Study on Entrainment From High-Viscosity Falling Liquid Film of Counter-Current Two-Phase Flow in a Vertical Pipe

2004 ◽  
Author(s):  
Yasuo Koizumi ◽  
Ryou Enari ◽  
Hiroyasu Ohtake
Keyword(s):  
Reynolds Number ◽  
Liquid Film ◽  
Silicon Film ◽  
Water System ◽  
Water Film ◽  
Two Phase ◽  
Silicon Oil ◽  
Falling Liquid Film ◽  
Wide Range ◽  
Counter Current

Behavior of a falling liquid film of highly viscous fluid in the counter-current flow condition was examined. In experiments, water and silicon oils of 500, 1000 and 3000 cSt were used as the liquid phase and air was adopted as the gas phase. A test section vertically oriented was a circular pipe of 30 mm in inner diameter and 5.4 m in length. Flooding velocities of the air-water system were well correlated with traditional correlations such as the Wallis correlation and the Kamei correlation. However, the flooding velocities of silicon films were greatly lower than the expected. When the effect of the viscosity was incorporated into the Wallis correlation, it predicted the experimental results well. The flooding in the air-silicon system was initiated by sudden growth of a wave on the film as in the air-water system although the film Reynolds number of the falling silicon film was considerably low; 0.02 ∼ 4. A considerable amount of droplets were detected a long time before the initiation of flooding in the air–silicon oil experiments as well as in the air–water experiments. The correlations tested for the onset condition of entrainment gave much higher gas velocities than the measured. Predicted velocities were rather close to the flooding velocities. The falling film thickness was predicted well by applying the universal velocity profile to the film flow over a wide range of a film Reynolds number; ranging from a water film to a 3000 cSt silicon oil film.

An Experimental Study on Liquid Film Dynamics and Interfacial Wave of Air-Water Two-Phase Flow in a Horizontal Channel

2013 ◽  
Author(s):  
Youjia Zhang ◽  
Weimin Ma ◽  
Shengjie Gong
Keyword(s):  
Liquid Film ◽  
Two Phase Flow ◽  
Rectangular Channel ◽  
Research Work ◽  
Water Film ◽  
Test Facility ◽  
Phase Flow ◽  
Interfacial Wave ◽  
Film Rupture ◽  
Two Phase

This study is concerned with liquid film dynamics and stability of annular flow, which plays an important role in understanding film rupture and dryout in boiling heat transfer. The research work starts from designing and making a test facility which enables the visualization and measurement of liquid film dynamics. A confocal optical sensor is applied to track the evolution of film thickness. A horizontal rectangular channel made of glass is used as the test section. Deionized water and air are supplied into that channel in such a way that an initial stratified flow forms, with the liquid film on the bottom wall. The present study is focused on characterization of liquid film profile and dynamics in term of interfacial wave and shear force induced film rupture under adiabatic condition. Based on the experimental data and analysis, it is found that given a constant water flowrate, the average thickness of water film decreases with increasing air flowrate, while the interfacial wave of the two-phase flow is intensified. As the air flowrate reaches a critical value, a localized rupture of the water film occurs.

scholarly journals On the transition between turbulence regimes in particle-laden channel flows

2018 ◽  
Vol 845 ◽  
pp. 499-519 ◽  
Author(s):  
Jesse Capecelatro ◽  
Olivier Desjardins ◽  
Rodney O. Fox
Keyword(s):  
Reynolds Number ◽  
Fluid Phase ◽  
Stokes Number ◽  
Channel Flows ◽  
High Mass ◽  
Inertial Particles ◽  
Mass Loading ◽  
Two Phase ◽  
Phase Dynamics ◽  
Wide Range

