properties of a high‐speed air flow, near a solid surface. To do so, we use a Lagrangian tracking approach for a large number of rigid spherical point particles, whose motion is forced by drag forces caused by the fluid flow; particle effects on the latter are in turn represented by distributed volume forces in the lattice Boltzmann method. Results suggest that, while mean flow properties are only slightly affected, unless a very large concentration of particles is used, the turbulent vortices present near the boundary are significantly damped and broken down by the turbulent motion of the heavy particles, and both turbulent Reynolds stresses and the production of turbulent kinetic energy are decreased because of the particle effects. We also find that the streamwise component of turbulent velocity fluctuations is increased, while the spanwise and wall‐normal components are decreased, as compared with the single fluid channel case. Additionally, the streamwise velocity of the carrier (air) phase is slightly reduced in the logarithmic boundary layer near the solid walls. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
12.
Present paper deals with temperature driven mass deposition rate of particles known as thermophoretic wall flux when a hot
flue gas in natural convection flow through a cooled isothermal vertical parallel plate channel. Present study finds application
in particle filters used to trap soot particles from post combustion gases issuing out of small furnaces with low technical
implications. Governing equations are solved using finite difference marching technique with channel inlet values as initial
values. Channel heights required to regain hydrostatic pressure at the exit are estimated for various entry velocities. Effect
of temperature ratio between wall and gas on thermophoretic wall flux is analysed and wall flux found to increase with decrease
in temperature ratio. Results are compared with published works wherever possible and can be used to predict particle deposition
rate as well as the conditions favourable for maximum particle deposition rate. 相似文献
13.
An analysis is presented for the steady one-dimensional flow behind a normal shock wave of a compressible gas containing small spherical particles of solid propellant. The solids mass fraction is assumed large enough to require that the void volume fraction be retained as a variable in the governing conservation equations. The particles are ignited by the shocked air and by viscous interaction. Propellant gases are then generated which depend on the instantaneous size of the particles and on the linear burning rate. The latter is assumed dependent upon the local pressure and the particle temperature. These calculations are of interest because of the potential hazards of such particle flows, in that extreme pressures are predicted within the relaxation zone, pressures even greater than those calculated for the final equilibrium conditions. The results stress the importance of the Mach number of the normal (strong shock) and the energy content of the propellant (J/kg). 相似文献
14.
Erosion is one of the major problems in many industrial processes, and in particular, in heat exchangers. The effects of flow velocity and sand particle size on the rate of erosion in a typical shell‐and‐tube heat exchanger were investigated numerically using the Lagrangian particle‐tracking method. Erosion and penetration rates were obtained for sand particles of diameters ranging from 10 to 500 µm and for inlet flow velocities ranging from 0.197 to 2.95 m/s. A flow visualization experiment was conducted with the objective of verifying the accuracy of the continuous phase calculation procedure. Comparison with available experimental data of penetration rates was also conducted. These comparisons resulted in a good agreement. The results show that the location and number of eroded tubes depend mainly on the particle size and velocity magnitude at the header inlet. The rate of erosion depends exponentially on the velocity. The particle size shows negligible effect on the erosion rate at high velocity values and the large‐size particles show less erosion rates compared to the small‐size particles at low values of inlet flow velocities. The results indicated that the erosion and penetration rates are insignificant at the lower end of the velocity range. However, these rates were found to increase continuously with the increase of the inlet flow velocity for all particle sizes. The particle size creating the highest erosion rate was found to depend on the flow velocity range. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
15.
Nowadays, the use of ventilation systems is very common. In museums and exhibition rooms, they are used to guarantee the optimal temperature and humidity conditions for valuable and irreplaceable objects. Ventilation systems are increasingly used even in residential and office buildings. In Austria and other similar climates, winter outdoor air is very dry. Because of the constant air exchange using a ventilation system, the relative humidity of indoor air is often lower than the comfort limit, so that air humidification is necessary. In the same rooms, air must be dehumidified during the summer months. Humidification and dehumidification should be minimized as they are processes that consume a large amount of energy. The problem is that until now, it has been unclear how much humidification or dehumidification is necessary and could not be calculated easily. In this investigation, a simplified method for determining the humidification and dehumidification demands taking into account the effective moisture capacity of the room was developed. The developed model is used for the calculation of the energy balance and will be integrated into the program for energy certification in Austria. 相似文献
16.
