A CFD study on optimal venting volume and air flow distribution in a special designed hood system for controlling dust flow

A novel hood structure has been designed for the dust control system in the foundry in order to improve the working environment. A composite strategy has been applied for comparative analysis of the optimal venting volume and the airflow distribution between the conventional hood and the novel one in this study. A Computational Fluid Dynamic (CFD) method is used to simulate the airflow fields and dust-polluted air moving paths. The CFD results show that a two-outlet hood, with one outlet located on the left of the hood, is better for improving dust-polluted air than the hood with one outlet only. It can be concluded that the number of the outlets as well as their location on the hood has a significant influence on the air flow pattern in the hood. The optimal venting volume is also a major consideration that is discussed in the study. The venting volume should be designed by considering both the effective level of air flow velocity around the dust source and the energy saving. The optimal airflow distribution may reduce the turbulence in the hood system.

Effect of Air Distribution on the Transport Characteristics of Solid Particles in the Thermal Storage and Release System of Circulating Fluidized Bed

Solid particle heat storage technology offers a potential solution to the challenges posed by the significant growth of renewable energy sources,particularly in terms of grid security and stability.Consequently,it has the capability to optimize the energy utilization efficiency of the power system.In order to investigate the transport regulation characteristics of solid particles in the thermal storage and release system of a circulating fluidized bed(CFB),a test rig with a capacity of 0.1 MW(th)was established.This rig was utilized to systematically study the transport regulation characteristics of solid particles under the double U-type valve feed structure and U-type valve discharge structure.The experimental findings indicate that the system's design enables efficient and rapid storage and release of solid particles in the CFB.The air distribution mode,specifically the double U-type valve feed structure and the U-type valve discharge structure,significantly influence the feed and discharge characteristics of the ash storage bin.It was observed that the impact of loose air on these characteristics is more substantial than that of the return air,irrespective of the feed structure or the return structure.When adjusting the feed and discharge rate,it is recommended to adopt a scheme that involves coarse adjustment through loose air and fine adjustment through return air.

Airflow characteristics by air curtain jets in full-scale room

A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow characteristics of this novel air curtain jet ventilation system,a full-scale room was used to measure the jet velocity with a slot-ventilated supply device,with regards to the airflow fields along the vertical wall as well as on the horizontal floor zones.The airflow fields under three supply air velocities,1.0,1.5 and 2.0 m/s,were carried out in the full-scale room.The experimental results show the velocity profiles of air distribution,the airflow fields along the attached vertical wall and the air lake zones on the floor,respectively.The current experimental research is helpful for heating,ventilation and air conditioning(HVAC) engineers to design better air distribution in rooms.

Adaptive Wall-Based Attachment Ventilation:A Comparative Study on Its Effectiveness in Airborne Infection Isolation Rooms with Negative Pressure

The transmission of coronavirus disease 2019(COVID-19)has presented challenges for the control of the indoor environment of isolation wards.Scientific air distribution design and operation management are crucial to ensure the environmental safety of medical staff.This paper proposes the application of adaptive wall-based attachment ventilation and evaluates this air supply mode based on contaminants dispersion,removal efficiency,thermal comfort,and operating expense.Adaptive wall-based attachment ventilation provides a direct supply of fresh air to the occupied zone.In comparison with a ceiling air supply or upper sidewall air supply,adaptive wall-based attachment ventilation results in a 15%–47%lower average concentration of contaminants,for a continual release of contaminants at the same air changes per hour(ACH;10 h^(-1)).The contaminant removal efficiency of complete mixing ventilation cannot exceed 1.For adaptive wall-based attachment ventilation,the contaminant removal efficiency is an exponential function of the ACH.Compared with the ceiling air supply mode or upper sidewall air supply mode,adaptive wall-based attachment ventilation achieves a similar thermal comfort level(predicted mean vote(PMV)of0.1–0.4;draught rate of 2.5%–6.7%)and a similar performance in removing contaminants,but has a lower ACH and uses less energy.

Numerical simulation of dust distribution at a fully mechanized face under the isolation effect of an air curtain

At a fully mechanized working face of a coal mine as prototype,we investigated,by simulation,the flow field and dust distribution during the process of its isolation by a curtain of air,using the CFD software, Fluent.The results show that the air curtain installed on the shearer can effectively prevent the dust （especially the respirable dust）from diffusing into the work area of the operator,reducing the dust concentration on the side of the operator and greatly improving his working environment.The field application of the air curtain shows that the dust-isolation effect of an air curtain is quite noticeable.The isolation efficiency for respiratory dust is over 70%and,as well,it has good dust-isolation effect for nonrespiratory dust.The air curtain is a useful way to resolve the problem of dust-isolation at a fully mechanized working face.It has a practical background elsewhere with more extensive applications.

