Performance of Twin-Fluid Atomizers for Atomization of Viscous Solutions

a Co esponding au ho : m[email p o ec ed]b .cz Pe o mance o Twin-Fluid A omize s o A omiza ion o Viscous Solu ions Ma ek Mlk ik1, a, Philipp S ähle2, Volke Gaukel2, Ma ouš Za emba1, Jan Jedelský1 and Mi osla Jícha1 1B no Uni e si y o Technology, Facul y o mechanical enginee ing, Depa men o he he modynamics and en i onmen al enginee ing, Technická 2896/2, 616 69 B no, Czech Republic 2 Ka ls uhe Ins i u e o Technology, Ins i u e o P ocess Enginee ing in Li e Sciences, Sec ion I: Food P ocess Enginee ing, Kaise s aße 12, 76131 Ka ls uhe, Ge many Abs ac . P esen ed pape deals wi h a compa ison o wo in e nally mixing win luid a omize s. The well - known Y- je a omize and so called ou side-in-liquid e e escen a omize (OUIL) we e in es iga ed. The wo king egimes we e de ined by he p essu e d op ( D p) and he gas o he liquid a io (GLR). The in e nal and he ex e nal wo-phase lows o bo h a omize s we e s udied. The in luence o he mixing mechanism on he in e nal low was e alua ed by he gas o he liquid momen um a io ( F ). In ad ance, he s abili y o he sepa a ed low (liquid ilm) was examined in e m o he c i ical wa eleng h o he su ace dis u bances ( l c). The ex e nal low was obse ed by he high – speed came a. The in luence o he basic o ces on he de o ma ion o he liquid was de e mined by a dimensionless c i e ion w· m / s . The alues o F < 1 o he OUIL a omize indica es ha he in e nal low o his a omize was annula . The in e nal low Y- je a omize was mo e complica ed, because he momen um a io a ies om F < 1, whe e he gas momen um is dominan , up o F > 3, whe e he liquid momen um o e comes he gas momen um. The alues o w· m / s > 20 o bo h a omize s indica es he dominan in luence o he iscosi y and he d ag o ce on he b eakup p ocess. 1 In oduc ion The pneuma ic nozzles a e commonly used o a omize he iscous liquids in many indus ial applica ions. They p oduce high shea s esses o igina ing om a high gas o liquid ela i e eloci y, which suppo s he a omiza ion p ocess [1]. Se e al ypes o he in e nal mixing a omize s, we e p esen ed in [7, 8]. The in e nal low is cha ac e ized by he mixing o he low componen s, mo ion and de o ma ion o he liquid and he gas s uc u es, as he esul o he a io o he o ces such as he d ag o ce, he iscous o ces ( m ) and he su ace ension (s). The de elopmen o he mul iphase low is also accompanied wi h he ene gy con e sion [2, 5]. The low pa e n o he wo - phase low o en depends on he GLR which is ela ed o he mass low o he mix u e componen s, o o he oid ac ion ( a ) which co esponds o he olume o he pa icula phase. Also he mixing mechanism in luences he low pa e n [7, 2]. A e passing he ou pu o i ice, he gas expands due o he p essu e d op, which leads o he inc ease o in e acial su ace, as he liquid memb anes and he ligamen s a e c ea ed [9]. P esen ed wo k compa es wo ypes o in e nally mixing win luid a omize s, he Y- je a omize [7] and so called “ou side in liquid” (OUIL) a omize which is no used in indus ial applica ions ye . The in e nal low is e alua ed using he dimensionless numbe s, such as GLR and he liquid o he gas momen um a io ( F ), which is calcula ed acco ding o Song [8]. The ex e nal low is in es iga ed by he isualiza ion and e alua ed in e ms o dimensionless numbe s o de e mine he ela i e in luence o he basic o ces on he liquid du ing he a omiza ion p ocess. 