Viscosity. Lub coefficient ntawm dynamic viscosity. Lub cev lub ntsiab lus ntawm lub coefficient ntawm viscosity

viscosity Performance index - ib tug tseem ceeb parameter ntawm tus ua hauj lwm kua los yog roj. Nyob rau hauv lub cev cov ntsiab lus, cov viscosity yuav tsum ua nrog kev sib txhuam tshwm sim los ntawm cov lus tsa suab ntawm tus hais constituting qhov loj ntawm lub kua (gaseous) nruab nrab, los yog, ntau tsuas, lub zog kuj.

Yuav ua li cas yog lub viscosity

Ib tug yooj yim empirical kev viscosity txiav txim: du sloped nto ib txhij poured mus rau hauv vaj huam sib luag npaum li cas ntawm cov dej thiab roj. Dej ntws ceev roj. Nws yog xav paub ntau kua. Tsiv sai sai ntws cov roj txwv tsis pub ib tug ntau dua kev sib txhuam nruab nrab ntawm nws molecules (internal kuj - viscosity). Yog li, kua viscosity inversely xwm yeem mus rau nws fluidity.

viscosity Performance index: cov mis

Nyob rau hauv ib tug yooj yim zog hauv daim ntawv ntawm cov txheej txheem ntawm khov dej nyob rau hauv lub raj dej yuav suav hais tias raws li tiaj tus thaum uas tig mus khaubncaws sab nraud povtseg A thiab B nrog cov tib deg hauv cheeb tsam S, qhov kev ncua deb ntawm uas yog tus magnitude ntawm h.

Cov ob khaubncaws sab nraud povtseg (A thiab B) txav nrog txawv velocities (V thiab V + ΔV). Ib tug txheej muaj lub siab tshaj plaws ceev (V + ΔV), yuav lub zog ntawm tus txheej B, tsiv ntawm ib lub qeeb qeeb ceev (V). Nyob rau tib lub sij hawm lub B txheej nyhav qeeb rau tus nqi ntawm cov txheej A. Lub cev lub ntsiab lus ntawm lub viscosity coefficient yog hais tias lub tsis sib haum xeeb ntawm cov molecules constituting lub flow kuj ntawm lub khaubncaws sab nraud povtseg ntaub ntawv ib tug dag zog yuam uas Isaak Nyuton piav los ntawm cov hauv qab no mis:

F = μ × S × (ΔV / h)

nyob ntawm no:

• ΔV - sib txawv ntawm cov kev ceev ntawm lub zog ntawm cov kua txaus khaubncaws sab nraud povtseg;
• h - kev ncua deb ntawm cov kua dej khaubncaws sab nraud povtseg;
• S - deg hauv cheeb tsam ntawm cov kua txaus txheej;
• μ (mu) - qhov zoo tshaj nyob rau thaj chaw ntawm ib cov kua, hu ua tsis dynamic viscosity.

Nyob rau hauv SI units mis yog raws li nram no:

μ = (F × h) / (S × ΔV) = [Pa × s] (× Pascal thib ob)

Qhov twg F - tus quab yuam ntawm lub ntiajteb txawj nqus (hnyav) chav tsev ntawm lub hydraulic kua volume.

tus nqi ntawm viscosity

Nyob rau hauv Feem ntau, lub coefficient ntawm dynamic viscosity yog ntsuas nyob rau hauv centipoises (CP) nyob rau hauv raws li cov system cgs (centimeter, gram, thib ob). Nyob rau hauv kev xyaum, cov viscosity ntawm cov kua loj piv muaj feem xyuam rau nws volume, i.e. kua ceev:

ρ = m / V

nyob ntawm no:

• ρ - ceev ntawm cov kua;
• m - loj ntawm kua;
• V - volume ntawm cov kua.

