THE EFFECT OF THE INTRODUCTION OF AN EXIT TUBE ON THE SEPARATION EFFICIENCY IN A CYCLONE

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1 Brazlan Journal of Chemcal Engneerng ISSN Prnted n Brazl Vol. 30, No. 03, pp , July - September, 2013 THE EFFECT OF THE INTRODUCTION OF AN EXIT TUBE ON THE SEPARATION EFFICIENCY IN A CYCLONE J. Cernecky 1 and K. Plandorova 2 1 Techncal Unversty n Zvolen, Faculty of Envronmental and Manufacturng Technology, Department of Envronmental Technology, T. G. Masaryka 24, Zvolen, Slovaka, Europe. E-mal: jozef.cernecky@tuzvo.sk 2 SIGMA SLOVAKIA, Zvolenska cesta 14 / Banska Bystrca, Slovaka, Europe. (Submtted: February 22, 2012 ; Revsed: August 14, 2012 ; Accepted: August 25, 2012) Abstract - The paper shows the analyss of the effect of ntroducton of an ext tube nto the cylndrcal part of a cyclone on the flow velocty, pressure losses and, above all, the separaton effcency. We made measurements and carred out CFD smulatons for three levels of the ext tube ntroducton. The ratos of the depth of the ext tube ntroducton to the cyclone dameter (Hp/D) were 0.4, and 0.89 at three velocty settngs of 8 m.s -1, 13 m.s -1 and 15 m.s -1. The Reynolds Stress Model (RSM), whch was compatble wth the expermental results, was used for numercal solutons. The effcency of cyclone separaton was explored on a sample of oak sawdust. The effcency of cyclone separaton ncreased wth the geometrc sze of the partcles, the nlet velocty and a deeper ntroducton of the ext tube. Keywords: Cyclone; Separaton; Computatonal flud dynamcs; Oak sawdust. INTRODUCTION Cyclones are techncal devces whch are used for separatng loose matter from carrer gas wth the utlzaton of gravtatonal, nertal and centrfugal forces. A smple constructon, possble operatng relablty, low nvestment and operatng costs and low energy consumpton are the basc qualtatve aspects of the cyclone. Low separaton of soft partcles, abrasve effects and adhesve power of partcles are among to the dsadvantages. The total cyclone effcency s nfluenced by factors such as the flow rate of a heterogeneous mxture through the cyclone, the propertes and concentraton of loose matter, cyclone desgn and ts settng, total separaton, fractonal separaton, cyclone resstance, deteroraton and other factors. The heterogeneous mxture enters the cylndrcal part of a separator and, after that, t s put nto a downward rotary movement towards the bottom concal part, where the separated materal does not usually descend any further. Under the nfluence of centrfugal forces and the negatvely nclned plane of a lateral surface of a cone, the partcles are conversely forced to ascend aganst the newly ncomng materal, wth whch t combnes and acqures volume. The fact that the partcles leave the hopper s due to the ncrease n volume, slowng down ther rotaton by the frcton aganst the lateral surface, gravty force and the pressure of other materal enterng the separator. The concal shape of the bottom part of the separator s necessary because of gradual closng of the central ascendng vacuum flow, whch s produced by rotaton together wth a change of medum flow drecton nearer to a separator axs. Ths mples that, on the axs of rotaton, t s not possble to have a bg outlet dameter because of reverse drag of the separated partcles. *To whom correspondence should be addressed

