Virtual design and performance prediction of a silencing air cleaner used in an I.C.engine intake system

This paper reports results of the authors’ studies on the virtual design method used in the development of low noise intake system of I.C. engine. The resulting high pass-by noise at level above the legislative target at full throttle when engine speed was around 5200 r/min necessitated a BEM-aided redesign task, following the typical process of design and development of an intake system. During the initial design, based on the acoustic theory and the requirements (1. The air flux of the redesigned should equal to or exceed the value of the original flux; 2. The filtering area must not be degraded), and considering the constraint of space in the engine compartment, total volume and rough internal dimensions were determined. During the detailed design, the exact internal dimensions of the air cleaner were determined, and an effective method was applied to improve the acoustic performance at low frequency. The predicted sound power of the intake system indicated that the objective of reducing the overall engine noise by minimizing intake system noise was achieved.

Experimental and numerical analysis of an air cleaner's acoustic performance

To improve acoustic performance of an air cleaner system,both experimental and theoretical studies were carried out.The air cleaner＇s acoustic numerical model was built by finite element methods（FEM）.Acoustic parameters of filter paper imported in the FEM model were calculated according to experiential formulas.Based on the models,the cleaner＇s acoustic character of transmission loss（TL） was computed.To verify the numerical results,TL results of the real air cleaner with or without filter paper were tested by four-microphone transferring function method.The experimental results show that the filter paper influence acoustic performance of the air cleaner significantly,especially in mid and high frequency band,and should be considered in numerical simulation.Comparisons between experimental and numerical results show that the numerical model is accurate enough to be used in multi-scheme acoustic optimization.Based on our study,TL results of two schemes were calculated and analyzed,which is useful to the air cleaner＇s final design decision.

Effectiveness of air cleaner on mitigating the transmission of respiratory disease in a dental clinic environment

In dental clinics with an open floor plan,the risk of patient-to-patient transmission of respiratory disease is a concern.During dental procedures large amounts of bioaerosol are produced and patients cannot wear personal protective equipment.This paper examines how to effectively deploy air cleaner to reduce the infection risk in dental clinics with an open floor plan.Various locations of air cleaners at various clean air delivery rates(CADRs)were investigated.The dispersion of bioaerosol was studied through numerical simulations,and risk assessment was performed by a dose-response method.The findings indicated that dental patients downstream of the background ventilation have a higher infection risk than those to the left and right of an infected patient(i.e.,the source).The lowest infection risks for the adjacent patients were found when the air cleaner was place opposite to the dentists,i.e.,on the floor at low CADR levels of 2.2 m^(3)/min or on the bench at CADR levels of 4.4 m^(3)/min or greater.The results of this study indicated that air cleaner can mitigate the risk of patient-to-patient transmission of SARS-CoV-2 in dental clinics with an open floor plan.Background CADR levels determine the optimal placement of air cleaners.

Field measurement of the impact of natural ventilation and portable air cleaners on indoor air quality in three occupant states

Natural ventilation(NV)has been considered a simple and effective method of ventilation.However,the intro-duction of NV does not achieve better indoor air quality(IAQ)when the outdoor atmospheric environment is polluted.Therefore,portable air cleaners(PACs)are increasing in use in recent years,but their effectiveness is highly dependent on the residents’habits.A typical residence in Xi’an,China was selected to examine the effects of the use of NV alone and the use of NV and PACs together on IAQ in the three occupant states,i.e.,unoc-cupied,sleeping and leisure.Parameters,such as temperature,relative humidity,CO_(2),and PM_(2.5)concentration were measured when changing the window opening and the position of the PAC.The results showed that in the unoccupied state,opening the inner door can promote a more uniform thermal and humid environment.In the sleeping state,the I/O ratio of the PM_(2.5)concentration was the lowest when the window opening of the bedroom was 1/2 or 3/4,with a mean value of 0.3.In the leisure state,only using NV,when the purification rate reaches 90%,the mean purification time of each window opening in the living room is 87.5 min.The mean purification time was reduced to 25 min when both NV and PAC were used.The on-site purification efficiencies were 91.0%and 94.5%,when the window opening was 1/2(i.e.,the PAC was placed in the center of the room)and 3/4(i.e.,the PAC was placed away from the outer window),respectively.

