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植被屏障滞尘特性研究与多孔屏障仿生设计

Study on Dust Retention Characteristics of Vegetation Barriers and Bionic Design of Porous Fence

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【Author in Chinese】 赵冬森

【Supervisor】 郭丽

【Author's Information】 吉林大学, 农业机械化工程, 2020, 硕士

【Abstract in Chinese】 随着经济快速发展,开放源颗粒物对大气环境的污染越发严重,逸散的大气颗粒物会引起雾霾、料堆材料浪费、危害人体健康以及制约经济的发展。减少开放源颗粒物最有效的管理策略之一是在大气颗粒物的扩散过程中设置植被屏障或者人工多孔屏障来阻滞拦截颗粒物。植被屏障能作为一种多孔介质,可将不同粒径颗粒物滞留于树冠内部,且可通过枝叶摆动调整孔隙度以适应风力变化,但植被生长受水资源、土壤质地和季节的限制。人工多孔屏障,包括刚性和柔性防风抑尘网,则没有以上限制,其主要是通过降低风速来减少颗粒物的逸散,然而对微细颗粒物的拦截效果较差,降风效果与作用在屏障上的风荷载存在矛盾,且最佳的屏障开孔形式限制在固定的孔隙度。因此,学习和借鉴植被屏障的滞尘优势特点,改进现有人工多孔屏障的设计,提高其改善风环境以及阻滞拦截微细颗粒物的性能,对减少开放源颗粒物的释放具有重要意义。本文以东北地区典型绿化树种紫叶稠李、樟子松、山丁子和三角枫为研究对象,通过研制蛋鸡舍颗粒物,模拟其逸散,对四种植被屏障进行颗粒物阻滞试验,得到不同树种对颗粒物的阻滞能力,分析了植被屏障的风速衰减效率、环境温度和相对湿度对颗粒物阻滞能力的影响,并从中了解植被屏障阻滞吸附颗粒物的宏观机理。结果表明,本研究中颗粒物扩散阻滞模拟试验可以采用,植被屏障能有效拦截滞留微细颗粒物。不同植被屏障对颗粒物的阻滞效率存在差异,依次为紫叶稠李>樟子松>山丁子>三角枫,其中紫叶稠李对PM1、PM2.5和PM10的阻滞效率分别为73.80±15.61%,73.73±15.80%和67.35±19.55%;植被屏障对风速的衰减效率依次为紫叶稠李>三角枫>樟子松>山丁子,紫叶稠李对风速的衰减效率为41.14±6.91%。二者排序并不相同,说明植被屏障阻滞颗粒物能力还受其他因素影响,因此采用灰色关联度分析发现植被屏障风速衰减率对植被阻滞颗粒物效率影响最大,其次为相对湿度,最弱为温度。得到的仿生滞尘原理是增加含尘气流与植被屏障的碰撞损耗风能来降低风速可以提高植被屏障对颗粒物的阻滞效率。此外,植被叶片的微观形貌也是影响其滞尘能力的关键因素。本研究采用扫描电镜对经过颗粒物阻滞试验后的四种树叶微观形貌进行观测,并用X射线能谱仪测定树叶表面滞留颗粒物的元素组成,之后采用超景深三维显微镜测定了干净叶片的面粗糙度,从微观角度探索植被屏障阻滞吸附颗粒物的仿生原理。结果表明,植被叶片面粗糙度高有利于植被滞尘,且四种树叶近轴面粗糙度高于远轴面,能更好的滞留自然沉降的颗粒物。紫叶稠李叶表附着颗粒物较多,越靠近叶片主叶脉,颗粒物沉积越多,有利于颗粒物附着的结构为“山脊状”条纹和由细条纹组成的大条纹,不利于颗粒物的附着的结构为气孔周围蜡管;樟子松叶面由气孔带和片状条纹带在纵向交叉排布,片状条纹空间比气孔区域滞留的颗粒物多,有利于颗粒物滞留的结构为条纹结构,且其所部位面粗糙度(11.35±3.41μm)高,多尘环境有絮状纤毛堵塞的气孔不利于颗粒物的滞留;山丁子叶面在条纹间、气孔周围和纤毛下都附着有颗粒物,叶面条纹区域面粗糙度低于紫叶稠李,不利于颗粒物滞留,远轴面的气孔和纤毛结构有利颗粒物滞留;三角枫叶片近、远轴面靠近叶脉的位置滞留颗粒物多,有利于附着颗粒物的结构为凹槽和网状纤毛结构,叶远轴面的气孔结构滞留颗粒物少。四种树叶表面的颗粒物包含蛋鸡舍颗粒物的所有元素:C、N、O、F、Na、Mg、Al、、Si、P、S、Cl、K、Ca、Fe、Ti、Mn。最后,受植物枝叶排列方式、叶面滞尘微结构和植被随风调整孔隙度的启发,在本研究中设计了5个仿生多孔屏障,并与商用的刚性和柔性防风抑尘网进行比较。在不同风速条件下的风洞中,对这些多孔屏障的遮蔽能力和阻滞颗粒物效率进行了评估。结果表明,与传统多孔屏障相比,所有仿生多孔屏障在降低风速和颗粒物浓度方面都有更好的效果。仿生多孔屏障能更有效地捕捉PM10,其中B-4L-n仿生多孔屏障在进口风速为1 m·s-1、2 m·s-1和3 m·s-1时对PM10的阻滞率分别为51.87%±4.09%、56.74±1.82%和52.03±2.30%。而在相同风速水平下,仿生多孔屏障对PM2.5的降幅最小。此外,在5个仿生多孔屏障中,材料为无纺布的四叶开口型仿生多孔屏障在风速和PM降低方面表现最好。仿生叶片的羽状复叶排列结构和可调的开口增加了空气的湍流度,从而增加了颗粒物与多孔屏障的相互作用表面积,从而提高多孔屏障的遮蔽能力和对PM的阻滞率。本研究提出的仿生多孔屏障可以进一步发展和研究,以制造出能适应环境不同风速且捕捉PM2.5能力更强的多孔屏障。

