ABSTRACT 1. INTRODUCTION AND HISTORY OF DEVELOPMENT

Transcription

1 Laser-ffracton base rop-szng system usng mage sensor T. Suzuk* an K. Harase Dept. of ec. Engng, Toyoas Unv. of Tec., Tempaku-cyo Toyoas, apan, ABSTRACT Drop-szng s nspensable n researc an evelopment of spray systems. Unfortunately, te commercal rop-szng evces are generally expensve. Ceaper evces woul be elpful for te researces on ter begnnng stage. One of te autors evelope te smple system of rop-szng an as been opene for acaemc researcers. Te system was base on te laser ffracton meto usng an mage sensor for obtanng te angular strbuton of scattere-lgt ntensty from roplets. But te system a several mperfectons. Tey were bascally owng to te sortage of lgtntensty ynamc-range of te mage sensor. Te system was mprove muc by puttng a small crcular awnng on te mage sensor. Te newly evelope system s outlne, an te results of tral measurements are presente n ts paper. Keywors: Spray, Drop-szng, Drop-sze strbuton, Laser ffracton meto, Lgt-scatterng, System evelopment.. TRODUCTO AD HSTORY OF DEVELOET Te lqu spray s wely use n many nustral fels. Because te performances of te systems wt spray epen on te spray caracterstcs, rop-szng of te spray s nspensable n te researc-an-evelopment of atomzers an spray systems. Varous types of rop-szng evces were evelope an ave been serve commercally 2. Altoug te commercal evces are easy to use an ave superor performance, tey are generally expensve. Smpler an ceaper rop-szng evce soul be welcome by te researcers n acaemc fel. From ts perspectve, one of te autors a stue amng to evelop smpler rop-szng system base on te laser ffracton meto 3. Te bref ntroucton of te laser ffracton meto s as follows: Wen a spercal partcle s llumnate by parallel laser-beam, t scatters te lgt as llustrate n fgure a. Angular strbuton of te scattere lgt ntensty epens on te partcle sze, as sown n fgure b. Usng te optcal setup of fgure 2a, te scattere lgt can be le to te focal plane of te Fourer transformaton lens regarless of te partcle locaton, an te angular strbuton of scattere lgt ntensty can be obtane as te raal strbuton of lgt ntensty. f tere are many partcles n te laser-beam, te lgt ntensty strbuton soul be te synteszaton of scattere lgts from te partcles. Terefore, te sze strbuton of partcles as well as te mean ameter can be estmate by analyzng te lgt-ntensty strbuton. ost of te commercal rop-szng evces employ te co-axally segmente poto-etectors, wc are locate on te focal plane, to obtan te lgt-ntensty strbuton. Te poto-etectors are exclusve esgn an expensve. Te lgt ntensty strbuton wll be obtane by usng an mage sensor, f te mage sensor of we ynamc-range s locate n te place of poto-etector an te mage of scattere lgt s capture clearly. n te prevous stuy, one of te autors evelope te smple rop-szng system base on ts ea 4,5. A conventonal C-OS mage sensor was locate on te focal plane. Te scattere lgt from partcles as well as te measurng laser-beam was attenuate by D-flter an le to te sensor. Te lgt-ntensty ynamc-range of te sensor was extene by te mage composte tecnque mages of fferent exposure tmes were compose nto one mage of g ynamc-range. Te optcal setup was compose of general optcal parts. Te controllng software was evelope, wc woul capture an composte mages, obtan te lgt ntensty strbuton from te mage, an calculate te sze strbuton an te mean ameter of roplets from te lgt ntensty strbuton. After several test measurements, t was supporte tat te rop-szng system was of use to evaluate te spray caracterstcs n laboratores. Te system as been opene for apanese acaemc researcers 6. However, te prevous system as several problems Altoug te mages for mage-composton soul be te recor of te same scattere-lgt strbuton, tey ave fferent exposure tmes an are capture one by one. So, te transent spray cannot be measure. 2 Because te ynamc-range of te mage sensor s stll nsuffcent an te lgt ntensty excees te upper-lmt aroun te pont were te measurng laser-beam focuses on. Terefore we ave to evaluate provsonally te transmttance of te measurng laser-beam usng te lgt ntensty n annular regon slgtly apart from te focusng pont, an te optcal ensty of spray cannot be estmate accurately. 3 Because te ntensty * takas@me.tut.ac.p pone fax

