Improvement of uniformity in cultivation environment and crop growth rate by hybrid control of air flow devices

A complete control type plant factory has high efficiency in terms of cultivation area by constructing vertical multiple layered cultivation beds.However,it has a problem of irregular crop growth due to temperature deviation at upper and lower beds and increases in energy consumption by a prolonged cultivation period.In this work,air flow rate inside a facility was improved by a hybrid control of air flow devices like air conditioning and air circulation fan with an established wireless sensor network to minimize temperature deviations between upper and lower beds and to promote crop growth.The performance of proposed system was verified with an experimental environment or Case A wherein air conditioning device was operated without a control algorithm and Case B wherein air conditioning and circulation fans were alternatively operated based on the hybrid control algorithm.After planting leafy vegetables under each experimental condition,crops were cultivated for 21 days.As a result,Case B wherein AC(air conditioning) and ACF(air-circulation fan) were alternatively operated based on the hybrid control algorithm showed that fresh mass,number of leaves,and leaf length for the crops grown were increased by 40.6%,41.1%,and 11.1%,respectively,compared to Case A.

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.

Effects of O_(2) addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges(DBDs)have been widely used in ozone synthesis,materials surface treatment,and plasma medicine for their advantages of uniform discharge and high plasmachemical reactivity.To improve the reactivity of DBDs,in this work,the O_(2) is added into Ar nanosecond(ns)pulsed and AC DBDs.The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O_(2) contents are investigated with optical and electrical diagnosis methods.The DBD uniformity is quantitatively analyzed by gray value standard deviation method.The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_(e).The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_(e) with the ratio of two emission lines.It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time.With the addition of O_(2),the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O_(2)^(-),which promotes the filamentary formation.While,in AC DBD,the added O_(2) can reduce the intensity of filaments,which enhances the discharge uniformity.The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD.The ratio of Ar emission intensities indicates that the T_(e) drops quickly with the addition of O_(2) both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_(e) and n_(e) than AC DBD.The results are helpful for the realization of the reactive and uniform low temperature plasma sources.

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.

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.

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.

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.

基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断研究

该文提出一种基于径向气隙磁密和定子电流的永磁同步电机均匀退磁故障诊断方法。首先,建立电机的d轴等效磁路模型,分析均匀退磁故障后径向气隙磁密的变化规律;然后,获取电机的径向气隙磁密和定子电流信号,对各极下径向气隙磁密幅值进行归一化处理,并绘制雷达图,根据雷达图和比较相同定子电流幅值下健康电机和故障电机的各极下径向气隙磁密幅值的平均值,来诊断均匀退磁故障;利用空载各极下径向气隙磁密幅值的平均值计算故障程度。最后,仿真和实验结果均验证所提均匀退磁故障诊断方法的有效性。

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。

气幕均匀性影响因素及其隔尘效果研究

近年来,空气幕作为一种有效隔绝易于扩散粉尘的装置,被频繁地用于矿山、隧道施工过程中产尘较多的场所,而均匀的气幕会带来更佳的隔尘效果。运用Fluent数值模拟结合相似实验的方法分析了气幕直径和气幕内部风道结构变化对气幕均匀性的影响,并将设计后可以均匀供风的气幕安装在实际施工隧道模型中模拟分析其隔尘效果。结果表明:直径增加,供风装置内气流轴向惯性力降低,有充足的时间改变流出方向,气幕装置轴向静压更加均匀,形成气幕更加均匀,但直径的变化对气幕均匀性的影响不是线性变化的,即存在一个临界直径使直径继续增加对均匀性的改善效果不明显,并且气幕临近直径的范围会随供风装置长度的增加而增加;在长度1 m、临界直径180 mm的气幕装置基础上,依据风道设计原理安装计算出的弧高为149.9 mm的楔形扇面阻体后,气幕装置内部平均压力梯度从38.4 Pa/m降低到19.3 Pa/m,出口风速均匀度从87.6%提高到93.2%,气幕均匀性显著提升;安装气幕后,隔尘区域内回弹的含尘气流被阻隔,区域内风流变得混乱复杂、涡流增加,粉尘停留时间增加,相对较大的粉尘颗粒有更长的时间沉降。整个隔尘区域粉尘浓度明显升高,气幕隔尘效果显著。

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。