Ntxhiab saum npoo vs viscosity
Viscosity thiab nto nro yog ob qho xwm txheej tseem ceeb hais txog cov tshuab thiab cov kua dej zoo li qub. Cov teb xws li hydrodynamics, aerodynamics thiab txawm tias aviation raug cuam tshuam los ntawm qhov tshwm sim ntawm cov xwm txheej no. Nws yog ib qho tseem ceeb kom muaj kev paub zoo hauv cov xwm txheej no kom ua tau zoo hauv cov teb. Kab lus no yuav piv cov viscosity thiab qhov nro thiab nthuav qhia qhov sib txawv ntawm ob.
Ntoo Ntog yog dab tsi?
Xav txog cov kua homogeneous. Txhua lub molecule nyob rau hauv nruab nrab ntawm cov kua yuav muaj raws nraim tib lub zog rub nws mus rau txhua sab. Cov molecules nyob ib puag ncig yog rub lub hauv paus molecule uniformly ntawm txhua qhov kev taw qhia. Tam sim no xav txog ib qho chaw molecule. Nws tsuas muaj zog ua rau nws mus rau cov kua. Cov huab cua - kua nplaum rog tsis yog ze li ntawm cov kua - cov kua nplaum ua kua. Yog li ntawd, cov molecules saum npoo tau txais kev nyiam ntawm qhov chaw ntawm cov kua, tsim kom muaj txheej txheej ntawm cov molecules. Qhov txheej txheej ntawm molecules no ua raws li cov yeeb yaj kiab nyias ntawm cov kua. Yog tias peb coj tus piv txwv ntawm lub neej tiag tiag ntawm tus neeg tua dej, nws siv cov yeeb yaj kiab no los tso nws tus kheej rau saum npoo dej. Nws swb ntawm txheej no. Yog tias tsis yog rau txheej no, nws yuav poob tam sim ntawd. Nto nro yog txhais raws li lub zog sib npaug mus rau qhov chaw perpendicular mus rau ib chav tsev ntev kab kos rau ntawm qhov chaw. Cov chav nyob ntawm qhov nro yog Nm-1 Ntog nro kuj txhais tau tias yog lub zog ib cheeb tsam. Qhov no kuj muab qhov nro ntawm qhov chaw tshiab Jm-2 Ntog nro, uas tshwm sim ntawm ob lub kua dej tsis sib haum, hu ua qhov nro ntawm lub ntsej muag.
Viscosity yog dab tsi?
Viscosity txhais tau tias yog qhov ntsuas ntawm qhov tsis kam ntawm cov kua dej, uas yog deformed los ntawm kev ntxhov siab los yog tensile stress. Hauv ntau lo lus, viscosity yog "kev sib txhuam sab hauv" ntawm cov kua dej. Nws tseem hu ua lub thickness ntawm cov kua. Viscosity tsuas yog kev sib txhuam ntawm ob txheej ntawm cov kua dej thaum ob txheej txav mus rau ib leeg. Sir Isaac Newton yog ib tug pioneer hauv dej mechanics. Nws postulated tias, rau ib tug Newtonian kua, lub shear kev nyuaj siab ntawm cov khaubncaws sab nraud povtseg yog proportional rau lub ceev gradient nyob rau hauv cov kev taw qhia perpendicular mus rau lub txheej. Qhov proportional tas li (proportionality factor) siv ntawm no yog viscosity ntawm cov kua. Lub viscosity feem ntau txhais los ntawm Greek tsab ntawv "µ". Viscosity ntawm cov kua tuaj yeem ntsuas tau siv Viscometers thiab Rheometers. Cov units ntawm viscosity yog Pascal-thib ob (los yog Nm-2s). Lub cgs system siv chav tsev "poise" npe tom qab Jean Louis Marie Poiseuille los ntsuas viscosity. Viscosity ntawm cov kua kuj tuaj yeem ntsuas los ntawm ntau qhov kev sim. Lub viscosity ntawm cov kua yog nyob ntawm qhov kub thiab txias. Lub viscosity txo qis thaum kub nce.
τ=μ ∂u/∂y
Viscosity sib npaug thiab cov qauv yog qhov nyuaj heev rau cov kua dej uas tsis yog-Newtonian.
Qhov txawv ntawm qhov nro thiab viscosity yog dab tsi?
• Ntog nro tuaj yeem suav tau tias yog qhov xwm txheej tshwm sim hauv cov kua dej vim yog lub zog tsis sib haum xeeb, qhov viscosity tshwm sim vim muaj zog ntawm cov molecules txav.
• Ntog nro muaj nyob rau hauv ob qho tib si txav thiab tsis txav, tab sis viscosity tsuas yog tshwm sim hauv cov kua txav.
