Cov thoob dej tiaj tiaj rau BEVs thiab FCEVs siv cov thermoplastic thiab thermoset composites nrog lub cev pob txha uas muab 25% ntau dua H2 cia. #hydrogen #trends
Tom qab kev koom tes nrog BMW tau qhia tias lub tank cubic tuaj yeem xa cov txiaj ntsig volumetric ntau dua li ntau lub tog raj kheej me me, Technical University of Munich tau pib ua ib qhov project los tsim cov qauv sib xyaw thiab cov txheej txheem tsim khoom scalable rau kev tsim khoom ntau zaus. Duab credit: TU Dresden (sab saum toj) sab laug), Technical University of Munich, Department of Carbon Composites (LCC)
Cov tsheb fais fab roj (FCEVs) uas siv roj hydrogen uas tsis muaj pa phem (H2) muab lwm txoj hauv kev los ua tiav cov hom phiaj ib puag ncig uas tsis muaj pa phem. Lub tsheb thauj neeg siv roj uas muaj lub cav H2 tuaj yeem puv tau hauv 5-7 feeb thiab muaj ntau txog 500 km, tab sis tam sim no kim dua vim muaj ntau lawm tsawg. Ib txoj hauv kev los txo cov nqi yog siv lub platform txheem rau BEV thiab FCEV qauv. Qhov no tam sim no tsis tuaj yeem ua tau vim tias cov tank cylindrical Hom 4 siv los khaws cov roj H2 uas raug nias (CGH2) ntawm 700 bar hauv FCEVs tsis haum rau cov chaw roj teeb hauv qab lub cev uas tau tsim zoo rau cov tsheb fais fab. Txawm li cas los xij, cov hlab siab hauv daim ntawv ntawm cov hauv ncoo thiab cov voos xwmfab tuaj yeem haum rau hauv qhov chaw ntim khoom tiaj tus no.
Daim Ntawv Pov Thawj Patent US5577630A rau "Composite Conformal Pressure Vessel", daim ntawv thov xa los ntawm Thiokol Corp. xyoo 1995 (sab laug) thiab lub thawv siab rectangular uas BMW tau txais daim ntawv pov thawj patent xyoo 2009 (sab xis).
Lub Tsev Haujlwm Saib Xyuas Carbon Composites (LCC) ntawm Technical University of Munich (TUM, Munich, Lub Tebchaws Yelemees) koom nrog ob qhov project los tsim lub tswv yim no. Thawj qhov yog Polymers4Hydrogen (P4H), coj los ntawm Leoben Polymer Competence Center (PCCL, Leoben, Austria). Lub pob haujlwm LCC yog coj los ntawm Fellow Elizabeth Glace.
Qhov project thib ob yog Hydrogen Demonstration and Development Environment (HyDDen), qhov chaw uas LCC yog tus thawj coj ntawm Researcher Christian Jaeger. Ob lub hom phiaj yog los tsim kom muaj kev qhia loj txog cov txheej txheem tsim khoom rau kev ua lub tank CGH2 uas siv cov khoom sib xyaw carbon fiber.
Muaj kev ua haujlwm volumetric tsawg thaum cov thooj voos kheej kheej me me raug teeb tsa rau hauv cov roj teeb tiaj tus (sab laug) thiab cubic hom 2 lub thawv siab ua los ntawm cov hlau liners thiab lub plhaub sab nraud carbon fiber / epoxy composite (sab xis). Qhov chaw ntawm cov duab: Cov duab 3 thiab 6 yog los ntawm "Numerical Design Approach for Type II Pressure Box Vessel with Internal Tension Legs" los ntawm Ruf thiab Zaremba et al.
P4H tau tsim ib lub thawv sim uas siv lub thav thermoplastic nrog cov hlua khi sib xyaw / struts qhwv hauv carbon fiber reinforced epoxy. HyDDen yuav siv tus qauv zoo sib xws, tab sis yuav siv automatic fiber layup (AFP) los tsim txhua lub thawv thermoplastic composite.
Txij li daim ntawv thov patent los ntawm Thiokol Corp. mus rau "Composite Conformal Pressure Vessel" xyoo 1995 mus rau German Patent DE19749950C2 xyoo 1997, cov hlab roj compressed "tej zaum yuav muaj cov qauv geometric", tab sis tshwj xeeb tshaj yog cov duab tiaj tus thiab tsis sib xws, hauv qhov chaw txuas nrog lub plhaub txhawb nqa. Cov ntsiab lus raug siv kom lawv tuaj yeem tiv taus lub zog ntawm kev nthuav dav ntawm cov roj.
