Particle velocity and concentration characteristics in a horizontal dilute swirling flow pneumatic conveying

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1 Ž. Powder Technology Prticle velocity nd concentrtion chrcteritic in horizontl dilute wirling flow neumtic conveying Hui Li,), Yuji Tomit b Dertment of Mechnicl Engineering, Kgohim UniÕerity, , Korimoto, Kgohim, Jn b Dertment of Mechnicl Engineering, Kyuhu Intitute of Technology, 1-1 Senuicho, Tobt, Kitkyuhu, Jn Received 22 Aril 1999; received in revied form 14 June 1999; cceted 17 June 1999 Abtrct An exerimentl tudy concerning rticle behvior in horizontl dilute wirling flow neumtic conveying w erformed. Meurement of rticle velocitie nd concentrtion rofile hve been crried out uing the hotogrhic imge technique. From the exerimentl reult, it i found tht men rticle velocity of wirling flow neumtic conveying i lower thn tht of conventionl neumtic conveying in the rnge of high g velocity, but the higher men rticle velocity in wirling flow neumtic conveying cn be obtined t low g velocity. The rticle concentrtion rofile in the wirling flow neumtic conveying exhibit ymmetric ditribution with reect to the ie xi nd the higher rticle concentrtion er ner the wll in the ccelertion region. In develoed region, the rticle concentrtion rofile of the wirling flow neumtic conveying how nti-ymmetric ditribution, nd the higher rticle concentrtion er t the bottom of ie. However, the rticle concentrtion of the wirling flow neumtic conveying t the bottom of ie re lower thn tht of xil flow neumtic conveying. q 2 Elevier Science S.A. All right reerved. Keyword: G olid two-he flow; Prticle flow ttern; Prticle velocity; Concentrtion; Pneumtic conveying; Swirling flow neumtic conveying 1. Introduction Pneumtic conveying ytem, which ue ir to trnort olid rticle through ieline, i n imortnt oertion in ignificnt number of chemicl nd indutril rocee. Tyicl exmle re the col energy converion ytem, ctlytic crcking in the etroleum indutry, nd drying nd trnort of olid mteril. Conventionl neumtic conveying, tht i xil flow neumtic conveying Ž AFPC., i frequently oerted in the dilute-he regime in the high ir velocity region. Power conumtion, ie eroion, nd rticle degrdtion conidertion dictte tht the conveying velocity be held to minimum. In the lt 35 yer, there h been increing interet in dene-he neumtic conveying, nd everl commercil ytem hve been develoed. Unfortuntely, thee ytem require high reure dro nd hve high initil cot. Furthermore, dene-he neumtic conveying my led to untble flow t low conveying velocitie. ) Correonding uthor. Tel.: q ; fx: q ; E-mil: li@mech.kgohim-u.c.j Thee untble flow often cue blockge nd ie vibrtion. To reduce ower conumtion, blockge, rticle degrdtion, nd ie wer, thi new wirling flow technique, clled wirling flow neumtic conveying Ž SFPC., w lied to neumtic conveying ytem by Li nd Tomit w1,2 x. In the low velocity conveying rnge, SFPC w determined to be effective. However, g-rticle two-he flow in SFPC ytem re n untedy nd comlicted nonliner dynmic ytem. A detiled undertnding of the behvior of rticle i imortnt for deign, otimiztion, nd oertion of SFPC ytem. Exerimentl tudie for the tructure of g-rticle two-he flow hve ttrcted coniderble interet in the t three decde. Coniderble dvnce hve been mde in undertnding the dynmic behvior of xil g-rw3,4 x. A to the wirling ticle two-he flow in ieline g-rticle two-he flow, number of invetigtion w5,6x reorted on the dierion nd behvior of rticle in the model combution chmber with the he of the centrl revere flow region. However, very few tudie re rr$ - ee front mtter q 2 Elevier Science S.A. All right reerved. Ž. PII: S