2 628 J. Cernecky and K. Plandorova The works of Lapple (1951) and Barth (1956) are consdered to be the frst studes dealng wth cyclone models. The studes were smple and provded acceptable results wth a lmted range of parameters. Later, those theores were mproved by Smth (1962) and Muschelknautz (1970). In ther theores they consdered more parameters such as surface roughness, area of dstrbuton of partcles, shape and sze of partcles, pressure losses and others. The effcency of vortex separators depends on the regme, whch s also nfluenced, apart from the already mentoned parameters, by nlet velocty, temperature and vscosty, whch are ntroduced n the work of Avc and Karagoz (2003). Ths work nvestgated the cyclone flow patterns ntroducng dfferent shapes and dameters of ext tube smulated at dverse flow rates. Lm et al. (2004) examned expermentally the effect of vortex fnder shape on the characterstcs of the collecton effcency at dfferent flow rates. Elsayed et al. (2010) evaluated the flow patterns and performance of a cyclone wth dfferent vortex fnder dameters to examne the effect of the vortex fnder dameter on the performance and velocty profle. In the expermental work of Hoffman et al. (1995) t was proved that the nlet velocty has a sgnfcant nfluence on the length of turbulence dependng on cyclone geometrc dmensons. The paper of Ldén and Gudmundsson (1996) descrbed the use of sem-emprcal polyhedra for separaton effcency dependng on the operatng condtons and cyclone dmensons. The length of turbulence n the cyclone ncreased wth ncreasng nlet velocty. In the work of Martgnon et al. (2007), the mpact of cyclone geometry was studed by means of creatng a symmetrcal double nlet and a cyclone model wth a spral outlet compared wth a common cyclone wth a tangental nlet. It was verfed that the total separaton effcency ncreases wth decreasng pressure drop n both cyclone shapes, but n a cyclone wth shaped symmetrcal nlets a bgger pressure drop was recorded than n the cyclone wth the spral outlet. The results of the expermental study of Km, Lee and Kuhlman (2001) provde nformaton about the effcency of partcle separaton for a modfed nner surface of the body of cyclones wth spral, crcumferental and vertcal grooves. The estmaton of separaton effcency dependent on the concentraton of partcles n axal flow n a cyclone dust collector was publshed by Ogawa (1999). Under the centrfugal force sold partcles slde along the cone surface and fall nto a dust hopper, where some partcles are trapped and some are blown away by secondary flow back to the cyclone body. A lterature survey showed that the vortex length can be mportant for predctng the separaton effcency, especally n short cyclones, but for longer cyclones the turbulence does not have to reach the cone top. If the length of a cyclonc cylnder ncreases, the separaton effcency ncreases to a certan value and then t begns to decrease; t s also smlar n an overflow ppe. By lengthenng the heght of the cyclonc cylnder or by shortenng the length of the overflow ppe we can lessen the pressure drop to a certan extent (Zhu and Lee, 1999). The defnton and composton of the pressure drop n the cyclone were analysed n the paper of Chen and Sh (2006). The pressure drop n the cyclone ncludes spreadng losses at the nlet nto the cyclone and outlet spnnng losses caused by the frcton near the walls of the cyclone and the dynamc energy of the dffused gas n the overflow ppe. The surface resstance or losses caused by frcton have a substantal nfluence on the vortex length; wth decreasng surface resstvty the length of turbulence n the cyclone ncreases. Numercal studes of separable propertes of dfferent concentratons of partcles n the cyclone at the nlet were nvestgated n the paper of Oan et al. (2007). The effects of nlet concentraton of partcles on the tangental velocty, partcle sze, pressure drop and separaton effcency n the cyclone were determned. The mpacts of cone dmensons on the cyclone performance were examned n the study of Xang et al. (2000). The mathematcal expresson for three-dmensonal flow n the cyclone s complex and has not been explored n depth. The calculatons of physcal laws are dependent on the attenton, tme and effort. Therefore, t was necessary to examne these theores on the computer by means of polyhedra and to compare the results obtaned wth expermental data or theoretcal knowledge. For a better dea of flow and physcal actons occurrng n the cyclone, CFD (Computatonal Flud Dynamcs) models are utlzed at present. The results of numercal calculatons and gas flow smulatons n the typcal Lapple cyclone are descrbed n the paper of Wang et al. (2006). The accuracy of the numercal soluton of a flow smulaton n the cyclone was acheved usng the RSM model. The CFD flow smulatons completed wth propertes of heat transfer n the cyclone wth a tangental nlet were publshed by Karagoz and Kaya (2007). The publcaton of Grffths and Boysan (1996) focused on the comparson of performance of three small cyclone types wth the use of CFD data from experments and three emprcal theores. Gas flow and a sold component n the cyclone are Brazlan Journal of Chemcal Engneerng

