shyaanata

upar ke drav ki shyaanata neeche ke drav ki shyaanata se bahut kam hai.

shyaanata (Viscosity) kisi taral ka vah gun hai jiske kaaran vah kisi baahari pratibl (stres) ya aparoopak pratibl (sheeyar stres) ke kaaran apne ko vikrut (deform) karne ka virodh karta hai. saamaanya shabdon mein, yeh us taral ke gaadhepan ya uske bahne ka pratirodh karne ki kshamata ka parichaayak hai. udaaharan ke liye, paani patala hota hai evam usaki shyaanata vanaspati tel ki apeksha kam hoti hai jo ki gaadhaa hota hai.

anukram

parichay

shyaanata (Viscosity) aam taur par yeh dekha jaata hai ki sabhi vastueain, chaahe ve gas, drav athva thos hon, yadi unka viroopan (deformation) hota hai, athva unke pind (body) ke vibhinn hisson mein saapeksh gati (relative motion) karaai jaati hai, to unamein avarodh karne ki pravrutti hoti hai. kuchh vastuon mein is pravrutti ki koti (degree) jyaada hoti hai aur kuchh mein kam. jab ham paani ko chikni satah par giraate hain, to yeh dekha jaata hai ki paani teji se bahata hai, lekin yadi ham sheera (treacle) ya glisreen ki utani hi maatra usi prakaar ki chikni sah par giraaeain, to yeh satah par failane mein jyaada samay leta hai. sheere ki kism ki vastuon ko, jo failane mein jyaada samay leti hain, saadhaaran logon ki bhaasha mein chipchipi ya shyaan (viscous) kehte hain, jab ki paani jaisi vastuon ko taral athva gatisheel (mobile) ki sanjnyaa di jaati hai. is prakaar ham yeh kah sakte hain ki sheera paani se jyaada shyaan hai. doosaron shabdon mein yeh bhi kaha jaata hai ki svaroopaparivrtan sheere mein dheere dheere hota hai, jab ki paani jaisi vastuon mein teji se. shyaanata taralon (fluids) ka vah gun hai jiske kaaran taral un baan (forces) ka virodh karta hai jo uske svaroop ko badalna chaahate hain. is prakaar ham shyaanata ko kisi bhi drav athva gas ke aantarik gharshan (internal friction), ke roop mein bhi dekh sakte hain. dravon tatha gaison, donon mein, shyaanata ka gun paaya jaata hai, lekin drav gaison ki apeksha jyaada shyaan hote hain. isi shyaanata ke kaaran drav ki ek parat (layer) doosari parat par hokar aage badhti hai.

shyaanata ka mahatva

jab jahaaj paani par vichran karta hai, tab samudra ka paani shyaan avarodh prastut karta hai. isi prakaar hava bhi hamaarein havaai jahaajon tatha kaaron ki raah mein avarodh upasthit karti hai. hamaari kalam ki syaahi ki visheshata kaafi had tak usaki shyaanata par nirbhar hai. snehakon (lubricants) ke prayog ka aadhaar hi shyaanata hai. ham sab logon ki dhamaniyon tatha shiraaon mein rudhirparisancharan (circulation of blood) rudhir ki shyaanata par hi nirbhar karta hai. is prakaar janajeevan mein shyaanata mahatvapoorn bhoomika ada karti hai.

dravon ki shyaanata (Viscosity of liquids)

