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.

Influence of the Channel Design on the Heat Exchange Characteristics of Pulsating Flows in the Supply System of an Engine

Heat engines based on reciprocating machines remain in demand as energy converters in a variety of industries around the world.The aim of the study was to evaluate the gas-dynamic,consumable and heat exchange characteristics of non-stationary air flows in a supply system with transverse profiling of valve channels based on experimental studies.Valve channels with cross sections in the form of a circle,square and triangle were used to control the consumable and heat exchange characteristics of the flows in the supply system of the reciprocatingengine model.The article presents data on changes in local velocity,volumetric airflow and instantaneous heat transfer coefficient of non-stationary airflow in supply systems with different valve channel designs.A spectral analysis of the pulsations of the local heat transfer coefficient was also performed.The Nusselt number was calculated for the studied supply systems.The figured valve channels lead to an increase in the volumetric airflow through the supply systemupto32%comparedwiththe basic configuration.The useof a square valve channel leads to suppression of heat transfer(drop is about 15%)compared to the basic supply system,and the use of a triangular valve channel causes an intensification of heat transfer(growth is about 17.5%).The obtained data can be useful for refining mathematical models,adjusting machine learning algorithms,and improving design methods for supply systems of reciprocating machines to improve their technical,economic,and environmental characteristics.

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.

Thermal stratification level of low sidewall air supply with air-conditioning system in large space

The thermal stratification level of low sidewall air supply system in large space was defined. Depending on the experiment of low sidewall air supply in summer 2008,the thermal stratification level was studied by simulation. Based on the simulation of experiment condition,the air velocity and vertical temperature distribution in a large space were simulated at different air-outlet velocities,and then the thermal stratification level line was obtained. The simulation results well match with the experimental ones and the average relative error is 3.4%. The thermal stratification level is heightened by increasing the air-outlet velocity with low sidewall air supply mode. It is concluded that when air-outlet velocity is 0.29 m/s,which is the experimental case,a uniform thermal environment in the higher occupied zone and a stable stratification level are formed. When the air-outlet velocity is low,such as 0.05 m/s,the thermal stratification level is too low and the air velocity is too small to meet the human thermal comfort in the occupied zone. So,it would be reasonable that the air-outlet velocity may be designed as 0.31 m/s if the height of the occupied zone is 2 m.

Air entrainment in a vertical dropshaft with limited air supply

Dropshafts are vertical structures widely used in urban drainage systems and buildings for water transportation.In this paper,a physical model study was conducted to investigate the air entrainment in the dropshaft under various flow regimes with and without air ventilation.Observed from the experiments,the air entrainment mechanisms varied with the water flow regimes in the dropshaft.When there was no water plug formed in the dropshaft,air could be supplied directly from downstream.Once the water plug was formed,while without venting,the air was replenished only from downstream intermittently and then in the form of large air bubble traveling upwards to the airspace at the top;while with venting,air was mainly replenished from the dropshaft top and no large air bubble was observed.The experimental results also showed that the amount of entrained air in the dropshaft with venting was greater than that without venting.

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.

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.

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.

拱架送/回风方式对日光温室冬季作物冠层区热环境的影响

传统日光温室被动的热环境调控模式难以满足温室作物冠层区空气温度和速度调控需求,且能源利用效率低下。为了改进日光温室热环境精准调控方法和提高温室能源利用效率,该研究结合日光温室围护结构特点,提出了一种日光温室拱架的送/回风方法,并基于温室作物多孔介质模型,建立了拱架送/回风系统温室的数值传热模型。采用空气温度与速度不均匀系数、气流速度适宜区面积比、能量利用系数以及累计有效积温等评价参数,研究了下送上回、中间回风和上送下回等3种温室拱架送/回风方式对日光温室冬季作物冠层区热环境的影响。结果表明,与中间回风和上送下回通风方式相比,下送上回通风方式对不同作物冠层高度处的空气温度和速度调控的结果最优,且不同作物冠层高度处气流速度适宜区面积比和累计有效积温都最大。当采用下送上回通风方式时,与送风干管风速为9、11和12 m/s相比,送风干管风速为10 m/s的能量利用系数最大,在作物冠层高度0.4、0.6、0.8和1.0 m处的能量利用系数分别为0.976、0.982、0.985和0.987,并且不同作物冠层高度处的空气温度不均匀系数和速度不均匀系数也都最小。因此,下送上回通风方式的推荐送风干管风速为10 m/s。该研究可为日光温室热环境的精准调控提供参考。

