Ua tsaug rau koj tuaj xyuas Nature.com.Koj siv lub browser version nrog kev txhawb nqa CSS tsawg.Rau qhov kev paub zoo tshaj plaws, peb xav kom koj siv qhov browser tshiab (lossis lov tes taw Compatibility Hom hauv Internet Explorer).Tsis tas li ntawd, txhawm rau xyuas kom muaj kev txhawb nqa tsis tu ncua, peb qhia lub vev xaib tsis muaj qauv thiab JavaScript.
Qhia ib lub carousel ntawm peb slides ib zaug.Siv cov nyees khawm dhau los thiab Tom ntej kom txav mus los ntawm peb qhov swb ib zaug, lossis siv cov khawm slider thaum kawg kom txav mus los ntawm peb qhov swb ib zaug.
Nyob rau hauv txoj kev tshawb no, lub hydrodynamics ntawm flocculation yog soj ntsuam los ntawm kev sim thiab cov zauv tshawb xyuas ntawm cov turbulent flow velocity teb nyob rau hauv ib tug laboratory scale paddle flocculator.Lub turbulent flow uas txhawb cov particle aggregation los yog floc breakup yog complex thiab raug txiav txim thiab muab piv rau hauv daim ntawv no siv ob turbulence qauv, xws li SST k-ω thiab IDDES.Cov txiaj ntsig tau pom tias IDDES muab kev txhim kho me me dhau ntawm SST k-ω, uas yog txaus los simulate ntws hauv lub paddle flocculator.Cov qhab nias haum yog siv los tshawb xyuas qhov sib koom ua ke ntawm PIV thiab CFD cov txiaj ntsig, thiab sib piv cov txiaj ntsig ntawm CFD turbulence qauv siv.Txoj kev tshawb no tseem tsom mus rau qhov ntsuas qhov cuam tshuam k, uas yog 0.18 ntawm qhov nrawm ntawm 3 thiab 4 rpm piv rau cov nqi ib txwm muaj ntawm 0.25.Txo k ntawm 0.25 mus rau 0.18 nce lub zog xa mus rau cov kua dej li ntawm 27-30% thiab nce qhov nrawm nrawm (G) li ntawm 14%.Qhov no txhais tau hais tias kev sib xyaw ua ke ntau dua yog ua tiav ntau dua li qhov xav tau, yog li siv lub zog tsawg dua, thiab yog li ntawd lub zog siv nyob rau hauv flocculation chav tsev ntawm cov dej haus kho cov nroj tsuag tuaj yeem qis dua.
Nyob rau hauv dej purification, qhov sib ntxiv ntawm coagulants destabilizes me me colloidal hais thiab impurities, uas ces muab sib xyaw ua flocculation ntawm lub flocculation theem.Flakes yog xoob khi fractal aggregates ntawm pawg, uas yog tom qab ntawd tshem tawm los ntawm kev daws teeb meem.Particle cov khoom thiab cov kua sib xyaw ua haujlwm txiav txim siab qhov ua tau zoo ntawm flocculation thiab txheej txheem kho.Flocculation yuav tsum muaj kev ntxhov siab qeeb rau lub sijhawm luv luv thiab lub zog ntau kom ua rau muaj dej ntau ntau.
Thaum lub sij hawm flocculation, lub hydrodynamics ntawm tag nrho cov system thiab cov chemistry ntawm coagulant-particle kev sib cuam tshuam txiav txim seb tus nqi ntawm ib tug nyob ruaj ruaj particle loj faib yog tiav2.Thaum cov khoom sib tsoo, lawv lo rau ib leeg 3.Oyegbile, Ay4 tau tshaj tawm tias kev sib tsoo yog nyob ntawm lub flocculation thauj mechanisms ntawm Brownian diffusion, kua shear thiab qhov sib txawv.Thaum cov flakes sib tsoo, lawv loj hlob thiab ncav cuag qhov loj me me, uas tuaj yeem ua rau tawg, vim cov flakes tsis tuaj yeem tiv taus lub zog ntawm hydrodynamic zog 5.Qee cov flakes tawg no recombine rau hauv me me los yog tib qhov loj 6.Txawm li cas los xij, cov flakes muaj zog tuaj yeem tiv taus qhov quab yuam no thiab tswj lawv qhov loj thiab txawm tias loj hlob 7.Yukselen thiab Gregory8 tau tshaj tawm txog cov kev tshawb fawb ntsig txog kev puas tsuaj ntawm flakes thiab lawv lub peev xwm rov tsim dua tshiab, qhia tias qhov tsis tuaj yeem raug txwv.Bridgeman, Jefferson9 tau siv CFD los kwv yees lub zog hauv cheeb tsam ntawm lub ntsiab lus ntws thiab turbulence ntawm floc tsim thiab fragmentation los ntawm lub zos tshaj tawm gradients.Nyob rau hauv lub tso tsheb hlau luam nruab nrog rotor hniav, nws yog ib qhov tsim nyog los sib txawv qhov ceev ntawm cov aggregates sib tsoo nrog lwm yam hais thaum lawv muaj txaus destabilized nyob rau hauv lub coagulation theem.Los ntawm kev siv CFD thiab qis kev sib hloov ceev ntawm ib ncig ntawm 15 rpm, Vadasarukkai thiab Gagnon11 tau ua tiav G qhov tseem ceeb rau flocculation nrog conical hniav, yog li txo qis zog noj rau agitation.Txawm li cas los xij, kev ua haujlwm ntawm G tus nqi siab dua tuaj yeem ua rau flocculation.Lawv tau tshawb xyuas cov txiaj ntsig ntawm kev sib xyaw ceev ntawm kev txiav txim siab qhov nruab nrab tshaj tawm gradient ntawm tus tsav paddle flocculator.Lawv tig ntawm qhov ceev ntawm ntau tshaj 5 rpm.
