Influences of the Fresh Air Volume on the Removal of Cough-Released Droplets in a Passenger Car of a High-Speed Train Using CFD

The spread and removal of pollution sources,namely,cough-released droplets in three different areas(front,middle,and rear areas)of a fully-loaded passenger car in a high-speed train under different fresh air flow volume were studied using computational fluid dynamics(CFD)method.In addition,the structure of indoor flow fields was also analysed.The results show that the large eddies are more stable and flow faster in the air supply under Mode 2(fresh air volume:2200m3/h)compared to Mode 1(fresh air volume:1100m3/h).By analysing the spreading process of droplets sprayed at different locations in the passenger car and with different particle sizes,the removal trends for droplets are found to be similar under the two air supply modes.However,when increasing the fresh air flow volume,the droplets in the middle and front areas of the passenger car are removed faster.When the droplets had dispersed for 60s,Mode 2 exhibited a removal rate approximately 1%–3%higher than Mode 1 for small and medium-sized droplets with diameters of 10 and 50μm.While those in the rear area,the situation is reversed,with Mode 1 slightly surpassing Mode 2 by 1%–3%.For large droplets with a diameter of 100μm,both modes achieved a removal rate of over 96%in all three regions at the 60 s.The results can provide guidance for air supply modes of passenger cars of high-speed trains,thus suppressing the spread of virus-carrying droplets and reducing the risk of viral infection among passengers.

Experimental study on thermal environment in large-space building with low sidewall air supply

The thermal environmental characteristics are experim-entally studied in terms of different air supply volumes and outdoor meteorological parameters in a large-space building which is air conditioned with a low sidewall air supply.The experimental results show that the indoor vertical temperature distributions under different condition are similar.The maximum vertical temperature difference（MVTD）is up to about 20 ℃,and it linearly changes with the sol-air temperature.The indoor vertical temperature gradients（VTGs）in the upper,central and lower zones are different.The influence of the sol-air temperature on the VTGs in the upper and the lower zones is greater than that in the central zone.The characteristics of the VTGs in the three zones affected by the air supply volume are the same as those affected by the sol-air temperature.Besides,because of the small air velocity,the predicted mean vote（PMV）on comfort in the occupied zone is slightly high and the air temperature difference between the head and the ankle is usually more than 3 ℃.

Draft sensation distribution of air jet supply system in large space building in summer

To study the draft sensation distribution of an air jet supply system in a large space building in summer,experiments are conducted in a large laboratory.The temperature,velocity and draft sensation distributions at a nozzle height of 4 m in the occupied zone are obtained.Then,the numerical simulation under the test condition is carried out by the computational fluid dynamics（CFD）method.The calculation results of the indoor vertical temperature and the draft sensation distribution are validated by the test data.Simulations with different nozzle heights are conducted.The satisfactory air supply condition is determined by analyzing the draft sensations and the temperatures in the occupied zone under three conditions.The simulation results show that the optimal draft sensation distribution and the uniform temperature and velocity fields can be obtained at a nozzle height of 5 m.

Adaptive inverse control of air supply flow for proton exchange membrane fuel cell systems

To prevent the oxygen starvation and improve the system output performance, an adaptive inverse control （AIC） strategy is developed to regulate the air supply flow of a proton exchange membrane fuel cell （PEMFC） system in this paper. The PEMFC stack and the air supply system including a compressor and a supply manifold are modeled for the purpose of performance analysis and controller design. A recurrent fuzzy neural network （RFNN） is utilized to identify the inverse model of the controlled system and generates a suitable control input during the abrupt step change of external disturbances. Compared with the PI controller, numerical simulations are performed to validate the effectiveness and advantages of the proposed AIC strategy.

Location Problem of Air Materials Supply Center for Air Force

Based on the analysis of three influencing factors on the air material supply center location, the location model of air material supply center was established. By solving the model, the rational supply center of air materials was also determined.