Turbulent wall-bounded flows exhibit a wide range of regimes with significant interaction between scales. The fluid dynamics associated with single-phase channel flows is predominantly characterized by the Reynolds number. Meanwhile, vastly different behaviour exists in particle-laden channel flows, even at a fixed Reynolds number. Vertical turbulent channel flows seeded with a low concentration of inertial particles are known to exhibit segregation in the particle distribution without significant modification to the underlying turbulent kinetic energy (TKE). At moderate (but still low) concentrations, enhancement or attenuation of fluid-phase TKE results from increased dissipation and wakes past individual particles. Recent studies have shown that denser suspensions significantly alter the two-phase dynamics, where the majority of TKE is generated by interphase coupling (i.e.  drag) between the carrier gas and clusters of particles that fall near the channel wall. In the present study, a series of simulations of vertical particle-laden channel flows with increasing mass loading is conducted to analyse the transition from the dilute limit where classical mean-shear production is primarily responsible for generating fluid-phase TKE to high-mass-loading suspensions dominated by drag production. Eulerian–Lagrangian simulations are performed for a wide range of particle loadings at two values of the Stokes number, and the corresponding two-phase energy balances are reported to identify the mechanisms responsible for the observed transition.

Study on Breakdown Features and Characteristics of Film at the Corrugated Plate Corner

2020 ◽  
Author(s):  
Bo Wang ◽  
Bowen Chen ◽  
Bingzheng Ke ◽  
Ru Li ◽  
Gongqing Wang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Film Thickness ◽  
Liquid Film ◽  
Relative Position ◽  
Water Film ◽  
Theoretical Formula ◽  
Film Rupture ◽  
Water Separation ◽  
Water Film Thickness ◽  
Film Breakdown

Abstract Corrugated plate dryer is a extremely vital equipment for steam-water separation in the fields of heat transfer and nuclear engineering. The corrugated plate is also a commonly used steam-water separator in steam generators in nuclear power plants. It is meaningful to study the breakdown characteristics and mechanism of the water film on corrugated plate wall. Water film thickness of steady flow is measured based on plane laser induced fluorescence (PLIF) technique and time series and its fitted equation of water film thickness are obtained, respectively. Besides, fluctuation characteristics of water film are analyzed by probability density function (PDF). Based on the dimensionless approach, the water film breakdown model at the corner of the corrugated plate is established. And the calculation equation of the relative position of the water film breakdown at the corner is deprived. The specific conclusions are as follows. The theoretical equation agrees well with the relative position of the water film breakdown at the corrugated plate corner. The evolution of the surface wave of water film is carried out in time and space. The PDF curve have no significant peak characteristics. Therefore, the spectrum has no characteristic frequency, that is, the water film has multi-frequency characteristics. Gravity of water film can be ignored in the water film model. The thickness sequences for falling film is measured and fitted. The two-dimensional model of water film breakdown at the corner is set up. The equation for the film thickness when the water film is just ruptured is obtained. Relative position of the water film rupture at the corner of the corrugated plate is theoretically related only to the structural parameters of the corrugated plate, the parameters of the gas phase and the liquid phase, and the Reynolds number of the liquid film. However, in the low Reynolds number region, the airflow velocity is extremely large, which causes certain fluctuations and nonlinear characteristics of the water film boundary position. Therefore, the theoretical formula is not particularly good at predicting the relative position of the breakdown in this region. I think that this nonlinear feature has obvious chaotic characteristics. The study of the chaotic characteristics generated by shearing the liquid film by high velocity flow airflow at the corner of the corrugated plate may become a prospect for future research.

Experimental Investigation of Falling Liquid Film in Vertical Downward Two-Phase Pipe Flow

2012 ◽  
Author(s):  
Jose M. Lopez ◽  
Ram Mohan ◽  
Ovadia Shoham ◽  
Shoubo Wang ◽  
Gene Kouba
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Liquid Droplet ◽  
Mineral Oil ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Measurements ◽  
Falling Liquid Film

