Experimental Observation of Nucleate Boiling Entrainment in a Liquid Film

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.

Effect of Heat Flux on Droplet Entrainment Using Annular Flow Dryout Model

2010 ◽  
Author(s):  
Masroor Ahmad ◽  
Evgeniy Burlutskiy ◽  
Simon P. Walker ◽  
Geoffrey F. Hewitt
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
High Pressure ◽  
Liquid Film ◽  
Annular Flow ◽  
High Pressures ◽  
Droplet Entrainment ◽  
Annular Film ◽  
Low Pressures ◽  
Flow Experiments

Annular film dryout depends upon the competition of entrainment, deposition and evaporation processes between the droplet-laden core and wall liquid film. In this paper, effect of heat flux on droplet entrainment is analyzed by modeling different low and high pressure diabatic annular flow experiments numerically using an annular flow dryout model (AFM). Overall, the AFM predicted the experimental data reasonably accurately. It is concluded that at high pressures increasing heat flux may enhance net entrainment considerably but this effect diminishes at low pressures.

The Influence of Vapor Bubble Sliding on Forced Convection Boiling Heat Transfer

1999 ◽  
Vol 121 (1) ◽  
pp. 73-79 ◽  
Author(s):  
G. E. Thorncroft ◽  
J. F. Klausner
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Single Phase ◽  
Flow Boiling ◽  
Heating Surface ◽  
Bulk Liquid ◽  
Transfer Rates

This paper describes experimental efforts aimed at examining the effect of vapor bubble sliding on forced convection boiling heat transfer. Flow boiling experiments using FC-87 were conducted for vertical upflow and downflow configurations. Both slightly subcooled single-phase and saturated annular flow boiling were considered. Significantly higher heat transfer rates were measured for vertical upflow than for downflow with the same wall superheat and slightly subcooled single-phase inlet conditions. This increase in heat transfer is directly attributable to sliding vapor bubbles, which remain attached to the wall during upflow and lift off the wall during downflow. Differences in the measured upflow and downflow heat transfer rates are not as significant for annular flow boiling, which is due in part to the similar vapor bubble dynamics which have been observed for upflow and downflow. Heat transfer experiments in single-phase subcooled upflow with air bubble injection at the heating surface suggest that sliding bubbles enhance the bulk liquid turbulence at the wall, which contributes significantly to the macroscale heat transfer. It is concluded from this work that vapor bubble sliding heat transport can be a significant heat transfer mechanism, and should be considered in the development of mechanistic flow boiling heat transfer models.

Momentum Conservation and Condensing Vapor Bubbles

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
I. Eames
Keyword(s):  
Vapor Bubble ◽  
Nucleate Boiling ◽  
Momentum Conservation ◽  
Total Momentum ◽  
Vapor Bubbles ◽  
Viscous Effects

Boiling is a common feature of many daily processes, such as making tea, cooking, and heating. The growth, rise, collapse, and final disappearance of vapor bubbles are ubiquitous features of nucleate boiling. New experimental observations show that a vortex is generated as a consequence of the bubble disappearing. We categorize the possible mechanisms that lead to the generation of a vortex by bubbles. When the bubble collapses but does not change topology, the vortex is created by viscous effects, where the attached wake behind the vapor bubble persists after the bubble has disappeared. But when the bubbles collapse so rapidly that they change topology, the vortex is created by an inviscid mechanism. The total momentum communicated to the flow by the collapse processes is calculated and compared with the measurements of the vortex impulse.

scholarly journals On the droplet entrainment from gas-sheared liquid film

2021 ◽  
Vol 33 (1) ◽  
pp. 011705
Author(s):  
Chihiro Inoue ◽  
Ikkan Maeda
Keyword(s):  
Liquid Film ◽  
Droplet Entrainment

Measurement of Liquid Film Thickness in Micro Tube Annular Flow

2010 ◽  
Author(s):  
Hiroshi Kanno ◽  
Youngbae Han ◽  
Yusuke Saito ◽  
Naoki Shikazono
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Annular Flow ◽  
Liquid Film Thickness ◽  
Phase Flow ◽  
Two Phase ◽  
Micro Scale ◽  
Film Model ◽  
Annular Film

Heat transfer in micro scale two-phase flow attracts large attention since it can achieve large heat transfer area per density. At high quality, annular flow becomes one of the major flow regimes in micro two-phase flow. Heat is transferred by evaporation or condensation of the liquid film, which are the dominant mechanisms of micro scale heat transfer. Therefore, liquid film thickness is one of the most important parameters in modeling the phenomena. In macro tubes, large numbers of researches have been conducted to investigate the liquid film thickness. However, in micro tubes, quantitative information for the annular liquid film thickness is still limited. In the present study, annular liquid film thickness is measured using a confocal method, which is used in the previous study [1, 2]. Glass tubes with inner diameters of 0.3, 0.5 and 1.0 mm are used. Degassed water and FC40 are used as working fluids, and the total mass flux is varied from G = 100 to 500 kg/m2s. Liquid film thickness is measured by laser confocal displacement meter (LCDM), and the liquid-gas interface profile is observed by a high-speed camera. Mean liquid film thickness is then plotted against quality for different flow rates and tube diameters. Mean thickness data is compared with the smooth annular film model of Revellin et al. [3]. Annular film model predictions overestimated the experimental values especially at low quality. It is considered that this overestimation is attributed to the disturbances caused by the interface ripples.

Predicting heat extraction due to boiling in the cooling channels during the pressure die casting process

2000 ◽  
Vol 214 (3) ◽  
pp. 465-482 ◽  
Author(s):  
L D Clark ◽  
I Rosindale ◽  
K Davey ◽  
S Hinduja ◽  
P J Dooling
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Die Casting ◽  
Casting Process ◽  
Nucleate Boiling ◽  
Heat Extraction ◽  
Film Boiling ◽  
Cooling Channels ◽  
Die Casting Process ◽  
Pressure Die Casting

The effect of boiling on the rate of heat extraction by cooling channels employed in pressure die casting dies is investigated. The cooling effect of the channels is simulated using a model that accounts for subcooled nucleate boiling and transitional film boiling as well as forced convection. The boiling model provides a continuous relationship between the rate of heat transfer and temperature, and can be applied to surfaces where forced convection, subcooled nucleate boiling and transitional film boiling are taking place in close proximity. The effects of physical parameters such as flow velocity, degree of subcooling, system pressure and bulk temperature are taken into account. Experimental results are obtained using a rig that simulates the pressure die casting process. The results are compared with the model predictions and are found to show good agreement. Instrumented field tests, on an industrial die casting machine, are also reported. These tests show the beneficial effects of boiling heat transfer in the pressure die casting process, including a 75 per cent increase in the production rate for the test component.

Sign in / Sign up

Export Citation Format

Share Document