Prediction Analysis on the Transport Distance of Supply Air in Warm Air Heating Room with Impinging Jet Ventilation Systems

To overcome the disadvantages of displacement ventilation( DV) and traditional mixing ventilation( MV) system,a new ventilation system known as impinging jet ventilation system( IJVS)has been developing. The warm air can be supplied with impinging jet ventilation( IJV), while the DV is only used for cooling.However,the flow and temperature field of IJV under heating scenario has had few references. The paper is mainly focused on computational fluid dynamics( CFD) and developing an adequate correlation between the distance L that warm air can reach and different parameters in the warm IJVS by using response surface methodology( RSM). The results indicate that L decreases as the supply velocity υ decreases but increases as the supply temperature difference ΔT or the discharge height h decreases. In the variable air volume( VAV) system, it is necessary to determine supply parameters both under the maximum-heat-load condition and the small-heat-load condition. Unlike the VAV system,the constant air volume( CAV) system has no need to study the small-heat-load condition. Draught discomfort near the nozzle becomes the issue of concern in IJVS, thus the suitable discharge height is of great importance in design and can be calculated based on the predictive model.

Numerical Analysis of Influencing Factors on Temperature Field and Airflow Distribution of the Displacement Ventilation System

Indoor air quality and thermal comfort are important features of indoor environment. In this paper, a numerical simulation based on the k-ε model of CFD is used to analyze factors such as loading, exterior-protected construction, blowing-in rate that play an important role in the temperature field and airflow field of the displacement ventilation system. Exterior-protected construction has little influence on indoor temperature distribution of displacement ventilation systems and the influence is limited only in a small area near the external wall when the indoor heat source is the main cooling load.The height of a room has little influence on indoor temperature field, and the temperature gradient of active region is basically unchanged. In the system combined with a displacement ventilation system and a cooling system, the height also has little influence. When the cooling load is high,the indoor heat source creates a strong convective plume, which will make the average indoor air age lower, the ventilation efficiency higher and the elimination of pollutant easier. Air supply rate plays an important role in displacement ventilation systems. The increase of air supply rate that can be realized by increasing the air supply velocity and enlarging the area of air inlet will increase the mass capability of the system and diminish the vertical temperature gradient. From the comparison between simulations and experiments, it is concluded that this simulation are creditable.

Determination of Effectiveness of Energy Management System in Buildings

Building Energy Management Systems(BEMS)are computer-based systems that aid in managing,controlling,and monitoring the building technical services and energy consumption by equipment used in the building.The effectiveness of BEMS is dependent upon numerous factors,among which the operational characteristics of the building and the BEMS control parameters also play an essential role.This research develops a user-driven simulation tool where users can input the building parameters and BEMS controls to determine the effectiveness of their BEMS.The simulation tool gives the user the flexibility to understand the potential energy savings by employing specific BEMS control and help in making intelligent decisions.The simulation is developed using Visual Basic Application(VBA)in Microsoft Excel,based on discrete-event Monte Carlo Simulation(MCS).The simulation works by initially calculating the energy required for space cooling and heating based on current building parameters input by the user in the model.Further,during the second simulation,the user selects all the BEMS controls and improved building envelope to determine the energy required for space cooling and heating during that case.The model compares the energy consumption from the first simulation and the second simulation.Then the simulation model will provide the rating of the effectiveness of BEMS on a continuous scale of 1 to 5(1 being poor effectiveness and 5 being excellent effectiveness of BEMS).This work is intended to facilitate building owner/energy managers to analyze the building energy performance concerning the efficacy of their energy management system.

Accelerating column leaching trial on copper sulfide ore

The main measures to accelerate leaching sulfide ore are large spraying intensity,manual oxygen supply,temperature control,and acclimated bacteria.The indoor experiment accelerating sulfide ore leaching detected the temperature during leaching process,dissolvability of oxygen,bacterial concentration,Cu concentration and slag grade.At the same time,this paper also analyzed the effect of four factors,which are bacterial diversity cultivation stage,spraying intensity,air supply,and whether to control temperature,on the leaching efficiency of copper.The results indicate that the oxygen content of leach solution has a close relationship with temperature but it is rarely affected by air supply.The bacterial concentration preserves from 106 to 107 mL^-1,and temperature has a great effect on the bacterial activity under the condition of proper temperature and oxygen supply,and the lack of nutrition prevents the bacterial concentration from rising in the late stage.The relationships of the copper leaching efficiency to temperature,air feed,and spraying intensity are directly proportional.The leaching efficiencies of the cultivated bacteria and acclimation bacteria are 1.2 and 1.4 times as large as that of the original bacteria.