Numerical Simulation of the Effect of Air Distribution on Turbulent Flow and Combustion in a Tubular Heating Furnace

A three-dimension full-size numerical simulation of the effect of air distribution on turbulent flow and combustion in a tubular heating furnace was carried out. A standard k –ε turbulent model, a simplified PDF combustion model and a discrete ordinate transfer radiation model were used. The hybrid grid combining a structured and a non-structured grid was generated without any simplification of the complicated geometric configuration around the burner. It was found that the multistage combustion could reduce and control the peak value of temperature. At the same time, it was concluded that the amount of primary air had little effect on the global distribution of velocity and temperature in the furnace, but a great effect on that around the burner. It is recommended that 45% - 65% of the total amount of air be taken in in primary air inlets in the furnace. All the results are important to optimize the combustion progress.

Research on segregation evaluation methods of asphalt pavement based on air voids distribution

Eye observation was used to evaluate the segregation degree of asphalt pavement, which was not much creditable. To the asphalt pavement, road surface texture measuring method which has appeared recently can identify gradational segregation; but it can’t reflect the influence of the temperature segregation. However, using infrared temperature detector to evaluate the segregation must be taken during paving, which brings much inconvenience. In this paper, measuring the air voids distribution using non-nuclear density gauge to evaluate asphalt pavement segregation was introduced. Result shows that this method can directly reflect the comprehensive results of the two types of segregation in a high efficient and accurate way. Moreover, using the sketch map of segregation area can help to analyze the segregation reason visually.

Effect of the secondary air distribution layer on separation density in a dense-phase gas–solid fluidized bed

Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages. During the process of dense coal gas-solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important infuencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the tradi- tional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13 mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6 ram, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas-solid separation fluidized with a high density coarse particle layer can be as low as 0.085 g/cm3.

Effect of Different Types of Structural Configuration on Air Distribution in a Compact Purification Device

In some old industrial plants,in order to meet the increasingly strict requirements of pollutant emission limits,it is necessary to install the compact filtration and/or purification devices in a given narrow machine room.Different types of structural configuration might influence air distribution inside these devices.The unreasonable air distribution might lead each part of filtration or purification media to operating at largely different air flow rates.Based on a computational fluid dynamics(CFD)model,this study explores the influence of different outlet positions and different upper heights on the flow field inside chamber.The porous medium model is employed to simulate the air flow in porous media.The changing structural configurations include three positioning cases of the outlet opening and eight height cases of the upper chamber.The root mean square is defined as the non-uniformity coefficient to evaluate the uniformity of air flow distribution.The results show that the farther distance between inlet and outlet openings will bring more uniform air distribution,and the increasing height of upper chamber totally trends to exhibit more uniform air distribution.

A Method of Assessing Parameters of Air-Void Structure in Air-Entrained Concretes

The air-void size distribution and number of air voids are crucial characteristics of air-entrainment. The standard spacing factor L is based on the Powers model, in which considerable simplifications are assumed. A better solution is provided by the Philleo factor, which determines the percentage content of protected paste located at a distance S from the edge of the nearest air void. Developing the concept put forward by Philleo, a method of determining the volume of protected paste on the basis of images generated from the numerical model of concrete grain structure including layout of aggregate-paste-air, is proposed. It is the ratio of the volume of the paste protected by air voids to the total paste volume. The PPV （protected paste volume） index accounts not only for sizes and number of air voids, but also for the role of aggregate particles in the placement of these pores, which is often disregarded in analyses. The PPV results obtained from image analysis were compared with standard spacing factor L and with the parameter developed by Philleo. The analyses conducted by the authors shows that accounting for aggregate grains in calculations substantially affects the assessment of the quality of the air-pore structure.

Distribution characteristics of respiratory aerosols in enclosed environments

This paper studies the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 to 10.0 μm in an office room with three air distribution methods,including mixing ventilation（MV）,displacement ventilation（DV）,and under-floor air distribution（UFAD）.The simulation results indicate that exhaled droplets with diameters up to 10.0 μm from normal respiration process are uniformly distributed in MV.However,they become trapped at the breathing height by thermal stratifications in DV and UFAD,resulting in a high droplet concentration and an increased exposure risk to other occupants.Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV.Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.

Research on optimization and design methods for air distribution system based on target values

To achieve sufficient air conditioning of large buildings,reasonable air distribution in indoor spaces is an effective method for creating stratified air conditioning.Therefore,optimizing the air distribution in large buildings is extremely significant.In this paper,we expound on a new method for air distribution design and optimization based on target value evaluation and summarize the relevant design processes based on an orthogonal test and by decoupling the effects of the size of the tuyere,airflow temperature,air-supply angle and velocity on air distribution.Then,we present a design case.To optimize the distribution of a lateral air supply in winter,the deflection angle,velocity and temperature of the air supply can be determined in turn.For the large and tall building types addressed in this paper,the optimal air-supply angle is 2°,the optimal air-supply velocity is 8 m/s,and the optimal air-supply temperature is 19℃.

