Utjecaj hidrodinamičkih uvjeta na prijenos topline u nanofluidu

undergraduate thesis

• Title (english): Influence of hydrodynamic conditions on heat transfer in nanofluids
• Author: Sara Čemeljić
• Mentor: Jasna Prlić Kardum (mentor)
• Committee member: Jasna Prlić Kardum (predsjednik povjerenstva)
• Committee member: Aleksandra Sander (član povjerenstva)
• Committee member: Ljubica Matijašević (član povjerenstva)
• Granter: University of Zagreb; Faculty of Chemical Engineering and Technology; Zagreb
• Defense date and country: 2015-05-26, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Chemical Engineering; Environmental Protection in Chemical Engineering

Abstract

U smjesu konvencionalnih baznih fluida (smjesa glicerol – voda i voda) dispergirane su
nanočestice aluminijeva (III) oksida, u različitim koncentracijama, s ciljem poboljšanja toplinske
vodljivosti nanofluida. Raspršenost nanočestica u suspenziji postignuta je djelovanjem
ultrazvučnih valova na kapljevinu, a stabilnost je poboljšana dodatkom polivinil alkohola.
Pripremljenim suspenzijama izmjeren je koeficijenti toplinske vodljivosti, gustoća i viskoznost te
je izračunat specifični toplinski kapacitet. Izmjerena termo-fizikalna svojstva uspoređena su s
podacima izračunatim iz različitih teoretskih modela. Također su uspoređene vrijednosti termofizikalnih
svojstva sa i bez dodatka aditiva (PVA). Dodatak PVA smanjuje koeficijent toplinske
vodljivosti i znatno povećava viskoznost nanofluida.
Pripremljeni nanofluidi korišteni su pri zagrijavanju vode u pločastom izmjenjivaču topline te je
određen koeficijent prijelaza topline na strani nanofluida. Povećanjem protoka povećava se
koefcijent prijelaza topline zbog smanjenja debljine hidrodinamičkog i toplinskog graničnog
sloja. Povećanjem koncentracije nanočestica poboljšava se prijenos topline bez obzira na
vrijednosti koeficijenta toplinske vodljivosti. Može se zaključiti da prisustvo nanočestica u fluidu
utječe na strukturu graničnog sloja, a Brown-ovo gibanje prisutno u nanofluidima uzrokuje
dodatnu konvekciju što rezultira poboljšanjem prijenosa topline u nanofluidima.

Abstract (english)

The conventional mixture of base fluid (mixture glycerol - water and water) are dispersed
nanoparticles of aluminum (III) oxide, in different concentrations, in order to improve thermal
conductivity of nanofluida. The dispersion of nanoparticles in suspension is achieved by the
action of ultrasonic waves in the liquid, and the stability is improved by the addition of polyvinyl
alcohol.
The coefficient of thermal conductivity, density, viscosity and specific heat capacity have been
measured for prepared suspensions. The measured thermo - physical properties were compared
with the data calculated from different theoretical models. The volume of thermo – physical
properties has been compared with and without additives (PVA). Addition of PVA reduces the
thermal conductivity and significantly increases the viscosity of nanofluida.
Prepared nanofluids were used while heating water in the plate heat exchanger and the heat
transfer coefficient is determined based on the nanofluid. Increasing of the flow increases the
coefficient of heat transfer due to reduced layer of the hydrodynamic and thermal boundary. By
increasing the concentration of nanoparticles the heat transfer improves regardless of the value
of thermal conductivity. It can be concluded that the presence of nanoparticles in the fluid
influences the structure of the boundary layer, and the Brownian movement which is present in
nanofluids causes convection which results in an additional improvement of heat transfer in
nanofluids.

• Keywords: nanofluidi; pločasi izmjenjivač topline; termo-fizikalna svojstva
• Keywords (english): nanofluids; plate heat exchanger; thermo-physical properties
• Language: croatian
• URN:NBN: urn:nbn:hr:149:896513
• Study programme: Title: Environmental Engineering - Undergraduate study; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka ekoinženjerstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka ekoinženjerstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Closed access
• Repository: Repository of Faculty of Chemical Engineering and Technology University of Zagreb
• Created on: 2016-09-08 12:05:56