Experimental characterization of the removal efficiency and energy effectiveness of central air cleaners

This study assessed six commercially available in-duct air cleaning devices which are designed to be mounted in the central ventilation system of offices or commercial buildings.The selected devices use different air cleaning technologies:mechanical filtration,electrostatic precipitation,gas filtration,ionization/cold plasma,photocatalytic oxidation(PCO)and catalysis under UV light.They were tested against particles,a mixture of volatile organic compounds containing acetone,acetaldehyde,toluene,heptane and formaldehyde,and two bio-contaminants:Aspergillus brasiliensis(fungus)and Staphylococcus epidermidis(bacteria).Two different test rigs were used.The single pass efficiency of each device was determined for three airflow rates,corresponding to face velocities ranging from 0.9 to 2.7 m/s,and two sets of temperature and humidity that are representative of indoor air conditions in wintertime and summertime.The concentration of the chal-lenge volatile organic compounds was also varied in the 30 to 100μg/m^(3)range as a way to characterize their influence on efficiency at realistic concentration levels for non-industrial buildings.Measurements of ozone and formaldehyde concentration downstream of the air cleaners were carried out to determine the emission rate of by-products into the air stream.Finally,the energy issue was addressed by measuring the electric power drawn and pressure loss of the devices.The results showed that two devices,namely a radiant catalytic ionizer and a plasma ionizer,had a very low single pass efficiency against all the challenge pollutants.The association of the plasma ionizer and the electrostatic precipitator did not produce a synergetic effect between the two technologies either,contrary to what their manufacturer claims.Finally,three of the six devices tested were effective in terms of pollutant removal,but only two had an acceptable energy effectiveness in view of their use in low or zero energy buildings.Their energy effectiveness ranged from a few thousand m^(3)/kWh for VOCs at the highest airflow rate(3600 m^(3)/h),to more than 60000 m^(3)/kWh for particles and bio-contaminants at 1200 or 1600 m^(3)/h.These results are at least one order of magnitude higher than the majority of stand-alone air cleaners.Moreover,they suggest that optimal IAQ and energy conditions can be achieved if variable air volume control methods are used to maintain indoor temperature and humidity.

Development of a Coil-Shape Photocatalysis-Plasma Synergistic Reactor for a Practical and Long-Term Usable Air-Cleaner

A novel air-cleaner with a coil-shape photocatalysis-plasma synergistic reactor was developed. The air-cleaner showed 95% ± 1% reduction of a TVOCs concentration in tobacco smoke at “single-pass” condition. Air-purification activity of the air-cleaner was stably-maintained after the treatment of 12,000 cigarettes of tobacco smoke.

GB/T 18801《空气净化器》新旧标准差异分析

通过对2022版和2015版国家标准《空气净化器》进行差异性分析,从范围、规范性文件、术语和定义、分类、要求、实验条件、检测规则和标志等角度全面解读2022版标准的主要变化,从而助力企业、消费者、相关检测机构更好地理解和运用本标准。

空气净化器甲醛净化能效的测量结果不确定度评定

净化能效作为评判空气净化器能耗高低的关键指标,更贴合国民需要。2023年5月1日GB/T 18801—2022《空气净化器》正式实施,新标准更改了净化器的能效要求,删除了能效分级,也提高了要求。因此,高能耗产品将因无法达标而被淘汰。本文主要依据标准中甲醛净化能效的测定方法,对测量结果的不确定度影响因素进行分析和评定。结果表明,仪器的重复性测量和示值误差引入的不确定度对测量结果的影响较大。