Computational fluid dynamics simulation of formaldehyde emission characteristics and its experimental validation in environment chamber

We investigated the effect of supply air rate and temperature on formaldehyde emission characteristics in an environment chamber.A three-dimensional computational fluid dynamics(CFD) chamber model for simulating formaldehyde emission in twelve different cases was developed for obtaining formaldehyde concentration by the area-weighted average method.Laboratory experiments were conducted in an environment chamber to validate the simulation results of twelve different cases and the formaldehyde concentration was measured by continuous sampling.The results show that there was good agreement between the model prediction and the experimental values within 4.3 difference for each case.The CFD simulation results varied in the range from 0.21 mg/m3 to 0.94 mg/m3,and the measuring results in the range from 0.17 mg/m3 to 0.87 mg/m3.The variation trend of formaldehyde concentration with supply air rate and temperature variation for CFD simulation and experiment measuring was consistent.With the existence of steady formaldehyde emission sources,formaldehyde concentration generally increased with the increase of temperature,and it decreased with the increase of air supply rate.We also provided some reasonable suggestions to reduce formaldehyde concentration and to improve indoor air quality for newly decorated rooms.

Effects of supply air temperature and inlet location on particle dispersion in displacement ventilation rooms

The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated （DV） room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources （such as particles released from work activities in an office）. However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.

Design of a new type of mine rescue relay cabin

This paper presents the design of an innovative mine emergency rescue relay cabin, and investigates a detailed comparison of existing shelter facilities, their function, service object, structures, size, and system components with the newly designed mine emergency rescue relay cabin. Air-tightness test indicated a test chamber relief rate of 26 Pa/min, which meets the design requirements. Furthermore,respirator replacement test showed an average time of 73.7 s to replace a respirator. The air cover air supply test indicated an air supply rate of 220 L/min, which is sufficient for the staff replacing the respirator in the emergency rescue relay cabin. The total air supply volume is 9680 L, which can be supplied via two compressed air cylinders of 40 L, pressurized to15 MPa.

Dust accumulated fungi in air-conditioning system:Findings based on field and laboratory experiments

This study analyzes the growth and reproduction of dust accumulated fungi(DAF)in an air-conditioning system based on field measurement and molecular biology,laboratory experiment and prediction modelling.The field measurement was conducted to collect dust in filter screen,surface cooler and air supply duct of two air handling units(AHUs).The results indicate that dust volume and fungal number in two AHUs generally met the hygienic specification of public buildings,but the cleansing did not fulfil requirements.High-throughput sequencing was conducted,revealing that the dominant fungal species were Alternaria_betae-kenyensis,Cladosporium_delicatulum,Aspergillus_sydowii,Verticillium_dahliae.Laboratory experiment was conducted to analyze the impact of several factors(e.g.growth time,temperature,relative humidity,duct material)and their combination on the DAF growth.The results indicate that fungal growth increased with time,peaking at 4 days or 5 days.Higher relative humidity or temperature was conducive to fungal growth.The orthogonal experiment revealed that the condition of“antibacterial composite,22±1℃and 45%-55%RH”had the strongest inhibiting impact on fungal growth.Logistic model,Gompertz model and square-root model were further developed to predict the fungal growth under different conditions.The results show that the Logistic model had high feasibility and accuracy,the Gompertz model was feasible with lower accuracy and the square-root model was feasible with high accuracy.Overall,this study facilitates the understanding of the DAF growth in air-conditioning ducts,which is important for real-time prediction and timely control of the fungal contamination.

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.

