International Journal o Research in Engineering an Science (IJRES) ISSN (Online): 3-9364, ISSN (Print): 3-9356 Volume 3 Issue 11 ǁ November. 15 ǁ PP.33-39 eat Transer Electric Precipitator an Its Dust Collecting Plate Dust Settling orce Analysis an Re-entrain Dust Qing Qing Jiang, Wei Jun Liu College o mechanical engineering, Shanghai Unersity o Engineering Science, Shanghai, China ABSTRACT:this paper presents a new type heat exchange electric ust collector, analyzes its ust collecting plate rom the Angle o microscopic ust particles by van er Waals orce, ahese orce an electrostatic orce an thermophoresis orce, through the establishment o the ust particles o ust collecting plate an bon moel, analyze the ust settling on ust collecting plate orce o attraction an backmixing, puts orwar the conitions o the ust particles can be returne to the airlow. The experimental results show that the evice has superior cleaning perormance, can eectely curb the reentrainment o ust. KEYWORDS:eat transer electric precipitator, ust particles, ust collecting plate, Bon moel, re-entrain ust I. INTRODUCTION Deusting technique with electricity is wiely use in inustry, the traitional electrostatic precipitators o PM1 above particle removal eiciency is higher, but or the collection o ine particulate matter,because o the shortage o charge an the reentrainment o ust, etc.the ust collection eiciency is unsatisactory. J.R melcher an Y.z huang etc. Think about 3% o escape rom the electric ust is cause by reentrainment o ust [1].as been collecte ust will happen reentrain epens on the orce o the ust particles,when ahesion strength is greater than the stripping orce, ust particles can be securely attache, or they may all o again into the air.such as, the ust eposition layer oten or cohese orce is too small an the airlow to scour, particle metho to reboun or reverse the eect o electrostatic orce an regurgitation, or because the cohese orce is too large, strong vibrating orce to the ust rom the ust collecting pole ell own.but at this time coul make the original has orme the masse ust eposition layer was break, hence the particles return low is much larger than when conventional shaking.even no vibration an beating, ust particles may not stay in the place where the eposit, an may even backmixing again into the air.when vibrating ust collecting plate, especially ine particles are easy to prouce ust seconary ust, seriously aect the ust collecting eiciency.eicient ust removal o PM.5 particles technology research has become the evelopment irection o the electric technology an current research hot spot []. II. STRUCTURE DIAGRAM The shell to make ouble electrostatic precipitators, interlayer cooling water, layer is a ust collecting wall an the heat transer surace, ust an heat exchange between the role o can promote each other organically as shown in igure 1. Because o heat exchange eect, the ust stream with certain temperature ierence exists between the ust collecting plate, ust was orce rom high to low temperature zone, prouce thermal subsience, promote the ust collecting. Dust collecting plate surace temperature is lower than another stream temperature eect is prouce can restrain the phenomenon o back corona. 33 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An eat transer electric precipitator structure schematic iagram 1- air inlet; - water inlet; 3- the outlet;4 - outlet; 5- corona pole; 6- outer cyliner; 7inner barrel 1TE ORCE ANALYSIS O DUST COLLECTING PARTICLE Attache to the soli surace ust particles, or particles attache to each other is calle ahesion. To overcome the ahesion phenomenon neee to orce (vertical acting on the particle centre o gravity )is calle ahesion orce. or the evice, ust particles were in thermoelectric composite iel, the inluence o ust particles an ust collecting plate stress mainly (not incluing chemical ahese orce), van er Waals orce, capillary ahesion orce, electrostatic orce an thermophoresis orce [3]. 1.1 Van er Waals orce Accoring to the theory o van er Waals orce ormation, neutral atoms an symmetry with the instantaneous ipole, it is because o the electron clou o luctuations aroun the nucleus, the instantaneous ipole make the neighboring atoms or molecules prouces ipole. By quantum theory can calculate the gravitational orce. Van er Waals orce between spherical particles with spherical particles V ormula (1) can be use to calculate, an van er Waals orce between the spherical particles an collecting plate can be calculate by as ininity [4]. 1 V (1) 1 z 1 In the ormula, as van er Waals orce constant, =.4 x 1 - j; 1 an as the iameter o two spherical particles, m.van er Waals orce between particles an plate, equalent to any o the 1 an tens to ininity, V 1 Z () In orer to pell the single partic which attache to the ust collection plate, suppose you want to ozen o vibration acceleration or a: V m a av (3) namely 34 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An 1Z 4 a 3 3 (4) Z, ormula (4) show that the particle size, the greater the nee o vibrating acceleration is smaller; The smaller the particle size, vibrating acceleration, the greater the nee when vibrating acceleration vibration increases an to make ine ust all, will prouce the seconary ust. Thereore, ine ust particles is not easy to all into vibration, van er Waals orce plays a role. Assume that the istance between particles or particles to plate the smallest istance between z = 4 x 1-1 m, can respectely calculate the particle iameter in the range o.1 ~.