Korpijärvi, Ahlstedt12 siv plaub qhov sib txawv turbulence qauv los kawm txog cov dej ntws ntawm lub tank xeem lub rooj ntev zaum.Lawv ntsuas qhov chaw ntws nrog lub laser Doppler anemometer thiab PIV thiab muab piv cov txiaj ntsig suav nrog cov ntsuas ntsuas.de Oliveira thiab Donadel13 tau npaj ib txoj hauv kev rau kev kwv yees qhov nrawm nrawm los ntawm hydrodynamic zog siv CFD.Txoj kev npaj tau raug sim ntawm rau lub flocculation units raws li helical geometry.soj ntsuam cov txiaj ntsig ntawm lub sijhawm khaws cia ntawm flocculants thiab tau npaj cov qauv flocculation uas tuaj yeem siv los ua ib qho cuab yeej los txhawb kev tsim qauv ntawm tes nrog lub sijhawm tuav tsawg 14.Zhan, You15 tau npaj ib qho kev sib koom ua ke CFD thiab cov qauv ntawm cov pej xeem sib npaug los simulate cov yam ntxwv ntws thiab tus cwj pwm floc hauv tag nrho cov nplai flocculation.Llano-Serna, Coral-Portillo16 tau tshawb xyuas cov yam ntxwv ntws ntawm Cox-type hydroflocculator hauv cov chaw kho dej hauv Viterbo, Colombia.Txawm hais tias CFD muaj nws qhov zoo, kuj tseem muaj kev txwv xws li cov lej yuam kev hauv kev suav.Yog li ntawd, txhua qhov txiaj ntsig tau txais yuav tsum tau ua tib zoo tshuaj xyuas thiab tshuaj xyuas txhawm rau txhawm rau txiav txim siab qhov tseem ceeb17.Muaj qee qhov kev tshawb fawb hauv cov ntaub ntawv ntawm kev tsim cov kab rov tav baffle flocculators, thaum cov lus pom zoo rau kev tsim cov hydrodynamic flocculators yog txwv 18.Chen, Liao19 tau siv qhov kev sim teeb tsa raws li kev tawg ntawm lub teeb polarized los ntsuas lub xeev ntawm polarization ntawm cov teeb tawg ntawm ib tus neeg.Feng, Zhang20 siv Ansys-Fluent los simulate kev faib cov eddy tam sim no thiab swirl nyob rau hauv lub ndlwg teb ntawm ib coagulated phaj flocculator thiab ib tug inter-corrugated flocculator.Tom qab simulating turbulent kua ntws hauv flocculator siv Ansys-Fluent, Gavi21 siv cov txiaj ntsig los tsim lub flocculator.Vaneli thiab Teixeira22 tau tshaj tawm tias kev sib raug zoo ntawm cov kua dej ntawm cov kauv raj flocculators thiab cov txheej txheem flocculation tseem tsis to taub los txhawb kev tsim qauv tsim nyog.de Oliveira thiab Costa Teixeira23 tau kawm txog kev ua tau zoo thiab ua kom pom cov khoom siv hydrodynamic ntawm cov kauv raj flocculator los ntawm kev sim physics thiab CFD simulations.Ntau tus kws tshawb fawb tau kawm coiled tube reactors lossis coiled tube flocculators.Txawm li cas los xij, cov ncauj lus kom ntxaws txog hydrodynamic cov lus teb ntawm cov reactors rau ntau yam kev tsim thiab kev ua haujlwm tseem tsis muaj (Sartori, Oliveira24; Oliveira, Teixeira25).Oliveira thiab Teixeira26 nthuav tawm thawj cov txiaj ntsig los ntawm theoretical, kev sim thiab CFD simulations ntawm kauv flocculator.Oliveira thiab Teixeira27 tau thov kom siv cov kauv kauj ua lub coagulation-flocculation reactor ua ke nrog cov pa decanter system.Lawv tshaj tawm tias cov txiaj ntsig tau txais rau turbidity tshem tawm efficiency yog qhov sib txawv ntawm cov uas tau txais nrog cov qauv siv los ntsuas flocculation, qhia ceev faj thaum siv cov qauv zoo li no.Moruzzi thiab de Oliveira [28] tau ua qauv coj tus cwj pwm ntawm cov kab ke ntawm kev nruam flocculation chambers nyob rau hauv ntau yam kev khiav hauj lwm, nrog rau kev hloov pauv ntawm cov chav siv thiab kev siv cov taag lossis scaled cell velocity gradients.Romphophak, Le Men29 PIV kev ntsuas qhov nrawm nrawm hauv quasi-ob-dimensional dav hlau ntxuav.Lawv pom muaj zog dav hlau induced ncig nyob rau hauv lub flocculation cheeb tsam thiab kwv yees lub zos thiab instantaneous shear tus nqi.
Shah, Joshi30 qhia tias CFD muaj lwm txoj hauv kev zoo rau kev txhim kho cov qauv tsim thiab tau txais cov yam ntxwv ntws zoo.Qhov no yuav pab kom tsis txhob muaj kev sim ntau yam teeb tsa.CFD tau siv ntau dua los txheeb xyuas cov dej thiab cov dej khib nyiab (Melo, Freire31; Alalm, Nasr32; Bridgeman, Jefferson9; Samaras, Zouboulis33; Wang, Wu34; Zhang, Tejada-Martínez35).Ntau tus neeg tshawb nrhiav tau ua qhov kev sim ntawm cov cuab yeej siv tau (Bridgeman, Jefferson36; Bridgeman, Jefferson5; Jarvis, Jefferson6; Wang, Wu34) thiab perforated disc flocculators31.Lwm tus tau siv CFD los ntsuas cov hydroflocculators (Bridgeman, Jefferson5; Vadasarukkai, Gagnon37).Ghawi21 tau tshaj tawm tias cov tshuab flocculators xav tau kev saib xyuas tsis tu ncua vim lawv feem ntau tawg thiab xav tau hluav taws xob ntau.
Kev ua haujlwm ntawm paddle flocculator yog nyob ntawm qhov hydrodynamics ntawm lub reservoir heev.Qhov tsis muaj kev nkag siab ntau ntawm cov dej ntws nrawm hauv cov flocculators yog qhia meej hauv cov ntaub ntawv (Howe, Hand38; Hendricks39).Tag nrho cov dej loj yog raug rau kev txav ntawm lub flocculator impeller, yog li xav tias slippage.Feem ntau, cov dej tshaj tawm yog tsawg dua li cov hniav tshaj tawm los ntawm qhov kev sib tw k, uas txhais tau tias yog qhov sib piv ntawm qhov nrawm ntawm lub cev ntawm cov dej mus rau qhov nrawm ntawm lub paddle log.Bhole40 tau tshaj tawm tias muaj peb yam tseem ceeb uas tsis paub yuav xav txog thaum tsim lub flocculator, uas yog qhov nrawm nrawm, tus cab coefficient, thiab qhov txheeb ze ntawm cov dej txheeb ze rau cov hniav.