【Abstract】 With the rapid development of economy,the pollution of particulate matters(PM)from open source becomes more and more serious.Escaped atmospheric particles can cause smog,waste of piled materials,negative effects on human health,and restrict economic development.One of the most effective management strategies to reduce particulate matter from open source is to set vegetation barrier or artificial porous barrier to block and intercept the particulate matter during the diffusion process.Vegetation barrier(VB)as a porous medium,can trap particles with different particle sizes in the canopy and adjust the porosity by swinging branches and leaves to adapt to wind changes.But the growth of vegetation is affected by water resources,soil and seasons.However,artificial porous barriers have no such limitations.Currently,commercial artificial porous barriers,including rigid and flexible windbreak fence,can reduce the dispersion of particles by reducing the wind speed.However,these commercial artificial fences are poor at trapping fine particles.In addition,there is a contradiction between the wind speed reduction and the wind load acting on the barrier.Moreover,the opening form of the hole on the porous barrier is fixed leading to fixed porosity of the fence.Therefore,it is of great significance to study the vegetation barrier as the bionic prototype to optimize the artificial porous barrier and improve the wind environment and retain fine particles from open sources.In this study,the typical tree species in northeast China were studied,including Padusvirginiana‘Canada Red’,Pinussylvestris var.mongolicaLitv.,Malusbaccata(L.)Borkh.andAcer buergerianumMiq.Powder particles were milled from the collected dust sources in a laying hen house to simulate the dispersion of PM from the laying hen house.The ability of different tree species blocking particles was investigated by establishing natural barriers and conducting tests on the four vegetation barriers.The effects of VBs on the attenuation efficiency of wind speed and PM concentration as well as the influcing factors,such as ambient temperature,relative humidity,and characteristics of vegetation leaves and barriersn,on particle blocking ability were analyzed.The macroscopic mechanism of vegetation barriers blocking and adsorbing particles was identified.The results showed that the simulation test of particle diffusion retardation designed in this study can be used,and the four kinds of vegetation barrier can effectively block fine particles.There were differences in the blocking efficiency of different vegetation barriers on particles,with the order of Padusvirginiana‘Canada Red’>Pinussylvestris var.mongolicaLitv.>Malusbaccata(L.)Borkh.>Acer buergerianumMiq..The blocking efficiency of Padusvirginiana‘Canada Red’on PM1,PM2.5 and PM10 was 73.80±15.61%,73.73±15.80%and67.35±19.55%,respectively.The order of attenuation efficiency of vegetation barriers to wind speed was Padusvirginiana‘Canada Red’>Acer buergerianumMiq.>Pinussylvestris var.mongolicaLitv.>Malusbaccata(L.)Borkh..The attenuation efficiency of Padusvirginiana‘Canada Red’to wind speed was 41.14±6.91%.The above two orders were not the same,indicating that the ability of the vegetation barrier to block particles was also affected by other factors.Therefore,the grey correlation analysis was used in this study.It was found that the wind speed attenuation rate of vegetation barrier had the greatest influence on the efficiency of vegetation blocking particles,followed by the relative humidity and the temperature.The inspiration in bionic fence design is that the collision of particle in the airflow with vegetation barrier can improve the particle blocking efficiency of vegetation barriers.In addition,the microstructure of vegetation leaves was also a key factor affecting their dust retention ability.After particle blocking test,the test of scanning