Viscosity coefficient yog qhov tseem ceeb ntawm cov kua dej lossis roj ua haujlwm. Hauv cov ntsiab lus ntawm lub cev, viscosity tuaj yeem txhais tau tias yog kev sib txhuam sab hauv los ntawm kev txav ntawm cov khoom uas ua rau cov khoom loj ntawm cov kua (gaseous) nruab nrab, lossis, yooj yim dua, kev tawm tsam rau kev txav.
viscosity yog dab tsi
Qhov kev sim ua piv txwv yooj yim tshaj plaws rau kev txiav txim siab viscosity: tib tus nqi dej thiab roj tau nchuav rau ntawm qhov chaw du nyob rau tib lub sijhawm. Dej ntws sai dua cov roj. Nws yog dej ntau. Cov roj txav yog tiv thaiv kom tsis txhob ntws tawm sai sai los ntawm kev sib txhuam ntau dua ntawm nws cov molecules (internal resistance - viscosity). Yog li, viscosity ntawm cov kua yog inversely proportional rau nws fluidity.
Viscosity ratio: formula
Nyob hauv daim ntawv yooj yim, cov txheej txheem ntawm kev txav ntawm cov kua dej khov hauv cov raj xa dej tuaj yeem txiav txim siab nyob rau hauv daim ntawv ntawm cov pav ca sib npaug A thiab B nrog tib thaj chaw S, qhov kev ncua deb ntawm uas yog h.
Ob txheej no (A thiab B) txav ntawm qhov sib txawv (V thiab V + ΔV). Txheej A, uas muaj qhov ceev tshaj plaws (V + ΔV), suav nrog txheej B, uas txav ntawm qhov qis dua (V). Nyob rau tib lub sijhawm, txheej B nyiam qeeb qeeb ntawm txheej A. Lub ntsiab lus ntawm lub cev ntawm cov viscosity coefficient yog qhov kev sib txhuam ntawm cov molecules, uas yog cov tsis kam ntawm cov txheej txheem ntws, tsim ib lub zog uas Isaac Newton tau piav qhia los ntawm cov txheej txheem. cov qauv hauv qab no:
F=µ × S × (ΔV/h)
Here:
- ΔV yog qhov sib txawv ntawm qhov nrawm ntawm cov kua dej ntws;
- h – nrug nruab nrab ntawm cov txheej dej ntws;
- S - thaj tsam ntawm cov kua dej ntws;
- Μ (mu) - coefficient nyob ntawm cov khoom ntawm cov kua, hu ua qhov tsis muaj zog viscosity.
Hauv SI units, cov qauv zoo li no:
µ=(F × h) / (S × ΔV)=[Pa × s] (Pascal × second)
Ntawm F yog lub zog ntawm lub ntiajteb txawj nqus (qhov hnyav) ntawm chav tsev ntim ntawm cov dej ua haujlwm.
Viscosity value
Feem ntau, qhov sib txawv viscosity coefficient yog ntsuas hauv centipoise (cP) raws li CGS system ntawm units (centimeter, gram, thib ob). Hauv kev xyaum, viscosity muaj feem xyuam rau qhov sib piv ntawm qhov loj ntawm cov kua rau nws ntim, uas yog, rau qhov ntom ntawm cov kua:
ρ=m / V
Here:
- ρ – kua ntom ntom;
- m - dej ntau;
- V yog ntim kua.
Kev sib raug zoo ntawm dynamic viscosity (Μ) thiab ntom (ρ) yog hu ua kinematic viscosity ν (ν - hauv Greek -liab qab):
ν=Μ / ρ=[m2/s]
Los ntawm txoj kev, cov txheej txheem rau kev txiav txim siab viscosity coefficient txawv. Piv txwv li, kinematic viscosity tseem ntsuas raws li CGS system nyob rau hauv centistokes (cSt) thiab nyob rau hauv fractional units - stokes (St):
- 1St=10-4 m2/s=1 cm2/s;
- 1sSt=10-6 m2/s=1 mm2/s.