µm between particles an particles with the size o the van er Waals orce between the plates, as shown in igure. igure the relationship between van er Waals orce an the iameter o the particles 1. Capillary ahesion orce Due to the humi air, in the gap between the two contact boies can prouce the water vapor conensation (as shown in igure 3), orme in the clearance o the meniscus pull particles to the surace. The tension o the particles is ere rom the two aspects, one is the surace tension, the secon is capillary action reuces the liqui pressure on the outsie. This tension is or particles increase ahesion, it can be written as the sum o two parts: = + p (5) igure 3 capillary orce iagram In the ormula, is total tension ue to the presence o water, is the surace tension, p is capillarity or capillary pressure prouce by the Laplace pressure [5]. Thus there are: 4R cos (6) 4R sin sin θis the contact Angle, α Angle usually is very small, so the irst item is not important, or iniltrating liqui cosθ= l, so, 35 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An 4πR (7) or (8) ormula o or capillary ahesion orce, N; γ to the water's surace tension, the general is.7 N/m, or ust iameter, µm. or particles = 1 m, = 4.5 x 1-7 N [6]. This orce compare to the van er Waals orce is important. Oil mist in the air will be conense uring the particles an the surace o the gap between a meniscus that also will increase the ahesion o particles ahesion, capillary orce contrast van er Waals orce is much larger, so in the presence o capillary orce, its size playe a ominant role its size, this conclusion also got many theories, an experimental veriication. 1.3 The electrostatic orce Uner normal circumstances, the ust particles charge by nature o the inluence o the bon orce is not very big, but in the electric, the electrostatic orce on ust particles collecte plays a vital role. Dust particles is aecte by the applie electric iel, an combine with the nature o the ust particles ierence is bigger, so the complicate situation o ust by electrostatic orce. Generally, the electrostatic orce o the ust can be ie into corona electrostatic orce, polarization electrostatic orce, contact electrostatic orce an inuction electrostatic orce. 1.3.1 corona electrostatic orce Dust particles uner the action o electric iel orce, the ust collecting pole movement an eposition on the ust collecting pole. Because o the ust particles o the insulation resistance is not ininite, take charge o saturate ust particles, reach the ust collecting pole began to leak charge, the ust eposition layer can be regare as leaky capacitor, the capacitor is plate or groun ust collecting plate, the cathoe is compose o negately charge ust particles. The electrostatic leakage o ust layer to capacitance ischarge rule, namely Q t Q e (9) W here Q at time t charge amount o ust particles, C; ρ is the speciic resistance o ust, Ω.Q is charge particle electric iel saturate loa capacity. Q 1 (1) 4 1 E Ater ust particles reach the ust collecting pole by corona electrostatic orce is QE Qe t E t 1 4 E e 1, (11) Where, ε is permittity o ree space, ε = 8.85 1-1 C / (V m); ε relate permittity ust (imensionless); E is the applie electric iel strength, V / m. 1.3. polarization electrostatic orce Polarization o ust particles in iel intensity o an electric iel is mae up o E an ust particles prouce by the boun charge on the aitional electric iel.aitional electric iel in ust particles insie the ball, with the original electric iel in opposite irections. Accoring to the principle o superposition o iel, 36 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An particle ball total electric iel is weaker than the original electric iel; Both non-polar molecules are polar molecules, as long as the polarization phenomenon occurs in the electric iel. Polarization boun charge ust particles can prouce the eect o electrostatic orce j.its calculation ormula is j 1 (1) 3 grae Where, E is the electric iel strength o the ust layer. Collecting ust particles eposite on the plate by electrostatic polarization an its spatial resolution in which the electric iel intensity square relate to static electricity an the polarization irection towar the irection o the electric iel becomes strong. Polarization static electricity strengthene the bon between the particles. 1.3.3 contact electrostatic orce In surace must contact potential ierence places will exist a electric iel. Assume that nonlinear process (breakown) electric iel strength reache the maximum Emax, an the collision o particles consiere point contact orm, as shown in igure 4. igure 4 ust particles contact moel θ- particle contact raius o the central Angle; Z - contact raius ege To the horizontal plane istance; S1, S, S3, ust particle contact respectely Three close near the cyliner surace I the space is lesser, between the two suraces o the electric iel may be very high, the ion or smaller Charge ions in motion or orce will prouce very big eect. Contact electrostatic orce Z calculating ormula or o electrostatic orce is Z (13).8 1..4 EmaxE Where is the iameter o a spherical particle, m; gas breakown electric iel strength E max o the time, KV / cm, E max esirable value KV / cm, uner conitions known outsie the iel intensity can be obtaine with ierent iameters ust suere electrostatic particle contact. 