2 A omize s The mul iphase low in he Y-je is c ea ed by injec ing o he liquid in o he ai s eam adially, unde a pa icula angle o he axis (Figu e 1 a). The wo-phase low is c ea ed inside he mixing chambe and i disin eg a es when i eaches he ou pu o i ice. In he OUIL a omize (Figu e 1 b), he ai is in oduced o he mixing chambe om he op and he liquid is in oduced h ough he se ies o liquid po s in he pe o a ed wall o he mixing chambe . Al hough he design o he wo examined a omize s is di e en , he mixing mechanism is simila . DOI: 10.1051/ C Owned by he au ho s, published by EDP Sciences, 2015 / 020 201epjcon EPJ Web o Con e ences , 020 59 92 2 (2015) 52 52                      !" A icle a ailable a h p://www.epj-con e ences.o g o h p://dx.doi.o g/10.1051/epjcon /20159202052 Table 1. Impo an geome ical pa ame e s o in es iga ed a omize s D l D 0  N Y- je 0.4 1 52 1 OUIL 1 9 90 20 * D l [mm]- liquid po diame e , D 0 [mm]– mixing chambe diame e ,  [ o ]- injec ing angle, N – numbe o liquid po s Figu e 1. Schema ic d awings o es ed a omize s a) Y-je , b) OUIL a omize . 3 The expe imen An eccen ic sc ew pump a cons an o a ion speed was used o d i e he liquid in o he a omize . The olume low a e owa ds he a omize was adjus ed using a needle al e. To p o ide he a omize wi h a omiza ion gas, comp essed ai om a house supply was used and adjus ed by a p essu e educing al e. A e ejec ion, he sp ay passed he measu emen zone and was collec ed in a essel which was u he connec ed o an exhaus ai an. Inside he essel a il e wi h la ge po es was used o p e en small sp ay d ops om ecycling in o he measu emen zone. The olume low a e owa ds he a omize was measu ed by a low me e (VSE GmbH, Neuen ande, Ge many). The gas p essu e was measu ed by a p essu e gauge sho ly ups eam o he a omize . A he mal gas mass low con olle (High-Tech EL-Flow, B onkho s Mä ig GmbH, Kamen, Ge many) was used o indica e he esul ing gas mass low. The expe imen s we e pe o med wi h h ee wa e solu ions o he mal odex ine. The iscosi ies o he solu ions we e 147 and 60 mPa · s. The su ace ensions o he solu ions we e 74.25 and 75.73 mN / m. 3.1 Measu emen s The ex e nal low was obse ed using a high-speed came a (OLYMPUS i-speed2) a he equency 10 k ps. The measu ing olume was illumina ed by a con inuous LED lamp in a backligh con igu a ion. A ligh di use was used o ob ain uni o m image backg ound. The exposi ion ime was se o 5 ms. The PENTAX TV lens (50 mm, 1:1.4) was used as a ocusing op ics. Fo he image magni ica ion, he ex ension ings o a o al leng h 25 mm we e used. Due o he es ig cons uc ion, he ou pu nozzle is no di ec ly isible. The a omize body allows us o obse e he low in he closes dis ance 3 mm downs eam he ou pu nozzle. To enhance he image quali y, he backg ound was emo ed by sub ac ing he backg ound image cap u ed when no liquid was p esen . When he backg ound is emo ed, he esul an images show only he liquid sp ay which appea s as he g ey o he black spo s. The aw images shown a isible egion o 6.3 × 4 mm. These images con ained he pa o he a omize body, which appea s as a black a ea in he igh side o he image (Figu e 2). Thus he isible a ea was c opped o he egion o 5.3 × 4 mm. Figu e 2. C opping o he aw images. 4 Conside a ions abou in e nal wo- phase low o examined a omize s When he mixing p inciple is neglec ed, he low pa e n can change, acco ding o he GLR, om he bubbly low (a low GLR) up o he dispe sed low (a high GLR). Song [8] showed, ha o he Y- je a omize , he in e nal low is in luenced by he mixing mechanism. To in es iga e his in luence, Song [8] used he gas o he liquid momen um a io . Because he mixing mechanism o he OUIL a omize is e y simila o he Y- je a omize , he in e nal low o bo h a omize s is e alua ed in e ms o F. Acco ding o he Tables 1 and 2, he liquid o he gas momen um a io is signi ican ly lowe o he OUIL a omize . Due o he di e en geome y o he examined a omize s (Table 1.), is FOUIL app oxima ely wo o de s lowe han FY o he same wo king egimes. Acco ding