Qhov ratio ntawm cov dynamic viscosity (μ) thiab ceev (ρ) yog hu ua ib tug kinematic viscosity ν (ν - Greek - nu):

ν = μ / ρ = [m ² / s]

Incidentally, txoj kev rau kev txiav txim viscosity coefficient yog cov sib txawv. Piv txwv li, lub kinematic viscosity yog tseem ntsuas nyob rau hauv raws li cov GHS system nyob rau hauv centistokes (CST) thiab ib tug submultiple ntau - Stokes (St):

• 1 Hoob = 10 ^-4 m ² / s = 1 cm ² / s;
• 1sSt = 10 ^-6 m ² / s = 1 hli ² / s.

Kev txiav txim ntawm lub viscosity ntawm dej

Viscosity coefficient ntawm dej yog txiav txim los ntawm ntsuas lub kua txaus lub sij hawm los ntawm lub kom capillary raj. Qhov no ntaus ntawv yog kom siv ib lub npe hu txheem kua viscosity. Yuav kom txiav txim kinematic viscosity, ntsuas nyob rau hauv hli ² / s, cov kua txaus lub sij hawm, ntsuas nyob rau hauv vib nas this, yog multiplied los ntawm ib tug tas mus li tus nqi.

Raws li ib tug sib piv chav tsev yog siv cov viscosity ntawm distilled dej, uas nws muaj nuj nqis yog yuav luag tas li txawm thaum kub hloov. Viscosity - ib qho ratio ntawm lub sij hawm nyob rau hauv vib nas this uas yuav tsum tau taag volume ntawm distilled dej rau cov expiry ntawm ib tug kom lub qhov, mus rau tib tus nqi rau cov kev xeem kua.

viscometers

Viscosity yog ntsuas nyob rau hauv degrees Engler (° E) Saybolt Universal vib nas this ( "sus) los yog redwood degrees (° RJ) nyob ntawm seb hom ntawm rheometer. Peb hom viscometers txawv xwb nyob rau hauv tus nqi ntawm cov ntws kua nruab nrab.

Viscometer ntsuas lub viscosity nyob rau hauv European tsev Engler degrees (° E), xam rau ib 200 cm ³ ntws kua nruab nrab. Viscometer ntsuas lub viscosity nyob rau hauv Saybolt Universal vib nas this ( "sus los yog" SSU), siv nyob rau hauv lub tebchaws United States, muaj 60 cm ³ ntawm kev xeem cov kua. Hauv As Kiv teb, nyob qhov twg siv redwood degrees (° RJ), qha kuas ua txhua viscometer ntsuas lub viscosity ntawm 50 cm ³ ntawm cov kua. Piv txwv li, yog tias 200 cm ³ los ntawm ib cov roj ntws ntawm kaum lub sij hawm qeeb qeeb tshaj tus nqi qub dej, lub viscosity yog 10 ° Engler E.

Txij li thaum kub yog ib tug tseem ceeb tshaj nyob rau hauv kev hloov lub viscosity ratio, cov kev ntsuam yog feem ntau yog nqa tawm chiv ntawm qhov kub ntawm 20 ° C thiab ces nyob rau hauv nws ntau dua qhov tseem ceeb. Cov tshwm sim, yog li, yog qhia los ntawm kev ntxiv ib qho uas tsim nyog kub, e.g. 10 ° E / 50 ° C los yog 2.8 ° E / 90 ° C. kua viscosity nyob rau hauv 20 ° C siab tshaj nws viscosity sov dua. Hydraulic roj muaj ib tug viscosity ntawm cov hauv qab no duas paub kub:

190 CST nyob rau hauv 20 ° C = 45,4 CST ntawm 50 ° C = 11,3 CST nyob rau ntawm 100 ° C.

translation qhov tseem ceeb

Kev txiav txim ntawm viscosity tshwm sim nyob rau hauv txawv tshuab (American, British, GHS) thiab yog li ntawd yog feem ntau yuav tsum tau los hais lus txhais ntaub ntawv los ntawm ib tug xab system mus rau lwm lub. Kom hloov qhov tseem ceeb ntawm viscosity ntawm cov kua qhia nyob rau hauv degrees Engler nyob rau hauv centistokes (mm ² / s) siv cov nram qab empirical mis:

ν (CST) = 7,6 × ° E × (1-1 / ° E3)

Piv txwv li:

• 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.