Ib daim ntawv xyoo 2006 los ntawm Lawrence Livermore National Laboratory (LLNL) piav qhia txog peb txoj hauv kev: lub hlab ntsha filament wound conformal pressure vessel, lub hlab ntsha microlattice pressure vessel uas muaj cov qauv orthorhombic lattice sab hauv (cov hlwb me me ntawm 2 cm lossis tsawg dua), nyob ib puag ncig los ntawm lub thawv H2 nyias-phab ntsa, thiab lub thawv replicator, uas muaj cov qauv sab hauv uas muaj cov khoom me me nplaum (piv txwv li, cov nplhaib yas hexagonal) thiab cov khoom sib xyaw ntawm daim tawv nqaij nyias nyias. Cov thawv ob npaug yog qhov zoo tshaj plaws rau cov thawv loj dua uas cov txheej txheem ib txwm muaj yuav nyuaj rau siv.
Daim ntawv pov thawj patent DE102009057170A uas Volkswagen tau xa tuaj rau xyoo 2009 piav qhia txog lub thawv siab uas tau teeb tsa rau hauv lub tsheb uas yuav muab kev ua haujlwm zoo thaum tseem txhim kho kev siv qhov chaw. Cov thoob dej plaub fab siv cov khoom sib txuas ntawm ob phab ntsa plaub fab sib txawv, thiab cov ces kaum yog puag ncig.
Cov ntsiab lus saum toj no thiab lwm yam tau hais los ntawm Gleiss hauv daim ntawv "Kev Txhim Kho Cov Txheej Txheem rau Cubic Pressure Vessels nrog Stretch Bars" los ntawm Gleiss et al. ntawm ECCM20 (Lub Rau Hli 26-30, 2022, Lausanne, Switzerland). Hauv tsab xov xwm no, nws hais txog kev tshawb fawb TUM luam tawm los ntawm Michael Roof thiab Sven Zaremba, uas pom tias lub thawv siab cubic nrog cov struts tension txuas cov sab rectangular zoo dua li ntau lub tog raj kheej me me uas haum rau hauv qhov chaw ntawm lub roj teeb tiaj tus, muab kwv yees li 25% ntau dua. qhov chaw cia khoom.
Raws li Gleiss, qhov teeb meem nrog kev teeb tsa ntau lub tog raj kheej me me hom 4 hauv lub thawv tiaj tus yog tias "qhov ntim ntawm cov tog raj kheej raug txo qis heev thiab lub kaw lus kuj muaj qhov chaw loj heev rau H2 roj permeation. Zuag qhia tag nrho, lub kaw lus muab qhov chaw cia khoom tsawg dua li cov thawv cubic."
Txawm li cas los xij, muaj lwm yam teeb meem nrog lub tank tsim lub voos xwmfab. "Nws yog qhov tseeb, vim yog cov roj compressed, koj yuav tsum tiv thaiv cov zog khoov ntawm cov phab ntsa tiaj tus," Gleiss hais. "Rau qhov no, koj xav tau cov qauv txhawb nqa uas txuas sab hauv rau cov phab ntsa ntawm lub tank. Tab sis qhov ntawd nyuaj ua nrog cov khoom sib xyaw."
Glace thiab nws pab neeg tau sim siv cov pas nrig uas txhawb nqa rau hauv lub thawv siab kom haum rau cov txheej txheem winding filament. "Qhov no yog qhov tseem ceeb rau kev tsim khoom ntau," nws piav qhia, "thiab tseem tso cai rau peb tsim cov qauv winding ntawm cov phab ntsa thawv kom zoo dua qhov kev taw qhia fiber rau txhua qhov thauj khoom hauv thaj chaw."
Plaub kauj ruam los ua lub tank sib xyaw ua ke rau qhov project P4H. Duab los ntawm: "Kev tsim cov txheej txheem tsim khoom rau cov thawv siab cubic nrog brace", Technical University of Munich, Polymers4Hydrogen project, ECCM20, Lub Rau Hli 2022.
