張儷安,刁永發(fā),莊加瑋,周發(fā)山,沈恒根

高梯度磁場(chǎng)提升單纖維捕集PM2.5性能的機(jī)理

張儷安,刁永發(fā)*,莊加瑋,周發(fā)山,沈恒根

(東華大學(xué)環(huán)境科學(xué)與工程學(xué)院,上海 201620)

以鋼鐵廠和有色金屬行業(yè)排放的PM2.5為研究對(duì)象,基于離散相模型DPM(Discrete Phase Model),并加入U(xiǎn)DF自定義編程,研究高梯度磁場(chǎng)下不同入口風(fēng)速、顆粒粒徑、外磁場(chǎng)強(qiáng)度、磁性纖維磁感應(yīng)強(qiáng)度以及磁化率對(duì)捕集效率的影響,并結(jié)合顆粒運(yùn)動(dòng)軌跡和受力情況對(duì)其進(jìn)行分析.結(jié)果表明:當(dāng)0.5μm￡p￡2.5μm,=0.1m/s時(shí),利用高梯度磁場(chǎng)(=0.1T,=0.06T)可以使單纖維捕集PM2.5的效率提高為原來(lái)的4.23倍,得出磁性纖維周圍存在2個(gè)引力區(qū)和2個(gè)斥力區(qū).同時(shí),在高梯度磁場(chǎng)中磁性纖維對(duì)PM2.5的捕集效率隨入口風(fēng)速呈先減小后趨于平穩(wěn)的規(guī)律;而捕集效率隨粉塵粒徑呈先增大后減小的規(guī)律.當(dāng)p=1.0μm時(shí)的捕集效率提升最大,無(wú)論是外磁場(chǎng)強(qiáng)度還是磁性纖維磁感應(yīng)強(qiáng)度,磁性纖維對(duì)顆粒的捕集效率與場(chǎng)強(qiáng)都呈一次函數(shù)關(guān)系,效率增長(zhǎng)率B>H;隨著顆粒磁化率的增加,磁性纖維對(duì)顆粒的捕集呈現(xiàn)兩段線性增長(zhǎng)規(guī)律,前后兩段效率增長(zhǎng)率1>2.當(dāng)顆粒經(jīng)過(guò)高梯度磁場(chǎng)區(qū)域時(shí),入口風(fēng)速、粉塵粒徑、場(chǎng)強(qiáng)對(duì)運(yùn)動(dòng)軌跡影響較大,而磁化率對(duì)運(yùn)動(dòng)軌跡影響較小.

高梯度磁場(chǎng)；PM2.5；捕集效率；磁化率

隨著鋼鐵和有色金屬行業(yè)的發(fā)展,其生產(chǎn)過(guò)程中會(huì)產(chǎn)生大量PM2.5,由于數(shù)量多、沉降速度慢、比表面積大、可作為其它污染物的載體,對(duì)人體健康和大氣環(huán)境質(zhì)量的影響很大[1-2].

為了更好的研究纖維對(duì)顆粒的捕集規(guī)律,國(guó)內(nèi)外研究者從機(jī)理上系統(tǒng)的研究了單纖維對(duì)顆粒物捕集.前期階段研究多集中在經(jīng)驗(yàn)公式和半經(jīng)驗(yàn)公式[3-5]的研究.隨后,為了更好的研究單纖維對(duì)顆粒的捕集規(guī)律,其中一些學(xué)者從不同工況的角度較為系統(tǒng)的考察了影響單纖維捕集顆粒的因素[6-8],這些研究深刻揭示了單纖維在捕集顆粒過(guò)程中隨工況改變的變化規(guī)律.而另一部分學(xué)者則專注于研究顆粒在纖維周圍積聚、沉積位點(diǎn)以及三維樹(shù)枝狀顆粒沉積物的形成過(guò)程[9-11].同時(shí),在研究方法上,DEM (Discrete Element Model)方法的使用[12-13]不僅可以分析單纖維在流場(chǎng)中的放置方式、表面黏附系數(shù)、顆粒直徑以及雷諾數(shù)對(duì)捕集效率等傳統(tǒng)工況的影響,而且顆粒的可視化可以更加清晰的觀察粉塵顆粒被纖維捕集過(guò)程.