Camp41 tau tshaj tawm tias thaum xav txog cov tshuab ceev ceev, qhov ceev yog li ntawm 24% ntawm cov rotor ceev thiab siab li 32% rau cov tshuab qis.Thaum tsis muaj septa, Droste thiab Ger42 siv ak tus nqi ntawm 0.25, thaum nyob rau hauv cov ntaub ntawv ntawm septa, k ranged ntawm 0 mus rau 0.15.Howe, Hand38 qhia tias k yog nyob rau hauv thaj tsam ntawm 0.2 txog 0.3.Hendrix39 muaj feem cuam tshuam rau qhov cuam tshuam rau kev sib hloov ceev uas siv cov qauv qhia pom thiab xaus lus tias qhov cuam tshuam hauv qab kuj tseem nyob hauv thaj tsam tsim los ntawm Camp41.Bratby43 qhia tias k yog li ntawm 0.2 rau impeller speeds ntawm 1.8 mus rau 5.4 rpm thiab nce mus rau 0.35 rau impeller speeds ntawm 0.9 mus rau 3 rpm.Lwm cov kws tshawb fawb tau tshaj tawm ntau qhov sib txawv ntawm cov coefficient (Cd) qhov tseem ceeb ntawm 1.0 txog 1.8 thiab nplawm coefficient k qhov tseem ceeb ntawm 0.25 txog 0.40 (Feir thiab Geyer44; Hyde thiab Ludwig45; Harris, Kaufman46; van Duuren47 thiab Brast; thiab Brat. ).Cov ntaub ntawv tsis qhia txog kev nce qib tseem ceeb hauv kev txhais thiab ntsuas k txij li Camp41 txoj haujlwm.
Cov txheej txheem flocculation yog ua raws li kev kub ntxhov los pab txhawb kev sib tsoo, qhov twg qhov nrawm nrawm (G) yog siv los ntsuas turbulence / flocculation.Kev sib tov yog cov txheej txheem sai thiab sib npaug ntawm cov tshuaj dispersing hauv dej.Qhov degree ntawm kev sib xyaw yog ntsuas los ntawm kev tshaj tawm gradient:
qhov twg G = velocity gradient (sec-1), P = power input (W), V = ntim dej (m3), μ = dynamic viscosity (Pa s).
Qhov siab dua tus nqi G, qhov sib xyaw ntau dua.Kev sib xyaw ua ke yog qhov tseem ceeb kom ntseeg tau tias coagulation tsis sib xws.Cov ntaub ntawv qhia tias qhov tseem ceeb tshaj plaws ntawm cov qauv tsim yog sib xyaw lub sijhawm (t) thiab nrawm nrawm (G).Cov txheej txheem flocculation yog ua raws li kev kub ntxhov los pab txhawb kev sib tsoo, qhov twg qhov nrawm nrawm (G) yog siv los ntsuas turbulence / flocculation.Tus qauv tsim qhov tseem ceeb rau G yog 20 txog 70 s–1, t yog 15 mus rau 30 feeb, thiab Gt (dimensionless) yog 104 txog 105. Fast mix tanks ua haujlwm zoo tshaj plaws nrog G tus nqi ntawm 700 txog 1000, nrog sijhawm nyob. txog 2 feeb.
qhov twg P yog lub hwj chim imparted rau cov kua los ntawm txhua lub flocculator hniav, N yog qhov kev sib hloov ceev, b yog cov hniav ntev, ρ yog cov dej ntom ntom, r yog lub vojvoog, thiab k yog tus swb coefficient.Qhov kev sib npaug no yog siv rau txhua tus hniav ntawm tus kheej thiab cov txiaj ntsig tau suav tias muab tag nrho lub zog nkag ntawm flocculator.Kev ua tib zoo kawm txog qhov kev sib npaug no qhia tau hais tias qhov tseem ceeb ntawm qhov cuam tshuam k hauv cov txheej txheem tsim ntawm paddle flocculator.Cov ntaub ntawv tsis qhia tus nqi tiag tiag ntawm k, tab sis nws pom zoo kom muaj ntau yam raws li tau hais dhau los.Txawm li cas los xij, kev sib raug zoo ntawm lub hwj chim P thiab tus swb coefficient k yog cubic.Yog li, yog tias txhua yam tsis zoo ib yam, piv txwv li, hloov k ntawm 0.25 mus rau 0.3 yuav ua rau txo qis ntawm lub zog xa mus rau cov kua hauv ib lub taub hau li 20%, thiab txo k ntawm 0.25 mus rau 0.18 yuav ua rau nws nce.los ntawm li 27-30% ib lub vane Lub zog muab tso rau hauv cov kua.Thaum kawg, qhov cuam tshuam ntawm k ntawm kev ruaj ntseg paddle flocculator tsim yuav tsum tau tshawb xyuas los ntawm kev ntsuas kev ntsuas.
Qhov tseeb empirical quantification ntawm slippage yuav tsum tau ntws visualization thiab simulation.Yog li ntawd, nws yog ib qho tseem ceeb uas yuav tau piav qhia txog qhov ceev ntawm tangential ntawm cov hniav hauv dej ntawm ib qho kev sib hloov ceev ntawm qhov sib txawv radial nrug ntawm tus ncej thiab ntawm qhov sib txawv ntawm qhov tob ntawm cov dej kom ntsuam xyuas cov nyhuv ntawm cov hniav sib txawv.
Nyob rau hauv txoj kev tshawb no, lub hydrodynamics ntawm flocculation yog soj ntsuam los ntawm kev sim thiab cov zauv tshawb xyuas ntawm cov turbulent flow velocity teb nyob rau hauv ib tug laboratory scale paddle flocculator.Cov kev ntsuas PIV raug kaw rau ntawm lub flocculator, tsim lub sij hawm nruab nrab ntawm qhov kev sib tw uas qhia qhov nrawm ntawm cov dej nyob ib ncig ntawm nplooj.Tsis tas li ntawd, ANSYS-Fluent CFD tau siv los simulate qhov swirling ntws hauv lub flocculator thiab tsim lub sij hawm nruab nrab tshaj tawm contours.Qhov txiaj ntsig CFD qauv tau lees paub los ntawm kev ntsuam xyuas cov ntawv xov xwm ntawm PIV thiab CFD cov txiaj ntsig.Lub hom phiaj ntawm txoj haujlwm no yog txhawm rau txhawm rau txhawm rau txhawm rau coefficient k, uas yog qhov tsis muaj qhov tsim qauv ntawm paddle flocculator.Cov haujlwm uas tau nthuav tawm ntawm no muab lub hauv paus tshiab rau kev suav cov nplawm coefficient k ntawm qhov nrawm ntawm 3 rpm thiab 4 rpm.Qhov cuam tshuam ntawm cov txiaj ntsig ncaj qha ua rau muaj kev nkag siab zoo dua ntawm hydrodynamics ntawm flocculation tank.