Kev txiav txim siab viscosity ntawm dej
Lub viscosity ntawm cov dej yog txiav txim los ntawm kev ntsuas lub sij hawm nws yuav siv sij hawm rau cov kua ntws los ntawm lub calibrated capillary raj. Cov cuab yeej no yog calibrated nrog tus qauv kua ntawm paub viscosity. Txhawm rau txiav txim siab kinematic viscosity, ntsuas hauv mm2 / s, lub sijhawm dej ntws, ntsuas hauv vib nas this, yog muab faib ua qhov tas li.
chav sib piv yog qhov viscosity ntawm cov dej distilled, tus nqi uas yuav luag tas li txawm tias qhov kub thiab txias hloov. Lub viscosity coefficient yog qhov piv ntawm lub sij hawm nyob rau hauv vib nas this nws yuav siv sij hawm ib tug tsau ntim ntawm distilled dej ntws tawm ntawm ib tug calibrated orifice rau cov kua uas raug kuaj.
Viscometers
Viscosity yog ntsuas hauv degrees Engler (°E), Saybolt Universal Seconds ("SUS") lossis degrees Redwood (° RJ) nyob ntawm seb hom viscometer siv. Peb hom viscometers txawv ntawm qhov ntau dej ntws tawm.
Viscometer ntsuas viscosity nyob rau hauv European unit degree Engler (°E), xam200cm3 tawm kua nruab nrab. Lub viscometer ntsuas viscosity hauv Saybolt Universal Seconds ("SUS" lossis "SSU" siv hauv Asmeskas) muaj 60 cm3 ntawm cov kua dej. Hauv tebchaws Askiv, qhov twg Redwood degrees (° RJ) siv, viscometer ntsuas qhov viscosity ntawm 50 cm 3 kua. Piv txwv li, yog tias 200 cm3 ntawm qee cov roj ntws qis dua kaum npaug qis dua tib lub ntim dej, ces Engler viscosity yog 10°E.
Vim tias qhov kub thiab txias yog qhov tseem ceeb hauv kev hloov cov viscosity coefficient, kev ntsuas feem ntau yog ua ntej ntawm qhov kub thiab txias ntawm 20 ° C, thiab tom qab ntawd ntawm cov nqi siab dua. Qhov tshwm sim yog li qhia los ntawm kev ntxiv qhov tsim nyog kub, piv txwv li: 10 ° E / 50 ° C lossis 2.8 ° E / 90 ° C. Lub viscosity ntawm cov kua ntawm 20 ° C yog siab dua nws viscosity ntawm qhov kub siab dua. Cov roj hydraulic muaj cov viscosities hauv qab no ntawm lawv qhov kub thiab txias:
190 cSt ntawm 20 ° C=45.4 cSt ntawm 50 ° C=11.3 cSt ntawm 100 ° C.
Tus nqi txhais lus
Kev txiav txim siab ntawm cov viscosity coefficient tshwm sim hauv cov tshuab sib txawv (Asmeskas, Lus Askiv, GHS), thiab yog li nws feem ntau yuav tsum tau hloov cov ntaub ntawv los ntawm ib qhov system mus rau lwm qhov. Txhawm rau hloov cov dej viscosity qhov tseem ceeb qhia hauv degrees Engler rau centistokes (mm2/s), siv cov qauv hauv qab no:
ν(cSt)=7.6 ×°E × (1-1/°E3)
Piv txwv:
- 2°E=7.6 × 2 × (1-1/23)=15.2 × (0.875)=13.3 cSt;
- 9°E=7,6 × 9 × (1-1/93)=68.4 × (0.9986)=68.3 cSt.