2 ( ) H. Li, Y. TomitrPowder Technology Fig. 1. Exerimentl equiment. vilble on the behvior of rticle in wirling g-rwx 7 tudied ticle two-he flow in ieline. Li nd Tomit the flow tructure of horizontl SFPC ytem by the three-dimenionl numericl imultion. In the reent work, the exerimentl tudy on the ditribution of rticle velocitie nd concentrtion in horizontl SFPC i crried out, in order to rovide better undertnding the chrcteritic of SFPC. 2. Exerimentl rtu nd rocedure The exerimentl fcility for the reent tudy i of the oitive reure tye nd i hown chemticlly in Fig. 1. A tbilizer ie with n inide dimeter of 156 mm nd bout 1.2 m long w ued t the inlet of tet ieline for tbilizing the flow field. The vned tye wirler, hown in Fig. 2, which w lced t the tbilizer ie exit, w emloyed to minimize the reure dro cro the wirler.the wirling flow i introduced by the vned wirler. Air from blower flow through the clibrted nozzle, the tbilizer ie nd the vned wirler, nd ick u the olid mteril fed by grvity from the feed tnk t the inlet of tet ieline. Then, the g-rticle mixture enter the tet ieline nd t the ieline exit the rticle re erted by the ertor. The tet ieline conited of horizontl mooth crylic tube with n inide dimeter of 8 mm nd length of bout 13 m. To tudy the chrcteritic of SFPC on different kind of rticle, we ued olyethylene nd olyvinyl ellet in thi exeriment. Their roertie re given in Tble 1. The irflow rte nd the olid m flow rte were meured by the orifice meter nd lod cell, reectively. The wirl number S w ued to evlute the intenity of wirling flow nd i defined by: H R 2 uwr dr 2r S, Ž 1. R 2r R u2 rdr H where u nd w re the xil nd circumferentil comonent of the ir velocitie, reectively, R i the ie rdiu, nd r i the ir denity. In thi tudy, three different vned wirler were ued for exmining the effect of the wirl number. The initil wirl number S w defined nd meured t the rticle feeding ection by Li nd Tomit wx 8. Fig. 3 how the meuring domin of rticle velocity nd concentrtion. It i fixed in given length of ie 2 mm t loction 4 nd 9 m from the olid feed oint long Fig. 2. Photogrh of vned wirler. Tble 1 Proertie nd dimenion for teted rticle Prticle She Averge Denity Floting dimeter Ž 3 kgrm. velocity Ž mm. Ž mr. Polyethylene Cylindricl Polyvinyl Dicl

3 146 ( ) H. Li, Y. TomitrPowder Technology velocity i ".8%, the olid m flow rte i "2.8%, the men rticle velocity i "19.3%, nd locl rticle velocity nd concentrtion re "3.3% nd "1.8%, reectively. 3. Reult nd dicuion Fig. 3. Schemtic of meuring domin. the flow direction. Thi meuring domin w divided into eight region from bottom to to of ieline. Photogrh of rticle flow ttern were tken uing cmer with hutter time 2 m. With the hotogrhic imge technique, the trck of rticle in the meuring domin of hotogrh were meured. The locl rticle velocity u t region i w clculted by: N i 1 u u, Ž 2. Ý N j1 ij where Ni i the number of rticle in region i, nd uij Ž trck lengthrhutter time. i rticle velocity. The men rticle velocity U t the meuring domin i given by: N 8 i 1 U 8 ÝÝ u ij. Ž 3. i1 j1 N Ý i i1 The normlized locl rticle concentrtion rrr region i i given by: ž / r A N 8, Ž 4. r i N Ý i i1 where r i the rticle concentrtion in the meuring domin, Ž i 1,2,...,8. i i the re of region i nd Ž 8 A Ý. i1 i i the re of tet ieline. The hotogrhic imge technique i one of the imlet method, nd cn meure intntneou rticle velocity nd concentrtion rofile in the full-domin. However, it cn only be lied in diered g-rticle two-he flow with reltively low concentrtion of the rticle he. In our exeriment, the men g velocity U w vried from 9 to 24 mr nd the olid g rtio w vried from.8 to 3.. According to the initil wirl number S, three kind of SFPC re defined, which re clled wirl1 flow Ž S.58., wirl2 flow Ž S.94. nd wirl3 flow Ž S 1.12., reectively. AFPC, condition where S i. Ž no wirl., w lo included for comrion. For the etimted verge uncertinty of the reent exeriment, the totl reure dro i "4.6%, the men ir in 3.1. Totl reure dro The reltion of the reure dro v. the ir velocity with the initil wirl number for different rticle i imortnt for wirling flow neumtic conveying technol- Fig. 4. Reltion between totl reure dro nd g velocity.