通過(guò)總結(jié)發(fā)現(xiàn),當(dāng)前對(duì)于單纖維捕集顆粒的研究主要體現(xiàn)在經(jīng)驗(yàn)公式、工況參數(shù)以及纖維沉積過(guò)程的研究,相關(guān)研究無(wú)法解決PM2.5等微細(xì)顆粒由于存在穿透窗口而難以捕集的問(wèn)題[14].因此,需要在原有的基礎(chǔ)上開(kāi)發(fā)新的技術(shù).

現(xiàn)階段高梯度磁場(chǎng)技術(shù)在處理細(xì)顆?；蛭⒓?xì)顆粒弱磁性物料方面因具有分離能力高,結(jié)構(gòu)簡(jiǎn)單和維護(hù)成本低等優(yōu)勢(shì)而被廣泛使用.Svoboda等[15]對(duì)高梯度磁場(chǎng)分離進(jìn)行研究,通過(guò)增加外磁場(chǎng)、磁介質(zhì)磁化強(qiáng)度可有效提高顆粒物的分離效率.Ravnik等[16]通過(guò)計(jì)算顆粒在流體和磁場(chǎng)力作用下的運(yùn)動(dòng)軌跡,驗(yàn)證了在窄通道中進(jìn)行高梯度磁選的可行性.Baik等[17]對(duì)高梯度磁場(chǎng)研究結(jié)果表明,在流體中作用于顆粒的磁場(chǎng)力與磁通密度和磁場(chǎng)梯度成正比,且捕集顆粒能力方面,高梯度磁場(chǎng)系統(tǒng)要強(qiáng)于永磁性系統(tǒng).Zheng等[18]研究表明高梯度磁場(chǎng)下橢圓截面矩陣和圓形截面矩陣對(duì)于微米級(jí)顆粒捕集效果明顯.通過(guò)總結(jié)發(fā)現(xiàn),雖然利用高梯度磁場(chǎng)對(duì)微細(xì)顆粒的捕集已有研究,但是利用該技術(shù)在纖維捕集粉塵領(lǐng)域的研究卻鮮見(jiàn)報(bào)道,尤其是在鋼鐵和有色金屬行業(yè),由于所排放的粉塵含有鐵磁性物質(zhì)[19]而更容易被捕集.因此為了解決目前單纖維模型存在預(yù)測(cè)與實(shí)驗(yàn)值差別較大的問(wèn)題,通過(guò)UDF編程的方法來(lái)提出改進(jìn)模型,以彌補(bǔ)研究的不足.

其次在研究高梯度磁場(chǎng)下纖維捕集粉塵顆粒的過(guò)程中,磁性纖維可直接通過(guò)紡絲或基體纖維的物理、化學(xué)改性制備.磁性纖維在工業(yè)使用中可分離含塵煙氣中的鐵磁性物質(zhì),通過(guò)后期的間歇性電磁振打方式實(shí)現(xiàn)回收[20];且磁性濾料配合磁性吸附劑可實(shí)現(xiàn)對(duì)燃煤煙氣中痕量Hg0[21]的脫除,在除塵的同時(shí)凈化有毒污染氣體;此外,外磁場(chǎng)的加入可使磁性纖維形成非均勻的致密磁場(chǎng),增加磁場(chǎng)強(qiáng)度.因此,本研究通過(guò)對(duì)高梯度磁場(chǎng)下磁性纖維對(duì)PM2.5的捕集過(guò)程為研究對(duì)象,建立捕集PM2.5的物理模型.基于CFD-DPM方法,加入U(xiǎn)DF自定義編程對(duì)PM2.5在高梯度磁場(chǎng)中的被捕集規(guī)律進(jìn)行數(shù)值模擬,計(jì)算在不同工況下PM2.5的運(yùn)動(dòng)軌跡,考察了入口風(fēng)速、粉塵粒徑、外磁場(chǎng)強(qiáng)度和磁性纖維磁場(chǎng)強(qiáng)度以及顆粒磁化率對(duì)捕集效率的影響,旨在為高梯度磁場(chǎng)下磁性纖維對(duì)PM2.5的捕集優(yōu)化設(shè)計(jì)提供理論指導(dǎo).