2 Fgure. ntensty strbutons of te scattere lgt from water partcle n laser-beam. Calculate usng Fortran coe of reference 7. Fgure 2. Te prncpal of prevous rop-szng system laser ffracton meto an te basc ea of mprovement. Fgure 3. Scematc agram of te optcal setup of te newly evelope rop-szng system. of focusng laser-beam s so strong, t reflects from te surface of sensor ffusely an backs to te sensor agan to cause optcal nose. Te lgt-ntensty strbuton may be sturbe by te nose, an te measurng error wll be nuce. After repeate tral an error, t was suggeste tat te problems of 2 an 3 coul be mtgate by puttng a small crcular awnng on te mage sensor, wc woul attenuate te focusng laser-beam onto te mage sensor, as llustrate n fgure 2b. Base on ts ea, te rop-szng system was mprove muc. Te newly evelope system s outlne, an te results of tral measurements are presente n ts paper. 2. Optcal setup 2. OUTLE OF DEVELOED SYSTE Te optcal setup of te evelope rop-szng system s sown scematcally n fgure 3. Te setup was compose of general optcal parts for te sake of cost-savng an versatlty. Te semconuctor laser wt collmator of 2mm lgt beam was employe as te measurng lgt source. Te conventonal C-OS mage sensor Epx SV900:.3pxels, monocrome, 0bt, wc was free from smear effect, was locate on te focal plane of te Fourer transformaton lens

3 Fgure 4. Te mages of backgroun lgt obtane by te mage sensor an te potomcrograp of awnng put on te sensor. Fgure 5. Te raal strbutons of te backgroun-lgt ntensty for te cases wt awnng an wtout awnng. of f =00mm focal-lengt. Te scattere lgt from all roplets n te laser-beam was le to te sensor after passng troug te D-flter. Te angular strbuton of scattere-lgt ntensty was gven as te raal strbuton on te sensor. Te measurng laser-beam was also focuse onto te sensor gvng te backgroun-lgt ntensty strbuton. Fgure 4a- sows typcal example of te backgroun-lgt mage obtane by te mage sensor. Te focusng pont was te center of mage. Te backgroun lgt was brgt n te central part an te ntensty ecrease monotonously wt te raal stance from te focusng pont. However, several pxels aroun te focusng pont were black-out ncatng te lgt-ntensty range-over of te sensor elements. any brgt ponts, arrange tly, were also foun on te mage. Te cause of te brgt ponts coul be consere as follows: Te focusng laser-beam was so strong tat te lgt reflecte from te surface of sensor ffusely wt optcal nterference. Ten te lgt reflecte agan at te nner surface of te cover glass of sensor an ncent nto te sensor agan to cause te brgt ponts. To mtgate tese problems, te awnng was put over te focusng pont of laser-beam on te mage sensor as llustrate n fgure 2b. Te awnng was mae wt te mcroflmng tecnology a crcular ot was prnte on transparent flm as sown n fgure 4b. Te ot ameter was etermne 40µm so as to attenuate te focusng laser-beam satsfactory. f te ameter of awnng was larger, te scattere lgt from large roplets coul not be etecte aequately. Fgure 4a- sows te mages of backgroun lgt wc was capture wt puttng te awnng. Te central black-out pxels an te tly arrange brgt ponts sappeare. Fgure 5 sows te raal strbutons of te backgroun-lgt ntensty. Te ntensty, BK, of te backgroun lgt ecrease monotonously wt te raal stance, R, from te focusng pont. Te strbuton was evaluate usng atonal D-flter n te case wtout awnng. n ts case, te lgt ntensty exceee te upper-lmt of lgt-nput n te central regon, altoug te lgt-ntensty ynamc-range of te sensor was extene by te mage composte tecnque. Wen te awnng was put on te mage sensor, te lgt ntensty n te central regon ecrease. Te awnng woul attenuate te ntensty of focusng laser-beam onto te sensor, but te ntensty strbuton was not affecte so muc n te outer regon of te awnng raus. t s essental tat te focusng pont of laser-beam soul be covere wt te awnng rgtly. Terefore te mage sensor was mounte on te fne austment bases. Vertcal an orzontal postons of te sensor were auste accurately by te a of te austment assstng software evelope n ts stuy, so tat te axs of laser-beam passe troug te center of awnng ot.