数据中心冷却系统研究及应用进展

为加速实现数据中心节能降耗的目标,在合理、高效、最大化地利用自然冷源的同时,更不能忽视机械制冷系统本身能效的提升。加强自然冷却与机械制冷的协同,降低数据中心PUE,充分发挥安全稳定、高效运行的数据中心冷却系统自身能效至关重要。本文通过对气流组织、供/回水温度和冷却系统部件及形式3个方面的研究梳理,总结分析数据中心冷却系统节能提效有关技术研究与应用进展,从而为绿色、高效数据中心冷却系统的研发提供参考和借鉴。

半封闭温室关键系统设计与应用

半封闭温室是近年来新兴温室,其中温室气候走廊和正压送风系统是半封闭温室的关键系统设计。通过对半封闭温室内夏季温度分布的均匀性和风道风速测试试验,验证温室的降温能力和送风系统性能。试验结果表明,SFG5-4型风机配套35 m长风道,送风相对均匀,风速4.3~4.7 m/s;对于温度分布规律来说,在同一水平方向上温室内各点的平均温差1.0~1.8℃,在同一高度方向上温室内各点的平均温差2.2~3.5℃,并且3.5 m湿帘比2.0 m湿帘降温效果好。

大跨度空间非等间距喷口送风空调设计方法

针对大跨度空间负荷分布不均匀的情况,在传统射流公式法的基础上,提出了一种非等间距布置喷口的送风设计方案。结合某酒店多功能厅案例,阐述了如何根据房间负荷分布特点进行喷口的非等间距设计,并利用CFD软件对空调区温度场、速度场及热舒适性指标(PMV、PPD、DR(吹风感造成的不满意度))进行了模拟。结果表明,该方案取得了明显的改进效果,同时也验证了非等间距喷口送风设计方法的可行性。

基于CFD的YJ17卷烟机风室流场分析与优化设计

目的针对ZJ17卷接机YJ17供丝系统中烟丝堵塞、竹节烟和烟支标偏大的现象进行改进。方法采用流体仿真分析软件Solidworks Simulation模拟分析、正交实验及试验验证的方法,设计优化YJ17供丝系统的风室装置,通过模拟仿真不同正压风入口形状、数量、位置对设备运行效率、产品质量的影响,找到三者最优的参数组合。模拟分析发现,在正压风入口形状为圆形,正压风入口数量为3个,正压风入口距离气室边缘的距离为15mm时,风室气流分布更均匀,同时烟丝在离开抛丝辊后受到的下吹风力最大,可使烟丝快速到达吸丝带。结果气室经改进后烟丝堵塞次数降低了39.3%,SD值(20支烟支质量标偏)降低了25%,有效提升了设备的运行效率和卷烟产品的质量。结论基于仿真及正交实验结果,优化了风速出风口位置和直径,气室的流场分析结果可为烟丝吸丝成型及风室结构优化提供一定技术支持。

PEMFC空气系统流量和压力协同控制策略设计

为提高质子交换膜燃料电池(PEMFC)空气系统的动态响应性能,避免局部缺气而导致其输出性能降低等问题的出现,针对空气系统存在流量和压力耦合的问题,分别采用PID、前馈解耦控制和模型预测控制(MPC)对空气系统进行控制,通过仿真和台架测试,验证控制算法的有效性。结果表明,两种控制算法相比较PID均具有较好的控制效果,空气流量和空气压力均能快速跟随设定值,PEMFC发动机的输出性能平稳。