Yuav kom ua tiav txoj saw hlau, pab neeg tau tsim ib lub tswv yim tshiab uas muaj plaub kauj ruam tseem ceeb, raws li qhia saum toj no. Cov struts nruj, qhia ua xim dub ntawm cov kauj ruam, yog cov qauv thav duab ua ntej uas tsim los ntawm kev siv cov txheej txheem coj los ntawm MAI Skelett project. Rau qhov project no, BMW tau tsim ib lub thav duab "framework" siv plaub lub fiber-reinforced pultrusion rods, uas tom qab ntawd tau molded rau hauv ib lub thav duab yas.
Lub thav duab ntawm lub tank cubic sim. Cov seem pob txha hexagonal 3D luam tawm los ntawm TUM siv cov PLA filament tsis muaj zog (sab saum toj), ntxig CF/PA6 pultrusion rods ua cov braces nruj (nruab nrab) thiab tom qab ntawd qhwv lub filament ncig cov braces (hauv qab). Duab credit: Technical University of Munich LCC.
"Lub tswv yim yog tias koj tuaj yeem tsim lub thav duab ntawm lub thawv cubic ua ib lub qauv modular," Glace hais. "Cov modules no ces muab tso rau hauv lub cuab yeej molding, cov struts tension muab tso rau hauv cov modules thav duab, thiab tom qab ntawd MAI Skelett txoj kev siv nyob ib puag ncig cov struts los koom ua ke nrog cov khoom thav duab." txoj kev tsim khoom loj, ua rau muaj cov qauv uas tom qab ntawd siv ua mandrel lossis core los qhwv lub thawv cia khoom composite plhaub.
TUM tsim lub thav duab lub tank ua lub "cushion" cubic nrog cov sab khov kho, cov ces kaum puag ncig thiab tus qauv hexagonal rau sab saum toj thiab hauv qab uas cov khi tuaj yeem ntxig thiab txuas. Cov qhov rau cov racks no kuj tau luam tawm 3D. "Rau peb lub tank sim thawj zaug, peb tau luam tawm 3D cov ntu thav duab hexagonal siv polylactic acid [PLA, ib qho thermoplastic bio-based] vim nws yooj yim thiab pheej yig," Glace hais.
Cov pab pawg tau yuav 68 tus pas nrig carbon fiber reinforced polyamide 6 (PA6) los ntawm SGL Carbon (Meitingen, Lub Tebchaws Yelemees) rau kev siv ua cov khi. "Txhawm rau sim lub tswv yim, peb tsis tau ua pwm," Gleiss hais tias, "tab sis tsuas yog ntxig cov spacers rau hauv lub thav duab honeycomb 3D luam tawm thiab nplaum lawv nrog cov kua nplaum epoxy. Qhov no ces muab lub mandrel rau winding lub tank. "Nws sau tseg tias txawm hais tias cov pas nrig no yooj yim rau winding, muaj qee qhov teeb meem tseem ceeb uas yuav piav qhia tom qab.
"Thaum thawj theem, peb lub hom phiaj yog los qhia txog kev tsim khoom ntawm tus qauv thiab txheeb xyuas cov teeb meem hauv lub tswv yim tsim khoom," piav qhia Gleiss. "Yog li cov struts nruj tawm ntawm qhov chaw sab nraud ntawm cov qauv pob txha, thiab peb txuas cov carbon fibers rau lub hauv paus no siv cov ntaub ntub dej. Tom qab ntawd, hauv kauj ruam thib peb, peb khoov lub taub hau ntawm txhua tus pas nrig khi. thermoplastic, yog li peb tsuas yog siv cua sov los kho lub taub hau kom nws tiaj tus thiab xauv rau hauv thawj txheej ntawm kev qhwv. Tom qab ntawd peb txuas ntxiv mus qhwv cov qauv dua kom lub taub hau tiaj tus raug kaw hauv lub tank. laminate ntawm phab ntsa.
Lub hau txuas rau kev sib txuas. TUM siv cov hau yas rau ntawm qhov kawg ntawm cov pas nrig kom tiv thaiv cov fibers kom tsis txhob sib xyaw thaum lub sijhawm sib txuas filament. Duab los ntawm: Technical University of Munich LCC.
