Izboljšan prenos toplote pri vrenju na kemično obdelanih bakrenih površinah

magistrsko delo magistrskega študijskega programa II. stopnje Strojništvo

Nejc Mlakar (Author), Iztok Golobič (Mentor), Matevž Zupančič (Co-mentor)

Abstract

Mehurčkasto vrenje spada med najbolj učinkovite mehanizme prenosa toplote in je tudi tehnično dobro obvladljivo. Prenos toplote pri vrenju izboljšamo s povečanjem koeficienta toplotne prestopnosti in dvigom kritične gostote toplotnega toka. Na izboljšanje prenosa toplote lahko vplivamo predvsem s spremembo mikro- in nanostrukture ter omočljivosti vrelne površine. V magistrskem delu smo ovrednotili vpliv kemičnega strukturiranja bakrenih površin na izboljšan prenos toplote pri mehurčkastem vrenju. Bakrene vzorce smo kemično strukturirali s potapljanjem v alkalne raztopine, s čimer smo želeli doseči tvorbo mikro- in nanostrukture, ki ugodno vpliva na proces vrenja. Površine smo ovrednotili s posnetki elektronske mikroskopije in meritvami kota omočenja. Prenos toplote pri vrenju na strukturiranih površinah smo ovrednotili na merilni progi za vrenje v bazenu pod pogoji nasičenega vrenja dvakrat destilirane vode pri atmosferskem tlaku. Na podlagi meritev oz. izračunov gostote toplotnega toka in pregretja površine smo izrisali vrelne krivulje in določili koeficiente toplotne prestopnosti. Na neobdelani referenčni površini smo dosegli kritično gostoto toplotnega toka 1385 kW m-2, ki smo jo s kemičnim strukturiranjem povečali na maksimalno 2000 kW m-2. Koeficient toplotne prestopnosti je na referenčni površini znašal 60 kW m-2 K-1, na obdelanih površinah pa smo zabeležili vrednosti do 125 kW m-2 K-1.

Keywords

magistrske naloge;mehurčkasto vrenje;izboljšan prenos toplote;kemično strukturiranje površin;kritična gostota toplotnega toka;koeficient toplotne prestopnosti;inženiring površin;

Data

Language:	Slovenian
Year of publishing:	2020
Typology:	2.09 - Master's Thesis
Organization:	UL FS - Faculty of Mechanical Engineering
Publisher:	[N. Mlakar]
UDC:	536.24:542.467:669.3(043.2)
COBISS:	28611587
Views:	524
Downloads:	136
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Chemical structured copper surfaces for enhanced nucleate boiling heat transfer
Secondary abstract:	Nucleate boiling is one of the most efficient heat transfer mechanisms and is a technically well-controllable process. Boiling heat transfer can be enhanced by increasing the heat transfer coefficient and raising the critical heat flux. The enhancement of boiling heat transfer can be achieved primarily by modifying the micro- and nanostructure of the boiling surface and its wettability. In this thesis, we evaluate the influence of chemical structuring of copper surfaces on enhanced nucleate boiling heat transfer. Copper samples were chemically structured through immersion in alkaline solutions with the aim of achieving the formation of micro- and nanostructures favorable for boiling heat transfer. Surface properties were evaluated using scanning electron microscopy and contact angle measurements. Heat transfer properties of structured surfaces were evaluated using a pool boiling experimental setup. Saturated nucleate boiling conditions were maintained throughout the experiments, which were carried out using twice-distilled water at atmospheric pressure. Boiling curves and heat transfer coefficients were determined based on measurements and calculations of the heat flux and boiling surface superheat. Critical heat flux of 1385 kW m-2 was recorded on an untreated reference surface, while values of up to 2000 kW m-2 were recorded on structured surfaces. Heat transfer coefficients of 60 kW m-2 K-1 and of up to 125 kW m-2 K-1 were recorded on the reference surface and chemically structured surfaces, respectively.
Secondary keywords:	master thesis;nucleate boiling;enhanced heat transfer;chemical surface structuration;critical heat flux;heat transfer coefficient;surface engineering;
Type (COBISS):	Master's thesis/paper
Study programme:	0
Thesis comment:	Univ. Ljubljana, Fak. za strojništvo
Pages:	XXII, 63 str.
ID:	12025821