Lub chaw soj nstuam flocculator muaj lub thawv qhib sab saum toj nrog qhov siab tag nrho ntawm 147 cm, qhov siab ntawm 39 cm, qhov dav dav ntawm 118 cm, thiab tag nrho ntev ntawm 138 cm (Fig. 1).Cov qauv tsim tseem ceeb tsim los ntawm Camp49 tau siv los tsim lub chaw kuaj ntsuas paddle flocculator thiab siv cov ntsiab lus ntawm qhov ntsuas qhov ntev.Qhov chaw sim tau tsim los ntawm Environmental Engineering Laboratory ntawm Lebanese American University (Byblos, Lebanon).
Kab rov tav axis nyob ntawm qhov siab ntawm 60 cm los ntawm hauv qab thiab haum rau ob lub log paddle.Txhua lub paddle log muaj 4 paddles nrog 3 paddles ntawm txhua paddle rau tag nrho ntawm 12 paddles.Flocculation yuav tsum maj mam agitation ntawm qhov ceev ntawm 2 mus rau 6 rpm.Qhov sib xyaw ua kom nrawm tshaj plaws hauv flocculators yog 3 rpm thiab 4 rpm.Lub chaw soj ntsuam nplai flocculator ntws yog tsim los sawv cev rau qhov ntws hauv lub flocculation tank compartment ntawm lub chaw kho dej haus.Lub zog yog suav nrog kev sib npaug ib txwm muaj 42 .Rau ob qhov kev sib hloov ceev, qhov ceev gradient \(\stackrel{\mathrm{-}}{\text{G}}\) yog ntau dua 10 \({\text{sec}}^{-{1}}\) , tus lej Reynolds qhia tias muaj kev kub ntxhov (Table 1).
PIV yog siv los ua kom tau qhov tseeb thiab ntau qhov kev ntsuas ntawm cov kua hluav taws xob vectors ib txhij ntawm ntau cov ntsiab lus 50.Qhov kev sim teeb tsa suav nrog lub ntsuas ntsuas paddle flocculator, LaVision PIV system (2017), thiab Arduino sab nraud laser sensor ua rau.Txhawm rau tsim lub sijhawm nruab nrab ntawm qhov nrawm nrawm, PIV cov duab raug kaw ua ntu zus ntawm tib qhov chaw.Lub PIV system yog calibrated xws li hais tias lub hom phiaj cheeb tsam yog nyob rau nruab nrab ntawm qhov ntev ntawm txhua ntawm peb cov hniav ntawm ib tug tshwj xeeb paddle caj npab.Sab nraud trigger muaj ib lub laser nyob rau ntawm ib sab ntawm lub flocculator dav thiab ib tug sensor receiver nyob rau sab nraud.Txhua zaus lub flocculator caj npab thaiv txoj kev laser, lub teeb liab raug xa mus rau PIV system kom ntes cov duab nrog PIV laser thiab lub koob yees duab synchronized nrog lub sijhawm programmable.Ntawm daim duab.2 qhia txog kev teeb tsa ntawm PIV system thiab cov txheej txheem tau txais cov duab.
Kev kaw lus ntawm PIV tau pib tom qab lub flocculator tau ua haujlwm rau 5-10 min kom normalize cov dej ntws thiab coj mus rau hauv tus account tib lub refractive index teb.Calibration yog ua tiav los ntawm kev siv lub phaj calibration rau hauv lub flocculator thiab muab tso rau ntawm qhov nruab nrab ntawm qhov ntev ntawm cov hniav ntawm kev txaus siab.Kho qhov chaw ntawm PIV laser los ua ib daim ntawv tiaj tus ncaj ncaj saum lub phaj calibration.Sau qhov ntsuas qhov ntsuas rau txhua qhov kev sib hloov ceev ntawm txhua lub ntsej muag, thiab qhov kev sib hloov ceev uas tau xaiv rau qhov kev sim yog 3 rpm thiab 4 rpm.
Rau tag nrho cov ntaub ntawv PIV, lub sijhawm ncua ntawm ob lub laser pulses tau teeb tsa nyob rau hauv thaj tsam ntawm 6900 txog 7700 µs, uas tso cai rau qhov tsawg kawg nkaus hloov pauv ntawm 5 pixels.Kev sim ntsuas tau ua tiav ntawm tus lej ntawm cov duab xav tau kom tau txais qhov ntsuas qhov tseeb ntawm lub sijhawm.Vector txheeb cais tau muab piv rau cov qauv uas muaj 40, 50, 60, 80, 100, 120, 160, 200, 240, thiab 280 duab.Ib qho piv txwv loj ntawm 240 cov duab tau pom los muab cov txiaj ntsig ruaj khov-nruab nrab muab tau tias txhua daim duab muaj ob daim duab.
Txij li thaum cov dej ntws hauv flocculator yog turbulent, ib lub qhov rai interrogation me me thiab ib tug loj tus nqi yuav tsum tau daws cov teeb meem me me.Ob peb qhov kev txo qhov loj me yog siv nrog rau kev sib raug zoo sib xws los xyuas kom meej.Thawj qhov kev xaiv tsa qhov rais loj ntawm 48 × 48 pixels nrog 50% sib tshooj thiab ib txoj kev hloov kho tau ua raws li qhov kawg ntawm qhov kev xaiv tsa qhov loj ntawm 32 × 32 pixels nrog 100% sib tshooj thiab ob txoj kev hloov kho.Tsis tas li ntawd, iav hollow spheres tau siv los ua cov noob hauv cov dej ntws, uas tso cai tsawg kawg 10 feem ntawm ib lub qhov rais xaiv tsa.PIV cov ntaubntawv povthawj siv yog tshwm sim los ntawm qhov tshwm sim hauv Programmable Timing Unit (PTU), uas yog lub luag haujlwm rau kev khiav haujlwm thiab synchronizing lub laser qhov chaw thiab lub koob yees duab.
