scholarly journals Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

1991 ◽  
Author(s):  
S. Wittig ◽  
J. Himmelsbach ◽  
B. Noll ◽  
H. J. Feld ◽  
W. Samenfink
Keyword(s):  
Shear Stress ◽  
Liquid Film ◽  
Gas Phase ◽  
Film Flow ◽  
Phase Interface ◽  
Liquid Films ◽  
Numerical Code ◽  
Optical Instrument ◽  
Turbulent Characteristics ◽  
Wide Range

Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument — based on the light absorption of the liquid — has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather then turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time averaged values for the thickness, the velocity and the roughness of the film the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

Motion and Evaporation of Shear-Driven Liquid Films in Turbulent Gases

1992 ◽  
Vol 114 (2) ◽  
pp. 395-400 ◽  
Author(s):  
S. Wittig ◽  
J. Himmelsbach ◽  
B. Noll ◽  
H. J. Feld ◽  
W. Samenfink
Keyword(s):  
Shear Stress ◽  
Liquid Film ◽  
Gas Phase ◽  
Film Flow ◽  
Phase Interface ◽  
Liquid Films ◽  
Numerical Code ◽  
Optical Instrument ◽  
Turbulent Characteristics ◽  
Wide Range

Detailed measurements of wavy liquid films driven by the shear stress of turbulent air flow are obtained for different air temperatures, air velocities, and flow rates of the liquid. The experimental conditions are chosen from characteristic data of liquid film flow in prefilming airblast atomizers and film vaporization employing combustors. For the measurement of the local film thickness and film velocity a new optical instrument—based on the light absorption of the liquid—has been developed, which can be used at high temperatures with evaporation. The measured data of the gas phase and the liquid film are compared with the results of a numerical code using a laminar as well as a turbulent model for the film flow and a standard numerical finite volume code for the gas phase. The results utilizing the two models for the liquid film show that the film exhibits laminar rather than turbulent characteristics under a wide range of flow conditions. This is of considerable interest when heat is transferred across the film by heating or cooling of the wall. With this information the optical instrument can also be used to determine the local shear stress of the gas phase at the phase interface. Using time-averaged values for the thickness, the velocity, and the roughness of the film, the code leads to relatively accurate predictions of the interaction of the liquid film with the gas phase.

scholarly journals Liquid Films Flowing Concurrently with Air in Horizontal Duct : 4th Report, Effect of the geometry of duct cross-section on liquid film flow

1984 ◽  
Vol 27 (230) ◽  
pp. 1644-1651 ◽  
Author(s):  
Tohru FUKANO ◽  
Hiroshi AKENAGA ◽  
Masayoshi IKEDA ◽  
Akihiko ITOH ◽  
Tessho KURIWAKI ◽  
...  
Keyword(s):  
Liquid Film ◽  
Cross Section ◽  
Film Flow ◽  
Liquid Films ◽  
Liquid Film Flow

Studies on Gas-Phase Turbulence Modification in Vertical Upward Annular Flow

2003 ◽  
Author(s):  
Kenji Yoshida ◽  
Hidenobu Tanaka ◽  
Keizo Matsuura ◽  
Isao Kataoka
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Gas Phase ◽  
Annular Flow ◽  
Film Flow ◽  
Velocity Profiles ◽  
Fluctuation Velocity ◽  
Turbulence Modification ◽  
Liquid Film Flow ◽  
Wavy Interface

Experimental and numerical studies were made to investigate the effects of wavy interface on the liquid film to gas-phase turbulence modification of air-water annular flow in a vertically arranged round tube. By using the constant temperature hotwire anemometer, time-averaged axial velocity profiles, turbulence fluctuation profiles, energy spectrum and auto-correlation coefficient for fluctuation velocity component of gas-phase axial velocity were precisely measured. The liquid film thickness was also measured by using point-electrode resistivity probe to make clear the time-averaged liquid film thickness and wave height moving on the liquid film. Direct observations using high speed video camera were also added to make clear the dynamic behavior and propergating velocity of ripple or disturbance waves on liquid film flow. Numerical simulations for gas-phase turbulence in annular flow considering the effect of wavy interface of liquid film flow were also carried out. Liquid film flow was modeled to be the wall surface roughness of interfacial wave height moving with the interfacial velocity. The roughness and moving velocity of the modeled liquid film for computational condition were provided by the present experimental results. Time-averaged velocity profiles and fluctuation velocity profiles were calculated with standard k-ε model. Numerical results were generally consistent with the experimental results obtained in the present study.