Txhawm rau txiav txim siab sai sai rau tus qauv viscosity ntawm cov roj hydraulic, cov qauv tuaj yeem ua kom yooj yim raws li hauv qab no:
ν(cSt)=7.6 ×°E(mm2/s)
Muaj kinematic viscosity ν hauv mm2/s lossis cSt, koj tuaj yeem hloov nws mus rau dynamic viscosity coefficient Μ siv cov kev sib raug zoo hauv qab no:
M=ν ×ρ
Piv txwv. Summary ntawm ntau yam kev hloov pauv cov qauv rau qib Engler (°E), centistokes (cSt) thiab centipoise (cP), xav tias cov roj hydraulic nrog qhov ceev ntawm ρ=910 kg/m 3 muaj kinematic viscosity ntawm 12 ° E, uas nyob rau hauv units ntawm cSt yog:
ν=7.6 × 12 × (1-1/123)=91.2 × (0.99)=90.3 mm2/s.
Vim 1cSt=10-6m2/s thiab 1cP=10-3N×s/m2, ces dynamic viscosity yuav:
M=ν × ρ=90.3 × 10-6 910=0.082 N×s/m2=82 cP.
Gas viscosity factor
Nws yog txiav txim siab los ntawm cov tshuaj muaj pes tsawg leeg (tshuaj lom neeg, tshuaj lom neeg) ntawm cov pa roj, qhov cuam tshuam ntawm qhov kub thiab txias, siab, thiab siv rau hauv kev suav roj-dynamic ntsig txog kev txav ntawm cov pa. Nyob rau hauv kev xyaum, lub viscosity ntawm gases yog coj mus rau hauv tus account thaum tsim gas teb kev loj hlob, qhov twg cov kev hloov coefficient yog xam nyob rau hauv cov kev hloov nyob rau hauv cov roj muaj pes tsawg leeg (tshwj xeeb tshaj yog tseem ceeb rau gas condensate teb), kub thiab siab.
Xaiv cov viscosity ntawm huab cua. Cov txheej txheem yuav zoo ib yam liob lub kwj deg tau tham saum toj no. Piv txwv li ob lub roj ntws U1 thiab U2 txav mus rau qhov sib npaug, tab sis ntawm qhov sib txawv. Convection (mutual penetration) ntawm molecules yuav tshwm sim ntawm cov khaubncaws sab nraud povtseg. Raws li qhov tshwm sim, lub zog ntawm cov cua nrawm nrawm yuav txo qis, thiab qhov pib txav qeeb qeeb yuav nrawm dua.
Cov viscosity coefficient ntawm huab cua, raws li Newton txoj cai, yog qhia los ntawm cov qauv hauv qab no:
F=-h × (dU/dZ) × S
Here:
- dU/dZ yog qhov nrawm nrawm;
- S – quab yuam cheeb tsam;
- Coefficient h - dynamic viscosity.
Viscosity index
Viscosity Performance index (VI) yog ib qho parameter uas cuam tshuam cov kev hloov pauv hauv viscosity thiab kub. Ib qho kev sib raug zoo yog ib qho kev sib raug zoo, nyob rau hauv cov ntaub ntawv no ob qhov ntau, qhov kev hloov ntawm qhov kub thiab txias nrog rau kev hloov pauv hauv viscosity. Qhov siab dua qhov viscosity Performance index, qhov me me ntawm qhov kev hloov pauv ntawm ob qhov tseem ceeb, uas yog, viscosity ntawm cov dej ua haujlwm yog qhov ruaj khov dua nrog qhov kub thiab txias.
Roj viscosity
Lub hauv paus ntawm cov roj niaj hnub muaj qhov ntsuas viscosity qis dua 95-100 units. Yog li ntawd, nyob rau hauv lub hydraulic systems ntawm cov cav tov thiab cov cuab yeej siv, ruaj khov ua hauj lwm kua yuav siv tau, uas txwv tsis pub lub dav hloov nyob rau hauv viscosity nyob rau hauv tej yam kev mob ntawm tseem ceeb kub.