4 Fgure 6. Te coaxal segmentaton of te mage for obtanng te raal strbutons of lgt-ntensty. 2.2 Analyss of mage Te mage of backgroun-lgt was capture by te mage sensor n avance, an te mages wt scatterng-lgt from roplets were capture for measurements. Te lgt-ntensty ynamc-range of eac mage was extene to 20bt by compostng tree mages of fferent exposure tmes. Te central pont, G x,g y, of te mage was etermne so tat te backgroun-lgt ntensty strbuton was axsymmetrcal wt respect to te pont, an te mages were segmente nto te coaxal annular regons, as sown n fgure 6. Te central rauses, R, of te annular regons were te geometrcal progresson of common rato,. Te central raus, R, of te nnermost regon was set to 5pxcels 78µm to be not sae by te awnng. Te lgt-ntensty of te mage was evaluate n eac annular regon, an te raal ntensty strbuton of te mage was obtane. Te ntensty of te measurng laser-beam was evaluate from te mean lgt-ntensty n te central crcular regon #0. Te raus of regon #0 was set to 2.5pxels. Wen tere were roplets n te laser-beam, te raal strbuton of te lgt-ntensty,, coul be approxmate by te synteszaton of te backgroun-lgt ntensty, BK, an te ntensty strbutons,, of scattere lgt from te roplets of several representatve ameters as follows: F F F T Were s te angle from measurng laser beam corresponng to raus, R, of te -t annular regon R = f. F s te number frequency of te -t representatve-ameter,. Te transmttance, T, of te measurng laser-beam was estmate at te rato of te lgt-ntensty, 0, of regon #0 urng measurement to tat of backgroun-lgt, BK 0. t mgt be consere tat te number frequency coul be obtane easly by operatng nversely equaton, f te number of annular regons,, agree wt te number of representatve ameters. However, te scattere-lgt ntensty was too weak n larger angles an te scattere-lgt ntensty from small roplets were too weak to solve equaton accurately. Accorngly te scattere-lgt ntenstes from roplets of representatve ameters were converte to te lgt ntenstes per unt volume of roplets, an te lgt ntenstes were ntensfe by multplyng -t power of : Fv Fv Fv T 2 Were Fv s te volume frequency of -t representatve ameter, an s te average scattere-lgt ntensty 3 3.

5 Table. Te results of test measurement of retcle flm on wc many ots of unform ameters were prnte. Dameter of Dots m easure Da. D 32 m Fgure 7. Tral measurements of glass-plate wt spray pattern. Fgure 8. Te test measurement of sol partcles suspene n lqu. Fgure 9. Te rop-sze strbutons of water-spray from fan-spray nozzle. Equaton 2 was solve numercally by te relaxaton meto to obtan te volume frequences, namely te stogram of rop-sze. Te mean roplet ameters were calculate from te stogram. Te value of was set to.5 so tat equaton 2 coul be solve easly. Te value of was set to 0 /2, an te number of te annular regons was 2. Data of for solvng te equaton was calculate usng te Fortran coe of reference 7. Te controllng software was also newly evelope, wc woul capture an composte mages, obtan te lgtntensty strbuton from te mage, an calculate te rop-sze strbuton stogram an te mean roplet ameters from te ntensty strbuton. Te ameter range of measurement was m for te current optcal setup of fgure 3. Te spray of smaller roplets coul also be measure by employng Fourer lens of sorter focal lengt. 3. TRAL EASUREETS Te ameter of unform crcular ots prnte on transparent flm was measure by te newly evelope system. Four flms wt fferent ot ameters were employe. Te flms were mae by mcroflmng tecnology. Te results are lste n table. n every case, Sauter mean ameter, D 32, measure by te system sowe goo agreement wt te ot

