doktorsko delo
Matic Može (Author), Iztok Golobič (Mentor), Matevž Zupančič (Co-mentor)

Abstract

V delu obravnavamo prenos toplote pri mehurčkastem vrenju in njegovo izboljšanje oz. intenzifikacijo preko modifikacije vrelne površine in njene interakcije z delovnim fluidom. V ta namen predstavljamo razvoj hibridnih strukturiranih površin, ki promovirajo mehurčkasto vrenje. Za funkcionalizacijo površin vzorcev iz aluminija, bakra in titana smo uporabili predobdelavo s kemičnim ali laserskim strukturiranjem in nanos hidrofobnega premaza v obliki fluoriranega silana. Na podlagi analize literature, v kateri obstaja velik raztros referenčnih vrednosti kritične gostote toplotnega toka kot posledica različnih metodologij procesiranja izmerkov, smo razvili novo merilno progo za spremljanje procesa vrenja z nizko merilno negotovostjo. Na razvitih površinah smo ovrednotili prenos toplote pri nasičenem vrenju vode pri atmosferskem tlaku, pri čemer smo zabeležili vrednosti kritične gostote toplotnega toka do 1943 kW m-2 (> 100 % izboljšanje v primerjavi z neobdelano površino) in koeficiente toplotne prestopnosti do 304,7 kW m-2 K -1 (> 500 % izboljšanje). Pokazali smo, da se zaradi večkratnega nastopa kritične gostote toplotnega toka ali dolgotrajnega vrenja spremenijo morfološke in kemične lastnosti vrelne površine, kar vpliva na prenos toplote pri vrenju. Ovrednotenje vrenja samoomočljivih fluidov na razvitih hibridnih površinah je pokazalo, da se parametri prenosa toplote v splošnem poslabšajo v primerjavi z vrenjem čiste vode na istih površinah, še vedno pa so zagotovljeni višji koeficienti toplotne prestopnosti kot pri vrenju istih fluidov na neobdelanih površinah. Rezultati doktorskega dela kažejo, da primerno razplinjene površine z nizko površinsko energijo in mikrostrukturo, ki promovira nukleacijo, zagotavljajo velike izboljšave parametrov prenosa toplote pri mehurčkastem vrenju, kar je v nasprotju s trenutno uveljavljenim prepričanjem, da takšne površine, ki na makroskali izkazujejo superhidrofobnost, niso primerne za izboljšanje prenosa toplote pri vrenju.

Keywords

mehurčkasto vrenje;izboljšan prenos toplote;strukturiranje površin;hibridne površine;samoomočljivi fluidi;staranje površin;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FS - Faculty of Mechanical Engineering
Publisher: [M. Može]
UDC: 536.24:66.046.7:532(043.3)
COBISS: 66998275 Link will open in a new window
Views: 515
Downloads: 179
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Other data

Secondary language: English
Secondary title: Hybrid structured surfaces for enhanced nucleate boiling heat transfer
Secondary abstract: This work deals with nucleate boiling heat transfer and its enhancement through modification of the boiling surface and the interaction of the latter with the working fluid. To this effect, we present the development of hybrid structured surfaces, which promote nucleate boiling. Surfaces of aluminum, copper and titanium samples are functionalized using chemical or laser surface texturing and subsequent hydrophobization through application of a fluorinated silane. Analysis of reference critical heat flux values from literature shows that considerable scatter results from different methodologies of processing measured values. This was used to develop a new experimental setup for boiling performance evaluation with reduced measurement uncertainty. Boiling heat transfer was evaluated on developed surfaces using saturated pure water at atmospheric pressure. Developed surfaces exhibited critical heat flux values of up to 1943 kW m-2 (> 100 % enhancement over the reference surface) and heat transfer coefficients of up to 304,7 kW m-2 K -1 (> 500 % enhancement). We have shown that repeated onset of critical heat flux or long-term boiling on the surface changes morphological and chemical properties of the boiling surface, which affects boiling heat transfer. Boiling of self-rewetting fluids on developed hybrid structured surfaces resulted in deterioration of heat transfer intensity compared to boiling of pure water on the same surfaces, although heat transfer is still enhanced compared to boiling of these fluids on untreated surfaces. The results of the doctoral thesis demonstrate that properly degassed surfaces with low surface energy and nucleate-boiling-promoting microstructure provide substantial enhancements of nucleate boiling heat transfer parameters, which challenges the currently established sentiment that such (macroscopically superhydrophobic) surfaces are unsuitable for boiling heat transfer enhancement.
Secondary keywords: dissertations;nucleate boiling;enhanced heat transfer;structured surfaces;hybrid surfaces;self-rewetting fluids;surface aging;Vrenje;Disertacije;
Type (COBISS): Doctoral dissertation
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za strojništvo
Pages: XXXII, 204 str.
ID: 12947125