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2016Vol. 1 No. 2: 10

Research Article

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1© Under License of Creative Commons Attribution 3.0 License | This article is available in: http://metrology.imedpub.com

www.imedpub.com Journal of Scientific and Industrial Metrology

ISSN 2472-1948

DOI: 10.21767/2472-1948.100010

Hu D1, Zhang Z1, Guo B2, Li B3 and Bi H1

1 CollegeofElectromechanicalEngineering,QingdaoUniversityofScience&Technology,Qingdao266061,China

2 ChemicalMeasurementLab,ShandongInstituteofMetrology,Jinan250000,China

3 QingdaoOceanShippingMarinersCollege,Qingdao266071,China

Corresponding author: HuD

[email protected]

CollegeofElectromechanicalEngineering,QingdaoUniversityofScience&Technology,Qingdao266061,China.

Tel: 861082388301

Citation:HuD,ZhangZ,GuoB,etal.TheDevelopmentofPM2.5StandardAerosolGeneratorBasedonPGSSMethod.JSciIndMetrol.2016,1:2.

The Development of PM2.5 Standard Aerosol Generator Based on PGSS Method

AbstractThegenerationofstandardaerosolisofvitalimportanceforthePM2.5monitorscalibration.Inthiswork,aPM2.5standardaerosolgeneratorwithhigh-pressuremixing kettle, crystal kettle and nozzle was developed based on the Particlefrom gas saturated solutions (PGSS) approach. The preliminary experiment onthegeneratorshowedthatmorethan90%oftheaerosolparticlesweresmallerthan 2.5 μm in diameter. This work can provide a theoretical basis for thePM2.5monitorscalibration.

Keywords:PM2.5;Aerosolgenerator;PGSS;Mixingkettle

Received: March08,2016; Accepted: March21,2016; Published: March28,2016

IntroductionThe standard aerosol generation is important for thePM2.5monitors calibration. Various techniques are known foraerosol generation such as Atomizationmethod, Fluidized BedmethodandAgglutinationmethod[1].However,thelimitationsofthesetraditionalmethodsmustbefocusedthatAtomizationmethod could only be applied to powder materials dissolvedeasilyinliquid[2],theFluidizedBedmethodiswellknownfortheunevenlydistributedaerosolparticles[3],andtheAgglutinationmethod is only applicable to the particular materials withreactioncharacteristic[4].AnewapproachisthereforeneededinthegenerationofPM2.5standardaerosol.

Thegenerationofnano-micronparticlesbasedon supercriticalfluids,especiallythePGSSapproach,hasmadeagreatprogressinrecentyears.PGSSinvolvesfirstdissolvingthesupercriticalfluidinthemoltenliquidtoformthesaturatedsolution,thensprayingsaturatedsolutionthroughthenozzles,causingthenano-micronparticlestobegenerated[5].Withtheadvantagesoftheloweroperatingpressure, lessdosageofCO2 andnoorganic solvent,etc.,comparedwithothersupercriticalfluidstechnologies,suchas Rapid Expansion of Supercritical Solutions and SupercriticalAnti-Solvent[6],PGSShasbeenwidelyapplied.PGSSwasfirstlyintroducedbyWeidner[7]in2003whochronicallycommittedtothe researchof themicronizationofpolyethyleneglycol [8, 9].Tandyaetal.[10]hadgeneratedcyclosporineparticlesfor1μmusingPGSS.Wang[11]hadgeneratedmenthol/waxmicrocapsulefrom2μmto30μm.TheseaboveshowedthatPGSSisabettermethod for the PM2.5 standard aerosol generation with theadvantage of controlling the diameter and distribution of theparticlesbyonlyadjustingthetemperatureandpressureofthemixing kettle. Therefore, a PM2.5 standard aerosol generation

processbasedon thePGSSwasdeveloped,aswellasaPM2.5standardaerosolgeneratorwasdesignedinthispaper.

Process of PM2.5 Standard Aerosol Generation ThePM2.5standardaerosolgeneratorbasedonPGSSisshowninFigure 1.

1. TheCO2fromtheCO2cylinderisfedthroughtheflowsystem,the value 27 is kept opening to exhaust, and then the CO2

cylindervalveshouldbeclosedbeforetheexperiment.

2. Materialspackedinhigh-pressuremixingkettle13or18,areheatedusingthethermostatinatemperaturehigherthanthefusionpointofthemafterapredeterminedperiodoftimetomeltthem.

3. Openingtherefrigerationequipmenttopresettothecoolingtemperature,thentherelevantvalves2,6,8,10,11(or15)areturnedon.TheCO2fromtheCO2cylinderpassesthroughpurifier,refrigerationequipment,high-pressurepumpinturn

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resulting in a supercritical state, and then flows into high-pressuremixingkettle.

4. The supercritical carbon dioxide in high - pressure mixingkettleismaintainedatthepresetpressureandtemperaturefor0.5hto5hsoastomixwellwiththemeltedmaterials.