o he wo k o Song [8], when F < 1, he momen um o he liquid is low and he liquid s eam o ms a ilm on he wall a he liquid po side. When 1 < F < 3, he liquid pene a es in o he cen e po ion o he mixing chambe . Fo F > 3, he liquid can each he wall opposi e o he liquid po and o ms he e he liquid ilm (simila as in he i s case). Fo he OUIL a omize , FOUIL emains e y low (lowe han 1). Hence, he momen um o he liquid canno o e come he momen um o he gas and we p esume ha he liquid lows along he wall o he mixing chambe . As he liquid po s a e placed symme ically we can also expec he symme ic EPJ Web o Con e ences 02052-p.2 liquid ilm. Because each ow o he liquid po s inc eases he low a e in he liquid laye , we can p esume, ha his laye has a conical shape as shown in Figu e 3. Figu e 3. P esumed wo-phase low pa e n in OUIL a omize . Table 2. Compa ison o F a p essu e le el 0.14 MPa Y-je OUIL m [mPa·s] m [mPa·s] 147 308 147 308 GLR [%] 2.5 8.81 5.35 0.36 0.43 5 2.12 1.80 0.08 0.09 10 0.552 0.677 0.023 0.027 20 0.138 0.264 0.006 0.007 Table 3. Compa ison o F a p essu e le el 0.28 MPa Y-je OUIL m [mPa·s] m [mPa·s] 147 308 147 308 GLR [%] 2.5 13.49 20.65 0.55 0.84 5 3.68 5.30 0.15 0.19 10 0.97 1.11 0.04 0.05 20 0.27 0.30 0.01 0.01 I we conside he annula low in he mixing chambe , we mus also conside he s abili y o a liquid su ace. The liquid su ace becomes uns able, when he Be noulli’s o ce [2] o e comes he s abilizing in luence o he su ace ension ( s ). The s abili y o he liquid su ace can be e alua ed by he alue o he c i ical wa eleng h (Eq. 1) [2]. This alue de ines he maximum s able wa eleng h o he su ace dis u bances. The w in his equa ion deno es he gas o he liquid eloci y slip. l c = 2· p · s / g·(w)2 (1) Fo he Y- je a omize , we can expec he eloci y o he gas in he mixing chambe wi hin he ange 12 – 40 m / s o all in es iga ed wo king egimes (acco ding o he measu ed low a es). This gi es he ange o l c wi hin 0.1 – 2 mm o all o he ope a ing egimes. As he expec ed gas eloci y in he mixing chambe o he OUIL a omize is in he ange 0.3 – 0.6 m / s, he c i ical wa eleng h is conside ably highe (400 – 3000 mm). This indica es ha o he Y- je a omize , e en dis u bance o sho wa eleng h becomes uns able and hus he liquid is o n apa in o he small d ople s which a e ca ied in he gas co e. On he o he hand, he alue o l c o he OUIL a omize exceeds he leng h o he mixing 10 o 100 imes. Thus he p obabili y o he uns able dis u bance is e y low and he gas co e wi hou a signi ican amoun o d ople s is expec ed. 5 Ex e nal low The low pa e ns, cap u ed by he high speed came a, a e shown in he Figu es 5 and 6. The egimes, whe e he a omize s did no p oduced he sp ay a e deno ed by he “X” symbol. No images we e cap u ed o hese egimes. The ypical obse ed shape o he liquid s uc u es is a ibe (ligamen ). The ela i e impo ance o he d ag o ce, he iscosi y and he su ace ension is e alua ed using he pa ame e w· m / s (Figu e 4). The high alues o his pa ame e indica es, ha he ela i e impo ance o s is low o all in es iga ed egimes. A hese condi ions, he liquid de o ma ion is d i en by he d ag o ce, while he liquid iscosi y damps he de o ma ion. As he esul , de o ma ion ime is longe so he long ligamen s a e p esen in u he dis ance om he ou pu o i ice [4]. Figu e 4. Rela i e impo ance o d ag o ce, m and s. The in luence o he liquid su ace s abili y can be obse ed in a mo phology o he p oduced ligamen s. Gene ally, he Y- je a omize p oduces he smoo h ligamen s. On he o he hand, he ligamen s p oduced by he OUIL a omize a e mo e b anched wi h high amoun o small s uc u es connec ed o hei su ace. I can be expec ed, ha he gas o he liquid in e ace is in luenced by he ins abili ies, simila as