doktorsko delo
Peter Zakšek (Author), Iztok Golobič (Mentor)

Abstract

Nenehno izboljševanje hlajenja energetskih naprav narekuje učinkovite načine prenosa zajetnih gostot toplotnega toka, zato se velikokrat uporablja mehanizem mehurčkastega vrenja vodnih zmesi za obvladovanje postrojev. V disertaciji eksperimentalno obravnavamo vrenje dveh n-butanol vodnih raztopin na 12,5 µm titanovi foliji ter dveh zmeseh etanola in vode na različno obdelanih 25 µm nerjavečih folijah. Opravljene meritve pomenijo korak k boljšemu razumevanju in vrednotenju mehurčkastega podhlajenega in nasičenega vrenja pri različnima koncentracijama višjeogličnih alkoholov v vodni raztopini. Na podlagi meritev nestacionarnih temperaturnih polj z IR termografijo smo uvedli drugačen pristop obravnavanja procesa vrenja zmesi, pri čemer smo potrdili vpliv dodajanja majhnih koncentracij višjeogličnih alkoholov na toplotno karakteristiko. Z nadaljnjo lokalno analizo nasičenega vrenja smo na podlagi opazovanj rasti in frekvenc mehurčkov sinhronega hitrega videa in meritev s hitrotekočo infrardečo termografijo, pokazali vpliv izčrpavanja okoliškega fluida. Na ta način smo omogočili pridobitev natančnih podatkov v zvezi z okoliščinami življenjskega cikla mehurčka. Vrenje zmesi etanola in vode na lasersko neobdelani površini v primerjavi z lasersko strukturirano površino, doseženo z laserskim obdelovalnim sistemom, je obdelava površin pomembno vplivala na vrelni proces. Meritve na lasersko obdelani površini so pokazale povečanje aktivnih nukleacijskih mest, zmanjšanje velikosti mehurčkov in povečanje frekvence nukleacij, poleg tega je bilo doseženo tudi nižje pregretje površine. Na integralnem nivoju so meritve na obdelani in neobdelani površini pri nasičenem in podhlajenem vrenju zmesi pokazale pomemben vpliv laserskega obdelovanja površine, pri čemer je bil dosežen bistven izboljšan prenos toplote.

Keywords

disertacije;izboljšan prenos toplote;mehurčkasto vrenje v bazenu;binarne vodne zmesi;lasersko strukturirane površine;samoomočljivi fluidi;hitrotekoča infrardeča termografija;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FS - Faculty of Mechanical Engineering
Publisher: [P. Zakšek]
UDC: 536.24:544.35(043.3)
COBISS: 156433667 Link will open in a new window
Views: 7
Downloads: 2
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Other data

Secondary language: English
Secondary title: Enhanced heat transfer by pool boiling of binary mixtures on structured surfaces
Secondary abstract: Continuous improvement of cooling for power installations dictates efficient ways of transmitting extensive heat fluxes, which is why a mechanism of nucleate boiling of water mixtures is often used to control assemblies. This doctoral thesis experimentally deals with the boiling of two n-butanol aqueous solutions on a 12,5 μm titanium foil and of two mixtures of ethanol and water on differently treated 25 μm stainless foils. The measurements taken represent a step towards a better understanding and to the evaluation of subcooled and saturated nucleate boiling with different concentrations of aqueous solutions with highercarbon alcohols. Based on the measurements of non-stationary temperature fields with IR thermography, a different approach has been introduced to the treatment of the process of boiling mixtures, whereby the impact of adding small concentrations of higher-carbon alcohols to the thermal characteristic has been confirmed. Further local analysis of saturated boiling based on the observation of growth and frequencies of bubbles using synchronous high speed video recordings and of the temperatures measured by high-speed IR thermography has demonstrated the impact of surrounding fluid depletion. This enabled us to obtain precise information on the circumstances of the life cycle of a bubble. The process of boiling water ethanol mixture on a surface not laser-treated compared to boiling the same mixture on a laser structured surface was significantly influenced by the structure of the surface. The measurements on the laser-treated surface have revealed an increase of active nucleation sites, a reduction in the size of bubbles and an increase in nucleation frequency as well as a reduction in surface overheating. Considering all of the results, the measurements on the treated and non-treated surface for saturated and subcooled boiling of mixtures have demonstrated an important impact of surface laser treatment with a significant improvement in heat transfer.
Secondary keywords: dissertations;enhanced heat transfer;nucleate pool boiling;binary water mixtures;laser structured surfaces;self-rewetting fluids;IR thermography;
Type (COBISS): Doctoral dissertation
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za strojništvo
Pages: XXVIII, 154 str.
ID: 19336043