In this research the hydrodynamics of falling liquid film in a vertical downward two-phase flow (liquid-gas) is experimentally studied. The 4 inch clear PVC test section is 6.1 meters long, with a length to diameter ratio (L/D) of 64. The fluids utilized are compressed air, water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil). The superficial liquid velocities tested range from 12 to 72 cm/s while the superficial gas velocities range from 0.2 to 29 cm/s. The vertical facility is equipped with the state-of-the-art instrumentation for two-phase flow measurements, the capacitance Wire-Mesh Sensor (WMS), allowing two-phase flow measurements with conducting and non conducting fluids. Experimental results show that the liquid film thickness has a quasi-linear relationship with the superficial liquid velocity for the air-water case. For the air-oil cases, at superficial liquid velocities higher than 50 cm/s, the liquid film thickness trend is affected by the liquid droplet entrainment. Furthermore, it was found that the liquid droplet entrainment increases as the superficial liquid velocity increases or the surface tension decreases. Details of the liquid droplets traveling in the gas core, wave formation, wave breakup and film thickness evolution are observed in the WMS phase reconstruction.

Turbulence Structures in Horizontal Two-Phase Flows Under Counter-Current Conditions

2006 ◽  
Author(s):  
Thomas D. Sta¨bler ◽  
Leonhard Meyer ◽  
Thomas Schulenberg ◽  
Eckart Laurien
Keyword(s):  
Liquid Film ◽  
Test Section ◽  
Gas Flow ◽  
Second Phase ◽  
Two Phase Flows ◽  
Two Phase ◽  
Flow Rates ◽  
Local Measurements ◽  
Counter Current ◽  
Film Flows

In order to improve the multi-dimensional numerical simulation of horizontal two-phase flows, the knowledge of local turbulent quantities is of great importance. In horizontal stratified flows, the denser (first) phase flows as a film beneath the other (second) phase. Under counter-current conditions, the second phase flows into the opposite direction of the first phase. In the present investigations a liquid film flows counter-currently to a gas flow. According to the flow rates of both phases, different flow regimes set in. In supercritical flows (Fr>1), the height of the liquid film increases in flow direction, while it decreases in subcritical flows (Fr<1). For sufficiently high gas flow rates the upper part of the liquid film flows into direction of the gas flow, while the lower part still flows into its initial direction opposite to the gas flow. Only a reduced amount of water reaches the end of the test section. This flow regime is referred to as partially reversed flow. The presented local measurements provide not only the mean and rms-velocities of the liquid film, but also the corresponding Reynolds stresses. Local measurements are carried out at two different positions along the test section for various boundary conditions. Furthermore, the liquid injection height has been varied. The kinematic and turbulent structures of the different flow patterns are presented and compared.

H222 Critical Heat Flux of Counter-Current Two-Phase Flow : Effect of Subcooled Liquid Film

2011 ◽  
Vol 2011 (0) ◽  
pp. 371-372
Author(s):  
Ayaka Fujiwara ◽  
Takuya Suzuki ◽  
Takeyuki Ami ◽  
Hisashi Umekawa ◽  
Mamoru Ozawa
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Flow Effect ◽  
Counter Current

Effect of wall corrugations on scalar transfer to a wavy falling liquid film

2018 ◽  
Vol 859 ◽  
pp. 1098-1128 ◽  
Author(s):  
Georg F. Dietze
Keyword(s):  
Liquid Film ◽  
Gas Flow ◽  
Chemical Engineering ◽  
Dirichlet Condition ◽  
Moving Frame ◽  
Small Scale ◽  
Fixed Amount ◽  
Falling Liquid Film ◽  
Limiting Case ◽  
Counter Current

Direct numerical simulation is employed to study the effect of small-scale wall corrugations on scalar transfer through the wavy surface of a vertically falling liquid film in interaction with a strongly confined counter-current gas flow. Three wall geometries are considered: (i) a flat wall for reference; (ii) a sinusoidal corrugation typically found on structured packings in chemical engineering devices; and (iii) a heuristic design consisting of isolated semicircular bumps distanced by the wavelength of the surface waves. We consider the limiting case of a Dirichlet condition for the transported scalar (temperature or mass fraction) at the liquid–gas interface and focus on liquid-side transport. We consider convection-dominated regimes at moderate and large Péclet numbers, representative of heat and mass transfer respectively, and confront forced and noise-driven wave regimes. Our results show that sinusoidal wall corrugations increase transfer by up to 30 per cent in terms of the exchange length required to transfer a fixed amount of the transported quantity. A slightly greater intensification is achieved through the bump-shaped corrugations, which intermittently disrupt the moving-frame vortex forming within the large-amplitude solitary waves, allowing these to replenish with unsaturated liquid. However, when the velocity of the strongly confined gas flow is increased above a certain threshold, the bumps can trigger the flooding of the channel.