微生物洁净空气量试验方法探索研究

当前国内空气净化器产品标准体系关于细菌、病毒等微生物气溶胶的净化性能评价指标主要为空间去除率,而市面上主流的空气净化产品大多数都能达到99.9%,这使得消费者难以从中区分微生物净化能力高低,不利于有微生物净化场景需求而的消费者合理选型。本研究结合传统GB/T18801的洁净空气量“衰减法”试验原理和GB21551.3-2010的除菌率试验方法,提出了一种可复现强、成本低的微生物洁净空气量试验方法,填补国内微生物洁净空气量试验方法空白,为空气净化产品国标标准体系完善微生物净化性能评价指标提供了新的思路方向。

某重型专用车进气系统设计开发

文章以某重型专用车进气系统为研究对象,利用有限元分析软件对空滤器及底座支架进行静强度和模态分析。基于频域加速方法,在电磁振动台上进行振动试验,通过台架试验验证了新设计支架的可靠性;同时,在实验室进行振动前后空滤器总成性能指标的验证,确保满足产品性能要求。综上所述,新的设计结构在满足设计要求的同时,还验证了仿真分析的准确性,缩短了整车开发周期和成本。为后续新产品研发积累经验并提供参考依据。

基于空气动力学谷物清选技术的研究进展

空气动力系统是谷物清选设备的重要组成部分。分析汇总了空气动力学技术在谷物清选中的应用及研究进展,并指出了未来的发展方向,旨在为空气动力学谷物清选技术的应用与发展提供帮助。为实现谷物清选目标,不同清选场合采用相应的清选方式,然而气流特性及谷物的颗粒特性对基于空气动力学谷物清选的清选效果影响显著。当谷物颗粒特性变动范围一定、清选设备机构调节量及喂料量不变时,细数谷物清选效率的影响因素,其中,空气动力场的分布形式、均匀性及稳定性对谷物清选效果有直接影响。谷物清选工作中,弄清空气动力场中气流稳定性、均匀性的分布规律及影响因素,厘清谷物分级质量作用机理,保证空气动力系统的均匀性、稳定性与整个清选系统的匹配性成为谷物高效分选的关键。

相对湿度对空气净化器颗粒物衰减速率的影响

为了探究室内相对湿度对空气净化器净化颗粒物效果的影响,通过实验研究空气净化器对不同粒径颗粒物衰减速率的影响,同时研究有无加湿环境条件以及不同相对湿度对空气净化器颗粒物衰减速率的影响。结果显示:室内颗粒物直径越大,污染物浓度衰减越快。空气净化器对颗粒物的净化过程分为3个阶段:初始段、快速净化段和稳定段。加湿器的运行只对快速净化段内颗粒物的净化有促进作用;室内空气相对湿度为30%~50%时,相对湿度的变化对颗粒物净化效果的影响较小;室内污染物初始浓度较低(10~900μg/m3)时,随着相对湿度增加,PM2.5的浓度迅速衰减,净化效果增强。

基于盲分离的飞机座舱空气净化器异常噪声故障检测方法

针对使用飞机座舱空气净化器异常噪声故障检测过程中面临的信号分离效果不明显而导致检测结果存在误差的问题,提出了基于盲分离的飞机座舱空气净化器异常噪声故障检测方法。根据飞机座舱空气净化器源信号性质,采用特征矩阵联合近似算法构建协方差矩阵,并分解特征。在对特征进行白化处理之后,对酉矩阵进行估计,从而获得源信号的估计结果。定义四阶累积量函数,采用盲源分离算法分离混合信号,获取回波信号。采用基于盲分离算法分析回波信号频谱,通过对比有无故障情况下的频谱特性,获取故障报警阈值,以该阈值为判断依据,检测空气净化器异常噪声故障情况。由实验结果可知,所提方法检测结果与实际异常故障状态结果拟合,与实际检测结果存在最大为2 dB的声压误差,具有精准检测效果。