1.3.4 inuction electrostatic orce or low resistity ust, because has goo electrical conuctity, carries a negate charge soon by ust collecting plate leak out, an the electrostatic inuction an bring the same as the ust collecting plate posite charge.at this point, the ust particles o opposite irection, the irection o the electrostatic orce with the original is a repulse orce, this orce makes the ust out o the ust collecting plate an return airlow, its value can be calculate with the ormulas below, namely π 6.83 εε E i = (14) 37 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An In plus iel uner the conition o 3, 5, 7 KV/cm, respectely, to calculate the ierent iameter ust grain inuction o electrostatic orce (igure 5) igure 5 The relationship o inuction electrostatic orce, the particle iameter an pplievoltage 1.4 the thermophoresis orce The high temperature lui molecule collision more than low temperature, so the particles by thermal pressure rom high temperature an low temperature zone migration, this orce is calle the thermophoresis orce. Through the preecessors' research results show that the thermophoresis orce with temperature graient o the low iel in the movement o the tiny particles is important, when particle size less than 1µm, he began more than gravity.here use Epstein thermophoresis orce ormula calculation [7]. th kg T Tg kg k 9 (15) p x ρ is the gas ensity, is the particle iameter, µ is turbulence viscosity, k g, K P is the coeicient o thermal conuctity o gases an particles, T g is gas temperature. Using the thermophoresis orce eect o the temperature iel is the removal o ine particulate matter especially submicron is an important way o ine particulate matter,chang-u You o the tsinghua unersity (1) esign o wet electrostatic ust removal system in the use o electrostatic iel makes particles by airlow movement center to the surace ust collecting wooen partition bounary layer, using high temperature lue gas an ust collecting plate prouce by the ierence in temperature on the thermophoresis orce increase near the surace o particle capture, signiicantly improve the ine particulate matter especially the capture eiciency o submicron particles.. Mechanical moel Look rom the action eects o ust, van er Waals orce, ahese orce an beore the thermophoresis orce an electrostatic orce is make ust ahesion on ust collecting plate an inuction electrostatic orce ust out o the ust collecting plate. In orer to analyze problem statement on convenience, the ormer three kins o electrostatic orce are collectely reerre to as bining gravity (e), inuction electrostatic orce is calle bining repulsion ( C ), to buil a bon moel compose o ust particles an ust collecting plate as shown in 6. igure 6 Dust particles boning moel 38 Page
eat Transer Electric Precipitator An Its Dust Collecting Plate Dust Settling orce Analysis An The bon orce equilibrium equations or the moel c (16) th e v When c > th + + e + v, sai ust is greater than in the guie attache to the orce o repulsion, ust asorption on ust collecting plate, on the other han, when the c < th + + e + v, sai ust by attracte than by repulsion, ust will be out o the ust collecting plate, the ust eposite on the ust collecting plate will backmixing particles into the air, or the phenomenon o. re-entrain ust.the theoretical calculation results show that when the ust particle size is 1µm or smaller particles, ust will not be returne to the mixe into the air. But when the ust speciic resistance less than 1 4 Q cm or ust particle size is larger, the ust is easy to return to mix into the air. III. CONCLUSION (1) through the analysis o the cohese orce o particles by size calculation ormula o ust particle bining moel, analyze the ust eposition on the ust collecting boar o appeal an backmixing orce, put orwar the necessary or seconary ust can occur. () ust particles by ahese power to ecie whether it again to return to the ust in the air, to contain ust backmixing can increase the ahesion strength o ust, or the purpose o this article, introuce the thermophoresis removal technology, on the basis o realize the hot ust removal, increase the thermophoresis orce ust ahesion o gravity, which woul strengthen the ust catcher, inhibit the generation o re-entrain ust. (3) the thermophoresis orce eect o removal o ine particles is an important way, but in the basic research stage at present, there have been no mature an easible technology, application o thermophoresis removal o ine particulate matter experimental research are very ew, an pure thermophoresis eect cause by the eposition eiciency is not high, rom the point o the experimental an theoretical research results at home an abroa, pure thermophoresis eect o top ust removal eiciency is only 3% or so, in this paper, heat transer type ust collector, a easible irection is propose. REERENCES [1] JibaoZhu. Stuy on the electric collection technology o ine particles [D]. Zhejiang: zhejiang unersity, 1:14. [] JinwenXia. The evelopment an research status o electrostatic precipitator [J]. Science an technology innovation an applications, 14 (5) : 55. [3] GuangaMa, air pollution control engineering [M]. Beijing: China environmental science press, 3:166. [4] Ono Nagataro. Theory an practice o ust removal, ust collection,wenchang Dan, Beijing: Science an Technology Literature Press, 54-1987.1 [5] Yanqiang Li. The mechanical moel o micro particles on surace ahesion. [J]. environmental science an technology, 8,31 (1): 8-11 [6] Dianyin Zhang, Xueyi Zhang, ust removal technology manual [M]. Beijing: Metallurgical Inustry [7] Kea Cen etal. Gas-soli separation theory an technology [M]. Zhejiang: Zhejiang Unersity press, 1996:3-31.Press, 3: 18-19. 39 Page