3 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone 629 descrbed n the paper of Meer and Mor (1998). In ths work, the CFD model was based on an Euleran approach for both phases wth the condton of a 3D symmetrcal doman, the mathematcal model was compled for the utlzaton of the k-ε turbulent model. The possblty of usng CFD technques enables one to make a proposal of more effectve separaton condtons wthout the need of conductng expensve experments. Currently, CFD smulatons have relatvely wde applcaton for relatvely precse mathematcal approxmaton of flow, whle the arduousness of ts performance and tme restrants n solvng concrete physcal problems must not be forgotten. TURBULENT MODEL DESCRIPTION The use of CFD (computatonal flud dynamcs) for numercal calculatons of gas flow n the cyclone has ncreasngly been appled. Three models are usually used for the smulaton n the cyclone: the k-ε model, Algebrac Stress Model (ASM) and Reynolds Stress Model (RSM). Wang et al. (2006) found that the standard k-ε turbulence model s nadequate to smulate the flow wth swrlng moton because t leads to excessve turbulence vscosty and unrealstc tangental velocty. Therefore, the accuracy of the numercal soluton can be mproved by usng the Reynolds Stress Model (RSM), whch was also utlzed n ths paper for the smulaton of physcal actons n the cyclone by usng the FLUENT commercal program. In turbulent flow, whch s accompaned by pulsaton and fluctuaton, the total velocty equals the sum of the central and fluctuaton components of velocty: u = u + u '. (1) By substtutng ths expresson nto the equaton of moton we get the averaged Naver-Stokes equatons of moton n the form: t ( ρ u) + ( ρuuj) x j u u j 2 uj = μ + μ x j xj x 3 x j p +ρ g+ F + ( ρu u ), x j xj (2) where ρ s the densty, u s the mean velocty, x s the poston, t s the tme, p s the pressure, μ s the dynamc vscosty, uu j s the Reynolds stress tensor, g s the acceleraton of gravty and F s the external body force whch arses due to the nteracton wth dspersed sold partcles. Ths equaton of moton now represents the averaged velocty values (or man flow). Turbulence s represented by means of the Reynolds stresses ρ uu j. FLUENT descrbes the effect of man flow and the Reynolds stresses by means of the above mentoned models. The Reynolds Stress Model ncludes the calculaton of partcular Reynolds stresses by means of a transport dfferental equaton n the form: uu uu + = j j uk t xk ( LTM) ( Cj) + δ +δ υ xk ρ p ( uuu j k) ( kju ku j) ( uu j) xk ( Dj) uj u p u u j uu k + uu k xk x + + k ρ xj x ( Pj) ( Φj) u u 2υ + S u, xk x k ( εj ) (3) where the left two terms are the local tme dervatve of stress (LTM) and the convectve transport term (C j ), respectvely. The rght fve terms are: D j s the stress dffuson term, P j s the shear producton term, Ф j s the pressure- stran term, ε j s the dsspaton term and S u s the source term. For better expresson, the ndvdual members are approxmated for the purpose of closng the set of smultaneous equatons from ths dfferental equaton. The Reynolds stresses are consequently substtuted nto the equaton of momentum transfer. Generally, the followng equatons are solved by usng the RSM model: 6 transport equatons n the form (3), 3 transport equatons for the mean component of velocty, contnuty equaton, Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