Kev lag luam CFD pob ANSYS Fluent v 19.1 tau siv los tsim cov qauv 3D thiab daws cov kev sib npaug hauv paus.
Siv ANSYS-Fluent, tus qauv 3D ntawm lub chaw soj nstuam-scale paddle flocculator tau tsim.Tus qauv yog tsim nyob rau hauv daim ntawv ntawm ib lub thawv, muaj ob lub log paddle mounted ntawm ib tug kab rov tav axis, zoo li cov qauv kuaj.Tus qauv tsis muaj freeboard yog 108 cm siab, 118 cm dav thiab 138 cm ntev.Kab rov tav cylindrical dav hlau tau ntxiv nyob ib ncig ntawm lub tov khoom.Cylindrical dav hlau tiam yuav tsum siv qhov kev sib hloov ntawm tag nrho cov tov khoom thaum lub sij hawm installation thiab simulate lub rotating flow teb nyob rau hauv lub flocculator, raws li qhia nyob rau hauv daim duab 3a.
3D ANSYS-nplua nuj thiab qauv geometry daim duab, ANSYS-fluent flocculator lub cev mesh ntawm lub dav hlau txaus siab, ANSYS-npaum daim duab ntawm lub dav hlau txaus siab.
Cov qauv geometry muaj ob thaj tsam, txhua qhov yog cov kua dej.Qhov no yog tiav los ntawm kev siv lub logical rho tawm muaj nuj nqi.Ua ntej rho tawm lub tog raj kheej (suav nrog tov khoom) los ntawm lub thawv los sawv cev rau cov kua.Tom qab ntawd rho tawm lub tov khoom los ntawm lub tog raj kheej, ua rau ob yam khoom: lub tov khoom thiab cov kua.Thaum kawg, zawv zawg interface tau siv los ntawm ob qhov chaw: lub tog raj kheej-lub tog raj kheej interface thiab lub tog raj kheej-tsim interface (Fig. 3a).
Lub meshing ntawm cov qauv tsim tau ua tiav kom tau raws li qhov yuav tsum tau ua ntawm cov qauv turbulence uas yuav siv los khiav cov lej simulations.Ib qho mesh uas tsis muaj kev sib txuas nrog cov txheej txheem nthuav dav nyob ze ntawm cov khoom nto tau siv.Tsim cov khaubncaws sab nraud povtseg rau txhua phab ntsa nrog kev loj hlob ntawm 1.2 los xyuas kom meej tias cov qauv ntws tau yooj yim raug ntes, nrog thawj txheej tuab ntawm \(7\mathrm{x }{10}^{-4}\) m kom ntseeg tau tias \ ({\text {y))^{+}\le 1.0\).Lub cev loj yog hloov kho siv txoj kev tetrahedron haum.Ib sab pem hauv ntej loj ntawm ob lub interfaces nrog lub ntsiab loj ntawm 2.5 × \({10}^{-3}\) m yog tsim, thiab ib tug mixer pem hauv ntej loj ntawm 9 × \({10}^{-3}\) m siv.Qhov pib tsim mesh muaj 2144409 ntsiab lus (Fig. 3b).
Ib tug ob-parameter k-ε turbulence qauv raug xaiv los ua tus qauv pib.Txhawm rau simulate qhov swirling ntws hauv lub flocculator kom raug, tus qauv kim kim dua raug xaiv.Lub turbulent swirling ntws nyob rau hauv lub flocculator yog suav nrog siv ob CFD qauv: SST k–ω51 thiab IDDES52.Cov txiaj ntsig ntawm ob tus qauv tau muab piv nrog kev sim PIV cov txiaj ntsig los ua pov thawj cov qauv.Ua ntej, tus qauv SST k-ω turbulence yog ib qho piv txwv ntawm ob qhov sib npaug viscosity qauv rau cov kua dej dynamics.Qhov no yog ib tug hybrid qauv combining Wilcox k-ω thiab k-ε qauv.Kev sib xyaw ua haujlwm ua rau Wilcox qauv nyob ze ntawm phab ntsa thiab cov qauv k-ε nyob rau hauv cov dej ntws.Qhov no ua kom paub tseeb tias tus qauv raug siv thoob plaws hauv qhov chaw ntws.Nws raug kwv yees tias ntws sib cais vim qhov tsis zoo siab gradients.Thib ob, Advanced Deferred Eddy Simulation (IDDES) txoj kev, dav siv hauv Individual Eddy Simulation (DES) qauv nrog SST k-ω RANS (Reynolds-Averaged Navier-Stokes) qauv, raug xaiv.IDDES yog ib tug hybrid RANS-LES (loj eddy simulation) qauv uas muab ib tug ntau saj zawg zog thiab user-friendly daws teeb meem scaling (SRS) simulation qauv.Nws yog ua raws li tus qauv LES los daws cov eddies loj thiab rov qab mus rau SST k-ω los simulate me me nplai eddies.Kev txheeb cais ntawm cov txiaj ntsig tau los ntawm SST k–ω thiab IDDES simulations tau muab piv nrog cov txiaj ntsig PIV kom siv tau tus qauv.
Ib tug ob-parameter k-ε turbulence qauv raug xaiv los ua tus qauv pib.Txhawm rau simulate qhov swirling ntws hauv lub flocculator kom raug, tus qauv kim kim dua raug xaiv.Lub turbulent swirling ntws nyob rau hauv lub flocculator yog suav nrog siv ob CFD qauv: SST k–ω51 thiab IDDES52.Cov txiaj ntsig ntawm ob tus qauv tau muab piv nrog kev sim PIV cov txiaj ntsig los ua pov thawj cov qauv.Ua ntej, tus qauv SST k-ω turbulence yog ib qho piv txwv ntawm ob qhov sib npaug viscosity qauv rau cov kua dej dynamics.Qhov no yog ib tug hybrid qauv combining Wilcox k-ω thiab k-ε qauv.Kev sib xyaw ua haujlwm ua rau Wilcox qauv nyob ze ntawm phab ntsa thiab cov qauv k-ε nyob rau hauv cov dej ntws.Qhov no ua kom paub tseeb tias tus qauv raug siv thoob plaws hauv qhov chaw ntws.Nws raug kwv yees tias ntws sib cais vim qhov tsis zoo siab gradients.Thib ob, Advanced Deferred Eddy Simulation (IDDES) txoj kev, dav siv hauv Individual Eddy Simulation (DES) qauv nrog SST k-ω RANS (Reynolds-Averaged Navier-Stokes) qauv, raug xaiv.IDDES yog ib tug hybrid RANS-LES (loj eddy simulation) qauv uas muab ib tug ntau saj zawg zog thiab user-friendly daws teeb meem scaling (SRS) simulation qauv.Nws yog ua raws li tus qauv LES los daws cov eddies loj thiab rov qab mus rau SST k-ω los simulate me me nplai eddies.Kev txheeb cais ntawm cov txiaj ntsig tau los ntawm SST k–ω thiab IDDES simulations tau muab piv nrog cov txiaj ntsig PIV kom siv tau tus qauv.
