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℃.

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.

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.

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.

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.

Effect of cooling pad installation on indoor airflow distribution in a tunnel-ventilated laying-hen house

Extra cooling pads on the sidewalls are needed for larger poultry houses using tunnel ventilation system.Preliminary study showed that the airflow velocity going through different aisles varies greatly when the extra pads are installed at the end of sidewalls,making a“[”-shape air inlet.Combined with field tests,the CFD(computational fluid dynamics)technology was used to study the uniformity of airflow distribution in a tunnel-ventilated laying-hen house.The air distribution was first monitored in a layer house to find the main reason resulting in the variations of airflows in different aisles.Then CFD simulations were carried out with different distances(D=2 m,3 m or 4 m)between the pads on end-wall and the extra pads on side walls.The field test showed that airflow streams from the different groups of cooling pads collided vertically at the house corners,mixed with each other,then flew towards the center of the house.This was the main reason that the wind speed in the middle aisle was much higher than in other aisles,leaving large zones of lower ventilation in the aisles adjacent to the sidewalls.The results of CFD simulations indicated that air distributions could be significantly improved when the extra pieces of pads were moved away for an appropriate distance from the end coolingpads.As far as conventional poultry house with a span of 12 m,the air speeds in different aisles were more uniform when this distance was about 3 m.

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.

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.

A new ventilation mode of air conditioning in subway vehicles and its air distribution performance

The traditional ventilation mode of subway vehicles adopts the form that the inlets and outlets are placed on the upper part of the cabin.The air distribution formed in this mode often cause serious problems of thermal comfort and energy consumption.In order to solve these problems caused by the traditional ventilation mode,a new hybrid ventilation mode was proposed.The hybrid ventilation mode uses both upper and underside air supply inlets.A method for evaluating the air distribution performance of subway air conditioning was developed.The method applies non-uniformity coefficients,maximum temperature difference,air diffusion performance index,modified energy utilization coefficient and Air short-circuit comprehensive coefficient.Air short-circuit comprehensive coefficient was a new index to evaluate the degree of air short-circuit of supply air.Based on the airflow simulation,the air distribution performance for the hybrid ventilation mode was evaluated using these indexes,and compared with the traditional ventilation mode.The results show that compared with the traditional ventilation mode,the hybrid ventilation mode has more uniform temperature distribution,better thermal comfort,higher energy utilization efficiency and lower degree of air short-circuit of supply air.

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.

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.

Effect of traffic restriction on atmospheric particle concentrations and their size distributions in urban Lanzhou, Northwestern China

During the 2012 Lanzhou International Marathon, the local government made a significant effort to improve traffic conditions and air quality by implementing traffic restriction measures. To evaluate the direct effect of these measures on urban air quality, especially particle concentrations and their size distributions, atmospheric particle size distributions （0.5-20μm） obtained using an aerodynamic particle sizer （model 3321, TSI, USA） in June 2012 were analyzed. It was found that the particle number, surface area and volume concentrations for size range 0.5-10 μm were （15.0±2.1） cm-3, （11.8±2.6） μm2/cm3 and （1.9±0.6） μm2/cm3, respectively, on the traffic-restricted day （Sunday）, which is 63.2%, 53.0% and 47.2% lower than those on a normal Sunday. For number and surface area concentrations, the most affected size range was 0.5-0.7 and 0.5-0.8 μm, respectively, while for volume concentration, the most affected size ranges were 0.5-0.8, 1.7-2.0 and 5.0-5.4 μm. Number and volume concentrations of particles in size range 0.5-1.0μm correlated well with the number of non-CNG （Compressed Natural Gas） powered vehicles, while their correlation with the number of CNG-powered vehicles was very low, suggesting that reasonable urban traffic controls along with vehicle technology improvements could play an important role in improving urban air quality.