"Favorable" viscosity coefficient tuaj yeem tswj tau los ntawm kev qhia rau hauv cov roj tshwj xeeb additives (polymer) tau txais thaum lub sij hawm distillation ntawm roj. Lawv nce viscosity Performance index ntawm roj rauaccount ntawm kev txwv qhov kev hloov ntawm tus yam ntxwv no nyob rau hauv lub sij hawm tso cai. Hauv kev xyaum, nrog kev qhia txog qhov xav tau ntawm cov khoom ntxiv, qhov qis viscosity Performance index ntawm cov roj hauv paus tuaj yeem nce mus rau 100-105 units. Txawm li cas los xij, qhov sib tov tau txais los ntawm txoj kev no deteriorates nws cov khoom ntawm kev kub siab thiab tshav kub load, yog li txo qhov ua tau zoo ntawm additive.
Hauv lub zog hluav taws xob ntawm cov tshuab hydraulic muaj zog, cov kua dej ua haujlwm nrog qhov ntsuas viscosity ntawm 100 units yuav tsum tau siv. Cov kua dej ua haujlwm nrog cov khoom siv ntxiv uas ua rau kom cov viscosity Performance index yog siv rau hauv hydraulic tswj circuits thiab lwm yam kev khiav hauj lwm nyob rau hauv qhov tsawg / nruab nrab siab ntau yam, nyob rau hauv ib tug txwv kub ntau yam, nrog me me leaks thiab nyob rau hauv batch ua hauj lwm. Nrog nce siab, viscosity kuj nce, tab sis cov txheej txheem no tshwm sim ntawm qhov siab tshaj 30.0 MPa (300 bar). Hauv kev xyaum, qhov no feem ntau tsis quav ntsej.
Kev ntsuas thiab ntsuas ntsuas
Raws li cov qauv ISO thoob ntiaj teb, cov viscosity coefficient ntawm dej (thiab lwm yam kua xov xwm) tau qhia hauv centistokes: cSt (mm2/s). Kev ntsuas viscosity ntawm cov txheej txheem roj yuav tsum tau ua ntawm qhov kub ntawm 0 ° C, 40 ° C thiab 100 ° C. Txawm li cas los xij, nyob rau hauv cov roj qib code, viscosity yuav tsum tau qhia los ntawm daim duab ntawm qhov kub ntawm 40 ° C. Hauv GOST, tus nqi viscosity tau muab rau ntawm 50 ° C. Cov qib feem ntau siv hauv engineering hydraulics ntau ntawm ISO VG 22 txog ISO VG 68.
Hydraulic roj VG 22, VG 32, VG 46, VG 68, VG 100 ntawm 40 ° C muaj viscosity tus nqi sib piv rau lawv cov cim: 22, 32, 46, 68 thiab 100 cSt. Qhov zooLub kinematic viscosity ntawm cov kua ua hauj lwm nyob rau hauv hydraulic systems ranges ntawm 16 mus rau 36 cSt.
Lub Koom Haum Asmeskas ntawm Automotive Engineers (SAE) tau tsim cov viscosity ntau ntawm qhov kub thiab txias thiab muab cov lej tsim nyog rau lawv. Tus lej tom qab W yog qhov tseeb viscosity Μ ntawm 0 ° F (-17.7 ° C) thiab kinematic viscosity ν tau txiav txim siab ntawm 212 ° F (100 ° C). Qhov kev ntsuas no siv tau rau txhua lub caij cov roj siv hauv kev lag luam tsheb (kev sib kis, lub cev muaj zog, thiab lwm yam).
Kev cuam tshuam ntawm viscosity ntawm hydraulics
Kev txiav txim siab ntawm cov coefficient ntawm viscosity ntawm cov kua tsis yog ntawm kev tshawb fawb thiab kev kawm nkaus xwb, tab sis kuj yog ib qho tseem ceeb ntawm cov txiaj ntsig. Hauv cov tshuab hydraulic, cov kua dej ua haujlwm tsis yog tsuas yog hloov lub zog ntawm lub twj tso kua mis mus rau hydraulic motors, tab sis kuj lubricate tag nrho cov khoom ntawm cov khoom thiab tshem tawm cov cua sov los ntawm kev sib txhuam. Lub viscosity ntawm cov kua dej ua haujlwm uas tsis tsim nyog rau kev ua haujlwm tuaj yeem cuam tshuam qhov kev ua haujlwm ntawm txhua qhov hydraulics.