Siv lub zog-raws li kev daws teeb meem thiab siv lub ntiajteb txawj nqus hauv Y kev taw qhia.Kev sib hloov yog ua tiav los ntawm kev muab lub mesh txav mus rau lub tov khoom, qhov twg lub hauv paus chiv keeb ntawm kev sib hloov axis yog nyob rau hauv nruab nrab ntawm kab rov tav axis thiab cov kev taw qhia ntawm kev sib hloov axis yog nyob rau hauv Z kev taw qhia.Ib lub mesh interface yog tsim rau ob qho tib si qauv geometry interfaces, uas ua rau ob qho tib si bounding box npoo.Raws li nyob rau hauv cov txheej txheem sim, qhov kev sib hloov ceev sib haum mus rau 3 thiab 4 revolutions.
Cov ciam teb tej yam kev mob rau phab ntsa ntawm lub tov khoom thiab lub flocculator yog teem los ntawm phab ntsa, thiab sab saum toj qhib ntawm lub flocculator yog teem los ntawm lub qhov hluav taws xob nrog xoom gauge siab (Fig. 3c).SIMPLE siab-ceev kev sib txuas lus tswv yim, discretization ntawm gradient qhov chaw ntawm qhov thib ob-order functions nrog tag nrho cov tsis raws li nyob rau hauv tsawg squares ntsiab.Lub convergence criterion rau tag nrho cov ndlwg variables yog scaled residual 1 x \({10}^{-3}\).Qhov siab tshaj plaws ntawm iterations ib lub sij hawm kauj ruam yog 20, thiab lub sij hawm kauj ruam loj sib hloov mus rau 0.5 °.Cov kev daws teeb meem sib txuas ntawm 8th iteration rau SST k–ω qauv thiab ntawm 12th iteration siv IDDES.Tsis tas li ntawd, tus naj npawb ntawm lub sij hawm cov kauj ruam tau xam kom lub tov khoom ua yam tsawg kawg yog 12 revolutions.Siv cov ntaub ntawv piv txwv rau lub sij hawm txheeb cais tom qab 3 kev sib hloov, uas tso cai rau normalization ntawm ntws, zoo ib yam li cov txheej txheem sim.Sib piv cov zis ntawm lub voj voog ceev rau txhua lub kiv puag ncig muab cov txiaj ntsig zoo ib yam rau plaub lub kiv puag ncig kawg, qhia tias lub xeev khov kho tau mus txog.Qhov ntxiv revs tsis txhim kho qhov nruab nrab ceev contours.
Lub sij hawm kauj ruam yog txhais nyob rau hauv relation mus rau qhov kev sib hloov ceev, 3 rpm los yog 4 rpm.Lub sij hawm kauj ruam yog refined rau lub sij hawm yuav tsum tau tig lub tov khoom los ntawm 0.5 °.Qhov no hloov tawm kom txaus, txij li qhov kev daws teeb meem sib txuas tau yooj yim, raws li tau piav qhia hauv ntu dhau los.Yog li, tag nrho cov lej suav rau ob tus qauv turbulence tau ua tiav siv lub sijhawm hloov pauv ntawm 0.02 \(\stackrel{\mathrm{-}}{7}\) rau 3 rpm, 0.0208 \(\stackrel{ \mathrm{-} {3}\) 4 rpm.Rau lub sijhawm ua kom zoo dua cov kauj ruam, Courant tus lej ntawm ib lub xovtooj ib txwm tsawg dua 1.0.
Txhawm rau tshawb nrhiav cov qauv-mesh kev vam khom, cov txiaj ntsig tau xub tau siv thawj 2.14M mesh thiab tom qab ntawd ua kom zoo dua 2.88M mesh.Grid refinement yog ua tiav los ntawm kev txo cov cell loj ntawm lub tov khoom ntawm 9 × \({10}^{-3}\) m rau 7 × \({10}^{-3}\) m.Rau qhov qub thiab ua kom zoo meshes ntawm ob lub qauv turbulence, qhov nruab nrab qhov tseem ceeb ntawm cov qauv nrawm hauv ntau qhov chaw nyob ib puag ncig cov hniav tau muab piv rau.Qhov feem pua ntawm cov txiaj ntsig sib txawv yog 1.73% rau tus qauv SST k–ω thiab 3.51% rau tus qauv IDDES.IDDES qhia qhov feem pua ntawm qhov sib txawv ntau dua vim tias nws yog tus qauv RANS-LES hybrid.Cov kev sib txawv no tau suav tias yog qhov tsis tseem ceeb, yog li kev simulation tau ua tiav siv cov mesh qub nrog 2.14 lab lub ntsiab lus thiab lub sijhawm sib hloov ntawm 0.5 °.
Kev rov ua dua tshiab ntawm qhov kev sim tau raug tshuaj xyuas los ntawm kev ua txhua qhov ntawm rau qhov kev sim thib ob thiab sib piv cov txiaj ntsig.Sib piv cov nqi ceev ntawm qhov nruab nrab ntawm cov hniav hauv ob txoj kev sim.Qhov nruab nrab feem pua ntawm qhov sib txawv ntawm ob pawg sim yog 3.1%.PIV system kuj tau rov ua dua tshiab rau txhua qhov kev sim.Sib piv cov kev ntsuas ntsuas ceev ntawm qhov nruab nrab ntawm txhua qhov hniav nrog PIV ceev ntawm tib qhov chaw.Qhov kev sib piv no qhia qhov sib txawv nrog qhov feem pua siab tshaj plaws ntawm 6.5% rau cov hniav 1.