kaalpanik pattiyon ki aapekshik gati se shyaan bal

do aisi aseemit samaantar pattikaaon (plates) ki kalpana karein jinke beech mein ek drav padaarth rakha hua hai (dekhein chitr). maan leejiye pattika abcd apne hi samatal (plane) mein, daahini disha mein, ek sthir veg (constant velocity) v se aage badh rahi hai, jise chitr mein teer dvaara dikhaaya gaya hai, tatha pattika a'b'c'd' apni sthir avastha mein hai. taatparya yeh hai ki pattika abcd ka saapeksh veg va hai. aisi avastha mein yeh kaha jaata hai ki drav padaarth poora ka poora veg v se teer dvaara pradarshit disha mein gatimaan hai. yadi drav ka pravaah dhaaraarekhi gati (streamline motion) se ho rahe ho, to drav ki vah parat jo sthir pattika a'b'c'd' ke sampark mein hai, achal avastha mein rahati hai, jabki anya doosari paraton ka pravaah satah ke samaantar hota rahata hai. lekin in paraton ka veg, jaise-jaise ham oopar ki or aate hain, dheere-dheere badhta chala jaata hai. antim parat, jo pattika abcd ke sampark mein hoti hai, usaka veg v hi hota hai. ab ham drav mein kisi kshaitij samatal (horizontal plane) par dhyaan deinge. is samatal ke anuon ko iske theek ooparavaali parat ke anuon dvaara tvaran (acceleration) milta hai, kyonki ooparavaali parat ke anuon ka veg is samatal ke anuon ke veg se jyaada hoto hai, jabki kshaitij samatal ke theek neeche ki parat ke anuon dvaara kshaitij samatal ke anuon ki gati mein mandan laaya jaata hai. isi prakaar drav ki pratyek parat apne theek ooparavaali parat par ek sparsharekheeya pashch bal (tangential backward force) daalati hai, jiske kaaran in donon paraton ke beech ki saapeksh gati nasht hoti hai. parinaamasvaroop yadi hamein drav ki samaantar paraton ke beech saapeksh gati rakhani ho, to yeh atyaavashyak hai ki ek baahari bal (external force) ko is pashchakarshan (backward drag) par haavi (overcome) hona chaahiye. yadi baahari bal naheen hoga, to kuchh samay ke baad drav ki vibhinn paraton ke beech saapeksh gati samaapt ho jaaegi. kisi drav ka vah gun jiske saamarthya ki badaulat, drav apni vibhinn paraton ke beech ki saapeksh gati ka virodh karta hai, drav ki shyaanata, athva aantarik gharshan (Internal friction), kahalaata hai. yeh gun, jo ek drav se doosare drav mein keval degree ya koti mein hi antar rakhata hai, har ek taral ka ek antarnihit gunadharm hai.

dhaaraarekhi gati ke liye, nyootan ke shyaan pravaah (Viscous flow) ke niyam ke anusaar, drav ki samaanaantar paraton ke beech sparsharekheeya shyaan bal F ko neeche diye gaye sambandh dvaara dikhlaaya jaata hai :

F = -h. A. dv/dz ...... ...... (1)

jahaaain A = samaantaar paraton ka kshetrafal, dz = paraton ke beech ki doori, dv = paraton ki saapeksh gati, dv/dz = veg pravanata (velocity gradient) tatha h ek sthiraank (constant) hai, jise "drav ki shyaanata ka gunaank" kaha jaata hai. yeh, athva iska maan, drav ki prakruti tatha bhautik dashaaon (physical conditions) par nirbhar karta hai. yadi ham oopar darshaae gaye sambandh (1) mein A = 1, dv/dz = 1 rakhein, to F = -h hoga. ataev kisi drav ki "shyaanata ke gunaank" ki paribhaasha is prakaar di ja sakti hai :

"kisi drav ke do samaantar talon ke beech ikaai veg pravanata rakhane ke liye jo sparsharekheeya bal prati ikaai kshetrafal ke liye aavashyak hota hai, use us drav ki shyaanata ka gunaank kehte hain."

yadyapi oopar do pattikaaon tatha unke beech drav ki upasthiti jaisi vyavastha ki kalpana kar, aasaani se "shyaanata ke gunaank" ki paribhaasha ki gayi hai, tathaapi prayogaatmak roop mein aisi vyavastha ko paana sambhav naheen hai. pehle pahal paani jaisi taral vastuon ka "shyaanata ke gunaank" paani ke bahaav ko, keshika nalikaaon se gujarane ke baad, maapakar nikaala gaya aur aajkal bhi yeh tareeka vishd roop se prayog mein laaya jaata hai.

maan leejiye ki, koi drav, jaise paani, kisi vrutteeya chhed ki sankeern nali se hokar gujar raha hai. yadi paani dhaaraarekhi gati se sankeern nali se hokar pravaahit ho raha hai tatha nali ke kisi anuprasth parichhed ke oopar dabaav ek samaan ho aur drav ki vah parat jo nali ki goleeya deevaar ke sampark mein ho evam prayogaatmak roop se sthir ho, to paani ka shyaanataagunaank neeche diye hue sambandh dvaara nikaala ja sakta hai :