4 ( ) H. Li, Y. TomitrPowder Technology minimum velocity i of rticulr imortnce in the deign of neumtic conveying ytem. Fig. 4 how D t v. U nd S rmeter for olyethylene nd olyvinyl rti- cle. The minimum velocity of SFPC i mller thn tht of AFPC for both of two kind of rticle. A it doe for AFPC, the reure dro of SFPC firt decree nd then rie below the minimum velocity, the g velocity decree. Comring SFPC with AFPC, the D t of SFPC i me tht of AFPC for olyethylene rticle nd become lower thn tht of AFPC for olyvinyl rticle U below the minimum velocity of SFPC. Eecilly, the tronger wirl exhibit the lower reure dro when the conveying velocity get cloer to the criticl velocity. Thi indicte tht the tronger wirling flow i more effective for conveying rticle hving lrge floting velocity. Thi i becue the tronger wirling flow h higher tngentil velocity, nd hence rticle re eily uended even in the rnge of low conveying velocity. The D for SFPC i higher thn tht for AFPC in the high t ir velocity region, however, it i ignificnt tht lower conveying velocity nd lower reure dro in rnge of lower velocity cn be relized by SFPC. Fig. 5. Flow ttern of olyvinyl rticle t loction of 4 m ŽG.2 kgr.. Flow direction: Ž. U mr, S.; Ž b. U17.47 mr, S.58; Ž. c U mr, S.94; Ž. d U17.3 mr, S ogy. Although we re minly intereting in the bic ect of rticle behvior, it i necery to know the chrcter of the reure dro in our exerimentl extent. In the reent tudy, we etimte the totl reure dro D t of SFPC or AFPC ytem uing the me method reviou er w1,2 x, which include the reure dro due to the vned wirler. Thi i given: ž / 1 D 2 D td y r 1y U, Ž 5. 2 D where D Ž y. 1 outlet rereent the ttic reure difference between the tbilizer ie nd the tet ieline exit, nd the econd term i the chnge in dynmic reure between the tbilizer ie nd tet ieline. The dimeter of the tet nd tbilizer ie re D nd D, reectively. In thi tudy, the g velocity t the minimum totl reure dro i defined the minimum velocity. Thi 4 Fig. 6. Flow ttern of olyvinyl rticle t loction of 9 m ŽG.2 kgr.. Flow direction: Ž. U mr, S.; Ž b. U17.47 mr, S.58; Ž. c U mr, S.94; Ž. d U17.3 mr, S 1.13.

5 148 ( ) H. Li, Y. TomitrPowder Technology trem of x9 m in Fig. 6, the rticle flow ttern of SFPC i imilr to tht of AFPC ince the wirl decy. Fig. 7. Men rticle velocity v. men g velocity t loction of 4 m Prticle flow ttern The rticle flow ttern of the horizontl SFPC for trnorting olyethylene rticle were viulized by Li nd Tomit wx 1. From the viul obervtion of rticle flow ttern, it h become n obviou fct tht rticle were eily uended by the effect of ir circumferentil velocity comonent even for low g velocity, nd the g velocity when deoition of rticle ered w lower thn tht of AFPC. Therefore, t lower velocity, both the totl reure dro nd energy conumtion in SFPC w reduced. In order to viulize the dilute SFPC in horizontl ie in thi exeriment, the hotogrh of olyvinyl rticle flow ttern from U 17.3 to mr nd G.2 kgr t loction x4 nd 9 m re hown in Fig. 5 nd 6. At the loction of x4 m, hown in Fig. 5, mot of rticle in AFPC re crried in the form of trnd liding long the bottom of the ieline while the reminder motion bove the liding trnd uended flow. In SFPC, however, wirling uended rticle flow ttern re oberved, nd the trong wirling flow how the trong wirling rticle flow ttern. At down- Fig. 8. Men rticle velocity v. men g velocity t loction of 9 m. Fig. 9. Profile of rticle velocity nd concentrtion for olyethylene rticle Ž G.9 kgr, x4m..

