Pool Boiling on Structured Surfaces: Heat Transfer and Critical Heat Flux: -Experiments and Mechanistic Modelling

Research output: ThesisDoctoral Thesis (compilation)

Abstract

In this thesis, pool boiling heat transfer was experimentally studied on structured surfaces with dielectric liquids (HFE-7200, NOVEC-649, FC-72), organic liquids (Acetone, Pentane) and deionized water.
In the first step, nanoparticle coatings on copper surfaces were prepared by an electrophoretic deposition method, with Cu-Zn nanoparticles (100 nm) and Cu nanoparticles (150 nm). Two types of nanoparticle-coating surfaces were prepared, namely nanoparticle coatings uniformly deposited on smooth surfaces and nanoparticle coatings partially deposited on smoothsurfaces. Pool boiling of HFE-7200 and acetone was tested on the coating surfaces. It is found that pool boiling heat transfer coefficients are significantly enhanced by nanoparticle coatings. However, the uniform coating cannot enhance the critical heat flux, while the partially-deposited coating can enhance critical heat flux. Mechanistic heat transfer models were developed to predict the heat transfer coefficients, considering natural convection, transient heat conduction, microlayer evaporation and micro convection, while the critical heat flux was analyzed from the point of wickability and hydrodynamic instability.
In the following step, microporous coatings on copper surfaces were generated by an electrochemical deposition method, with electrolyte solutions (CuSO4+H2SO4). Pool boiling of HFE-7200, NOVEC-649 and water was tested. The results show that heat transfer coefficients and critical heat flux are enhanced, and the heat transfer coefficients are obviously dependent on deposition-relevant parameters, like deposition time and electrolyte concentration. Heat transfer coefficients were discussed mechanistically and empirically by a mechanistic model and correlations, while the critical heat flux was predicted by a modified force balance model which considers the forces exerted on vapor and assumes occurrence of the critical heat flux when the vapor expands on surfaces.
Finally, hybrid micro/nano structures were fabricated on copper surfaces by femtosecond laser machining and electrophoretic deposition, and on silicon wafers by dry etching and electrostatic deposition. Pool boiling of acetone and FC-72 was investigated on the copper surfaces and the silicon wafers, respectively. It is found that the hybrid structures induce higher heat transfer coefficients than sole structures and wickability plays an important role on enhancement of the critical heat flux.

Details

Authors
Organisations
Research areas and keywords

Keywords

  • pool boiling, heat transfer, critical heat flux, bubble dynamics, surface modification
Original languageEnglish
QualificationDoctor
Supervisors/Assistant supervisor
Award date2019 Oct 25
Publisher
  • Department of Energy Sciences, Lund University
Print ISBNs978-91-7895-231-1
Electronic ISBNs978-91-7895-232-8
Publication statusPublished - 2019 Sep 30
Publication categoryResearch

Bibliographic note

Defence details Date: 2019-10-25 Time: 10:15 Place: Lecture hall M:B, building M, Ole Römers väg 1, Lund University, Faculty of Engineering LTH, Lund External reviewer(s) Name: Jungho Kim Title: Professor Affiliation: University of Maryland, USA ---

Total downloads

No data available