..... ..... (2)

jahaaain Q = paani ka vah aayatan jo prati second nali se hokar gujarata hai, r = sainkari nali ka ardhavyaas = dabaav ka antar jo nali ke donon siron ke beech hota hai, l = sankeern nali ki lanbaai tatha = shyaanata ka gunaank hai.

shyaanata ka maapan

mukhya lekh shyaanataamaapi

shyaanata aur taap (Viscosity and Temperature)

prayogon dvaara yeh paaya gaya hai ki, kaafi had tak, dravon ki shyaanata taap par nirbhar hai. yadyapi is kshetr mein kaafi prayog kiye ja chuke hain, tathaapi koi aisa saadhaaran sootr naheen mila jo shyaanata tatha taap ke sambandh ki uchch yathaarthata ko pradarshit kare. praaya: yeh paaya jaata hai ki poore kshetr mein taap ke badhne ke saath saath shyaanata ghatati chali jaati hai, lekin shyaanata mein yeh ghataav prati ansh nimn taap par ooainche taap ki apeksha jyaad hota hai. shyaanata tatha taap ke sambandh mein sarvapratham slaut (Slotte) dvaara ek moolaanupaati sootr (empirical formula) diya gaya, jo baad mein sanshodhit hua tatha shuddh dravon ke sambandh mein hi laagoo hota hai. aage chalakar aindraade ke siddhaant (Andrade's theory) par ek jatil shyaanata-taap-sambandh diya gaya, jo prayogon se kaafi santoshaprad paaya gaya hai aur vah is prakaar hai :

h v1/3 = AeC/vT ..... ..... .... (6)

jahaaain A tatha C sthiraank (constants) hain, T = taap tatha v = vishisht aayatan (specific volume) hai.

taap ke badhne ke saath saath gaison ka shyaanata ka gunaank badhta hai. iske sambandh mein sadaralaind (Sutherland) ne ek sootr diya hai, jo is prakaar hai :

jahaaain:

  • = taap T par shyaanata gunaank ka maan (Pa·as)
  • = sandarbh taap par shyaanata gunaank ka maan (Pa·as)
  • = taap [K]
  • = sandarbh taap [K]
  • = sadaralaind sthiraank [K]..... ...... (7)

shyaanata aur dabaav (Viscosity and Pressure)

jin dravon ki shyaanata jyaada hoti hai, jaise khanij tel ki, unki shyaanata ka gunaank dabaav ke badhne ke saath saath badhta hai. keval paani ko chhodkar anya sabhi dravon mein kareeb kareeb aisi hi sthiti pai gayi hai. paani mein pehle kai sau vaayu dabaav (few hundred atmospheric pressures) tak shyaanataagunaank ghatata jaata hai, taduparaant iska shyaanataagunaak anya dravon ki tarah dabaav ke saath saath badhta hai.

gaison ke baare mein yeh paaya gaya hai ki saadhaaranataya uchch dabaav ka shyaanataagunaank par koi prabhaav naheen padta, kintu nyoon dabaav par shyaanataagunaank dabaav ke ghatne ke saath saath hi ghatata jaata hai. jis dabaav par yeh prabhaav aarambh hota hai, vah in do baaton par nirbhar karta hai :

  • (1) baratan ke aakaar par, jismein gas bhari hoti hai, tatha
  • (2) gas ki prakruti par.

shyaanata aur raasaayanik rachana (Viscosity and Chemical Constitution)

sarvapratham taumas Graham (Thomas Graham) ne yeh sujhaav diya ki ek hi prakaar ki rachana ke yaugikon ka shyaanata gunaank niyamit dhang se badh sakta hai, yadi unke anuon ya samoohon ki sankhya badhaai jaae. prayogon se thaurp tatha Roger (Thorpe and Rodger) ne yeh paaya ki kisi sajaateeya shreni ka shyaanataagunaank uske anubhaar ke saath badhta jaata hai. yeh vruddhi niyamit dhang se hoti hai, jabki sajaateeya shreni ke pratham do ya teen yaugik aniymata darshaate hain.

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