4 630 J. Cernecky and K. Plandorova transport equaton for the rate of dsspaton ε. Generally, ths system solves 12 equatons. In comparson wth the prevous models, a dsproportonally greater arduousness s placed on the numercal model (Launder et al., 1975). The equaton of moton of a small partcle, ncludng the effects of nonlnear drag and gravtatonal forces, s gven by: P du dt ( ) 3νCDRep P = u 2 u + g, (4) 4d S u P dx =. (5) dt P where u s the velocty of the partcle and x s ts poston, d s partcle dameter, S s the rato of partcle densty to flud densty, g s the acceleraton of gravty and accordng to Raouf et al. (2008) the drag coeffcent C D s gven as: C D 24 =, for Re P < 1, (6) Re P /3 C D = (1+ Re P ), for 1 < Re P < 400, (7) Re 6 P where Re P s the partcle Reynolds number defned as: Re P duj u = ν P j. (8) CONDITIONS OF THE EXPERIMENT AND CFD SIMULATION Fgure 1 shows a desgned cyclone model wth a tangental nlet and Table 1 shows basc cyclone dmensons. The cyclone model s placed n an expermental overpressure system for the loose matter separaton of dverse composton and concentraton. Ths devce was used for expermental purposes wth an nlet concentraton of partcles of 0.01 kg. N -1.m -3. In terms of ar flow t s an artechncal system where the transport ar s drawn from the room to a ppe system and from the cyclone separator transported back to the ambent envronment. Fgure 1: A cyclone model wth the man dmensons Table 1: Basc dmensons of a cyclone model (mm) D d p d k b 1 h 1 H v H k H p H c d m H m A set of measurements was carred out for three postons of ntroducton of an ext tube nto the nner part of the cyclone at a barometrc pressure of hpa. The ext tube s n the shape of a cylnder wth a length of 300 mm and was desgned n a way so that t s possble to set the necessary depth of ntroducton of the tube n the cyclone. The frst measurements were made at a rato of Hp/D = 0.89, Fgure 2 (a). The second measurements were performed at a rato of Hp/D = 0.475, just below a bottom wall of the nlet cyclone ppelne. The thrd measurements were carred out at a rato of Hp/D = 0.4, Fgure 2 (c). A fve-port dynamc probe clamped n a specal holder was used for these measurements. The probe was calbrated on a calbraton devce before the measurements (Polansky and Stech, 2011). A sample of oak sawdust wth a densty of 670 kg.m -3 and dampness of 6.5% was used for fndng out the cyclone separaton effcency. These experments were carred out to verfy the numercal model. The nlet ar velocty as well as the partcle velocty were set wth a control damper on the ntake openng of the fan at the values of 8 m.s -1, Brazlan Journal of Chemcal Engneerng

5 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone m.s -1 and 15 m.s -1. Three types of CFD models were created. They represented three dfferent examples of the ntroducton of an ext tube nto the cylndrcal part of the cyclone. Surfaces were covered wth a hexagonal grd of tetra-hybrd type, Fgure 3, whch was converted to a grd of the polyhedral type n the FLUENT program. A computatonal doman for the varant of Hp/D = 0.4 comprses 79,393 CFD cells, for the varant of Hp/D = t s 92,606 CFD cells and for Hp/D = 0.89 t s 111,661 CFD cells. Due the use of the polyhedral grd, whch s of hgh qualty, the grd optmzaton was not done durng the computaton. In order to calculate the partcle trajectores the followng parameters of DPM (Dscrete phase modellng) were set: the total flow rate kg/s, the partcle dameter 1 mm, unform partcle dstrbuton and partcle materal oak. Fgure 2: The ntroducton of an ext tube nto the cylndrcal part of the cyclone Fgure 3: A CFD cyclone grd Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

6 632 J. Cernecky and K. Plandorova RESULTS AND DISCUSSION Fgure 4 shows a statc pressure at the velocty of 15 m.s -1 and three examples of the ntroducton of an ext tube. The B-B secton represents an nlet plane for all measurements and ts dstance s 218 mm from the top part of the cyclone cap. The statc pressure s the greatest along the nner wall of the lateral surface of the cyclone. On the cyclone axs the statc pressure has lower values than on the walls and they are dependent on the vortex core and the ntroducton of an ext tube. Fgure 5 shows the relaton between the dynamc pressure and the nlet gas velocty nto the cyclone at Hp/D = Wth an ncrease n nlet velocty the dynamc pressure n the cyclone decreases. The expermental results concde well wth the numercal ones, although they are a bt hgher. Fgure 6 shows the comparson of numercal and calculated tangental veloctes n the cylndrcal cyclone part at the nlet velocty of 15 m.s -1 to the cyclone. The results of the CFD smulaton are n agreement wth the calculated ones. The flow pattern ndcates quas-forced and free vortex flow. The turbulence on the cyclone axs agrees approxmately wth the axs of cyclone geometry just at ths measurement. The axal and tangental veloctes were measured expermentally for three velocty settngs at the ratos Fgure 4: Contours of statc pressures at the velocty of 15 m.s -1 and at Hp/D of: (a) 0.89; (b) 0.475; (c) 0.4. Fgure 5: A comparson of numercal and calculated dynamc pressure. Fgure 6: A comparson of numercal and calculated tangental veloctes. Brazlan Journal of Chemcal Engneerng