基于试验验证的家用新风机净化性能评价方法

相比空气净化器,家用新风机能进一步地排出室内累积的二氧化碳CO_(2)和甲醛、TVOC等化学污染物,带有热交换器的新风机还可以减少热/冷损失,是新兴的室内空净产品。通过试验舱模拟家用新风机的实际工作状态,针对室外污染物颗粒物建立净化性能评价方法;并选用大约30台不同类型新风机机型进行多次测试,同时对约10个型号的同一新风机重复测试,重复试验的偏差在3%以内,通过验证净化效果的一致性证明了方法的可行性。以上结果说明,采用的试验模拟舱及净化性能测算方法可以用于相关产品的性能评价。

空气净化器对车内挥发性有机物去除率的研究

文章简述了车内挥发性有机物(VOCs)危害,介绍了客车、乘用车空气质量和客车用空气净化器现行标准的情况。根据现有标准的缺点提出了延时评价法和对比评价法,分析两种方法的利弊及两种方法的测试结果,并对空气净化器进行了评价,为企业对空气净化器的选择提供了科学依据,倡导引领企业执行健康出行的理念。提出的延时评价法可以与车内空气质量的测试方法相结合,不需要单独进行空气净化器对VOCs去除率的检测试验,为企业节省时间和检测费用成本。

2021版《全球空气质量指南》所传递的重要启示

新冠瘟疫猛袭全球,让世界各国民众意识到,关注人类健康和生存应是当前重要的课题。在此背景下世界卫生组织2021发布了新版的《空气质量指南》(WHO AQG-2021),新版较2005年旧版,对空气环境质量提出了更严格的要求,扩宽了与国内现行标准的差距,此动向值得空调净化行业特别重视。介绍了WHOAQG-2021的主要修订内容及其科学依据,讨论了国内空气质量持续改善的现状和未来的走势,分析了国内应对WHOAQG-2021的措施,以及空调净化行业为适应WHO对室内空气环境更高要求所带来的机遇,并具体提出了一些需要关注与研发的方面,供同行参考。

基于仿真模型的空气净化器性能试验关键影响因素研究

本文通过构建30 m3标准试验舱仿真模型进行数值模拟,并依据GB/T 18801-2022《空气净化器》标准要求,对空气净化器性能开展对比试验,结合仿真分析结果与对比试验数据综合研究循环风扇风量、产品摆放位置、产品摆放朝向、新风量等关键试验因素对空气净化器性能试验的影响,以指导优化试验条件,获取最佳试验效果。研究结果表明:循环风扇风量和产品摆放位置对气流组织分布影响较大,产品摆放朝向影响较小,新风量影响可忽略。最佳采样区域可优先选取“相对试验舱地面高度0.5 m~1.0 m,离墙壁距离应大于0.7 m,避开循环风扇和空气净化器新风口”。

空气净化器长效净化气态污染物评价方法研究

在现行国标GB/T18801-2022《空气净化器》基础上,开发了低浓度单成分甲醛加载模型和低浓度混合成分(甲醛和甲苯)加载模型,通过对三种加载方式的加载量、加载前/后洁净空气量(CADR)变化率的分析,比较三种加载方式对空气净化器长效净化气态污染物性能的影响。结果表明,使用同一空气净化器,按现行国标评价,当加载量达到指定量时,甲醛CADR仅衰减6.2%。而使用本文两种长效评价方法,随着长时间处理低浓度污染物,净化器的甲醛CADR指标会明显下降,且污染物成分越复杂,甲醛CADR下降越明显。因此采用低浓度混合成分(甲醛和甲苯)加载模型,测试条件更加严苛,更贴近真实使用场景,故能够准确评价空气净化器真实性能,为相关测试方法及标准的制定提供借鉴。

基于BP神经网络预测某空气净化器环境电压的研究

为实现某空气净化器环境电压的智能检测,运用sigmoid激活函数,构建了一种基于温升曲线预测环境电压的BP神经网络模型。结果显示,当输入层神经元数为27~53个,隐含层神经元数为25个时,对环境电压的预测能力较好。训练集的环境电压的实际值与预测值的相关系数为0.996,模型误差范围为-2.24%~5.26%,评估新数据的相对误差较小,具有良好的预测性,研究结果显示电压识别模型可用于智能预测环境电压。