Glace rov hais dua tias lub tank thawj zaug no yog ib qho pov thawj ntawm lub tswv yim. "Kev siv 3D luam ntawv thiab kua nplaum tsuas yog rau kev sim thawj zaug thiab muab lub tswv yim rau peb txog qee qhov teeb meem uas peb ntsib. Piv txwv li, thaum lub sijhawm winding, cov filaments raug ntes los ntawm qhov kawg ntawm cov pas nrig nruj, ua rau cov fiber tawg, fiber puas tsuaj, thiab txo cov fiber ntau los tawm tsam qhov no. peb siv ob peb lub hau yas ua cov khoom siv tsim khoom uas tau muab tso rau ntawm cov ncej ua ntej thawj kauj ruam winding. Tom qab ntawd, thaum cov laminates sab hauv tau ua, peb tshem tawm cov hau tiv thaiv no thiab rov kho qhov kawg ntawm cov ncej ua ntej qhwv kawg."
Cov pab pawg tau sim ntau yam kev tsim kho dua tshiab. "Cov neeg uas saib ib puag ncig ua haujlwm zoo tshaj plaws," Grace hais. "Tsis tas li ntawd, thaum lub sijhawm prototyping, peb tau siv cov cuab yeej vuam hloov kho los siv cua sov thiab rov kho dua qhov kawg ntawm cov pas nrig khi. Hauv lub tswv yim tsim khoom loj, koj yuav muaj ib lub cuab yeej loj dua uas tuaj yeem kho thiab tsim txhua qhov kawg ntawm cov struts rau hauv ib daim laminate tiav sab hauv tib lub sijhawm. ."
Cov taub hau ntawm lub drawbar tau hloov kho dua tshiab. TUM tau sim nrog ntau lub tswv yim sib txawv thiab hloov kho cov welds kom phim cov kawg ntawm cov khoom sib xyaw ua ke rau kev txuas rau ntawm phab ntsa tank laminate. Duab credit: "Kev tsim cov txheej txheem tsim khoom rau cov thawv siab cubic nrog brace", Technical University of Munich, Polymers4Hydrogen project, ECCM20, Lub Rau Hli 2022.
Yog li ntawd, cov laminate tau kho tom qab thawj kauj ruam winding, cov ncej tau rov ua dua tshiab, TUM ua tiav qhov thib ob winding ntawm cov filaments, thiab tom qab ntawd lub tank phab ntsa sab nraud laminate tau kho dua zaum ob. Thov nco ntsoov tias qhov no yog hom 5 tank tsim, uas txhais tau tias nws tsis muaj lub hnab yas ua lub roj thaiv. Saib cov lus sib tham hauv ntu Cov Kauj Ruam Tom Ntej hauv qab no.
"Peb txiav thawj qhov kev qhia ua ntu zus thiab kos duab thaj chaw txuas nrog," Glace hais. "Ib qho ze ze qhia tau tias peb muaj qee qhov teeb meem zoo nrog lub laminate, nrog rau lub taub hau strut tsis tso tiaj tus rau ntawm lub laminate sab hauv."
Kev daws cov teeb meem nrog qhov sib txawv ntawm cov laminate ntawm phab ntsa sab hauv thiab sab nraud ntawm lub tank. Lub taub hau khi hloov kho tsim qhov sib txawv ntawm thawj thiab thib ob tig ntawm lub tank sim. Duab credit: Technical University of Munich LCC.
Lub thawv thawj zaug 450 x 290 x 80mm no tau ua tiav lub caij ntuj sov dhau los. "Peb tau ua tiav ntau yam txij li thaum ntawd los, tab sis peb tseem muaj qhov sib txawv ntawm sab hauv thiab sab nraud laminate," Glace hais. "Yog li peb tau sim sau cov qhov sib txawv ntawd nrog cov resin huv si, siab viscosity. Qhov no ua rau kev sib txuas ntawm cov studs thiab laminate zoo dua, uas ua rau muaj kev ntxhov siab ntau ntxiv."
Cov pab pawg neeg tau txuas ntxiv tsim cov qauv tsim thiab cov txheej txheem ntawm lub tank, suav nrog cov kev daws teeb meem rau cov qauv winding xav tau. "Cov sab ntawm lub tank kuaj tsis tau curled tag nrho vim nws nyuaj rau qhov geometry no los tsim ib txoj kev winding," Glace piav qhia. "Peb lub kaum sab xis winding thawj zaug yog 75 °, tab sis peb paub tias ntau lub voj voog tau xav tau los ua kom tau raws li qhov hnyav hauv lub thawv siab no. Peb tseem tab tom nrhiav kev daws teeb meem rau qhov teeb meem no, tab sis nws tsis yooj yim nrog cov software tam sim no hauv kev ua lag luam. Nws yuav dhau los ua ib qho project tom qab.