electron microscopy(SEM)was conducted to observe microstructure of four kinds of leaves,and the test of X-ray energy spectrometer(EDX)was conducted to determine the element composition of particles retained on the leaves surface.The surface roughness of clean leaves was also measured by super-high magnification lens zoom3D microscope.The results showed that the high roughness of vegetation leaf surface was beneficial to the dust retention.And the roughness of the near-axis surface of the four kinds of leaves was higher than that of the far-axis surface,which can better retain the naturally settled particles.There were more particles attached to the leaf surface of Padusvirginiana‘Canada Red’leaves.The closer to the main leaf vein of the leaves,the more particles were deposited.The structures conducive to the adhesion of particles were"ridge-like"stripes and large stripes composed of pinstripes.The structure which was not conducive to the attachment of particles was the wax tube around the stomata.Both sides of the needles of Pinussylvestris var.mongolicaLitv were intersected longitudinally by stomata belt and long flaky stripe belt.There were more particles in the flaky stripe space than that in the stomatal area.The structure favorable for particle retention was the stripe structure,and the surface roughness(11.35±3.41μm)of this sampling position was higher than that at other positions.For Malusbaccata(L.)Borkh.,there were particles attached between the stripes,around the stomata,and under the cilia.The surface roughness of the leaf stripe was lower than that of the Padusvirginiana‘Canada Red’leaf,which was not conducive to particle retention.The structures of stomata and cilia in the far-axial surface were favorable for particle retention.The Acer buergerianumMiq.leaves near the vein had more particles.The structures favorable for particle retention were grooves and reticular cilia.The stomatal structure on the far-axial surface of the leaves had fewer particles.The particles on the surface of the tested leaves contained all the elements of the laying hen house particle:C,N,O,F,Na,Mg,Al,Si,P,S,Cl,K,Ca,Fe,Ti and Mn.Finally,inspired by the arrangement of plant branches and leaves,the dust retention microstructure of the leaves and the wind-adjusted porosity of vegetation,five bionic porous barriers were designed and compared with commercial artificial porous barriers.The shielding capacity and particle blocking efficiency of these porous barriers were evaluated in wind tunnels with different wind speed.The results showed that all bionic porous barriers were more effective in reducing wind speed and particle concentration than traditional porous barriers.The bionic porous barriers were more effective in capturing PM10.Among them,the bionic porous barrier of B-4L-n had an retardation rate of 51.87%±4.09%,56.74±1.82%and 52.03±2.30%for PM10when the inlet wind speed was 1 m·s-1,2 m·s-1 and 3 m·s-1,respectively.At the same wind speed level,the bionic porous barrier had the smallest reduction in PM2.5.Among the 5 kinds of bionic porous barriers,the non-woven cloth material with four-leave opening presented the best capability both in reducing wind speed and PM.The arrangement of bionic blades and the adjustable openings increased the turbulence of the air,thus increasing the interaction area between particles and the porous barriers,ultimately improving the shielding capacity of the porous barrier and its retardation rate for PM.The bionic porous barriers proposed in this study can be further developed and studied to create a porous barrier which can adapt to different wind speeds and has a stronger ability to capture PM2.5.

【Keywords in Chinese】 植被屏障多孔屏障风洞阻滞效率
【Key words】 Vegetation barriersporous barrierswind tunnelsretardation efficiency
  • 【Contributor】 吉林大学
  • 【Year of Internet Publish】202008
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