Madzimadzi, zinthu zamadzimadzi ndi za gasi zamitundu yosiyanasiyana, zimakhala ndi milingo yosiyana ya kukhuthala. Kukhuthala ndi kukangana pakati pa mamolekyu omwe amapanga madzimadzi. Chifukwa chake, mamolekyu amapanga kukangana kwa madzimadzi pamene madziwo akuyenda. Mu zamadzimadzi, kukhuthala kumachitika chifukwa cha mphamvu zogwirizanitsa (kukoka mphamvu pakati pa mamolekyu ofanana). Pomwe mu zinthu za gasi, kukhuthala kumachitika chifukwa cha kugundana pakati pa mamolekyu.
Madzi amadzimadzi ndi osavuta kuyenda, mwachitsanzo, madzi. Mosiyana ndi zimenezi, madzi okhuthala ndi ovuta kuyenda, mwachitsanzo, mafuta odzola. Mutha kutsimikizira mwa kuthira madzi ndi mafuta pamalo opendekeka. Madzi amayenda mofulumira kuposa mafuta. Mlingo wa kukhuthala kwa madzi umadaliranso kutentha. Kutentha kwa madzimadzi kukakhala kwakukulu, madziwo amakhala ochepa kwambiri. Mwachitsanzo, mayi akaphika nsomba kukhitchini, mafuta ophikira omwe poyamba amakhuthala amakhala madzi ambiri akatenthedwa. Mosiyana ndi zimenezi, kutentha kwa chinthu cha gasi kukakhala kwakukulu, mafuta a gasi amakhala okhuthala kwambiri.
Koyefiya ya Kukhuthala
Chizindikiro η chikuyimira kukhuthala kwa madzi (werengani: eta). η = coefficient of viscosity. Chifukwa chake, mulingo wa kukhuthala kwa madzi umawonetsedwa ndi kukhuthala kwa madzi.
Pakati pa mbale ziwiri pali gawo lochepa la madzi. Kugwirizana ndi mphamvu yokoka pakati pa mamolekyu ofanana, pomwe kugwirizana ndi mphamvu yokoka pakati pa mamolekyu osiyanasiyana. Mphamvu yokoka imagwira ntchito pakati pa mbale ndi gawo la madzi lomwe limalumikizidwa ku mbale (mamolekyu amadzimadzi ndi mamolekyu a mbale amakokana). Pakadali pano, mphamvu yokoka imagwira ntchito pakati pa nembanemba yamadzimadzi (madzimadzi amakoka mamolekyu).
Poyamba, mbale ndi gawo lamadzimadzi zimakhala pamalo opumulira (chithunzi 1). Pambuyo pake, mbale yomwe ili pamwamba imakokedwa kumanja (chithunzi 2). Ma mbale omwe ali pansi sakokedwa (mbale yapansi ili pamalo opumulira). Kukula kwa mphamvu yokoka kumakonzedwa kotero kuti mbale yomwe ili pamwamba imasunthira kumanja pa liwiro losasintha (v nthawi zonse). Chifukwa pali mphamvu yomatira yomwe imagwira ntchito pakati pa m'mphepete mwa mbale ndi gawo la madzimadzi lomwe limalumikizidwa ndi mbaleyo, madzimadzi omwe ali pansi pa mbaleyo amasunthiranso kumanja. Chifukwa pali mphamvu yogwirizana pakati pa mamolekyu amadzimadzi, madzimadzi omwe amapita kumanja amakoka madzi omwe ali pansi.
Gawo la madzi lomwe lili pamwamba limakoka madzi omwe ali pansi kuti asunthire kumanja,
pomwe gawo la madzi pansi limasunga madzi pamwamba, kotero liwiro la madzi limasiyana. Gawo la madzi lomwe lili pamwamba limayenda ndi liwiro lalikulu (v), madzi omwe ali pansi amayenda ndi v yaying'ono, ndi zina zotero. Chifukwa chake, otsika pansi v, ndi ochepa. Mwanjira ina, liwiro la gawo la madzi limasintha nthawi zonse kuchokera pamwamba kupita pansi mpaka l.
Kusintha kwa liwiro la gawo lamadzimadzi (v) kugawidwa ndi mtunda wa kusintha (l) = v / l. V/l imadziwika kuti liwiro la gradient. Ma plates omwe ali pamwamba amatha kusuntha chifukwa pali mphamvu yokoka (F). Pa madzi ena, kuchuluka kwa kukopa komwe kumafunika kumagwirizana mwachindunji ndi dera la madzimadzi omwe ali pa mbale (A), liwiro la madzimadzi (v) komanso mosagwirizana ndi mtunda l. Mwa masamu, zitha kulembedwa motere:
Poyamba, zidafotokozedwa kuti madzi opyapyala nthawi zambiri amakhala osavuta kuyenda, pomwe madzi okhuthala amakhala ovuta kuyenda. Kuchuluka kwa kukhuthala kumasonyeza kuchuluka kwa kukhuthala kwa madzi. Ngati madziwo ndi okhuthala, mphamvu yokakamiza yomwe imafunika nayonso imakhala yayikulu. Pankhaniyi, mphamvu yokakamiza imafanana mwachindunji ndi kukhuthala kwa kukhuthala. Pa masamu zitha kulembedwa motere:
η = coefficient ya kukhuthala, F = mphamvu, l = mtunda, A = malo a pamwamba, v = liwiro, ∝ = kuyerekeza
Chigawo cha International System (SI) cha coefficient of viscosity ndi Ns/m2 = Pa.s (sekondi ya pascal). CGS unit (masentimita gram sekondi) ya coefficient viscosity ndi dyn.s/cm2 = poise (P). Kukhuthala kumafotokozedwanso nthawi zambiri mu centipoise (cP). 1 cP = 1/100 P. Chigawo cha poise chimagwiritsidwa ntchito polemekeza wasayansi waku France, Jean Louis Marie Poiseuille (werengani: pwa-zoo-yuh).
1 poise = 1 dyn. s/cm2 = 10-1 Ns/m2