Coupling Eulerian‐Lagrangian method of air‐particle two‐phase flow with population balance equations to simulate the evolution of vehicle exhaust plume
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Yuanping He Zhaolin Gu Junwei Su Chungang Chen Mingxu Zhang Liyuan Zhang Weizhen Lu 《国际流体数值方法杂志》2018,88(3):117-140
In this paper, we present a new numerical scheme to describe the dynamic evolution of multiphase polydisperse systems in terms of time, space, and properties by coupling the Eulerian‐Lagrangian method for air‐particle two‐phase flow and population balance equations to describe particle property evolution due to microbehaviors (eg, aggregation, breakage, and growth). This coupling scheme was used to comprehensively simulate the two‐phase flow structure, particle size spectrum, particle number, and volume concentrations. These were characterized by a high‐resolution particle tracking using the Lagrangian approach and the high precision of moments of the particle size spectrum by solving the population balance equation with the quadrature method of moments. The algorithm of the coupling scheme was incorporated into the open source computational fluid dynamics software OpenFOAM to simulate the dynamic evolution of vehicle exhaust plume. The impacts of vehicle velocity, exhaust temperature, and aggregation efficiency on the distribution of auto exhaust particles in space and changes in their properties were analyzed. The results indicate that the particle number concentration, volume concentration, and average diameter of particles in the vehicle exhaust plume could be strongly affected by the plume structure and flow properties. 相似文献
17.
多相流局部混合型质点网格法 总被引:1,自引:0,他引:1
提出模拟多相流的局部混合型质点网格法,该方法能稳定地模拟高浓度流体颗粒两相
流. 在每一个颗粒团尺度的欧拉网格下(本文称之为欧拉微元),基于Lagrangian
追踪原理,可直接估计体积内颗粒的总量,从而准确求出欧拉微元和控制容积内颗粒的
浓度(即颗粒在容积内的体积含量). 同时,假设在新的时间步下,颗粒在欧拉微元里充分
混合,形成新颗粒团. 作者对竖直和倾斜容器中单粒径颗粒沉降和竖直容器中双粒径颗粒双
峰悬浮液沉降过程进行了计算,结果与实测数据相符. 相似文献
18.
Il Ayranc Guillaume Pinguet Dany Escudi Nevin Seluk Rodolphe Vaillon Frdric Andr 《Experimental Thermal and Fluid Science》2007,31(8):839-847
Measurement of particle concentration by laser Doppler anemometry (LDA) is studied on a vertical air jet seeded by a powder disperser with controlled particle and air flow rates. Particle arrival rate is utilized to retrieve particle number densities from conventional LDA operation. The effect of polydisperse nature of the particles is assessed. Comparisons between measured and estimated particle number densities suggest that only a certain portion of the particle population with a particle size to fringe spacing ratio around unity can be detected. Results indicate that reliable measurement of absolute particle concentration is possible for a particle population of narrow size distribution with an average diameter equivalent to fringe spacing. Present number density measurement technique which is useful for practical purposes with conventional LDA systems is found to yield physically reasonable profiles in both laminar and turbulent regimes. 相似文献
19.
Short particle residence time in entrained flow gasifiers demands the use of pulverized fuel particles to promote mass and heat transfer, resulting high fuel conversion rate. The pulverized biomass particles have a wide range of aspect ratios which can exhibit different dispersion behavior than that of spherical particles in hot product gas flows. This results in spatial and temporal variations in temperature distribution, the composition and the concentration of syngas and soot yield. One way to control the particle dispersion is to impart a swirling motion to the carrier gas phase. This paper investigates the dispersion behavior of biomass fuel particles in swirling flows. A two-phase particle image velocimetry technique was applied to simultaneously measure particle and gas phase velocities in turbulent isothermal flows. Post-processed PIV images showed that a poly-dispersed behavior of biomass particles with a range of particle size of 112–160 µm imposed a significant impact on the air flow pattern, causing air flow decelerated in a region of high particle concentration. Moreover, the velocity field, obtained from individually tracked biomass particles showed that the swirling motion of the carrier air flow gives arise a rapid spreading of the particles. 相似文献
20.
Tao Geng Fei Zheng Andrey V. Kuznetsov William L. Roberts Daniel E. Paxson 《Flow, Turbulence and Combustion》2010,84(4):653-667
Pulsed combustion is receiving renewed interest as a potential route to higher performance in air breathing propulsion and
ground based power generation systems. Pulsejets offer a simple experimental device with which to study unsteady combustion
phenomena and validate simulations. Previous computational fluid dynamics (CFD) simulations focused primarily on pulsejet
combustion and exhaust processes. This paper describes a new inlet sub-model which simulates the fluidic and mechanical operation
of a valved pulsejet head. The governing equations for this sub-model are described. Sub-model validation is provided through
comparisons of simulated and experimentally measured reed valve motion, and time averaged inlet mass flow rate. The updated
pulsejet simulation, with the inlet sub-model implemented, is validated through comparison with experimentally measured combustion
chamber pressure, inlet mass flow rate, operational frequency, and thrust. Additionally, the simulated pulsejet exhaust flowfield,
which is dominated by a starting vortex ring, is compared with particle imaging velocimetry (PIV) measurements on the bases
of velocity, vorticity, and vortex location. The results show good agreement between simulated and experimental data. The
inlet sub-model is shown to be critical for the successful modeling of pulsejet operation. This sub-model correctly predicts
both the inlet mass flow rate and its phase relationship with the combustion chamber pressure. As a result, the predicted
pulsejet thrust agrees very well with experimental data. 相似文献