1 計(jì)算模型

1.1 氣固兩相流模型

對(duì)于內(nèi)部氣?固兩相流動(dòng)進(jìn)行數(shù)值模擬需先計(jì)算氣相場(chǎng).可采用標(biāo)準(zhǔn)k-ε模型、穩(wěn)態(tài)及不可壓縮模型進(jìn)行數(shù)值模擬.控制方程(連續(xù)性方程、動(dòng)量方程)[22]如下:

文中用二階迎風(fēng)格式SIMPLE算法對(duì)離散化動(dòng)量方程進(jìn)行壓力速度耦合求解,并將連續(xù)性方程及動(dòng)量方程在直角坐標(biāo)系,,方向上的收斂殘差設(shè)定在10?6以內(nèi).一旦獲得穩(wěn)定的氣相流場(chǎng),就將顆粒從進(jìn)口以面射流源形式注入計(jì)算區(qū)域.假定顆粒在流場(chǎng)中做無(wú)旋運(yùn)動(dòng),顆粒的運(yùn)動(dòng)平衡方程表達(dá)式[23]如下:

式中:vp,v分別為顆粒運(yùn)動(dòng)速度和流體速度, m/s;FD為流體的曳力,N;g為重力加速度,m/s2;ρp,ρa(bǔ)分別為顆粒和空氣的密度,kg/m3;FM為通過(guò)UDF編程在高梯度磁場(chǎng)中所受的磁場(chǎng)力,N;Fother為受到的一些可忽略的力,N.

圖1中,通過(guò)建立極坐標(biāo)系將M沿徑向和切向進(jìn)行分解,如下[24]:

式中:0為真空磁導(dǎo)率,2.256′10-6;p為磁化率;和分別為外磁場(chǎng)強(qiáng)度和磁性纖維的磁感應(yīng)強(qiáng)度,T;和分別為極坐標(biāo)下的極徑和極角.

雖然作用在顆粒上的力相當(dāng)復(fù)雜,會(huì)受到壓力梯度力、Basset力、Magnus力、Saffman升力等一系列的作用力[25-26].但是在單纖維捕集顆粒模型中,由于各力在適用條件下對(duì)顆粒的影響很小,為了簡(jiǎn)化計(jì)算,均可忽略不計(jì)[27].

1.2 單纖維捕集效率的計(jì)算方法

式中:為單纖維捕集的效率;in為入口通入的顆粒數(shù);out為出口逃逸的顆粒數(shù).

1.3 邊界條件設(shè)置

圖2 計(jì)算區(qū)域及邊界條件設(shè)置示意

具體的邊界條件如圖2所示,以單纖維捕集顆粒模型為例,具體邊界條件設(shè)置如下:計(jì)算域入口邊界設(shè)為速度進(jìn)口,出口邊界設(shè)為壓力出口;在模型計(jì)算中,將纖維橫截面面積與假想控制面的比值作為填充率對(duì)待[28],即=f2/2,同時(shí)根據(jù)Davies結(jié)合實(shí)驗(yàn)結(jié)果得出的結(jié)論,在0.6%~30%的范圍內(nèi)都是正確的[3].當(dāng)入口高度=5.3f時(shí),則填充率=0.035,因此模型的長(zhǎng)、寬、高分別定為240,120,80μm是可行的;纖維的直徑為15μm;計(jì)算區(qū)域四周的邊界則根據(jù)單纖維結(jié)構(gòu)特點(diǎn)設(shè)為對(duì)稱邊界條件;纖維表面邊界設(shè)為無(wú)滑移邊界條件;圖3為高梯度磁場(chǎng)的磁場(chǎng)形式,高梯度磁場(chǎng)的形成則是在均勻的背景磁場(chǎng)中填充飽和聚磁介質(zhì)以產(chǎn)生高磁場(chǎng)梯度磁場(chǎng);圖4為鋼鐵廠生產(chǎn)過(guò)程中產(chǎn)生粉塵的XRD圖譜,主要成分為CaCO3,當(dāng)2=35.42°和2=44.14°,分別出現(xiàn)了Fe3O4和Fe的特征峰,說(shuō)明鋼鐵廠排放的粉塵具有一定的鐵磁性,容易被磁化.