Ua ntej ntsuas qhov cuam tshuam, nws yog ib qho tsim nyog yuav tsum nkag siab txog lub tswv yim ntawm plam hauv lub paddle flocculator, uas yuav tsum tau kawm cov qauv ntws nyob ib ncig ntawm lub paddles ntawm flocculator.Conceptually, lub plam coefficient yog tsim rau hauv tus tsim ntawm paddle flocculators coj mus rau hauv tus account qhov ceev ntawm cov hniav txheeb ze rau cov dej.Cov ntaub ntawv pom zoo tias qhov ceev no yog 75% ntawm cov hniav ceev, yog li feem ntau cov qauv siv ak ntawm 0.25 los suav rau qhov kev hloov kho no.Qhov no yuav tsum tau siv cov kev nrawm nrawm uas tau txais los ntawm PIV cov kev sim kom nkag siab txog qhov ntws nrawm thiab kawm daim ntawv no.Hniav 1 yog cov hniav sab hauv tshaj plaws nyob ze rau ntawm ncej, hniav 3 yog cov hniav sab nrauv, thiab hniav 2 yog cov hniav nruab nrab.
Lub nrawm nrawm nrawm ntawm cov hniav 1 qhia qhov ncaj qha rotating ntws ncig ntawm cov hniav.Cov qauv ntws no tawm los ntawm qhov taw tes ntawm sab xis ntawm cov hniav, nruab nrab ntawm lub rotor thiab cov hniav.Saib ntawm thaj chaw uas qhia los ntawm lub npov liab dotted hauv daim duab 4a, nws yog qhov nthuav kom txheeb xyuas lwm yam ntawm cov dej ntws rov qab saum toj thiab ib ncig ntawm cov hniav.Flow visualization qhia me ntsis ntws mus rau hauv cheeb tsam recirculation.Qhov no ntws mus los ntawm sab xis ntawm cov hniav ntawm qhov siab txog 6 cm los ntawm qhov kawg ntawm cov hniav, tejzaum nws yog los ntawm tus thawj hniav ntawm tes ua ntej cov hniav, uas yog pom nyob rau hauv daim duab.Flow visualization ntawm 4 rpm qhia tib tus cwj pwm thiab cov qauv, pom meej nrog kev nrawm dua.
Kev nrawm nrawm thiab daim duab tam sim no ntawm peb cov hniav ntawm ob qhov kev sib hloov ceev ntawm 3 rpm thiab 4 rpm.Qhov siab tshaj plaws nruab nrab ntawm peb cov hniav ntawm 3 rpm yog 0.15 m / s, 0.20 m / s thiab 0.16 m / s feem, thiab qhov siab tshaj plaws nruab nrab ntawm 4 rpm yog 0.15 m / s, 0.22 m / s thiab 0.22 m / s, ua.ntawm peb daim ntawv.
Lwm daim ntawv ntawm helical ntws tau pom nyob nruab nrab ntawm vanes 1 thiab 2. Lub vector teb qhia meej meej tias cov dej ntws tau nce mus rau hauv qab ntawm vane 2, raws li qhia los ntawm vector.Raws li pom los ntawm lub npov dotted hauv daim duab 4b, cov vectors no tsis mus vertically upward los ntawm cov hniav nto, tab sis tig mus rau sab xis thiab maj mam nqis.Nyob rau saum npoo ntawm cov hniav 1, downward vectors yog txawv, uas mus rau ob lub hniav thiab nyob ib puag ncig lawv los ntawm cov recirculation ntws ntawm lawv.Cov qauv ntws tib yam tau txiav txim siab ntawm ob qho tib si kev sib hloov ceev nrog lub siab ceev amplitude ntawm 4 rpm.
Qhov nrawm nrawm ntawm cov hniav 3 tsis ua rau muaj txiaj ntsig zoo los ntawm kev tshaj tawm vector ntawm cov hniav yav dhau los koom nrog cov ntws hauv qab hniav 3. Lub ntsiab ntws hauv qab hniav 3 yog vim qhov ntsug ntsug vector nce nrog dej.
Cov vectors tshaj tawm saum npoo ntawm cov hniav tuaj yeem muab faib ua peb pawg, raws li qhia hauv daim duab 4c.Thawj txheej yog ib qho ntawm sab xis ntawm cov hniav.Cov qauv ntws hauv txoj haujlwm no yog ncaj nraim mus rau sab xis thiab nce (piv txwv li ntawm cov hniav 2).Cov pab pawg thib ob yog qhov nruab nrab ntawm cov hniav.Lub nrawm vector rau txoj haujlwm no yog qhia ncaj nraim, tsis muaj kev sib txawv thiab tsis muaj kev sib hloov.Qhov txo qis ntawm tus nqi nrawm tau txiav txim siab nrog qhov nce hauv qhov siab tshaj qhov kawg ntawm cov hniav.Rau pab pawg thib peb, nyob rau sab laug periphery ntawm cov hniav, cov ntws tam sim ntawd mus rau sab laug, piv txwv li mus rau phab ntsa ntawm flocculator.Feem ntau ntawm cov ntws uas sawv cev los ntawm kev tshaj tawm vector nce mus, thiab ib feem ntawm qhov ntws mus horizontally down.
Ob tus qauv turbulence, SST k–ω thiab IDDES, tau siv los tsim lub sijhawm nruab nrab ntawm qhov kev tshaj tawm rau 3 rpm thiab 4 rpm hauv cov hniav txhais tau tias ntev dav hlau.Raws li pom hauv daim duab 5, lub xeev khov kho yog ua tiav los ntawm kev ua tiav qhov zoo sib xws ntawm cov kev sib tw nrawm tsim los ntawm plaub qhov kev sib hloov ua tiav.Tsis tas li ntawd, lub sij hawm nruab nrab ntawm qhov kev sib tw uas tsim los ntawm IDDES tau qhia hauv daim duab 6a, thaum lub sij hawm nruab nrab ntawm qhov kev tshaj tawm uas tsim los ntawm SST k – ω yog qhia hauv daim duab 6a.6 ib b.
Siv IDDES thiab lub sijhawm nruab nrab ntawm qhov nrawm tsim los ntawm SST k–ω, IDDES muaj feem ntau dua ntawm qhov nrawm nrawm.
Ua tib zoo tshuaj xyuas qhov ceev profile tsim nrog IDDES ntawm 3 rpm raws li qhia hauv daim duab 7. Lub tov khoom tig clockwise thiab qhov ntws yog sib tham raws li cov ntawv qhia.
