Electrochemical Numerical Simulation of Atmospheric Corrosion Sensors Covered by Thin Liquid Film

Abstract A numerical simulation was performed on the condensation of water and ethanol vapor mixture on a horizontal wall in a plane two-dimensional field. The analysis solves unsteady flow and heat-and-mass transfer both for liquid and vapor with the phase equilibrium condition at the interface, using FDM and boundary-fitted coordinates to track the deformation of interface. The calculation was started from a very thin smooth liquid film, and it was found that instability occurs when the film thickness reaches a certain value resulting in the formation of relatively small droplets. With the growth of the droplets, they coalesce into larger ones. Between the droplets an extremely thin liquid film exists, and the surface tension gradient sustains the droplets. With the increase of the wall subcooling the maximum droplet becomes large due to the increase of the Marangoni effect.

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Numerical Investigation of a Novel Grooved Vapor Chamber

ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B ◽

10.1115/mnht2008-52017 ◽

2008 ◽

Author(s):

Ming Zhang ◽

Zhongliang Liu ◽

Guoyuan Ma

Keyword(s):

Numerical Simulation ◽

Heat Source ◽

Liquid Film ◽

Thin Liquid Film ◽

Source Region ◽

Transfer Model ◽

Vapor Chamber ◽

Starting Point ◽

Condensation Surface ◽

Simulation Results

An effective thermal spreader can achieve more uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Vapor chamber is one of highly effective thermal spreaders. In this paper, a novel grooved vapor chamber was designed. The grooved structure of the vapor chamber can improve its axial and radial heat transfer and also can form the capillary loop between condensation and evaporation surfaces. A two dimensional heat and mass transfer model for the grooved vapor chamber is developed. The numerical simulation results show the thickness distribution of liquid film in the grooves is not uniform. The temperature and velocity field in vapor chamber are obtained. The thickness of the liquid film in groove is mainly influenced by pressure of vapor and liquid beside liquid-vapor interface. The thin liquid film in heat source region can enhance the performance of vapor chamber, but if the starting point of liquid film is backward beyond the heat source region, the vapor chamber will dry out easily. The optimal filling ratio should maintain steady thin liquid film in heat source region of vapor chamber. The vapor condenses on whole condensation surface, so the condensation surface achieves great uniform temperature distribution. By comparing the experimental results with numerical simulation results, the reliability of the numerical model can be verified.

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CFD Modeling of Two-Phase Gas-Liquid Slug Flow Using VOF Method in Microchannels

Volume 1: Symposia, Parts A, B and C ◽

10.1115/fedsm2009-78438 ◽

2009 ◽

Cited By ~ 4

Author(s):

A. Mehdizadeh ◽

S. A. Sherif ◽

W. E. Lear

Keyword(s):

Numerical Simulation ◽

Liquid Film ◽

Slug Flow ◽

Thin Liquid Film ◽

Liquid Films ◽

Vof Method ◽

Cfd Modeling ◽

Two Phase ◽

Mesh Resolution ◽

Gas Volume

Despite of the fact that numerical simulation of two-phase flows in microchannels has been attempted by many investigators, most efforts seem to have failed in correctly capturing the flow physics, especially the slug flow regime characteristics. The presence of a thin liquid film in the order of 10 μm around the bubble (sometimes called gas pocket or gas slug) may be a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field. Thus, there is a strong motivation to employ numerical simulation methods in order to avoid some of the experimental difficulties. In this paper, the characteristics of two-phase slug flows in microchannels are calculated with the help of the Volume-of-Fluid (VOF) method. Formation of the slugs for different superficial velocities, Capillary numbers, and gas volume fractions are investigated. The minimum mesh resolution required to capture the liquid film surrounding the gas bubble is reported employing a dynamic mesh adaption methodology with interface tracking. Results are shown to be in good agreement with experimental data and empirical correlations.

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