圖3 高梯度磁場(chǎng)內(nèi)圓柱形磁纖維周圍磁場(chǎng)示意

圖4 鋼鐵廠產(chǎn)生粉塵的XRD圖譜

1.4 網(wǎng)格獨(dú)立性檢驗(yàn)

為了去除網(wǎng)格數(shù)量對(duì)數(shù)值模擬計(jì)算準(zhǔn)確性的影響,對(duì)模型進(jìn)行網(wǎng)格獨(dú)立性驗(yàn)證,計(jì)算不同網(wǎng)格密度下的壓力損失,模擬結(jié)果如圖5所示.隨著網(wǎng)格密度的增加,單纖維模型結(jié)構(gòu)的壓力損失逐漸增大,且網(wǎng)格數(shù)為14萬(wàn)、55萬(wàn)、90萬(wàn)左右時(shí),單纖維模型結(jié)構(gòu)的壓力損失隨入口風(fēng)速變規(guī)律一致,與Davies壓力損失經(jīng)驗(yàn)公式(6)的對(duì)比誤差都在5％范圍內(nèi). 選取其中一種工況進(jìn)行效率計(jì)算,當(dāng)速度=0.2m/s,p=2.5μm時(shí),單纖維捕集效率與Davies效率經(jīng)驗(yàn)公式(7)的誤差分別為8.51%、3.50%、1.50%,后兩者的誤差都在5%范圍內(nèi),根據(jù)網(wǎng)格數(shù)量和誤差綜合考慮選取55萬(wàn)的網(wǎng)格用于數(shù)值模型的計(jì)算,且本文的計(jì)算模型網(wǎng)格采用的是六面體結(jié)構(gòu)化網(wǎng)格.

1.5 與經(jīng)驗(yàn)公式對(duì)比

為了驗(yàn)證單纖維結(jié)構(gòu)捕集粉塵顆粒數(shù)值模擬的準(zhǔn)確性,計(jì)算了單纖維結(jié)構(gòu)模型的捕集效率,并與實(shí)驗(yàn)計(jì)算公式進(jìn)行對(duì)比,由圖6,7可知,過(guò)濾效率的誤差在10%范圍內(nèi).粒徑較小時(shí)模擬值與經(jīng)驗(yàn)公式相差較大,這是因?yàn)镈avies效率經(jīng)驗(yàn)公式(7)只考慮了顆粒的攔截作用和慣性碰撞,而當(dāng)粉塵顆粒0.5μm

式中:P為直接碰撞系數(shù);St為斯托克斯數(shù);0為計(jì)算修正后的捕集效率;為計(jì)算捕集效率;為填充率.

圖6 不同粒徑下單纖維捕集效率計(jì)算

圖7 不同St下單纖維捕集效率計(jì)算

計(jì)算結(jié)果與經(jīng)驗(yàn)公式間的誤差基本可接受,表明采用該方法進(jìn)行單纖維捕集粉塵顆粒的研究可行.

2 結(jié)果與討論

2.1 高梯度磁場(chǎng)下PM2.5顆粒的運(yùn)動(dòng)規(guī)律

當(dāng)PM2.5被氣體攜帶進(jìn)入高梯度磁場(chǎng)時(shí),由于纖維的長(zhǎng)度遠(yuǎn)大于纖維的直徑,因此不考慮各流場(chǎng)和磁場(chǎng)中各物理量沿磁性纖維軸向的變化.PM2.5剛進(jìn)入時(shí),分布均勻.隨著顆粒的繼續(xù)移動(dòng),當(dāng)粉塵顆粒進(jìn)入高梯度磁場(chǎng)區(qū)域時(shí),由于主要受到磁場(chǎng)力、曳力、重力以及布朗力的共同作用,運(yùn)動(dòng)狀態(tài)發(fā)生改變.通過(guò)顆粒的運(yùn)動(dòng)軌跡8(a)和8(b)對(duì)比可知,在高梯度磁場(chǎng)中,磁性纖維周圍存在2個(gè)引力區(qū)和2個(gè)斥力區(qū).這與孫仲元等[28]的磁選理論研究一致.通過(guò)與傳統(tǒng)流場(chǎng)形式下單纖維對(duì)顆粒的捕集進(jìn)行對(duì)比,可知當(dāng)加入高梯度磁場(chǎng)時(shí),單纖維捕集顆粒能力明顯提高.