Nyob rau hauv thiaj li yuav sai sai txiav txim seb tus txheej txheem viscosity ntawm lub hydraulic mis yuav yooj yim zog roj raws li nram no:

ν (CST) = 7,6 × ° E (mm ² / s)

Muaj ν kinematic viscosity nyob rau hauv hli ² / s los yog CST, nws yuav hloov dua siab tshiab rau hauv ib tug dynamic viscosity coefficient μ, siv cov nram qab kev sib raug zoo:

μ = ν × ρ

Piv txwv li. Ntsiab lus ntau yam qauv translation Engler degrees (° E) centistokes (CST) thiab centipoises (CPS), xav hais tias hydraulic roj nrog ib tug ntom ρ = 910 kg / m ³ muaj ib tug kinematic viscosity ntawm 12 ° E, nyob rau hauv cov chav nyob ntawm centistokes:

ν = 7,6 × 12 × (1-1 / 123) = 91,2 × (0,99) = 90,3 hli ² / s.

Txij li thaum 1sSt = 10 ^-6 m ² / s thiab 1br = N × 10 ^-3 s / m ^2, ces tus dynamic viscosity yuav ua ncaj rau:

μ = ν × ρ = 90,3 × 10 ^-6 · 910 = 0.082 × N s / m ² = 82 CPS.

Viscosity coefficient ntawm cov roj

Nws yog txiav txim los ntawm lub muaj pes tsawg leeg (tshuaj, neeg kho tshuab) gas mus rau ib tug kub thiab siab thov nyob rau hauv cov roj-dynamic suav txuam nrog pa zog. Nyob rau hauv kev xyaum, cov viscosity ntawm cov roj yog muab rau tus account nyob rau hauv lub tsim txoj kev loj hlob ntawm cov roj teb, nyob qhov twg lub xam yog ua coefficient hloov nyob rau hauv lub gas muaj pes tsawg leeg cov kev hloov (tshwj xeeb tshaj yog ib qho tseem ceeb rau cov pa roj condensate deposits), kub thiab siab.

Peb xam cov coefficient ntawm viscosity ntawm huab cua. Cov dab yuav tsum zoo xws li cov tau piav saum toj no ob tug dej ntws. Xav hais tias thaum uas tig mus tsiv ob roj ntws U1 thiab U2, tab sis nyob rau txawv cov nqi. Nruab nrab ntawm lub khaubncaws sab nraud povtseg ntawm convection yuav tshwm sim (interpenetration) molecules. Raws li ib tug tshwm sim, momentum sai mus cua khiav yuav txo thiab chiv mus maj mam - ceev.

Lub coefficient ntawm viscosity ntawm huab cua, raws li rau Newton txoj cai, qhia los ntawm cov nram qab no mis:

F = -h × (du / dZ) × S

nyob ntawm no:

• Du / dZ yog tus tshaj tawm gradient;
• S - cheeb tsam ntawm tej yam quab yuam;
• Qhov zoo tshaj yuav h - lub dynamic viscosity.

viscosity Performance index

Viscosity Index (VI) - ib tug parameter correlating qhov kev hloov nyob rau hauv viscosity thiab kub. Lub correlation yog ib tug statistical dependence kev sib raug zoo, nyob rau hauv rooj plaub no tus ob qhov tseem ceeb uas tus kub hloov yog nrog los ntawm systematic variation ntawm viscosity. Lub siab dua cov viscosity Performance index, tsawg qhov kev hloov ntawm ob qhov tseem ceeb, i.e. lub viscosity ntawm cov ua hauj lwm kua ruaj khov nrog kub.

Lub viscosity ntawm lub roj

Thaum cov me nyuam yaus ntawm tus niaj hnub roj viscosity Performance index ntawm tsawg tshaj li 95-100 units. Yog li ntawd nyob rau hauv hydraulic machinery thiab cov khoom siv yuav tsum siv sufficiently ruaj khov kua uas txwv tsis pub ntau variation nyob rau hauv viscosity nyob rau hauv tej yam kev mob ntawm ib qho tseem ceeb kub.

