Priprava i karakterizacija uljnih nanofluida s ugljikovim nanocijevima

master's thesis

• Title (english): Preparation and characterization of oil nanofluids with carbon nanotube
• Author: Lucijana Milanović Litre
• Mentor: Elvira Vidović (mentor)
• Committee member: Elvira Vidović (predsjednik povjerenstva)
• Committee member: Fabio Faraguna (član povjerenstva)
• Committee member: Ana Vrsalović Presečki (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2015-07-14, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering; Chemical Engineering in Material Development

Abstract

Cilj ovog rada je priprava i karakterizacija nanofluida koji posjeduju dva najpoželjnija svojstva
što se tiče prijenosa topline: dugotrajnu stabilnost i visoku toplinsku vodljivost. U tu svrhu su
pripravljene suspenzije višestjenčanih ugljikovih nanocijevi (MWCNT), odnosno grafita u
baznom fluidu PAO 8 ulju uz dodatak površinski aktivne tvari (PAT).
U prvoj fazi eksperimentalnog rada određeno je koja od površinski aktivnih tvari, za PAO 8 ulje,
omogućava najveću stabilnost nanofluida. U drugoj fazi je istraživan utjecaj različitih
koncentracija punila i odabrane površinski aktivne tvari (DPS) na stabilnost sustava. Stabilnost
pripravljenih nanofluida određivana je pomoću sedimentacijskog testa (vizualno) to pomoću UVVis
spektrofotometrije. Karakterizacija nanofluida je provedena određivanjem viskoznosti,
toplinske vodljivosti, otpornosti na trošenje i kontaktnog kuta na granici faza čvrsto-kapljevito
plinovito.
Površinski aktivna tvar s kojom je postignuta najveća stabilnost nanofluida je disperzantni
polimerni aditiv na osnovi stirena i metakrilata (DPS). Povećanjem njegove koncentracije dolazi
do porasta viskoznosti nanofluida, a time i do veće stabilnosti sustava (Stokesov zakon). Jedini
porast toplinske vodljivosti zabilježen je kod nanofluida koji sadrži 2600 mg MWCNT, a razlog
tome je što se prijenos topline odvija samo preko nanočestica u kontaktu. Rezultati testa trošenja
ukazuju na smanjenje srednjeg promjera istrošenja svih uzoraka, što ukazuje na bolja svojstva
podmazivanja. Iz rezultata mjerenja kontaktnog kuta zaključeno je da interakcije između uzoraka
i teflonske površine nisu povoljne, dok su staklena i metalna površina zatvarale manji kontaktni
kut sa uzorcima. Kod rezultata za metalnu površinu se opaža trend opadanja kontaktnog kuta s
povećanjem količine ugljikovih nanocijevi. Iz standardnih devijacija kod sva tri slučaja, vidi se
da metoda ima velika odstupanja te zbog toga nije moguće izvesti valjane zaključke.

Abstract (english)

The aim of this work is preparation and characterization of nanofluids with two features most
desired for heat transfer systems: long term stability and high thermal conductivity. For this
purpose, suspensions of multi-wall carbon nanotubes (MWCNTs) / graphite were prepared in a
base oil fluid PAO 8 with the addition of surface-active substances (surfactants).
In the first phase of the experimental work, it was determined which of surfactants, for PAO 8
oil, provides the greatest stability of nanofluids. In the second phase, the effect of different
concentrations of filler and selected surfactant (DPS) on system stability was studied. Stability of
prepared nanofluids was determined by sedimentation test (visually) and by UV-Vis
spectrophotometry. Characterization of nanofluids is accomplished by determining the viscosity,
thermal conductivity, wear resistance and the contact angle at the solid-liquid-gas interface.
The surfactant, that had enabled the greatest stability of nanofluids, was dispersant polymer
additive based on styrene and methacrylate (DPS). By increasing its concentration there was an
increase in viscosity of nanofluids, and thus greater system stability (Stokes' law) was
accomplished. The only increase in thermal conductivity was noted in nanofluid containing 2600
mg of MWCNTs, because the heat transfer takes place only via nanoparticles in touch. The
wearing test results indicate a reduction of mean wear diameter of all nanofluids, which indicates
better lubricating properties. The results of the contact angle measurement indicate that the
interaction between the sample and teflon surfaces are not favorable, while glass and metal
surfaces had lower contact angle with samples. Results for metal surface indicate decreasing
trend of the contact angle with the increase of carbon nanotubes. From the standard deviations for
all three cases, it can be seen that the method has a big deviation and it is not possible to draw
valid conclusions.

• Keywords: nanofluidi; ugljikove nanocijevi; stabilnost; toplinska vodljivost
• Keywords (english): nanofluids; carbon nanotubes; stability; thermal conductivity
• Language: croatian
• URN:NBN: urn:nbn:hr:149:572020
• Study programme: Title: Chemical Engineering - Graduate study; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka kemijskog inženjerstva (magistar/magistra inženjer/inženjerka kemijskog inženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2016-12-19 13:47:24