Study of 3-D Numerical Simulation for Gas Transfer in the Goaf of the Coal Mining

In order to simulate field distribution rules,mathematical models for 3-D air flows and gas transfer in the goaf of the coal mining are established,based on theories of permeability and dynamic dispersion through porous media. A gas dispersion equation in a 3-D field is calculated by use of numerical method on a weighted upstream multi-element balance. Based on data of an example with a U type ventilation mode,surface charts of air pressure distribution and gas concentration are drawn by Graphtool software. Finally,a comparison between actually measured results in the model test and the numerical simulation results is made to proves the numerical implementation feasible.

Experimental Research on Plasma Induced by TEA CO_2 Laser Propulsion

Results in the air-breathing propulsion experiments with a parabolic light craft and a self-made UV-preionized 100 J TEA CO2 laser device are presented. Air disturbance and the spectrum of the plasma after the interaction of pulsed laser radiation with the light craft were studied. It was found that the focal length of the parabolic light craft had a significant effect on the air-disturbance. Two shock waves were detected for the longer focal length, while only one shock wave detected for the short focal length. The spectrum of the laser-induced plasma, the distribution of the characteristic lines, and the temporal behaviors of the air plasma were studied in detail. The results showed that, the evolution of the laser-induced plasma lasted 20μs, and the plasma spectrum would reach the maximum intensity at 7μs.

Investigation on a vertical radial flow adsorber designed by a novel parallel connection method

Due to the increasing global demand for industrial gas, the development of large-scale cryogenic air separation systems has attracted considerable attention in recent years. Increasing the height of the adsorption bed in a vertical radial flow adsorber used in cryogenic air separation systems may efficiently increase the treatment capacity of the air in the adsorber. However, uniformity of the flow distribution of the air inside the adsorber would be deteriorated using the height-increasing method. In order to reduce the non-uniformity of the flow distribution caused by the excessive height of adsorption bed in a vertical radial flow adsorber, a novel parallel connection method is proposed in the present work. The experimental apparatus is designed and constructed; the Computational Fluid Dynamics(CFD) technique is used to develop a CFD-based model, which is used to analyze the flow distribution, the static pressure drop and the radial velocity in the newly designed adsorber. In addition, the geometric parameters of annular flow channels and the adsorption bed thickness of the upper unit in the parallelconnected vertical radial flow adsorber are optimized, so that the upper and lower adsorption units could be penetrated by air simultaneously. Comparisons are made between the height-increasing method and the parallel connection method with the same adsorber height. It is shown that using the parallel connection method could reduce the difference between the maximum and minimum radial static pressure drop by 86.2% and improve the uniformity by 80% compared with those of using the height-increasing method. The optimal thickness ratio of the upper and lower adsorption units is obtained as 0.966, in which case the upper and lower adsorption units could be penetrated by air simultaneously, so that the adsorbents in adsorption space could be used more efficiently.

CFD–DEM simulation of particle deposition characteristics of pleated air filter media based on porous media model

In this study, the three-dimensional physical model of pleated air filtration media was simplified to porous media model, and the calculation parameters of porous media were obtained based on experimental data. The model of V-shaped pleated air filter media is constructed, the height of the media pleat is 50 mm and the pleat thickness is 4 mm, the pleat angle is 3.7°. The Hertz-Mindlin contact model was modified by Johnson Kendall Roberts (JKR) adhesion contact model. The deposition process of particles in media was simulated based on computational fluid dynamics (CFD) theory and discrete element method (DEM). Results show that the CFD–DEM coupling method can be effectively applied to the macro research of pleated air filter media. The particles will form dust layer and dendrite structure on the fiber surface, and the dust layer will affect the subsequent air flow organization, and the dendrite structure will eventually form a “particle wall”. The formation of the “particle wall” will prevent the particles from moving further in the fluid domain, which makes area of pleated angle become the “low efficiency” part about the particle deposition. Compared with area of pleated angle, the particles are concentrated in the opening area and the middle area of the pleated to agglomerate and deposit.

Rapid identification of single constant contaminant source by considering characteristics of real sensors

For the release of hazardous contaminant indoors, source identification is critical for developing effective response measures. A method which can quickly and accurately identify the position, emission rate, and release time of a single constant contaminant source by using real sensors was presented. The method was numerically demonstrated and validated by a case study of contaminant release in a three-dimensional office. The effects of the measurement errors and total sampling period of sensor on the performance of source identification were thoroughly studied. The results indicate that the adverse effects of the measurement errors can be mitigated by extending the total sampling period. For reaching a desirable accuracy of source identification, the total sampling period should exceed a certain threshold, which can be determined by repeatedly running the identification method tmtil the results tend to be stable. The method presented can contribute to develop an onsite source identification system for protecting occupants from indoor releases.