6 ameters measure by te potomcrograpy. Te measurng errors soul be ue to te fnte bn-wt of rop-sze stogram wc was use to calculate te mean ameter. Spray pattern prnte on glass plate was also measure as tral. Te results are sown n fgure 7. Obtane rop-sze strbuton almost agree wt tat of potomcrograp analyss. Te suspenson of sol partcle was measure, next. ult-sperse spercal termoplastc power suspene n slcone-ol #0 was measure usng te setup of fgure 8a, wt ncreasng te mass concentraton,, of te power step by step. Te results are sown n fgure 8b. Te transmttance, T, ecrease almost monotonously wt ncrease of te mass-concentraton, namely te optcal ensty of te suspenson. n te range of relatvely small massconcentratons, obtane Sauter mean ameter, D 32, an volume mean ameter, D V50, almost agree wt te power specfcatons evaluate by te potomcrograp analyss, but ecrease slgtly wt ncrease of te mass-concentraton n larger mass-concentratons. Te ecrease soul be ue to te multple-scatterng 3 of laser-beam. However, te effects of te multple-scatterng on te mean ameters were not so serous wtn ts expermental range. Base on tese results, te newly evelope system was apple to te measurement of water-spray from fan-spray nozzle. Te rop-sze strbuton was measure n two cases solo fan-spray an ouble parallel fan-sprays. Te results are sown n fgure 9b. Samplng te spray roplets by te mmerson lqu meto, te rop-sze strbuton was also measure. Te results are sown n fgure 9a. Te rop-sze strbuton by te evelope system almost agree wt tat of te roplet samplng. Tese results support te valty of te evelope system. Te system soul be of use to evaluate te spray caracterstcs of steay sprays wt not so g spray-enstes. 4. COCLUDG REARKS Te smple system of rop-szng was newly evelope by mprovng muc te prevous system base on te laser ffracton meto. Te optcal setup was compose of general optcal parts. Te sem-conuctor laser wt collmator was use as lgt source. Te scattere lgt from roplets was capture by conventonal C-OS mage sensor. Te rop-sze strbuton as well as te mean ameters of spray was measure by analyzng te lgt-ntensty strbuton obtane from te mage. To avo te lgt-ntensty over-range of te sensor, te ynamc-range of lgt-ntensty was extene by te mage composte tecnque. An also, a small crcular awnng was put on te sensor wc woul attenuate te focusng laser-beam onto te sensor. Te poston of sensor was auste precsely so as te focusng pont of laser-beam soul be covere wt te awnng rgtly. Te controllng software was also evelope, wc woul assst te austment of sensor poston, capture te mages of scattere lgt an measure te sze strbuton an te mean ameter of roplets. Several test measurements were performe, an te results supporte te valty of te system. Te newly evelope system woul be of use for te rop-szng of sprays n laboratores. Te system wll also be opene for acaemc researcers, as was te prevous system, after atonal test measurements an tunng. Acknowlegment: Ts work was supporte by SS KAKEH Grant umber REFERECES [] asr,g.g., Yule,A.. an Beng,L., [nustral Atomzaton], Sprnger-Verlag [2] Kuo,K.K.e., [Recent Avances n Spray Combuston: Spray Combuston easurements an oel Smulaton ], AAA 996. [3] SO, [artcle Sze Analyss -Laser Dffracton etos- art : General rncples], SO [4] Suzuk,T., Sato,A., Fumatsu,T. an Hayasa,K., Development of A Smple System of Drop-szng art : Development Story an Outlne of Te System, Atomzaton: ournal of te LASS-apan, 6, n apanese [5] Suzuk,T., Sato,A., Fumatsu,T. an Hayasa,K., Development of A Smple System of Drop-szng art 2: Some Examples of easurements, Atomzaton: ournal of te LASS-apan, 7, n apanese [6] Suzuk, T., Smple System of Drop-szng, Slate, 5 ovember 203, <ttp:// ~ takas/ DSLD/ nex.tml > 5 ovember 203. n apanese ttp:// ~ takas/ [7] to,., Lgt Scatterng Calculaton by e's eto, Researc Report of RC4 Fnal, SE, n apanese