Project

Back to overview

Fundamental Study on Micro-layer Forming Process in Nucleate Boiling

English title Fundamental Study on Micro-layer Forming Process in Nucleate Boiling
Applicant Sato Yohei
Number 175893
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Fluid Dynamics
Start/End 01.10.2018 - 30.09.2021
Approved amount 257'918.00
Show all

All Disciplines (2)

Discipline
Fluid Dynamics
Theoretical Physics

Keywords (4)

Computational Fluid Dynamics; Micro-layer; Heat transfer; Nucleate boiling

Lay Summary (German)

Lead
In diesem Projekt werden wir durch numerische Simulationen und experimentelle Messungen ein umfassendes Verständnis der Phänomene des Blasensiedens, einschließlich des Mikroschichtbildungsverfahrens auf der Wärmeübertragungsoberfläche, erhalten.
Lay summary

Hauptziel
Um den Bildungsprozess der Mikroschicht zu verstehen, die ein dünner Flüssigkeitsfilm ist, der unter einer wachsenden Blase existiert, beobachten wir experimentelle Messungen und reproduzieren die Phänomene durch Lösen von grundlegenden Gleichungen. Die numerische Simulationsmethode wird von den Hauptforschern entwickelt und die Experimente werden vom Projektpartner am Kyushu Institute of Technology durchgeführt.

Ziele des Projekts
Blasensieden Wärmeübertragung ist eine der effizientesten Methoden von Wärmeübertragung, und wird in vielen technischen Anwendungen verwendet. Das Blasensieden schreitet zum Übergangs- / Filmsiederegime, was zu einem Brennen der Vorrichtung führt, sobald der Wärmefluss die sogenannte kritische Wärmestromdichte (CHF) überschreitet. In einem derartigen hohen Wärmeflußzustand spielt die Mikroschicht eine wichtige Rolle, da angenommen wird, daß ein großer Betrag der Wärmestromdichte von der Verdampfung der Mikroschicht herrührt. Das Verständnis der Mechanismen des Mikroschichtbildungsprozesses ermöglicht die Vorhersage von CHF durch numerische Simulationen.

Direct link to Lay Summary Last update: 12.10.2017

Lay Summary (English)

Lead
In this project, we will derive complete understanding of the nucleate boiling phenomena, including micro-layer forming process on heat-transfer surface, by means of numerical simulations and experimental measurements.
Lay summary
Main goal
To understand the forming process of micro-layer, which is a thin liquid film existing underneath a growing bubble, we observe experimental measurements and reproduce the phenomena by solving basic governing equations.  The numerical simulation method will be developed by the principal investigators, and the experiments will be performed by the project partner at Kyushu Institute of Technology.

Aims of project
Nucleate boiling heat transfer is one of the most efficient modes of heat transfer under high heat-flux condition, and is used in many engineering applications. The nucleate boiling transitions to transition/film boiling regime which results in burn-out of the apparatus, once the heat flux exceeds so-called Critical Heat Flux (CHF). In such high heat-flux condition, the micro-layer plays an important role since large ratio of heat flux is considered to come from the evaporation of the micro-layer. The understanding of mechanisms of micro-layer forming process enables to predict CHF through numerical simulations.
Direct link to Lay Summary Last update: 12.10.2017

Responsible applicant and co-applicants

Employees

Name Institute

Project partner

Abstract

Nucleate boiling heat transfer is one of the most efficient modes of heat transfer under high heat-flux conditions, and is used in many engineering applications, such as refrigeration, cooling systems, boilers, heat exchangers. Although there is a multitude of applications, accurate prediction of boiling heat transfer still relies heavily on empirical methods, because Direct Numerical Simulation (DNS), including Computational Fluid Dynamics (CFD), is not yet sufficiently mature to produce reliable results. Recently we have succeeded in simulating pool boiling flow from isolated bubble to film boiling regime including Departure from Nucleate Boiling (DNB), which is state-of-the-art in this field. The computed heat transfer coefficient agreed well with the experiment, and the bubble shapes computed with an interface tracking method is also in good agreement with the experiment. However, one empirical correlation is still used for the modelling of the micro-layer evaporation, which indicates that the boiling process has not been simulated based on the governing equations.Micro-layer is a thin liquid film existing underneath a growing bubble on a heat-transfer surface in nucleate boiling flow. Recent measurement shows that 30 - 40 % of heat transfer is resulting from vaporization of the micro-layer for the isolated bubble regime. However the mechanism for forming of micro-layer has not been understood sufficiently yet. Namely there are no proven answers to the following questions:- Why is the thin liquid film formed on the heat-transfer surface?- Does an attractive force in short distance (e.g. intermolecular force) play important role?- How does the material property of working fluid influence the thickness?- How does the system pressure influence the thickness?- How do material property of the heat-transfer surface and surface roughness have influence on the thickness?- How is the thickness changed by the heat flux?In this project, we will reveal the mechanisms of this micro-layer forming process using DNS in which no empirical correlation is employed. The liquid-vapor interface is captured with the color function, and the conjugate heat transfer between the solid and fluid is strictly taken into account. In addition, the thermo-capillary force and the disjoining pressure are taken into account in order to attempt to reproduce the micro-layer on the heat transfer surface. The computational mesh size is anticipated to be 0.1 µm, and the supercomputer at Swiss National Supercomputer Center (CSCS) will be used to handle huge number of computational mesh in transient simulation.In parallel to the development of numerical scheme, experiments for micro-layer forming process will be performed by the project partner: Prof. Yabuki at Kyushu Institute of Technology, who has undertaken pool and convective boiling experiment using MEMS sensor. The working fluid will be water at atmospheric pressure, and the distribution of micro-layer thickness, the temperature distribution over the heat-transfer surface and the temperature distribution in liquid phase will be measured in addition to bubble shape. The applied heat flux will be in the isolated bubble regime. If the numerical simulation for the micro-layer forming process is validated against experiment, it indicates the complete understanding of micro-layer forming process.Should the validation succeed, numerical simulation will be performed for the cases with different heat flux, system pressures and contact angle in order to obtain deeper understandings of the boiling phenomena on wall.
-