"Peb tau ua pov thawj tias lub tswv yim tsim khoom no ua tau," Gleiss hais, "tab sis peb yuav tsum ua haujlwm ntxiv kom txhim kho qhov kev sib txuas ntawm cov laminate thiab rov kho cov pas nrig khi. "Kev sim sab nraud ntawm lub tshuab sim. Koj rub cov spacers tawm ntawm cov laminate thiab sim cov khoom siv kho tshuab uas cov pob qij txha tuaj yeem tiv taus."
Qhov no ntawm Polymers4Hydrogen project yuav ua tiav rau thaum kawg ntawm xyoo 2023, thaum lub sijhawm ntawd Gleis vam tias yuav ua tiav lub tank ua qauv qhia thib ob. Qhov nthuav yog, cov qauv tsim niaj hnub no siv cov thermoplastics zoo nkauj hauv lub thav duab thiab cov thermoset composites hauv phab ntsa tank. Puas yuav siv txoj hauv kev sib xyaw no hauv lub tank ua qauv qhia zaum kawg? "Yog," Grace hais. "Peb cov neeg koom tes hauv Polymers4Hydrogen project tab tom tsim cov epoxy resins thiab lwm cov ntaub ntawv sib xyaw matrix nrog cov khoom zoo dua hydrogen barrier." Nws teev ob tus neeg koom tes ua haujlwm rau txoj haujlwm no, PCCL thiab University of Tampere (Tampere, Finland).
Gleiss thiab nws pab neeg kuj tau sib pauv cov ntaub ntawv thiab tham txog cov tswv yim nrog Jaeger ntawm qhov project HyDDen thib ob los ntawm lub tank LCC conformal composite.
"Peb yuav tsim ib lub thawv siab conformal composite rau kev tshawb fawb drones," Jaeger hais. "Qhov no yog kev koom tes ntawm ob lub chaw haujlwm ntawm Aerospace thiab Geodetic Department ntawm TUM - LCC thiab Department of Helicopter Technology (HT). Qhov project yuav ua tiav rau thaum kawg ntawm xyoo 2024 thiab tam sim no peb tab tom ua tiav lub thawv siab. ib qho kev tsim uas yog ntau dua ntawm aerospace thiab automotive txoj hauv kev. Tom qab theem pib lub tswv yim no, kauj ruam tom ntej yog ua cov qauv tsim kom ntxaws thiab kwv yees qhov kev ua tau zoo ntawm cov qauv phab ntsa.
"Lub tswv yim tag nrho yog los tsim ib lub drone tshawb nrhiav nrog lub roj teeb hybrid thiab lub roj teeb propulsion system," nws hais ntxiv. Nws yuav siv lub roj teeb thaum lub zog siab (piv txwv li takeoff thiab landing) thiab tom qab ntawd hloov mus rau lub roj teeb thaum lub sijhawm caij nkoj me me. "Pab pawg HT twb muaj lub drone tshawb fawb thiab tsim dua lub zog los siv ob qho tib si roj teeb thiab roj teeb," Yeager hais. "Lawv kuj tau yuav lub tank CGH2 los sim qhov kev sib kis no."
"Kuv pab neeg tau raug muab lub luag haujlwm los tsim lub tank siab uas yuav haum, tab sis tsis yog vim muaj teeb meem ntim khoom uas lub tank cylindrical yuav tsim," nws piav qhia. "Lub tank tiaj tus tsis muaj zog cua ntau. Yog li koj tau txais kev ua tau zoo dua ntawm kev ya." Qhov loj ntawm lub tank kwv yees li 830 x 350 x 173 hli.
Lub tank thermoplastic AFP ua raws li thermoplastic. Rau qhov project HyDDen, pab pawg LCC ntawm TUM tau tshawb nrhiav ib txoj hauv kev zoo sib xws rau qhov uas Glace siv (saum toj no), tab sis tom qab ntawd tau hloov mus rau txoj hauv kev siv kev sib xyaw ua ke ntawm ntau lub modules, uas tom qab ntawd tau siv ntau dhau los ntawm AFP (hauv qab no). Duab credit: Technical University of Munich LCC.