"Paaj" coefficient ntawm viscosity yuav tsum tau tswj los ntawm qhia ib tug tshwj xeeb cov roj additives (polymers) tau los ntawm lub distillation ntawm roj av. Lawv ua rau kom cov viscosity Performance index roj los ntawm limiting hloov nyob rau hauv cov yam ntxwv ntawm cov permissible ntau yam. Nyob rau hauv kev xyaum cov kev taw qhia ntawm tsim nyog kom muaj nuj nqis ntawm additives cov uas tsis muaj viscosity Performance index puag roj yuav raug tsa mus rau 100-105 units. Txawm li cas los, yog li tau sib tov yog impairs nws cov khoom nyob rau hauv kub siab thiab tshav kub load, li no kom txhob muaj cov hauj lwm zoo ntawm cov additive.

Nyob rau hauv hwj chim circuits yuav tsum tau siv haib hydraulic kua nrog ib tug viscosity Performance index ntawm 100 units. Kua muaj additives uas ua rau kom cov viscosity Performance index, yog siv nyob rau hauv hydraulic tswj circuits thiab lwm yam systems kev khiav hauj lwm nyob rau hauv lub chav uas tsis muaj / nruab nrab siab, nyob rau hauv ib tug tsawg kub ntau cov kev hloov me me txia thiab batchwise. Raws li lub siab nce thiab cov viscosity nce, tab sis cov txheej txheem tshwm sim nyob rau pressures saum toj no 30,0 MPa (300 bar). Nyob rau hauv kev xyaum, qhov no zoo tshaj yog feem ntau tsis saib tsis xyuas.

Ntsuas thiab indexation

Nyob rau hauv raws li cov thoob ntiaj teb ISO qauv, cov viscosity ntawm dej (thiab lwm yam kua) yog qhia nyob rau hauv centistokes: CST (mm ² / s). Cov kev ntsuam ntawm viscosity txheej txheem roj yuav tsum tau ua nyob rau ntawm kub ntawm 0 ° C, 40 ° C thiab 100 ° C. Nyob rau hauv txhua rooj plaub, nyob rau hauv lub code cim roj viscosity yuav tsum tau qhia thaum tus nab npawj 40 ° C. Tseg viscosity yog muab rau thaum 50 ° C. Marks, feem ntau siv nyob rau hauv engineering hydraulics, ntau yam los ntawm ISO VG 22 mus rau ISO VG 68.

Hydraulic roj VG 22, VG 32, VG 46, VG 68, VG 100 ntawm ib tug kub ntawm 40 ° C muaj viscosities coj mus rau lawv cov labeling: 22, 32, 46, 68 thiab 100 CST. Lub optimum kinematic viscosity ntawm cov ua hauj lwm kua nyob rau hauv hydraulic tshuab dag nyob rau hauv lub chav 16 mus rau 36 CST.

American Society of Automotive Engineers (Society of Automotive Engineers - SAE) tau tsim muaj yog hom twg ntawm viscosities ntawm kev kub thiab tsim nyog cov lis dej num uas muab rau lawv. Tus xov tooj nram qab no tsab ntawv W, - ib tug tsis dynamic viscosity coefficient μ ntawm 0 ° F (-17.7 ° C), thiab ν lub kinematic viscosity txiav txim ntawm 212 ° F (100 ° C). Qhov no indexing txog multigrade roj siv nyob rau hauv lub tsheb lag luam (kis tau tus mob, lub cev muaj zog, thiab thiaj li nyob. D.).

Cov nyhuv ntawm viscosity rau hydraulic ua hauj lwm

Kev txiav txim ntawm lub viscosity ntawm cov kua tsis yog tsuas yog scientific thiab kev kawm, tab sis kuj yog ib qho tseem ceeb cov tswv yim tseem ceeb. Cov hydraulic kua tsis tau tsuas yog hloov zog los ntawm lub twj tso kua mis mus rau lub hydraulic lub cev muaj zog, tab sis kuj yuav ntub tag nrho cov qhov chaw thiab cheebtsam yog rho los ntawm lub tshav kub generated txhuam officers. Tsis sib haum mus rau lub chaw ua hauj lwm ntawm cov ua hauj lwm kua viscosity muaj tiag txhob cuam tshuam txog cov hauj lwm zoo ntawm cov hydraulics.