Thermal sensation and percentage of dissatisfied in thermal environments with positive and negative vertical air temperature differences

Considering the percentage of dissatisfied due to local thermal sensation(PD LTSV),a vertical air temperature difference(ΔT_(d))threshold of about 3°C was recommended in standards.However,some novel air distribution methods might create large positive(which means the head warmer than the feet,vice versa)or negativeΔT_(d),with no suitable proved criteria to be used.In this study,sixteen subjects were seated in a climatic box placed in a climate chamber to evaluate thermal sensation and percentage of dissatisfied with negative and positiveΔT_(d) in different whole-body thermal conditions.Air temperatures were controlled independently at the upper and lower body parts,with 13 different air temperature sets combined with 22°C,25°C,28°C,and 31°C(i.e.-9°C≤ΔT_(d)≤9°C).Results showed that subjects were more thermally sensitive at the upper body and with positiveΔT_(d) than at the lower body or with negativeΔT_(d).The 80%acceptableΔT_(d) range is about-8 to 7°C in overall neutral(TSV=0),-7°C to 6°C in slightly cool(TSV=-0.5)conditions,which is wider than-3 to 3°C in slightly warm conditions(TSV=+0.5).By considering the factors of both TSV andΔT_(d),a new overall percentage of dissatisfied index(OPD P)was proposed.Case studies show that the new OPD P index is more precise and suitable for the evaluations of different air distributions to predict overall percentage of dissatisfied in thermal environments with vertical air temperature difference.

Design and experiment of a six-row air-blowing centralized precision seed-metering device for Panax notoginseng

Panax notoginseng is grown mainly in Yunnan Province.Under the present high-density planting patterns for the plant,to solve the problems of a high rate of seed damage and the inability to use a traditional single air-blowing metering device,this paper designs a six-row air-blowing centralized precision seed-metering device for P.notoginseng to realize mechanized precision seeding of this species.This paper describes the working principle of the seed-metering device,and the main structural parameters are determined by combining theoretical calculations with simulation analysis.A mechanics model of the seed filling,cleaning and pressing processes of the seed-metering device was constructed.The seeds of P.notoginseng in Yunnan Province were selected as experimental subjects.An experimental study on the seed-metering performance of the seed-metering device was carried out using the quadratic rotation orthogonal combination test method.The outlet pressure of the air nozzle,forward velocity and cone angle of the hole were selected as test factors.Mathematical models of the grain spacing qualified index,miss index,multiple index and the coefficient of variation of the row displacement consistency were established to analyze the order of factors affecting indicators.Through parameter optimization,the optimum combination of parameters was determined as follows:the cone angle of the hole is 50°,the forward velocity is less than 0.73 m/s,and the outlet pressure of the air nozzle is 0.32-0.52 kPa.The qualified index of grain spacing is higher than 94%,the miss index is less than 3%,the multiple index is less than 5%,and the coefficient of variation of the row displacement consistency is less than 5%.The test results are essentially consistent with the optimization results.The metering device meets the requirements of precision seeding of P.notoginseng.This study provides a basis for the design of a six-row air-blowing centralized precision seed-metering device for P.notoginseng.

A numerical study on the effect of column layout on air distribution and performance of column attachment ventilation

Based on the structural characteristics of existing buildings and the disadvantages of current mixed ventilation mode in the application to large space buildings,an original column attachment ventilation(CAV)has been proposed.In this study,the experiment utilized a room space with four columns uniformly distributed in the space to visualize the movement of attached airflow along the cylinder surface and the floor,the numerical technique was employed to study the effects of the column layout(i.e.,uniform,centralized,dispersed,and crossed distribution)on the air distribution of CAV mode in a standard four-column full scale model of a shopping mall.Seven indices,including airflow pattern,air diffusion performance index(ADPI),air temperature distribution,heat removal effectiveness,draught rate(DR),predicted mean vote(PMV),and carbon dioxide(CO2)concentration,were used to assess the ventilation performance.In the CAV mode with a uniform column layout scheme,the experimental results indicated that the air supply flows downward along the wall surface,forming a secondary attachment with the ground and spreading along the floor in a fan radiation flow mode.Further,an“air lake”-like speed and temperature distribution similar to displacement ventilation(DV)was formed in the occupied zone.In all simulation cases,it was found that the average air velocity was less than 0.25 m/s in occupied zone,the effectiveness for heat removal was more significant than 1.0,DR value was less than 20%,the PMV level can also satisfy most people.The average CO2 concentration was around 470 ppm in the occupied breathing zone.These results indicated that the CAV mode could be an efficient air distribution method.They demonstrated the technical feasibility of applying the CAV in the space under different column layout schemes.