7 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone 633 of Hp/D = 0.4, and Fgures 7 9 show the contours of tangental velocty for the ntroducton of an ext tube at Hp/D = 0.4, and 0.89 and for three settngs of the nlet velocty of 8 m.s -1, 13 m.s -1 a 15 m.s -1. From the fgures t s obvous that, wth ncreasng nlet velocty, the vortex core n the whole cyclone secton s changed. The domnant velocty n the cyclone s a tangental velocty component. The value of the tangental velocty equals to zero on the wall and n the centre of feld flow. The hghest tangental velocty s acheved by suckng from the nlet ppelne; then the velocty s decreased by the vortex gas moton downwards along the cyclone wall. Negatve values of the tangental velocty are acheved n a created, forced vortex along the cyclone axs and n a closed contaner. In all three cases of the ntroducton of an ext tube, the vortex core s n the shape of a twsted cylnder and s not axally completely symmetrcal, especally n the concal part of the cyclone towards the contaner of trapped partcles. The axs of the forced vortex s not dentcal n tme wth the geometrc cyclone axs, whch s n the shape of a curve. Wth ncreasng nlet velocty the length of turbulence n the cyclone ncreases. Fgure 10 shows the contours of tangental velocty for the ntroducton at three nlet veloctes. From the fgures t can be seen that, wth ncreasng nlet velocty, the tangental velocty rses proportonally. Fgure 7: Contours of tangental velocty for the rato of Hp/D = 0.4 at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Fgure 8: Contours of tangental velocty for the rato of Hp/D = at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

8 634 J. Cernecky and K. Plandorova Fgure 9: Contours of tangental velocty for the rato of Hp/D = 0.89 at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Fgure 10: Contours of tangental velocty for the ratos of Hp/D = 0.4, and Fgures show the contours of axal velocty for Hp/D = 0.89 and at the nlet velocty of 8 m.s -1, 13 m.s -1 and 15 m.s -1. In the fgures t s possble to see that the axal velocty near the cyclone wall acheves negatve values and towards the cyclone centre these velocty values turn nto postve ones. Hgher values of the axal velocty were recorded n the centre of the cylndrcal part than n the concal cyclone part. The cyclone hopper has negatve values of axal velocty n the whole cross-secton. The hghest axal velocty s acheved near the wall of an ext tube. Fgure 14 shows the contours of axal velocty for the ntroducton at three nlet veloctes. The separaton effcency was nvestgated on a sample of oak sawdust wth a densty of 670 kg. m -3 at three veloctes and at three settngs of an ext tube, Fgure 15. The partcle szes of the sample used were 1 mm, 0.6 mm and mm and the separaton perod was 60 s. From the measurement results t can be sad that the separaton effcency decreased wth the sze of the partcles. The next mportant factor by whch the separaton effcency can be nfluenced s separaton velocty and the ntroducton of an ext tube. Wth ncreasng nlet velocty the separaton effcency ncreased for all three settngs of an ext tube. At Hp/D = 0.4 the separaton was lower because the partcles were dragged from the trajectory of swrlng moton nto the ext tube where they escaped from the cyclone as lght ashes. Brazlan Journal of Chemcal Engneerng

9 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone 635 Fgure 11: Contours of axal velocty for the rato of Hp/D = 0.4 at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Fgure 12: Contours of axal velocty for the rato of Hp/D = at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Fgure 13: Contours of axal velocty for the rato of Hp/D = 0.89 at the nlet velocty of: (a) 8 m.s -1 ; (b) 13 m.s -1 ; (c) 15 m.s -1. Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

10 636 J. Cernecky and K. Plandorova Fgure 14: Contours of axal velocty for the ratos of Hp/D = 0.4, and Fgure 15: The effcency of cyclone separaton for oak sawdust at the ratos of Hp/D = 0.4, and Brazlan Journal of Chemcal Engneerng

11 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone 637 In Fgure 16 there s a smulaton of the trajectory of oak partcles wth a sze of 1 mm coloured accordng to the velocty sze for Hp/D = at the nlet velocty of 15 m.s -1 ; the tme step was 0.2 s and the tme stop was 10 s. From the fgure t s possble to see that the partcles acheve the hghest velocty at the nlet nto the cyclone and the downwards along the concal cyclone part the velocty decreases. The fact that the velocty decreases s due to the abrason of partcles on the cyclone wall, the acton of gravty and also the weght of newly arrvng partcles n the cyclone. Fgure 16: Partcle trajectores coloured by partcle tme (s). Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