Characteristics of air flow driven by the free surface of the open channel

Spillway tunnels are a key structure in large-scale water conservancies. The high-head water inlet makes the water surface-velocity extremely high, and the air is driven by the free surface of the water to move downstream. This paper studies the air velocity distribution above the water surface through the model tests, under the assumption that the airflow is a turbulent boundary layer with a rough interface, and the influence of the water depth and the water velocity on the air velocity distribution is analyzed. It is shown that the air velocity is in an exponential distribution. As the measured position moves upward, the air velocity gradually decreases, and the gradient decreases. When the water depth increases, the air velocity increases but with the same distribution form. With the increase of the water surface-velocity, the air velocity at the same measuring point increases, the variation range near the water surface is large, the air boundary layer height increases slightly, and the index coefficient of the air velocity distribution function decreases. Through numerical fitting, the calculation formula of the air boundary layer thickness at different water surface velocities is obtained, along with the numerical value of the index coefficient.

Large Eddy Simulation of Flow Field in Vector Flow Clean-Room

The turbulent large eddy simulation (LES) technique and the finite element method (FEM) of computational fluid dynamics (CFD) are used to predict the three-dimensional flow field in a vector flow clean-room under empty state and static state conditions. The partly expanded Taylor-Galerkin (TG) discretization scheme is combined with implicit stream-upwind diffusion in the finite element formulation of the basic equations with Gauss filtering. The vortex viscosity subgrid model is used in the numerical simulation. The numerical results agree well with the available experimental data, showing that the LES method can more accurately predict the size and location of large eddies in clean-rooms than the standard k-ε two equation model.

HYDRAULIC CHARACTERISTICS OF CHUTE AERATORS FOR RELEASE WORKS

On the basis of model tests and theoretical analysis, hydraulic characteristics, air demand, air concentration distribution and their relationships between prototype and model of an aerator were studied. Some computational examples show that the present methods have higher accuracy, and can meet the need of engineering design.

Six-day measurement of size-resolved indoor fluorescent bioaerosols of outdoor origin in an office

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.

Direct capture efficiency of range hoods in the confined kitchen space

Range hood is a local ventilation device applied widely in residential kitchen for maintaining healthy environment. This study firstly defines the direct capture efficiency (DCE) based on the two-zone model in a confined kitchen space. A mass flux ratio of the secondary captured pollutant to the entrained pollutant from the room zone is proposed for the determination of DCE, where the distribution coefficient is firstly solved, and then its sensitivity analysis on the DCE is carried out. To validate the mass flux ratio and concisely identify the DCE, a virtual purification method that artificially sets the escaped pollutant to zero, is further applied. Compared with the newly developed DCE, the existing indexes, such as contaminant removal efficiency (CRE), total capture efficiency (TCE), fail to differentiate the direct capture from the total capture. Finally, the effects of such factors as makeup airflow pattern, exhaust flow rate, cooking source temperature and the individual occupied/unoccupied on the DCE are fully studied. It is confirmed that different makeup airflow pattern results in distinguished airflow distribution, which makes a significant difference of more than 30% in DCE. Over 50% increase of DCE can be achieved when the exhaust flow rate is increased from 300 to 600 m3/h. About 30% decrease of DCE is observed with the increased cooking source temperature from 100 to 300 °C, and 10% increase of DCE is appeared in the individual occupied case. This reasonable definition and determination of DCE would help to improve the real capture performance of range hoods.

Quantitative analysis of coherent structures affecting instantaneous fluctuation of point-source plumes based on PIV-POD method

For an enclosed space like an industrial plant where devices and equipment generate a large amount of heat,the fluctuation characteristics of thermal plume become more crucial.This paper aims to study the unique air distribution of the point-source plume by shutting down all valves in a thermostatic chamber.250 consecutive instantaneous flow fields(in each zone)were measured by a two-dimensional particle image velocimetry(PIV)system at a sampling frequency of 3 Hz to quantify the air distribution of the plume.Based on the experimental data,the indoor instantaneous velocity and vorticity fields were analyzed,and the transient velocity fluctuation characteristics of typical points were discussed.The fluctuation periods of the plume at different heights were ini-tially estimated.Through the proper orthogonal decomposition(POD)analysis,the dominant coherent structures in complex instantaneous flow fields were excavated,and the turbulent kinetic energy of coherent structures was calculated.In addition,POD analysis provided a new method for validating and improving transient numerical simulation models.