A Separation Criterion With Experimental Validation for Shear-Driven Films in Separated Flows

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
M. A. Friedrich ◽  
H. Lan ◽  
J. L. Wegener ◽  
J. A. Drallmeier ◽  
B. F. Armaly
Keyword(s):  
Liquid Film ◽  
Gas Phase ◽  
Experimental Validation ◽  
Thin Liquid Film ◽  
Complete Separation ◽  
Separated Flows ◽  
Force Ratio ◽  
Wide Range ◽  
Inertial Surface ◽  
Film Separation

The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum.

Flow Patterns and CHF in a Locally Heated Liquid Film Shear-Driven in a Minichannel

2010 ◽  
Author(s):  
D. V. Zaitsev ◽  
O. A. Kabov
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Gas Flow ◽  
Liquid Films ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Film Rupture ◽  
Space Applications ◽  
Flow Rates ◽  
Wide Range

Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel is a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments. Experiments with water in flat channels with height of H = 1.2–2.0 mm (mini-scale) show that a liquid film driven by the action of a gas flow is stable in a wide range of liquid/gas flow rates. Map of isothermal flow regime was plotted and the length of smooth region was measured. Even for sufficiently high gas flow rates an important thermocapillary effect on film dynamics occurs. Scenario of film rupture differs widely for different flow regimes. It is found that the critical heat flux for a shear driven film can be 10 times higher than that for a falling liquid film, and exceeds 400 W/cm2 in experiments with water for moderate liquid flow rates. This fact makes use of shear-driven liquid films promising in high heat flux chip cooling applications.

scholarly journals Determination of dryout localization using a five-equation model of annular flow for boiling in minichannels

2017 ◽  
Vol 38 (1) ◽  
pp. 123-139 ◽  
Author(s):  
Jan Wajs ◽  
Dariusz Mikielewicz
Keyword(s):  
Liquid Film ◽  
Mass Balance ◽  
Gas Phase ◽  
Annular Flow ◽  
Film Flow ◽  
Equation Model ◽  
Two Phase ◽  
Model Predictions ◽  
Cross Correlations

AbstractDetailed studies have suggested that the critical heat flux in the form of dryout in minichannels occurs when the combined effects of entrainment, deposition, and evaporation of the film make the film flow rate go gradually and smoothly to zero. Most approaches so far used the mass balance equation for the liquid film with appropriate formulations for the rate of deposition and entrainment respectively. It must be acknowledged that any discrepancy in determination of deposition and entrainment rates, together with cross-correlations between them, leads to the loss of accuracy of model predictions. Conservation equations relating the primary parameters are established for the liquid film and vapor core. The model consists of three mass balance equations, for liquid in the film as well as two-phase core and the gas phase itself. These equations are supplemented by the corresponding momentum equations for liquid in the film and the two-phase core. Applicability of the model has been tested on some experimental data.

Microgap Cooling Technique Based on Evaporation of Thin Liquid Films

2009 ◽  
Author(s):  
D. V. Zaitsev ◽  
O. A. Kabov
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Gas Flow ◽  
Liquid Films ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Film Rupture ◽  
Space Applications ◽  
Flow Rates ◽  
Wide Range

Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel is a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. The paper focuses on the recent progress that has been achieved by the authors through conducting experiments. Experiments with water in flat channels with height of H = 1.2–2.0 mm show that a liquid film driven by the action of a gas flow is stable in a wide range of liquid/gas flow rates. Map of isothermal flow regime was plotted and the length of smooth region was measured. Even for sufficiently high gas flow rates an important thermocapillary effect on film dynamics occurs. Scenario of film rupture differs widely for different flow regimes. It is found that the critical heat flux for a shear driven film can be 10 times higher than that for a falling liquid film, and exceeds 400 W/cm2 in experiments with water for moderate liquid flow rates. This fact makes use of shear-driven liquid films promising in high heat flux chip cooling applications.

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