"Muaj ib lub tswv yim zoo ib yam li Elisabeth [Gleiss] txoj kev," Yager hais tias, "kom siv cov khoom siv nruj rau ntawm phab ntsa ntawm lub nkoj kom them rau cov zog khoov siab. Txawm li cas los xij, es tsis txhob siv cov txheej txheem winding los ua lub tank, peb siv AFP. Yog li ntawd, peb xav txog kev tsim ib ntu cais ntawm lub nkoj siab, uas cov racks twb tau koom ua ke lawm. Txoj hauv kev no tso cai rau kuv los sib xyaw ntau lub modules sib xyaw ua ke no thiab tom qab ntawd siv lub hau kawg los kaw txhua yam ua ntej qhov kawg AFP winding."
"Peb tab tom sim ua kom tiav lub tswv yim zoo li no," nws hais ntxiv, "thiab pib sim cov ntaub ntawv xaiv, uas yog qhov tseem ceeb heev kom ntseeg tau tias muaj kev tiv thaiv rau H2 roj nkag mus. Rau qhov no, peb feem ntau siv cov ntaub ntawv thermoplastic thiab tab tom ua haujlwm ntawm ntau yam uas cov ntaub ntawv yuav cuam tshuam rau tus cwj pwm permeation thiab kev ua tiav hauv lub tshuab AFP. Nws yog ib qho tseem ceeb kom nkag siab tias kev kho mob yuav muaj txiaj ntsig thiab yog tias xav tau kev ua tiav tom qab. Peb kuj xav paub seb cov pawg sib txawv puas yuav cuam tshuam rau hydrogen permeation los ntawm lub thawv siab.
Lub tank yuav ua los ntawm cov thermoplastic tag nrho thiab cov strips yuav muab los ntawm Teijin Carbon Europe GmbH (Wuppertal, Lub Tebchaws Yelemees). "Peb yuav siv lawv cov khoom PPS [polyphenylene sulfide], PEEK [polyether ketone] thiab LM PAEK [low melting polyaryl ketone]," Yager hais. "Kev sib piv tom qab ntawd ua kom pom qhov twg zoo tshaj plaws rau kev tiv thaiv kev nkag mus thiab tsim cov khoom nrog kev ua tau zoo dua." Nws vam tias yuav ua tiav kev sim, kev tsim qauv thiab cov txheej txheem thiab thawj qhov kev ua qauv hauv xyoo tom ntej.
Cov haujlwm tshawb fawb tau ua tiav hauv COMET module "Polymers4Hydrogen" (ID 21647053) hauv COMET qhov kev pab cuam ntawm Federal Ministry for Climate Change, the Environment, Energy, Mobility, Innovation and Technology thiab Federal Ministry for Digital Technology and Economics. . Cov kws sau ntawv ua tsaug rau cov neeg koom tes Polymer Competence Center Leoben GmbH (PCCL, Austria), Montanuniversitaet Leoben (Faculty of Polymer Engineering and Science, Department of Chemistry of Polymer Materials, Department of Materials Science and Polymer Testing), University of Tampere (Faculty of Engineering Materials). ) Science), Peak Technology thiab Faurecia tau pab txhawb rau txoj haujlwm tshawb fawb no. COMET-Modul tau txais nyiaj los ntawm tsoomfwv Austria thiab tsoomfwv ntawm lub xeev Styria.
Cov ntawv txhim kho ua ntej rau cov qauv uas muaj lub nra hnyav muaj cov fibers txuas ntxiv - tsis yog los ntawm iav xwb, tab sis kuj los ntawm carbon thiab aramid.
Muaj ntau txoj hauv kev los ua cov khoom sib xyaw ua ke. Yog li ntawd, kev xaiv txoj hauv kev rau ib qho tshwj xeeb yuav nyob ntawm cov khoom siv, kev tsim qauv ntawm qhov, thiab kev siv kawg lossis daim ntawv thov. Nov yog phau ntawv qhia xaiv.
Shocker Composites thiab R&M International tab tom tsim cov saw hlau carbon fiber rov ua dua tshiab uas muab kev tua tsiaj xoom, tus nqi qis dua li cov fiber tshiab thiab thaum kawg yuav muab cov qhov ntev uas ze rau cov fiber txuas ntxiv mus rau hauv cov khoom siv.
Lub sijhawm tshaj tawm: Lub Peb Hlis-15-2023