Lub siab viscosity ntawm cov ua hauj lwm kua (roj heev kev kub ceev) ua rau cov hauv qab no tsis zoo los:

• Tus muaj zog txaus kuj ntawm lub hydraulic kua ua ntev li siab nco rau hauv lub hydraulic system.
• Deceleration tswj kev ceev thiab cov neeg kho tshuab cov ntawv tsa suab ntawm lub actuators.
• Kev loj hlob ntawm twj tso kua mis cavitation.
• Xoom los yog heev tsawg cua tso tawm los ntawm lub hydraulic roj tank.
• Ib tug hnov li tsis muaj hwj chim (txo efficiency) ntawm hydraulics vim lub high nqi ntawm lub zog rau overcoming tus nrog sib txhuam ntawm cov kua.
• Nce torque ntawm lub prime Mover ntawm lub tshuab tshwm sim los ntawm nce lub load rau ntawm cov twj tso kua mis.
• Qhov kub sawv ntawm lub hydraulic kua generated los ntawm ntau zog txhuam.

Yog li, lub cev lub ntsiab lus ntawm lub coefficient ntawm viscosity yog nyob rau hauv nws cov feem (positive los yog negative) nyob rau lub Cheebtsam thiab mechanisms rau cov tsheb, machinery thiab cov khoom siv.

Poob ntawm hydraulic hwj chim

Qhov tsawg viscosity ntawm cov ua hauj lwm kua (tsawg ceev roj) ua rau cov nram qab no tsis zoo los:

• Ntog volumetric efficiency ntawm cov twj raws li ib tug tshwm sim zuj zus nrog to.
• Qhov nce nyob rau hauv internal to ntawm hydraulic cheebtsam hauv tag nrho hydraulic system - twj, li qub, valve, hydraulic motors.
• Nce coj ntawm siv chav nyob thiab twj jamming vim tsis txaus hydraulic kua viscosity tsim nyog rau lubrication ntawm muab tshuaj ntxuav qhov chaw.

compressibility

Tej kua nyob rau hauv siab yog compressed. Nrog rau kev hwm mus roj, coolants thiab lubricants siv nyob rau hauv mechanical engineering hydraulics, empirically nws pom hais tias tus compression txheej txheem yog inversely xwm yeem mus rau kua loj rau nws cov ntim. Tus nqi ntawm cov compression neeg ntxhia roj no ho qis rau dej thiab ntau npaum li cas qis rau cov hluavtaws kua.

Nyob rau hauv tej yam yooj yim uas tsis muaj siab hydraulic kua compressibility negligible ntxim rau kom txhob muaj cov thawj lub ntim. Tab sis haib cav tov nrog high-siab hydraulic tsav thooj voos kheej kheej thiab loj, tus txheej txheem no manifests nws tus kheej xab. Nyob rau hauv hydraulic ntxhia roj ntawm ib tug siab ntawm 10.0 MPa (100 bar), lub volume txo los ntawm 0.7%. Nyob rau hauv cov ntaub ntawv no, ib tug kev hloov nyob rau hauv lub compression ntim rau ib tug me me raws li feem xyuam rau txoj kinematic viscosity thiab hom ntawm cov roj.

xaus

Kev txiav txim ntawm viscosity tso cai rau kom twv seb lub lag luam los ntawm cov khoom thiab machinery nyob rau hauv ntau yam tej yam kev mob, noj mus ua nyiaj cov kev hloov nyob rau hauv cov kua los yog roj muaj pes tsawg leeg, siab, kub. Tsis tas li ntawd, cov kev tswj ntawm cov ntsuas uas muaj feem rau roj thiab cov nkev kev lag luam, hlauv taws xob thiab lwm yam lag luam.