Numerical Simulation of Droplets Impacting on a Liquid Film with a Vapor Bubble Growing

The technique of horizontal-tube falling film has been used in the cooling and heating industries such as refrigeration systems, heating systems and ocean thermal energy conversion systems. The comprehensive performance of evaporator is directly affected by the film distribution characteristics outside tubes. In this paper, numerical investigation was performed to predict the film characteristics outside the tubes in horizontal-tube falling film evaporator. The effects of liquid flow rate, tube diameter and the circular degree of tube on the film thickness were presented. The numerical simulation results were compared with that of the empirical equations for calculating the falling film thickness, and agreements between them were reasonable. Numerical simulation results show that, at the fixed fluid flow density, the liquid film is thicker on the upper and lower tube and the thinnest liquid film appears at angle of about 120°. The results also indicate that, when the fluid flow density decreases to a certain value, the local dryout spot on the surface of the tube would occur. In addition, the film thickness decreases with the increases of the tube diameter at the fixed fluid flow density.

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Numerical simulation of the influence of non-condensable molecules on collapsing vapor bubble

The Proceedings of the Fluids engineering conference ◽

10.1299/jsmefed.2019.os2-08 ◽

2019 ◽

Vol 2019 (0) ◽

pp. OS2-08

Author(s):

Kyohei YAMAMOTO ◽

Kazumichi KOBAYASHI ◽

Masao WATANABE ◽

Hiroyuki FUJII ◽

Misaki KON ◽

...

Keyword(s):

Numerical Simulation ◽

Vapor Bubble

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Experimental Observation of Nucleate Boiling Entrainment in a Liquid Film

10.1115/icone28-63813 ◽

2021 ◽

Author(s):

Junpei Tabuchi ◽

Yuki Narushima ◽

Kenichi Katono ◽

Tomio Okawa

Keyword(s):

Liquid Film ◽

Forced Convection ◽

Vapor Bubble ◽

Water Surface ◽

Annular Flow ◽

Nucleate Boiling ◽

Vapor Bubbles ◽

Droplet Entrainment ◽

Bubble Bursting ◽

Filament Breakup

Abstract Many studies have been conducted on droplet entrainment in an annular flow regime, but little is known about droplet entrainment caused by nucleate boiling. In this report, visualization results of droplet entrainment caused by nucleate boiling are described. We observed two processes of droplet entrainment. The first one causes bubble bursting at a water surface. The second one causes filament breakup which occurs when the vapor bubble reaches and collapses at the interface between air and liquid. From comparison of the phenomena for the two processes, we found that the diameters of the droplets and vapor bubbles were considerably different. Using the results of this research allows the effect of forced convection to be taken into account. In the future, we plan to expand the amount of data and develop a boiling entrainment model under forced convection conditions.

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