5. Uponopeningthevalve16,thesupercriticalcarbondioxideis introduced throughbypass pipeline into thenozzle, thenthevalve14or19 is turnedonthatthemixturefromhigh-pressuremixing kettle is sprayed through thenozzlewithadecompression andexpansion, to avoid theblocking in thegeneration of PM2.5 aerosol, and the supercritical carbondioxideinsidethenozzledesignedthisworkcanfurthermixeswiththemeltedmaterials,aswellasfurtherdispersessmalldroplets.Thentheaerosolgeneratedgetsthroughthevalve27intosubsequentequipment.

The PM2.5 Standard Aerosol Generator Design ThePM2.5standardaerosolgeneratorbasedonPGSSconsistedof the following main components: CO2 cylinders, purifier,refrigerationequipment,andhigh-pressurepump,thermostat,twohigh-pressuremixingkettle,crystalkettle,nozzles.The lastthreecomponentsweredesignedasthemaintaskinthiswork.Thisdesigncanmeetwiththerequirementofthetemperatureandpressureaccording toChineseStandards. Theotherswereselectedfromstandardcomponentwhichcouldalsomeetwiththeexperimentrequirements.

The design of high - pressure mixing kettleThedesignparametersofthehigh-pressuremixingkettlewereasfollows:maximumworkingpressureof15MPa,maximumdesign

temperatureof100°C,andinnerdiameterof30mm.Accordingtothesedesignparameters,thehigh-pressuremixingkettlewasdesigned and calculated according to Chinese Standard TSGR0004-2012[12]andChineseStandardGB150-2011[13].Thethicknessof the shell, themaximumworkingpressureand thethicknessoftheheadcanbecalculatedusingtheformula1-3,respectively.Thestructureofthehigh-pressuremixingkettlewasshowninFigure 2.

c it

c

16.5 55 4.3mm2[ ] 2 114 1.0 16.5

P DP

δσ φ

×= = =

− × × − (1)

t

ew

i e

2 [ ] 2 5 114 1.0[ ] 19MPa55 5

PDδ σ φ

δ× × ×

= = =+ +

(2)

1 4 16 559 26 6114 1 0

cp G t

Kp . .D . mm[ ] .

×δ = = × =

σ ϕ × (3)

Where,δ isshellthickness; Di isinnerdiameter;[σ]tisallowablestressofmaterial;φ isseamcoefficient;

cp isdesignpressure,eδ

iseffectivethickness,DGisthecenterdiameterunderthepressingforce,

pδ isthicknessofthehead,andKisstructurecoefficientof

SchematicdiagramofPM2.5standardaerosolgeneratorbasedonPGSS.1-CO2cylinder;2,6,8,10,11,12,14,15,16,17,19,20,21,27-Valve;3-Purifier;4-FlowMeter;5-RefrigerationEquipment;7-High-PressurePump;9-BufferKettle;13-High-PressureMixingKettle;18-High-PressureMixingKettleII; 22-BufferKettle;23-FlowMeter;24-CrystalKettle;25-MeteringPump;26-SolutionTank.

Figure 1

Diagramofhigh-pressuremixingkettle.1–Nut;2-Bolt;3-CylindricalShell;4-Flange;5,12-FlatHead;6-InletConnection;7-OutletNozzle;8-FlatGasket;9-SinteredPlate;10-SinteredPlateFixedRing;11-EmptyingTube.

Figure 2


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thehead(Figure 2).

The design of crystal kettleThe design parameters of the crystal kettle were as follows:maximum working pressure of 15 MPa and inner diameterof 55 mm. The crystal kettle structure was also designed upto China's Nation Standard and Profession Standard [13], forcalculatingthethicknessoftheshellandtheheadobtainedfromtheEquation(1)and(2),respectively,itwasshowninFigure 3.

The design of nozzleThe nozzle shown in Figure 4 is a coaxial three - channelinternal-mixingsize-adjustingnozzle.Themaincomponentsofitincludethelocknut,sealring,tapersleeveandcore.ThetapersleevewasdesignedaccordingtoChineseStandardJB4732-2005[14].Thethicknessofthetapersleevecanbecalculatedaccordingtotheformula6.Thethreadstresscanbecalculatedaccordingto the formula7.Thesprayingofmixturewasacritical step inthegenerationofPM2.5aerosol,andthesizeofaerosolparticleswasaffectedbyadjustingthenozzleoutletfortheclearancesizewhichwould decrease as the taper sleeve rising owing to thecertainanglebetweenthecoreandtapersleeve. Itmeantthatdifferentdiameterswereachieved inonenozzle rather than in

severaldifferentconventionalnozzles.Thisworknotonlygreatlyreducedthenumberofnozzlesandthemanufacturingcost,butalsowasconvenienttoreplacethenozzlesfrequentlyduringtheexperimentwork.

16 5 29 2 32 2 1 0 114 16 5

c i

m c

P D . . mmKS P . .