-
siab viscosity ntawm cov dej ua haujlwm (roj ntau ntom ntom) ua rau cov lus tsis zoo hauv qab no:
- Txhim tiv thaiv cov kua dej hydraulic ua rau muaj kev poob siab ntau hauv hydraulic system.
- Kev txo qis ntawm kev tswj ceev thiab kev txav chaw ntawm cov actuators.
- Kev txhim kho cavitation hauv lub twj tso kua mis.
- Zero lossis qis dhau cua tso tawm los ntawm cov roj tank hydraulic.
- Nco ntsoovpoob ntawm lub zog (txo qis hauv kev ua haujlwm) ntawm hydraulics vim cov nqi hluav taws xob siab kom kov yeej cov kev sib txhuam sab hauv ntawm cov kua.
- Ntau lub tshuab prime mover torque tshwm sim los ntawm kev nce twj tso kua mis.
- Rise hauv hydraulic kua kub vim muaj kev sib txhuam ntxiv.
Yog li, lub ntsiab lus ntawm lub cev ntawm viscosity coefficient nyob hauv nws cov cawv (zoo lossis tsis zoo) ntawm cov khoom thiab cov txheej txheem ntawm tsheb, tshuab thiab khoom siv.
Poob hydraulic zog
Tsawg viscosity ntawm cov kua ua haujlwm (roj ntawm qhov ntom ntom) ua rau cov xwm txheej tsis zoo hauv qab no:
- Kev txo qis hauv kev ua haujlwm ntawm cov twj tso kua mis raws li qhov tshwm sim ntawm kev ua kom nkag mus rau sab hauv.
- Ntau ntxiv hauv cov xau sab hauv hauv cov khoom siv hydraulic ntawm tag nrho cov hydraulic system - twj, li qub, hydraulic distributors, hydraulic motors.
- Ntau ntxiv ntawm cov twj tso kua mis thiab jamming ntawm cov twj tso kua mis vim tsis txaus viscosity ntawm cov dej ua haujlwm tsim nyog los muab lubrication ntawm cov khoom txhuam.
Compressibility
Txhua cov kua compresses nyob rau hauv siab. Hais txog cov roj thiab cov coolants siv nyob rau hauv mechanical engineering hydraulics, nws tau raug tsim empirically tias cov txheej txheem compression yog inversely proportional rau qhov loj ntawm cov kua ib ntim. Qhov sib piv compression yog siab dua rau cov roj ntxhia, txo qis rau dej, thiab qis dua rau cov kua hluavtaws.
Hauv cov tshuab hydraulic uas tsis tshua muaj siab, qhov compressibility ntawm cov kua muaj qhov cuam tshuam tsis zoo rau qhov txo qis ntawm qhov pib ntim. Tab sis nyob rau hauv cov cav tov haib nrog high hydraulicsiab thiab loj hydraulic thooj voos kheej kheej, cov txheej txheem no manifests nws tus kheej noticeably. Rau hydraulic ntxhia roj ntawm lub siab ntawm 10.0 MPa (100 bar), lub ntim txo los ntawm 0.7%. Nyob rau tib lub sijhawm, qhov kev hloov pauv hauv compression ntim yog me ntsis cuam tshuam los ntawm kinematic viscosity thiab hom roj.
Zoo kawg
Kev txiav txim siab ntawm cov viscosity coefficient tso cai rau koj los kwv yees kev ua haujlwm ntawm cov cuab yeej thiab cov txheej txheem raws li ntau yam xwm txheej, suav nrog kev hloov pauv ntawm cov kua lossis roj, siab, kub. Tsis tas li, kev tswj hwm ntawm cov ntsuas no muaj feem cuam tshuam rau hauv cov roj thiab roj, kev siv hluav taws xob, thiab lwm yam lag luam.