圖8 高梯度磁場(chǎng)下磁性纖維捕集顆粒的運(yùn)動(dòng)軌跡

2.2 高梯度磁場(chǎng)下磁場(chǎng)對(duì)粉塵捕集效率的影響

2.2.1 入口風(fēng)速對(duì)捕集效率的影響 如圖9可知,磁性纖維對(duì)PM2.5顆粒的捕集效率隨入口風(fēng)速呈先減小后趨于平穩(wěn)的規(guī)律.隨著入口風(fēng)速的增加,磁性纖維對(duì)粉塵顆粒捕集效率逐漸減小.

圖9 高梯度磁場(chǎng)下捕集效率與入口風(fēng)速的關(guān)系

圖10中,其余軌跡圖中速度與磁場(chǎng)方向都與本圖相同.當(dāng)p=1.0μm時(shí),隨著入口風(fēng)速的增加,在引力區(qū)落在磁性纖維上的顆粒數(shù)逐漸減小,且斥力區(qū)的“空腔”縮小.這是因?yàn)?當(dāng)顆粒接近磁性纖維時(shí),雖然在斥力區(qū)所受的斥力相同,但是顆粒速度越大,運(yùn)動(dòng)狀態(tài)越不易改變,在斥力區(qū)運(yùn)動(dòng)的距離越長(zhǎng),導(dǎo)致斥力區(qū)的“空腔”縮小.當(dāng)顆粒進(jìn)入引力區(qū)時(shí),由于氣流越大對(duì)顆粒的攜帶能力越強(qiáng),在引力區(qū)被流體帶走的顆粒越多,被引力區(qū)吸引捕集的顆粒就越少.同時(shí),氣流速度越大,相應(yīng)的顆粒在磁場(chǎng)中的作用時(shí)間越短,顆粒所受的磁場(chǎng)作用效果就會(huì)在一定程度上減弱,因此捕集效率減少.

圖10 不同入口風(fēng)速下磁性纖維捕集顆粒軌跡圖(H=0.1T,B=0.06T,cp=0.025)

2.2.2 粉塵粒徑對(duì)捕集效率的影響 由圖11可知,當(dāng)0.5μm￡p￡2.5μm,=0.1m/s時(shí),隨著粉塵粒徑的增加,磁性纖維對(duì)PM2.5的捕集效率呈現(xiàn)先增大后減小的趨勢(shì),利用高梯度磁場(chǎng)(=0.1T,=0.06T)可以使單纖維捕集PM2.5的效率提高為原來(lái)的4.23倍.當(dāng)p=1.0μm,此時(shí)的捕集效率提高最大.通過(guò)粉塵顆粒的運(yùn)動(dòng)軌跡圖12可知,當(dāng)粉塵粒徑較小時(shí),氣流攜帶顆粒能力強(qiáng),被氣流攜帶的顆粒在經(jīng)過(guò)引力區(qū)時(shí)很少被磁性纖維捕獲,因此捕集效率較低.隨著顆粒的粒徑增大,在引力區(qū)磁場(chǎng)對(duì)顆粒的磁力增大,磁性纖維對(duì)顆粒捕集效率提高,隨著粉塵顆粒的繼續(xù)增大,顆粒在斥力區(qū)受到斥力作用同步增強(qiáng),在接近纖維的過(guò)程中由于受斥力作用而遠(yuǎn)離磁性纖維.顆粒粒徑越大,遠(yuǎn)離纖維距離越大,即“空腔”增大.當(dāng)顆粒再經(jīng)過(guò)引力區(qū)時(shí),由于磁場(chǎng)強(qiáng)度會(huì)隨著與纖維間距的增大而減弱,顆粒與纖維間距的增加使得顆粒所受的磁場(chǎng)力減小,再加上流場(chǎng)的作用,在引力區(qū)顆粒受引力運(yùn)動(dòng)方向幾乎與流場(chǎng)垂直,受流場(chǎng)影響很大,此時(shí)很難再被纖維捕集,捕集效率降低.