×δ = = =

− × × −(4)

2 2 2

4 4 10898 6 26 337 29m

o i

F . . MPa( D D ) ( )

×σ = = =

π − π× − (5)

Where, iD istheinnerdiameteroftapersleeve,oD istheouter

diameteroftapersleeve,Pcisthedesignpressure,K1isloadcombinationfactors, mS isstressintensity, 1δ isthethicknessoftapersleeve,

mσ isthethreadstress,andF is axialload.

Manufacturing and Testing of the PM2.5 Standard Aerosol GeneratorManufacturing of the equipmentThe PM2.5 standard aerosol generator was manufacturedby Nantong Huaan Chaolinjie Co. LTD. High-pressure mixingkettle, crystal kettleand thePM2.5 standardaerosol generatorassembledareshowninFigures 5a-5c,respectively.

Diagramofcrystalkettle.1-FlatHead;2-FlatGasket;3–Nut;4-StudBolt;5-SealingGasket;6-KettleBody;7,9-SupercriticalFluidInletConnection;8-MixtureEntrance;10–Nozzle;11-PressureStrip;12–Window;13-SinteredPlateFixedRing;14-SinteredPlate;15-EmptyingTube

Figure 3

Diagramofcoaxialthree-channelinternal-mixingsize-adjustingnozzle.1-Outlet;2-CentralPipeline;3-BypassPipeline;4-LockNut;5-SealRing;6-TaperSleeve;7-MixingChamber;8-Core

Figure 4

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Testing of the equipmentThe experiment was firstly carried out with the high-pressuremixing kettle keeping at 15 MPa and 90°C for 90 min. Thenmixturewas sprayed through thenozzle into the crystal kettlewhich was maintained in 5.6 MPa at ambient temperatureskeeping the sprayed time for 120 min. In this research, theparticlesofpolyethyleneglycol8000weregeneratedusingPGSSmethod,collectedonthe1000meshsieveinFigure 6a,andthe

Micro-morphologyofthemwastheninvestigatedbythescanningelectronmicrograph(SEM)showninFigure 6b.

Subsequentlyexperimentwasconductedwiththehigh-pressuremixing kettle keeping at 20 MPa and 80°C for 90 min. Thenmixturewas sprayed through the nozzle into the crystal kettlewhich was maintained in 5.6 MPa at ambient temperatureskeeping the sprayed time for 120 min. The particles ofpolyethylene glycol 8000 generated using PGSS method wereshowninFigures 7a and 7b.

(a)

(b)

(c)

PicturesaboutPM2.5standardaerosolgenerator.(a)High-pressuremixingkettle(b)Crystalkettle(c)PM2.5standardaerosolgenerator.

Figure 5

(a)

(b)

Theexperimentresultobtainedwithhigh-pressuremixingkettlekeepingat15MPa,90°Cfor90min(a)Polyethyleneglycolparticles(b)SEMphotograph.

Figure 6


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As shown in Figures 6b and 7b, the particles were small anduniform for overall distribution with more than 90% smallerthan 2.5 μm in diameter, and the others were larger than2.5 μm because a large number of tiny particles aggregatedon the mesh sieve in the colleting process. In order to solvethe particle aggregation problem, the crystal kettle wouldbe equipped with electrostatic ion-generator to electrify theparticles and produce repulsive force so as to overcome theeffects of van derWaals forces to avoid aggregation, and theaerosol was directly sprayed into the aerosol spectrometer todetecttheaerodynamicdiameterofaerosolparticles.

SummaryIn this paper, the PM2.5 standard aerosol generator based onthePGSSwasfirstlydesignedandmanufactured.Andtheresultsofpreliminaryexperiments, inwhichthenano-micronparticlesweregeneratedwithpolyethyleneglycol8000astherawmaterial,showedthatmorethan90%oftheaerosolparticlesweresmallerthan2.5μmindiameter,thisresultissimilartotheAtomizationmethodwithdiameterintherangeof1.3μm-5.8μm[1],andtheotherswerelargerthan2.5μmduetotheaggregationoftinyparticlesonthemeshsieveinthecollectingprocess.Andfurtherstudy on the generation process conditions is still required insubsequentexperimentstorealizesteadygenerationofstandardPM2.5aerosolandmakethedeviceasasteadysourceofPM2.5aerosol. PM2.5 standard aerosol generator will have greatsignificance for the realization of PM2.5 monitors testing andcalibration.

AcknowledgementThe work reported here was supported by the ShandongInstitute of Metrology and the Department of Shandongprovince. We express our grateful thanks to the Science andTechnology Development Plan Project of Shandong Province(2014GSF117026) and Project of Shandong Province HigherEducationalScienceandTechnologyProgram(J13LM08)fortheirfinancialsupport.

(a)

(b)

Theexperimentresultobtainedwithhigh-pressuremixingkettlekeepingat20MPaand80°Cfor90min(a)Polyethyleneglycolparticles(b)SEMphotograph.

Figure 7

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