12 638 J. Cernecky and K. Plandorova The followng fgure (Fgure 17) shows a graphcal dependence of the fractonal separaton by partcle sze for Hp/D = for the flow veloctes of 8, 13 and 15 m.s -1. The separaton was nvestgated expermentally for the fractons of 1 mm, 0.6 mm and mm, partcle szes that occur manly n the wood-processng ndustry. A comparson of the expermental results wth the outputs of CFD smulatons can be seen n the Fgure 18. Fgure 17: A curve of fractonal separaton for the rato of Hp/D = for three flow veloctes. Brazlan Journal of Chemcal Engneerng

13 The Effect of the Introducton of an Ext Tube on the Separaton Effcency n a Cyclone 639 Fgure 18: The effcency of cyclone separaton for dverse flow veloctes, partcle szes and ratos of Hp/D. CONCLUSIONS 1) From the expermental results and the CFD smulatons t can be sad that the ntroducton of an ext tube has a sgnfcant nfluence on the ar flow and pressure losses n the cyclone and on the separaton effcency. By ntroducng an ext tube nto a cylndrcal cyclone at the rato of Hp/D = 0.89, the vortex core was not created symmetrcally along the whole central cyclone axs as t was at the ratos of Hp/D = and ) Deep ntroducton of an ext tube nto a cylndrcal cyclone causes hgher flud flow velocty n the separaton space of the cyclone, whch s manfested n hgher pressure cyclone losses. 3) In all three cases of the ntroducton of an ext tube, the vortex core s n the shape of a twsted cylnder and s not completely axally symmetrcal, especally n the part of the concal cyclone towards the dust hopper. The axs of the forced vortex s not temporally concdent wth the geometrc cyclone axs, whch s n the shape of a curve. Wth ncreasng nlet velocty, the length of turbulence n the cyclone s ncreased. CFD smulatons were appled for partcle szes of mm, mm, mm, 0.6 mm and 1 mm. The curve of fractonal separaton was also created from CFD smulatons. It s obvous from the graph that the separaton decreases upon reducng the partcle sze. Apart from the partcle sze mpact, separaton was also nfluenced by the geometrcal ratos of the partcular parts of the vortex separator. 4) Wth ncreasng nlet velocty to the cyclone the tangental velocty ncreases proportonally and ths leads to an ncrease n the separaton effcency n the cyclone. 5) CFD smulatons were used n the study of the physcal phenomena occurrng n the cyclone. The numercal results presented for axal and tangental velocty are n good agreement wth the expermental ones. 6) The poston of the ext tube and the partcle sze nfluenced greatly the cyclone separaton. At the smaller ntroducton of the tube, the separaton was lower because the partcles were dragged from the trajectory of swrlng moton nto the ext tube where they escaped from the cyclone as lght ashes. In all measurements t was found that the partcles wth a smaller sze had smaller separaton than the partcles wth a bgger dameter. Wth ncreasng nlet velocty the separaton effcency ncreases and pressure losses ncrease. The purpose of geometrcal rato optmzaton n a vortex separator s to ensure the hghest separaton effcency at the lowest pressure losses. Based on the results obtaned from the expermental measurements, the generalzed optmzaton of the separaton of dust partcles n the woodprocessng ndustry does not lead to explct conclusons. In the real operaton of the wood-processng ndustry the process of dust partcle separaton s nfluenced by many factors (bluntng of cuttng tools, partcle shape, humdty of processng materal, envronmental humdty, etc.). In terms of the optmal geometrcal ratos n the expermental separator we focused manly on the balancng of the nfluence of the rato of Hp/D on the separaton effcency. From the expermental and CFD results t can be concluded that wth the ncrease n Hp/D the separaton effcency also ncreases, whch was reflected manly n the dust partcles wth larger dameters (1 mm and 0.6 mm). For smaller partcles, a more sgnfcant nfluence on the separaton Brazlan Journal of Chemcal Engneerng Vol. 30, No. 03, pp , July - September, 2013