6 ( ) H. Li, Y. TomitrPowder Technology Men rticle Õelocity ditribution Fig. 7 how the men rticle velocity U t the loction of x4 mž xrd5. v. U with S.,.58 nd Comring SFPC with AFPC for olyethylene rticle in Fig. 7, the U of SFPC re lower thn tht of AFPC in the rnge of Ž U G 13 mr., becue rticle tke on wirling motion nd rticle-wll colliion frequency incree t the high g velocity. However, the U of SFPC become higher thn tht of AFPC in the low g velocity rnge Ž U F13 mr., ince rticle re uended by the effect of g circumferentil velocity comonent nd re eily ccelerted even for low g velocity. It i ignificnt tht higher rticle velocity cn be obtined with ue of SFPC in rnge of the lower g velocity. When olyvinyl rticle re ued tet rticle, hown in Fig. 7, the U of SFPC re lower thn tht of AFPC whole, ince olyvinyl rticle re of lrge floting velocity nd re not eily ccelerted. However, the U of SFPC how higher tendency in rnge of low g velocity. The U of olyvinyl rticle i lrger thn tht of olyethylene rticle for both SFPC nd AFPC in our exerimentl extent. At the loction of x9 mž xrd112.5., the U v. U with S.,.58 nd 1.13 re hown in Fig. 8. For conveying olyethylene rticle, the U of wirl1 flow Ž S.58. i the highet whole, nd the U of wirl3 flow Ž S i lo higher thn tht of AFPC in rnge of U F14 mr. A to olyvinyl rticle, lthough the U of SFPC i light lower thn tht of AFPC in rnge of the high g velocity, the U of SFPC how higher vlue in rnge of the low g velocity. By comring wirl1 flow Ž S.58. nd wirl3 flow Ž S 1.13., it cn be found tht men rticle velocitie of wirl1 flow re higher thn tht of wirl3 flow. Eecilly, thi henomenon i more obviou in the ccelertion region for both of the two kind of rticle. It i becue rticle tke on the trong wirling motion Ž hown in Fig. 5Ž.. d nd rticle-wll colliion frequency incree when trong wirling flow i lied. Thi reult in the reduction of rticle velocitie, even if the trong wirling flow h higher xil velocity comonent ner the wll. From bove exerimentl reult, n imortnt chrcter of SFPC ytem tht the higher men rticle velocity er in low conveying velocity rnge cn be obtined. It i one of imortnt reon why the minimum conveying velocity nd totl reure dro cn be reduced by SFPC ytem. in either SFPC or AFPC re oberved. The rticle concentrtion rofile of SFPC exhibit ymmetric ditribution with reect to the ie xi Ž yrd.5. nd the higher rticle concentrtion er ner the wll Ž yrd nd 3.4. Profile of rticle Õelocity nd concentrtion At the loction of x 4m Ž xrd 5., rofile of normlized locl rticle velocity nd concentrtion t different g velocitie with three different initil wirl number nd no wirling flow for olyethylene rticle re hown in Fig. 9. The uniform rticle velocity rofile Fig. 1. Profile of rticle velocity nd concentrtion for olyvinyl rticle Ž G.2 kgr, x4m..

7 15 ( ) H. Li, Y. TomitrPowder Technology even for the lower conveying velocity. Thi i becue the circumferentil comonent of wirling flow force rticle to move to the wll, nd rticle re eily uended in the wirling flow. Since the xil comonent of wirling flow i lrger thn tht of the xil flow in AFPC ner the wll wx 8, rticle re eily ccelerted in the ccelertion region. Thi i why rticle velocity of SFPC with S.58 Žin Fig. 9Ž c.. i higher thn tht of AFPC. However, the nti-ymmetric rofile of the rticle concentrtion re more remrkble in AFPC, nd higher rticle concentrtion i oberved t the bottom of ie Ž yrd. becue of the grvity force. The rticle concentrtion t the bottom of ie incree with decreing the conveying velocity, becue AFPC h only n xil velocity comonent of g nd the uending force cting on rticle i too mll in the rnge of lower conveying velocity. Further reduction of g velocity reult in edimenttion nd blockge. Fig. 1 how rofile of normlized rticle velocity nd concentrtion with different g velocitie nd initil wirl number for meuring olyvinyl rticle t the me loction. The rticle velocity rofile in SFPC re lo the uniform ditribution. A to the rticle velocity rofile in AFPC, the uniform ditribution re oberved in rnge of high velocity, but the mximum velocity er in the uer rt of ie t U mr in Fig. 1Ž. c. Since mot of rticle in AFPC re trnorted in the form of trnd liding long the bottom of the ieline Ž hown in Fig. 5Ž.., the rticle wll nd rticle rticle colliion reult in the reduction of rticle velocity. In the high velocity rnge, the rticle concentrtion rofile in SFPC exhibit ymmetric ditribution with reect to the ie xi in Fig. 1Ž. nd Ž. b. However, the nti-ymmetric rofile of the rticle concentrtion, hown in Fig. 1Ž. c, re found for different initil wirl number t low conveying velocity. Thi i becue the circumferentil comonent of thee wirling flow hve inufficient force to mke olyvinyl rticle hving lrge floting velocity to form the wirling flow ttern nd uenion. At downtrem of x9 m Ž xrd112.5., hown in Fig. 11, the rticle velocity rofile in SFPC for olyethylene rticle re lo the uniform ditribution, nd the rticle velocity of SFPC with S.58 how the highet vlue. The oition of mximum velocity in rticle velocity rofile of AFPC till er in the uer rt of ie t low conveying velocity. The nti-ymmetric rofile of the rticle concentrtion in SFPC with different initil wirl number re oberved, nd the higher rticle concentrtion er t the bottom of ie. However, the rticle concentrtion of SFPC re lower thn tht of AFPC t the bottom of ie, nd re higher thn tht of AFPC in the uer rt of ie. Thi imlie tht the effect of wirling flow on the rticle motion exit, lthough the wirling flow become weker nd it xil g velocity rofile become lmot the me AFPC t the downtrem. Fig. 11. Profile of rticle velocity nd concentrtion for olyethylene rticle Ž G.9 kgr, x9m.. Fig. 12 how the meured reult for olyvinyl rticle t the loction of x9 mž xrd Becue the olyvinyl rticle h lrge floting velocity, the effect of the circumferentil comonent of wirling flow