Thermal environment investigation of asymmetric radiation coupled with convection heating

The couple of radiation with convection heating owned advantages of less energy utilization,healthier and more comfortable indoor environment.However,local thermal discomfort was often induced by large vertical temperature difference and radiation asymmetry temperature.This work studied indoor thermal environment characteristics under different coupling ways of radiation and convection heating terminals through experiments and CFD simulation.The studied five scenarios were denoted as:(Ⅰ)lateral air supply+adjacent side wall radiation,(Ⅱ)lateral air supply+opposite side wall radiation,(Ⅲ)lateral air supply+floor radiation,(Ⅳ)lateral air supply+adjacent side wall radiation+floor radiation,and(Ⅴ)lateral air supply+opposite side wall radiation+floor radiation.The overall thermal comfort indices(including air diffusion performance index(ADPI),predicted mean vote(PMV),and predicted percent of dissatisfaction(PPD))and local thermal comfort indices under different scenarios were investigated.For Scenarios Ⅰ-Ⅲ,the local dissatisfaction rates caused by vertical air temperature difference were 0.4%,0.1%,and 0.2%,respectively,which belonged to"A”class according to the ISO-7730 Standard.While the vertical asymmetric radiation temperature of Scenario Ⅰ-Ⅱ was about 6.5℃ lower than that of Scenario Ⅲ-Ⅳ-Ⅴ.The ADPI for Scenarios Ⅲ-Ⅴ were about respectively 5.7%,16.7%,and 21.0%higher than that of Scenarios Ⅰ-Ⅱ,indicating that a large radiation area and radiation angle coefficient could reduce the discomfort caused by radiant temperature asymmetry.The coupling mode improved local discomfort by decreasing vertical temperature difference and radiation asymmetry temperature wherefore improving the PMV from-1.6 to-1.The lateral air supply coupled with asymmetric radiation heating could potentially improve the thermal comfort of occupied area,while the comprehensive effect of thermal environmental improvement,energy-saving,and cost-effectiveness needes to be further investigated.

Experimental and numerical investigation of gas diffusion under an urban underground construction

Rapid increase of urban underground constructions has a great consideration of underground environment safety and how to expel toxic gasses out of tunnels effectively.The utility tunnel is a typical urban tunnel construction with multiple underground pipelines including gas pipelines,and it is necessary to investigate characteristic of gas diffusion and monitor gas leakage to ensure tunnel safety.In this study,the experimental measurements of airflow and gas distributions were conducted in a 10 m full-scaled utility tunnel mockup,and gas diffusion characteristic was also investigated.Numerical simulation of utility tunnel leakage was also conducted by computational fluid dynamics(CFD).Different turbulence models and different air supply diffuser models were compared via the experimental results based on visualization and the relative root-mean-square error(RRMSE)index,which quan-titated the difference between the numerical and experimental results.The results showed that the standard k−εturbulence model and random air opening model could provide better results than other models.According to the experimental data analysis,it was necessary to consider the optimization of monitoring detector arrangements in actual utility tunnels.This study provided basic experimental data and the validated numerical model for the leakage source identification and underground tunnels simulation research.

Uniformity and energy evaluation of equal cross-section ventilation system(ECVS)for long tunnel in underground buildings

Uniform ventilation is important for the safety of long tunnel in underground buildings,it is difficult to install the large size air duct to ensure the centerline of each cross-section of the traditional variable cross-section ventila-tion system(VCVS)superimposed on the same horizontal axis,which is significant to the ventilation uniformity,energy consumption and installation convenience of the VCVS.On the contrary,each cross-section of the Equal Cross-section Ventilation System(ECVS)has the same horizontal axis,therefore,it is more convenient to manu-facture and install the large size air duct in the underground long tunnel and achieve uniform ventilation.This study proposes an ECVS,using computational fluid dynamics(CFD)numerical simulation analyzed the influences of main duct velocity,aspect ratio,and outlet numbers on uniformity and energy consumption per unit air vol-ume(ECPV).It revealed that when each ventilation equalizer’s valve Angle𝛽is given,uniformity of air supply decreases slightly with an increase in the inlet velocity.When the air supply main duct aspect ratio increases,the outlet velocity standard deviation range is from 0.22 to 0.34.When outlet numbers N=7~12 and𝛽are constant,air supply uniformity and resistance coefficient𝜉also decrease with the decrease of outlet numbers.The outlet number has a significant influence on the uniformity of system air supply,main duct velocity,and aspect ratio are relatively small.ECPV is positively correlated with the main duct velocity and outlet number,and is negatively correlated with aspect ratio.