2.2.3 磁場(chǎng)強(qiáng)度對(duì)捕集效率的影響 由圖13(a)可知,磁性纖維對(duì)粉塵顆粒的捕集效率與磁性纖維磁感應(yīng)強(qiáng)度呈一次函數(shù)關(guān)系.隨著磁性纖維磁感應(yīng)強(qiáng)度增加,磁性纖維對(duì)PM2.5的捕集作用逐漸增強(qiáng),與此同時(shí),當(dāng)施加的外磁場(chǎng)強(qiáng)度不同時(shí),如圖13(b)所示,磁性纖維對(duì)粉塵顆粒的捕集效率與外磁場(chǎng)強(qiáng)度同樣呈一次函數(shù)關(guān)系.隨著外磁場(chǎng)強(qiáng)度的增加,磁性纖維對(duì)粉塵的捕集作用逐漸增強(qiáng),通過(guò)擬合得出圖13(a)和13(b)中兩個(gè)一次函數(shù)的平均增長(zhǎng)斜率分別為137.54和12.79,即捕集效率的增長(zhǎng)率B>H,磁性纖維磁感應(yīng)強(qiáng)度對(duì)PM2.5顆粒捕集效率的影響程度要大于外磁場(chǎng)強(qiáng)度的影響程度.

圖11 高梯度磁場(chǎng)下捕集效率與粉塵粒徑的關(guān)系

圖12 不同粒徑下磁性纖維捕集顆粒軌跡(H=0.1T,B=0.06T,=0.025)

圖13 高梯度磁場(chǎng)下捕集效率與磁場(chǎng)強(qiáng)度的關(guān)系

(a)磁性纖維磁感應(yīng)強(qiáng)度; (b)外加磁場(chǎng)強(qiáng)度

通過(guò)粉塵顆粒的運(yùn)動(dòng)軌跡(圖 14)可知,當(dāng)=0.2m/s,p=1.0μm時(shí),隨著外磁場(chǎng)強(qiáng)度的增加,在引力區(qū)中落入磁性纖維表面的顆粒增多.主要原因是當(dāng)外磁場(chǎng)增加時(shí),磁場(chǎng)范圍和強(qiáng)度增大,且磁性纖維附近的磁場(chǎng)梯度增加,粉塵顆粒所受的磁場(chǎng)力相應(yīng)增強(qiáng),因此捕集效率增大.

圖14 不同外磁場(chǎng)強(qiáng)度下磁性纖維捕集顆粒軌跡圖(B=0.06T,=0.025)

圖15 高梯度磁場(chǎng)下捕集效率與顆粒磁化率的關(guān)系

2.2.4 顆粒的磁化率對(duì)捕集效率的影響 當(dāng)PM2.5進(jìn)入高梯度磁場(chǎng)時(shí),粉塵顆粒被磁化,繼而受到磁場(chǎng)力的作用.由圖15可知,當(dāng)=0.2m/s,p=1.0μm時(shí),隨著粉塵顆粒磁化率的增加,磁性纖維對(duì)粉塵顆粒的捕集規(guī)律呈現(xiàn)出兩段線性增加規(guī)律,且起始段線性增加斜率要大于后段線性增加的斜率.這是因?yàn)楫?dāng)PM2.5磁化率較小時(shí),此時(shí)顆粒磁性雖然很弱,但是相對(duì)于無(wú)磁性的PM2.5,磁場(chǎng)力的出現(xiàn)會(huì)使得顆粒在磁場(chǎng)中所受的磁場(chǎng)力顯著變化,因此增長(zhǎng)的斜率較大.隨著磁化率的繼續(xù)增加,此時(shí)顆粒的磁性同樣增強(qiáng),但磁場(chǎng)力的變化相比之前減弱,因此增長(zhǎng)的斜率減小.通過(guò)PM2.5的運(yùn)動(dòng)軌跡(圖16)可知,當(dāng)=0.2m/s,p=1.0μm時(shí),隨著顆粒磁化率的增加,在引力區(qū)中被磁性纖維表面捕集顆粒數(shù)逐漸增加.根據(jù)“空腔”的大小可知磁化率的大小對(duì)運(yùn)動(dòng)軌跡影響較小.

圖16 不同磁化率下磁性纖維捕集顆粒軌跡圖(H=0.1T,B=0.06T)

3 結(jié)論

3.1 PM2.5在高梯度磁場(chǎng)中運(yùn)動(dòng)時(shí),磁場(chǎng)力對(duì)于PM2.5的運(yùn)動(dòng)軌跡影響較大,當(dāng)0.5μm￡p￡2.5μm,=0.1m/s時(shí),利用高梯度磁場(chǎng)(=0.1T,=0.06T)可以使單纖維捕集PM2.5的效率提高為原來(lái)的4.23倍,且在磁性纖維周圍存在2個(gè)引力區(qū)和2個(gè)斥力區(qū).