14 640 J. Cernecky and K. Plandorova process was envronment humdty, whch was reflected n the outputs from the expermental measurements as an nfluence of small partcle agglomeraton. It can be concluded that the optmal rato of Hp/D under our condtons s NOMENCLATURE C D drag coeffcent dmensonless d partcle dameter m F external body force N/m 3 g acceleraton of gravty m/s 2 p dsperson pressure Pa Re p partcle Reynolds number dmensonless S rato of partcle densty to dmensonless flud densty t tme s u dsperson velocty m/s u tme average velocty n the m/s axal drecton p u velocty of the partcle m/s v velocty m/s x poston m Greek Letters μ dynamc vscosty Pa.s ν knematc vscosty m 2 /s ρ densty kg/m 3 Subscrpts, j, k 1,2,3 p partcle ACKNOWLEDGMENTS The contrbuton was created wthn the KEGA project no. 027TUZVO-4/2011 funded by the Mnstry of Educaton, Scence, Research and Sport of the Slovak Republc. REFERENCES Avc, A. and Karagoz, I., Effects of flow and geometrcal parameters on the collecton effcency n cyclone separators. Journal of Aerosol Scence, 34, No. 7, 937 (2003). Barth, W., Desgn and layout of the cyclone separator on the bass of new nvestgatons. Brennstoff- Kraft (BWK), 8, 1 (1956). Elsayed, Kh. and Lacor, C., The effect of vortex fnder dameter on cyclone separator performance and flow feld. ECCOMAS CFD Conf., J. C. F. Perera and A. Sequera (Eds.) Lsbon (2010). Grffths, W. D. and Boyson, F., Computatonal Flud Dynamcs (CFD) and emprcal modelng of the performance of a number of cyclone samplers. Journal of Aerosol Scence 27, No. 2, 281 (1996). Hoffman, A. C., Jonge, R., Arends, H. and Hanrats, C., Evdence of the natural vortex length and ts effect on the separaton effcency of gas cyclones. Fltraton & Separaton, 32, No. 8, 799 (1995). Chen, J. and Sh, M., A unversal model to calculate cyclone pressure drop. Powder Technology, 171, No. 3, 184 (2007). Karagoz, I. and Kaya, F., CFD nvestgaton of the flow and heat transfer characterstcs n a tangental nlet cyclone. Internatonal Communcatons n Heat and Mass Transfer, 34, No. 9-10, 1119 (2007). Km, H. T., Lee, K. W. and Kuhlman, M. R., Exploratory desgn modfcatons for enhancng cyclone performance. Journal of Aerosol Scence, 32, No. 10, 1135 (2001). Lapple, C. E., Processes use many collector types. Chemcal Engneerng, 58, 144 (1951). Launder, B. E., Reece, G. J. and Rod, W., Progress n the development of a Reynolds-stress turbulent closure. Journal of Flud Mechancs, 68, No. 3, 537 (1975). Ldén, G. and Gudmundsson, A., Sem-emprcal modelng to generalse the dependence of cyclone collecton effcency on operatng condtons and cyclone. Journal of Aerosol Scence, 28, No. 5, 853 (1996). Lm, K. S., Km, H. S. and Lee, K. W., Characterstcs of the collecton effcency for a cyclone wth dfferent vortex fnder shapes. Journal of Aerosol Scence, 35, No. 6, 743 (2004). Martgnon, W. P., Bernardo, S. and Quntan, C. L., Evaluaton of cyclone geometry and ts nfluence on performance parameters by computatonal flud dynamcs (CFD). Brazlan Journal of Chemcal Engneerng, 24, No. 1, 83 (2007). Meer, H. F. and Mor, M., Gas-sold flow n cyclones: The Euleran approach. Computers & Chemcal Engneerng, 22, No. 1, 641 (1998). Muschelknautz, E. and Krambrock, W., Aerodynamsche Bewerte des Zyklonabscheders aufgrund neuer und veberssertter Messungen. Cheme- Ingeneur-Technk, 42, No. 5, 247 (1970). (In German). Ogawa, A., Estmaton of collecton effcency depended on feed partcle concentraton for axal Brazlan Journal of Chemcal Engneerng

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