Ntawm daim duab.7 Nws tuaj yeem pom tau tias nyob rau saum npoo ntawm cov hniav 3 hauv I quadrant muaj qhov sib cais ntawm qhov ntws, vim tias qhov ntws tsis txwv vim qhov muaj qhov siab.Hauv quadrant II tsis muaj kev sib cais ntawm qhov ntws, vim tias qhov ntws tau txwv tag nrho los ntawm cov phab ntsa ntawm flocculator.Hauv quadrant III, cov dej tig ntawm qhov qis dua lossis qis dua li ntawm cov plaub fab dhau los.Cov dej hauv quadrants I thiab II yog txav mus (piv txwv li tig los yog thawb tawm) nqes los ntawm kev ua ntawm lub tov khoom.Thiab nyob rau hauv quadrant III, cov dej raug thawb tawm los ntawm cov hniav ntawm cov agitator.Nws yog pom tseeb tias cov dej loj hauv qhov chaw no tiv thaiv lub tes tsho flocculator.Lub rotary ntws nyob rau hauv no quadrant yog tag nrho sib cais.Rau quadrant IV, feem ntau ntawm cov airflow saum lub vane 3 yog qhia rau ntawm phab ntsa flocculator thiab maj mam poob nws qhov loj me raws li qhov siab nce mus rau sab saum toj qhib.
Tsis tas li ntawd, qhov chaw hauv nruab nrab suav nrog cov qauv ntws uas ua rau cov quadrants III thiab IV, raws li qhia los ntawm xiav dotted ellipses.Qhov chaw cim npe no tsis muaj dab tsi cuam tshuam nrog kev swirling ntws hauv paddle flocculator, vim tias lub voj voog tuaj yeem txheeb xyuas tau.Qhov no yog qhov sib piv rau quadrants I thiab II qhov twg muaj kev sib cais meej ntawm cov dej ntws sab hauv thiab tag nrho cov kev hloov pauv.
Raws li qhia hauv daim duab.6, sib piv cov txiaj ntsig ntawm IDDES thiab SST k-ω, qhov sib txawv tseem ceeb ntawm qhov nrawm nrawm yog qhov loj ntawm qhov tshaj tawm tam sim hauv qab cov hniav 3. Tus qauv SST k-ω qhia meej meej tias txuas ntxiv qhov nrawm nrawm yog nqa los ntawm cov hniav 3. piv rau IDDES.
Lwm qhov sib txawv tuaj yeem pom hauv quadrant III.Los ntawm IDDES, raws li tau hais ua ntej, kev sib hloov ntws sib cais ntawm cov caj npab flocculator tau sau tseg.Txawm li cas los xij, txoj haujlwm no muaj kev cuam tshuam loj heev los ntawm qhov qis qis ntws los ntawm cov ces kaum thiab sab hauv ntawm thawj cov hniav.Los ntawm SST k–ω rau tib qhov chaw, cov kab contour qhia cov kev nrawm dua piv rau IDDES vim tias tsis muaj qhov sib txuam ntawm lwm thaj chaw.
Kev nkag siab zoo ntawm qhov nrawm vector teb thiab streamlines yog xav tau kom nkag siab qhov tseeb ntawm tus cwj pwm ntws thiab cov qauv.Muab hais tias txhua tus hniav yog 5 cm dav, xya lub ntsiab lus nrawm tau raug xaiv thoob plaws qhov dav los muab tus neeg sawv cev tshaj tawm qhov profile.Tsis tas li ntawd, kev nkag siab ntau ntawm qhov loj ntawm qhov nrawm raws li qhov ua haujlwm ntawm qhov siab saum npoo ntawm cov hniav yog xav tau los ntawm kev teeb tsa qhov kev tshaj tawm ncaj qha rau txhua tus hniav saum npoo thiab dhau qhov kev ncua deb ntawm 2.5 cm vertically mus txog qhov siab ntawm 10 cm.Saib S1, S2 thiab S3 hauv daim duab kom paub ntau ntxiv.Cov ntawv txuas ntxiv A. Daim duab 8 qhia qhov zoo sib xws ntawm qhov sib npaug ntawm qhov sib faib tawm ntawm txhua qhov hniav (Y = 0.0) tau siv PIV kev sim thiab ANSYS-Fluent tsom xam siv IDDES thiab SST k-ω.Ob tus lej ua qauv ua rau nws ua tau kom raug simulate cov qauv ntws ntawm qhov chaw ntawm flocculator hniav.
Kev faib tawm nrawm PIV, IDDES thiab SST k–ω ntawm cov hniav nto.Lub x-axis sawv cev rau qhov dav ntawm txhua daim ntawv hauv millimeters, nrog lub hauv paus chiv keeb (0 mm) sawv cev rau sab laug periphery ntawm daim ntawv thiab qhov kawg (50 mm) sawv cev rau sab xis periphery ntawm daim ntawv.
Nws tau pom meej meej tias qhov kev sib faib ceev ntawm cov hniav 2 thiab 3 yog qhia hauv Fig.8 thiab Fig.8.S2 thiab S3 hauv Appendix A qhia cov qauv zoo sib xws nrog qhov siab, thaum hniav 1 hloov ntawm nws tus kheej.Qhov nrawm nrawm ntawm cov hniav 2 thiab 3 ua ncaj ncaj thiab muaj tib lub amplitude ntawm qhov siab ntawm 10 cm los ntawm qhov kawg ntawm cov hniav.Qhov no txhais tau hais tias qhov ntws los ua ib yam ntawm lub sijhawm no.Qhov no tau pom meej los ntawm PIV cov txiaj ntsig, uas tau tsim tawm zoo los ntawm IDDES.Lub caij no, cov txiaj ntsig SST k–ω qhia qee qhov sib txawv, tshwj xeeb tshaj yog ntawm 4 rpm.
Nws yog ib qho tseem ceeb uas yuav tsum nco ntsoov tias cov hniav 1 khaws zoo tib yam ntawm qhov nrawm profile nyob rau hauv txhua txoj haujlwm thiab tsis yog qhov qub nyob rau hauv qhov siab, txij li lub viav vias tsim nyob rau hauv nruab nrab ntawm lub tov khoom muaj thawj hniav ntawm tag nrho cov caj npab.Tsis tas li ntawd, piv rau IDDES, PIV hniav ceev profiles 2 thiab 3 qhia me ntsis siab dua qhov tseem ceeb ntawm feem ntau qhov chaw kom txog rau thaum lawv ze li ntawm 10 cm saum npoo ntawm cov hniav.
Post lub sij hawm: Dec-27-2022