火电耦合压缩空气储能技术研究进展及展望

火电耦合压缩空气储能技术作为一种提升传统火电机组灵活性和经济性的有效手段,近年来受到了广泛关注。该文从分析火电耦合压缩空气储能技术在提升电网调峰能力、促进可再生能源整合等方面的重要意义出发。首先,介绍典型耦合系统的结构组成与工作原理;然后,探讨耦合系统中关键设备的技术现状和面临的挑战;之后,梳理火-储耦合系统的集成方案设计、调峰运行优化以及经济性评估的研究现状;最后,针对当前技术难点,展望未来火电耦合压缩空气储能技术的研究方向与重点。该文旨在为今后相关领域研究提供参考与借鉴,推动其持续发展和创新。

隧道防火门分流对端部临界送风风速的影响

在单洞双线轨道交通隧道发生火灾时,人员从火源上游防火门疏散,防火门的分流作用将影响端部送风风速。采用理论计算与数值模拟相结合的方法探究其影响关系,首先通过理论分析推导出了端部临界送风风速公式;随后,利用PyroSim软件建立了全尺寸模型,并针对不同数量防火门、火源热释放速率、隧道高度的分流情况进行了研究。结果表明:在相同火源热释放速率下,防火门的分流流速随着防火门开启数量的增多而减少;相同位置防火门的分流流速随火源热释放速率的增大呈指数增长的关系;防火门总分流量随防火门开启数量与热释放速率的0.3次方之积呈线性增长的关系,而受隧道高度的影响较小;结合理论推导,建立了端部临界送风风速的数学模型。研究结果为隧道火灾情况下的人员疏散和通风设计提供了科学依据。

强制通风空浴式翅片管送风方式优化

基于FLUENT模拟研究底送顶排、顶送底排、侧送顶排、侧送底排4种送风方式对液化天然气(liquefied natural gas,LNG)空浴式翅片管气化性能的影响,采用Lee模型研究管内LNG的相变气化过程,结合管内流体温度变化分析单根翅片管气化性能受送风方式和送风速度的影响。结果表明:侧送风时翅片管周围出现低风速边界层,背风侧易形成低换热效率的尾流区;当送风速度由2.8 m/s增大到3.8 m/s和由3.8 m/s增大到4.8 m/s时,侧送底排方式下空气侧换热系数最大值分别增长3.92 W/(m^(2)·K)和2.16 W/(m^(2)·K);直送风时边界层分布均匀,最大推荐送风速度为3.2 m/s,顶送底排方式对翅片管气化性能的提升效果优于底送顶排方式;当其他条件相同时,侧送顶排为最佳送风方式;采用侧送顶排强制通风的空浴式气化器(ambient air vaporizer,AAV)气化性能显著优于自然通风AAV。

基于响应面模型的智能台架供风系统开发

为解决瞬态工况下,汽车主动进气格栅(AGS)开度及风扇转速实时调整,换热器进风量时刻改变,热管理测试台架风机无法实时为换热器提供精准瞬态供风这一问题,应用计算流体力学(CFD)仿真技术,分析了换热器进风量与车速、AGS开度及风扇转速之间的关系,并构建了数学模型,模型预测误差小于6.6%。将该模型置于CANOE设备中,与VN1640设备及风机系统连接,可实时采集车速、AGS开度及风扇转速CAN信号,计算换热器进风量,从而控制风机输出相应风量,实现了台架风机为换热器提供精准、实时供风这一目标。

地铁站台公共区弥散送风系统结构参数研究

地铁站台公共区弥散送风系统(DASS)可以提供舒适的热环境,其结构设计参数会影响DASS送风效果。采用数值模拟方法,研究不同弥散送风板开口率、送风口数量、静压室高度以及下部空间高度等结构参数对站台公共区DASS送风效果的影响。结果表明:站台公共区气流分布均匀性和人员热舒适性随弥散送风板开口率和送风口数量的增加而增加;静压室高度在1.1m左右时的送风效果最好;下部空间高度越高,气流分布越均匀,但冷风感越强,综合初投资和系统送风效果,下部空间最优高度为3m。