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Simulation on the flow and heat transfer characteristics of confined bubbles in micro-channels
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.ORCID iD: 0000-0002-9902-2087
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-5595-1952
2012 (English)In: ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and Minichannels Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 Fluids Engineering Division Sum, ICNMM 2012, 2012, 63-70 p.Conference paper, Published paper (Refereed)
Abstract [en]

3D simulations on confined bubbles in micro-channels with diameter of 1.24 mm were conducted. The working fluid is R134a with a mass flux range from 125kg/m2s to 375kg/m2s. The VOF model is chosen to capture the 2 phase interface while the geo-construction method was used to re-construct the 2-phase interface. A heated boundary wall with heat flux varying from 15kW/m2 to 102kW/m2 is supplied. The wall temperature was calculated. The effects of mass flux and heat flux are studied. The shape of the bubble was predicted by the simulation successfully and the results show that they are independent of the initial shape. Both thin film evaporation and micro convection enhance the heat transfer. However, the micro convection which is caused by bubble motion has greater contribution to the total heat transfer at the stage of bubble growth studied.

Place, publisher, year, edition, pages
2012. 63-70 p.
Keyword [en]
3D simulations, Boundary walls, Bubble growth, Bubble motion, Flow and heat transfer, Initial shape, Thin film evaporation, Wall temperatures, Heat flux, Microchannels, Phase interfaces, Refrigerants, Heat transfer
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-131334DOI: 10.1115/ICNMM2012-73108ISI: 000335090900009Scopus ID: 2-s2.0-84882351460ISBN: 978-079184479-3 (print)OAI: oai:DiVA.org:kth-131334DiVA: diva2:656399
Conference
ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and Minichannels, ICNMM 2012 Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 Fluids Engineering Division Sum, ICNMM 2012; Rio Grande; Puerto Rico; 8 July 2012 through 12 July 2012
Note

QC 20131015

Available from: 2013-10-15 Created: 2013-10-14 Last updated: 2017-03-30Bibliographically approved
In thesis
1. Numerical study of flow boiling in micro/mini channels
Open this publication in new window or tab >>Numerical study of flow boiling in micro/mini channels
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Boiling phenomena in micro scale has emerged as an interesting topic due to its complexity and increasing usage in micro electronic and mechanical systems (MEMS). Experimental visualization has discovered five main flow regimes: nucleate boiling, isolated bubbles, confine bubbly flow, elongated bubbly (or slug) flow, and annular flow. Two of these patterns (confine bubbles and slug flow) are rarely found in macro channels and are believed to have very different heat transfer mechanisms to that of nucleate boiling.

The development of a phenomenological model demands a deep understanding of each flow regime as well as the transition process between them. While studies in every individual flow pattern are available in literature, the mechanisms of transition processes between them remain mysterious. More specifically, how the isolated bubbles evolve into a confined bubbly flow, and how this further evolves into elongated bubbles and finally an annular flow. The effects of boundary conditions such as wall heat flux, surface tension, and interfacial velocity are unclear, too.

The aims of this thesis are to develop and validate a new numerical algorithm, perform a comprehensive numerical study on these transition processes, uncover the transition mechanisms and investigate effects of boundary and operating conditions.

Firstly, a sophisticated and robust numerical model is developed by combining a coupled level set method (CLSVOF) and a non-equilibrium phase change model, which enables an accurate capture of the two-phase interface, as well as the interface temperature.

Secondly, several flow regime transitions are studied in this thesis: nucleate bubbles to confined bubbly flow, multi confined bubbles moving consecutively in a micro channel, and slug to annular flow transition. Effects of surface tension, heat flux, mass flux, and fluid properties are examined. All these regimes are studied separately, which means an appropriate initial condition is needed for each regime. The author developed a simplified model based on energy balance to set the initial and boundary conditions.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 74 p.
Series
TRITA-REFR, ISSN 1102-0245 ; 17/02
Keyword
numerical, boiling, micro channel, phase change.
National Category
Mechanical Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-204639 (URN)978-91-7729-342-2 (ISBN)
Public defence
2017-05-19, b1, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20170403

Available from: 2017-04-03 Created: 2017-03-30 Last updated: 2017-05-10Bibliographically approved

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Palm, BjörnAnglart, Henryk

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