in he case o in e nal low EFM 2014 02052-p.3 (see sec ion 4). Because he diame e o he ou pu o i ice o he OUIL a omize is only 0.7 mm, gas eloci y in ange wi hin 50 – 100 m / s can be expec ed when he gas expands. This alue is based on he measu ed mass low- a es, when he p essu e jus behind he ou pu o i ice is conside ed as he a mosphe ic p essu e. The Y- je a omize has he same diame e o he ou pu o i ice as he diame e o mixing chambe (1 mm), hus he gas eloci y in ange 12 – 40 m / s is expec ed. The l c o ex e nal low o Y-je is in he ange 0.3 – 3 mm and o he OUIL in ange 0.04 – 0.2 mm. The conside ably lowe alue o l c o he OUIL a omize causes ha smalle dis u bances on he ligamen s su ace become uns able. This leads o he o ma ion o small s uc u es and consequen ly o he b eakup o hese s uc u es in o he small d ople s. The alues o l c o he Y- je a omize a e compa able o he ligamen leng h, especially o he lowe p essu e. As he p essu e d op inc eases (0.28 MPa), he alue o l c becomes smalle which leads o he o ma ion o highly b anched ligamen s. This e ec can be obse ed especially o he liquid o highe iscosi y, whe e he b eakup p ocess is slow and long, b anched ligamen s a e p esen . Figu e 5. Sp ay pa e n o liquid iscosi y 308 mPa·s, GLR [%], D p [MPa]. Figu e 6. Sp ay pa e n o liquid iscosi y 147 mPa·s, GLR [%], D p [MPa]. 6 Conclusions The sp ay, gene a ed by he Y- je a omize and he OUIL a omize , was examined. The design and mixing mechanism o hese a omize s a e desc ibed in he sec ion 2.1. The in e nal mul iphase low is e alua ed in e ms o he liquid o he gas momen um a io, which is he c i e ion used o es ima ing he in e nal low, in luenced by he mixing mechanism, in Y-je a omize s [8]. Di e en ypes o he in e nal low pa e n we e es ima ed o he Y- je a omize . The alues o FY, om 20 o 0.3, and e y low l c ( om 0.1 o 2 mm) indica es he in ensi e gas o he liquid in e ac ion and p esence o he small d ople s in he gas co e in he mixing chambe o he Y- je a omize . Fo he OUIL a omize FOUIL < 1 and l c is compa able o he leng h o he mixing chambe , which indica es he annula low and he high le el o low sepa a ion (Figu e 3). The ela i e compa ison o he basic o ces a ec ing ex e nal low (Figu e 4) indica es, ha he liquid de o ma ion p ocess was in luenced mainly by he d ag o ce and damping iscous o ce, which leads o p esence o he long ligamen s (Figu e 5 and 6). The highe gas o he liquid eloci y slip leads o he b anching and as e dis up ion o ligamen s in case o he OUIL a omize . Consequen ly, when as a omiza ion is he p io i y (unde he same wo king pa ame e s), he OUIL a omize seems o be a be e choice o a omiza ion o he examined iscous liquids. Acknowledgemen Au ho s acknowledge inancial suppo om p ojec # 101/11/1264 unded by he Czech G an Agency, om p ojec NETME CENTRE PLUS (LO1202) co- unded by he Minis y o Educa ion, You h and Spo s wi hin he suppo p og amme „Na ional Sus ainabili y P og amme I“ and p ojec # CZ.1.07/2.3.00/30.0005 o Ope a ional P og am Educa ion o Compe i i eness o Minis y o Educa ion, You h and Spo o he Czech Republic. Re e ences 1. L.P. Bay el, Z. O zechowski, Liquid a omiza ion (Taylo & F ancis, Washing on, 1993) 2. C. E. B ennen, Fundamen als o wo-phase lows (Camb idge uni e si y p ess, 2005) 3. H. P. Gadgil, B. N. Raghunandan, Exp. Fluids (2011) 4. L. P. Hsiang, In . J. Mul iphase Flow, (1995) 5. J. Jedelsky, M. Jícha, Fuel 111 (2013) 6. R. Olsiak, B. Kniza , M. Mlk ik, Komunikacie, 14 (4 A), pp. 58-62 7. P. J. Mullinge , N.A. Chigie , J. Ins . Fuel 47 (1974) 8. S. H. Song, S. Y. Lee, A omiza ion and sp ays ol. 6 (1993) 9. S. So ani, P. Sojka, A. Le eb e, P og. Ene g. Combus . 27(4), (2001) EPJ Web o Con e ences 02052-p.4