3.2 當(dāng)粉塵粒徑、磁場(chǎng)強(qiáng)度、磁化率一定時(shí),在高梯度磁場(chǎng)中,磁性纖維對(duì)PM2.5的捕集效率隨入口風(fēng)速呈先減小后趨于平穩(wěn)的規(guī)律,當(dāng)入口風(fēng)速、磁場(chǎng)強(qiáng)度、磁化率一定時(shí),磁性纖維對(duì)PM2.5的捕集效率隨粉塵粒徑的增加呈先增大后減小的趨勢(shì),當(dāng)p= 1.0μm時(shí)的捕集效率提高最大.

3.3 無(wú)論是外磁場(chǎng)強(qiáng)度還是磁性纖維磁感應(yīng)強(qiáng)度,當(dāng)入口風(fēng)速、顆粒粒徑一定時(shí),磁性纖維對(duì)粉塵顆粒的捕集效率與磁場(chǎng)強(qiáng)度都呈一次函數(shù)的關(guān)系,隨著磁場(chǎng)強(qiáng)度的增加,捕集效率增加,且增長(zhǎng)斜率B>H.

3.4 當(dāng)入口風(fēng)速、粉塵粒徑、磁場(chǎng)強(qiáng)度一定時(shí),隨著PM2.5磁化系數(shù)的增加,磁性纖維對(duì)PM2.5的捕集規(guī)律呈現(xiàn)兩段線性增加規(guī)律,且開(kāi)始段線性增加的斜率要大于后段,磁化率對(duì)顆粒的運(yùn)動(dòng)軌跡影響較小.

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The mechanism of high gradient magnetic field improving the performance of single fiber capture PM2.5.

ZHANG Li-an, DIAO Yong-fa*, ZHUANG Jia-wei, ZHOU Fa-shan, SHEN Heng-gen

(College of Environmental Science and Engineering, Dong Hua University, Shanghai 201620, China)., 2019,39(7)：2765~2773

PM2.5emissions from iron and steel and nonferrous industries as object, based on the discrete particle model DPM and UDF custom programming, The effects of inlet velocity, particle diameter, external magnetic field strength, magnetic fiber magnetic flux density and magnetic susceptibility on the capture efficiency were studied and analyzed by combination between the particle motion trajectory and force. The results showed that when 0.5μm￡p￡2.5μm,=0.1m/s, the efficiency of single fiber to capture PM2.5could be improved by using high gradient magnetic field(=0.1T,=0.06T)4.23times. It was also found that there were two gravitational zones and two repulsive zones around the magnetic fibers. At the same time, in the high gradient magnetic field, the capture efficiency of the magnetic fiber to PM2.5decreased first and then stabilized with the inlet velocity; while the capture efficiency increased first and then decreased with the particle diameter of the dust. Whenp=1.0μm, the increasing of capture efficiency was maximized at this time; whether it was the external magnetic field strength or the magnetic fiber magnetic flux density, the capturing efficiency of magnetic fiber to particles was a linear function of the field intensity, with the efficiency growth rate ofB>H; with the increase of the magnetic susceptibility of the particles, the capturing of particles by magnetic fibers presented a two-stage linear growth law, and the growth rate1>2. When the particles passed through the high gradient magnetic field, the inlet velocity, dust particle diameter and field strength had a great influence on the motion trajectory, while the magnetic susceptibility had little effect on the motion trajectory.

high gradient magnetic field；PM2.5；capturing efficiency；magnetic susceptibility

X513

A

1000-6923(2019)07-2765-09

張儷安(1990-),男,安徽淮北市人,東華大學(xué)博士研究生,主要從事PM2.5顆粒的磁團(tuán)聚研究.發(fā)表論文1篇.

2018-12-20

國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2018YFC0705300);中央高?；究蒲袠I(yè)務(wù)費(fèi)重點(diǎn)項(xiàng)目(2232017A-09)

* 責(zé)任作者, 教授, diaoyongfa@dhu.edu.cn