8 ( ) H. Li, Y. TomitrPowder Technology SFPC i lmot the me AFPC, ince rticle in both ce hve the me xil g velocity rofile. 4. Concluion The min reult re ummrized follow. Ž. 1 Men rticle velocity of SFPC i lower thn tht of AFPC in the rnge of high g velocity, however, the higher men rticle velocity in SFPC cn be obtined in low g velocity rnge. Ž. 2 The uniform rticle velocity rofile in SFPC re oberved. Ž. 3 The rticle concentrtion rofile of SFPC exhibit ymmetric ditribution with reect to the ie xi nd the higher rticle concentrtion er ner the wll in the ccelertion region. Ž. 4 In develoed region, the rticle concentrtion rofile of the SFPC exhibit nti-ymmetric ditribution, nd the higher rticle concentrtion er t the bottom of ie. However, the rticle concentrtion of the SFPC t the bottom of ie re lower thn tht of AFPC. Ž. 5 For rticle hving higher floting velocity, the rticle behvior of the SFPC re lmot the me AFPC in develoed region. 5. Nomenclture Fig. 12. Profile of rticle velocity nd concentrtion for olyvinyl rticle Ž G.2 kgr, x9m.. on it motion become weker t downtrem. Therefore, the uniform ditribution of the rticle velocity rofile nd the nti-ymmetric rofile of the rticle concentrtion re clerly oberved in SFPC. The rticle behvior of D Conveying ie dimeter D Stbilizer ie dimeter G M flow rte of olid 1 Wll ttic reure of tbilizer ie before the vned wirler outlet Wll ttic reure of the tet ie exit R Conveying ie rdiu r Rdil coordinte S Swirl number S Initil wirl number U Men ir velocity U Men rticle velocity u Locl rticle velocity u, w Axil nd circumferentil como - nent of ir velocity, reectively x Stremwie ditnce meured from the olid feed oint y Verticl ditnce meured from the bottom of tet ieline D 1y outlet Wll ttic reure difference be- tween the tbilizer ie nd the tet ie exit D t Totl reure dro r Air denity r Men rticle concentrtion r Locl rticle concentrtion

9 152 ( ) H. Li, Y. TomitrPowder Technology Acknowledgement Thi work w erformed rt of the reerch uorted by cientific reerch fund grnted by Jnee Minitry of Eduction Ž No Reference wx Ž. 1 H. Li, Y. Tomit, ASME Journl of Fluid Engineering wx 2 H. Li, Y. Tomit, ASME Journl of Fluid Engineering 12 Ž wx 3 Y. Tuji, Y. Morikw, J. Fluid Mech. 12 Ž wx 4 Y. Tuji, Y. Morikw, H. Shiomi, J. Fluid Mech. 139 Ž wx 5 H. Altgeld, W.P. Jone, J. Wilhelmi, Exeriment in Fluid 1 Ž wx 6 M. Sommerfeld, A. Ando, D. Wennerberg, ASME Journl of Fluid Engineering 114 Ž wx 7 H. Li, Y. Tomit, Third World Congre on Prticle Technology, No. 224, wx 8 H. Li, Y. Tomit, ASME Journl of Fluid Engineering 116 Ž