Simulation of Sweating/Evaporation Boosted Convective Heat Transfer Under Laminar Flow Condition

2017 ◽  
Author(s):  
Sudipta Saha ◽  
Rajib Mahamud ◽  
Jamil Khan ◽  
Tanvir Farouk
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Water Film ◽  
The Heat Transfer Coefficient

Phase change driven heat transfer has been the topic of interest for a significantly long time. However, in recent years on demand sweating boosted evaporation which requires substantially less amount of the liquid medium has drawn attention as a possible way of increasing/supplementing heat transfer under convective conditions where the convective heat transfer coefficient has already reached its maximum value as well as where dry cooling is a desired objective. In this study, a numerical study is conducted to obtain insight into the ‘hybrid’ system where evaporation and convection both contribute to the heat transfer effect. The system modeled consists of evaporation of thin liquid (water) film under a laminar flow condition. The mathematical model employed consists of coupled conservation equations of mass, species, momentum and energy for the convection-evaporation domain (gaseous), with only mass and energy conservation being resolved in the liquid film domain. The evaporative mass flux is obtained from a modified Hertz-Knudsen relation which is a function of liquid-vapor interface temperature and pressure. A two-dimensional rectangular domain with a pre-prescribed thin liquid water film representative of an experiment is simulated with the developed model. The thin rectangular liquid film is heated by uniform heat flux and is placed in the convection-evaporation domain with an unheated starting length. A moving boundary mesh is applied via the“Arbitrary Lagrangian-Eulerian” technique to resolve the receding liquid interface resulting from evaporation. The prescribed relative displacement of the moving interface is calculated from the net mass flux due to evaporation and is governed by the principle of mass conservation. Simulations were conducted over a range of Reynolds number, heat flux conditions and liquid film thickness. The numerical predictions indicate that under convective-evaporative conditions the overall heat transfer coefficient increases significantly (∼factor of a five) in comparison to the purely forced convection scenario. An increase in the heat transfer coefficient is observed with Reynolds number and vice versa for film thickness. A critical Reynolds number is identified beyond which the heat transfer coefficient does not continue to increase significantly rather tends to plateau out.

Application of Mixing Length Theory to Wavy Turbulent Liquid—Gas Interface

1981 ◽  
Vol 103 (3) ◽  
pp. 492-500 ◽  
Author(s):  
S. Levy ◽  
J. M. Healzer
Keyword(s):  
Liquid Film ◽  
Transition Layer ◽  
Volume Fraction ◽  
Density Ratio ◽  
Constant Density ◽  
Mixing Length ◽  
Two Phase ◽  
Liquid Entrainment ◽  
Wide Range ◽  
Mixing Length Theory

A fully developed and adiabatic two-phase annular model with liquid entrainment is derived for flow in a pipe with negligible gravity effects. The model is based upon application of the single phase mixing length theory to a wavy liquid-gas interface. The model subdivides the flow cross section into three regions: a liquid film, a gas core of constant density, and a transition wavy layer between them. The combination of a constant velocity and a density varying exponentially with distance from the wall is employed in the transition layer. This approach plus appropriate logarithmic velocity distributions in the liquid film and gas core make it possible to specify the two-phase pressure drop, volume fraction, wave velocity, and thickness of the liquid film and transition layer. The liquid entrainment is obtained in terms of the exponent of the density profile in the transition layer, and interface stability considerations are used to express this entrainment parameter semiempirically in terms of an apparent Weber number and density ratio. Comparisons of the model are made with air-water and steam-water test data, and the results generally are satisfactory over a wide range of conditions and for all the important characteristics of this flow pattern.

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