scholarly journals Evaluation of a vertical downward water film thickness using visualization and image recognition techniques

2020 ◽  
Vol 21 (1) ◽  
pp. 1-13
Author(s):  
Edgar Fernando Larrainzar Solís ◽  
José Javier Moctezuma Reyes ◽  
Florencio Sánchez Silva ◽  
Ignacio Carvajal Mariscal ◽  
Lino García Demedices
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
High Speed ◽  
Water Film ◽  
Surface Characteristic ◽  
Turbulent Regime ◽  
Falling Film ◽  
Two Phase ◽  
Set Up ◽  
Average Film Thickness

The present work is focused on the experimental study of a vertical downward annular flow to determine the thickness and stability of a falling film water flow. For this purpose, it was designed and implemented an experimental set up to generate the annular two-phase flow pattern, provided with an injection head with a special geometry to induce a liquid film inside a cylinder. Due to the small dimensions, the film was visualized using a pulsated laser to illuminate the region and the pictures were taken with a high-speed camera. This technique allowed the determination of the falling film thickness by means of an algorithm to recognize image contours. In some of the studied cases, a concurrent air flow was injected in the center of the cylinder in order to evaluate its influence on the interfacial hydrodynamics of the liquid film. Average film thickness were obtained for different Reynolds numbers in different axial observation points, and it was observed that the liquid film annular area and the shape of the header to inject the water, are important factors for the surface characteristic and thickness of the film, and its stability as well. The experimental results show that the standard deviation increases in proportion to the average film thickness, especially in the turbulent regime.

Modeling of Falling Film in Vertical Downward Two-Phase Pipe Flow

2012 ◽  
Author(s):  
Jose M. Lopez ◽  
Ram Mohan ◽  
Ovadia Shoham ◽  
Luis Gomez ◽  
Gene Kouba
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Liquid Droplet ◽  
Mechanistic Model ◽  
Mineral Oil ◽  
Liquid Film Thickness ◽  
Falling Film ◽  
Two Phase ◽  
Droplet Entrainment ◽  
Falling Liquid Film

Falling liquid films in vertical pipes are found in a variety of different industrial applications and industrial equipment, such as downcomers, caisson separators and reactors. The hydrodynamics of the falling film in vertical two-phase pipe flow can affect droplet entrainment, gas entrainment, and pressure drop. Therefore, a mechanistic model for prediction of falling liquid film thickness, falling liquid film velocity and a correlation for liquid droplet entrainment fraction in vertical downward liquid-gas systems has been proposed. The falling film model developed is based on applying momentum balance on the liquid film. The liquid film is assumed to be in steady-state, incompressible and free of entrained gas. The mechanistic model includes both the developing and the developed regions. The shear effect between the gas core and the falling liquid film is considered. The liquid droplet entrainment fraction traveling in the gas core is considered and a new correlation for its prediction is proposed. Detailed uncertainty analysis is performed for liquid film thickness and liquid film velocity model predictions, including Monte Carlo simulation. Predicted liquid film thickness, liquid film velocity and liquid droplet entrainment fraction are validated against experimental data for different liquid fluid properties, such as water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil).

scholarly journals Experimental study of wavy-annular flow in a rectangular microchannel using LIF method

2021 ◽  
Vol 2119 (1) ◽  
pp. 012061
Author(s):  
G V Bartkus ◽  
V V Kuznetsov
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
High Speed ◽  
Annular Flow ◽  
Flow Characteristics ◽  
Superficial Velocity ◽  
Graphical Form ◽  
Rectangular Microchannel ◽  
Gas Phases ◽  
Average Film Thickness

Abstract This article aims at studying gas-liquid flow in a rectangular microchannel with a high aspect ratio (200 × 2045 μm). Liquid and gas phases were 95% ethanol and nitrogen mixture. Experimental flow characteristics are obtained using high-speed visualization and laser-induced fluorescence (LIF) methods. Using the LIF method for wavy-annular flow, the average film thickness, liquid film distribution, and liquid film width were measured. The dependences of the liquid film width and the average film thickness on gas superficial velocity are presented in graphical form and analyzed. An increase in gas superficial velocity causes growth of the liquid film width and thickness of the liquid film, which indicates the process of liquid transfer from the menisci area to the liquid film. For different liquid velocities and the same gas superficial velocities, close values of averaged liquid film thickness were observed for flow with 2D waves and 3D waves on liquid film.

Lubrication Model and Dynamic Characteristics of Distributed Liquid Film for Hydrodynamic Bearing

2013 ◽  
Vol 744 ◽  
pp. 194-198 ◽  
Author(s):  
Ou Yang Wu ◽  
Jia Qian ◽  
Zhang Fan ◽  
Xiao Yang Yuan ◽  
Qing Feng Meng
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Dynamic Characteristics ◽  
Water Film ◽  
Coupling Model ◽  
Lubrication Theory ◽  
Dominant Factor ◽  
Thin Film Lubrication ◽  
Two Phase ◽  
Hydrodynamic Bearing

For the thin film lubrication, boundary lubrication, and local dry friction lubrication state of hydrodynamic bearing, a lubrication model of distributed liquid film is established in this paper which is designed to service for calculating or predicting the full life cycle design performance of water-lubricated bearing. The limitations of the fluid-solid-thermal coupling model for describing the distributed liquid film are investigated. Two new methods to build the lubrication model of distributed liquid film are given. The first one takes fluid-solid-thermal model that can guide the design of bearings parameters as dominant factor, and combines with wear, corrosion, two-phase of gas-liquid and other additional factors. A comprehensive model integrating simulation and mechanism can be built. Through researching the regional properties or distributed parameter of water film and solid interface, the second way proposes a decomposition and synthesis modeling method of water film and rubber. A distributed parameters model of dynamic characteristics for water-lubricated bearing is built. The lubrication theory of distributed liquid film proposed in this paper is appropriate for the situation when the film thickness is less than 10μm or contact. When the film thickness is greater than 10μm, classical lubrication theory is applicable.

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.

NUMERICAL INVESTIGATION OF FILM DISTRIBUTION IN HORIZONTAL-TUBE FALLING FILM EVAPORATOR

2011 ◽  
Vol 19 (03) ◽  
pp. 177-183 ◽  
Author(s):  
JIN-BO CHEN ◽  
QING-GANG QIU
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Numerical Investigation ◽  
Horizontal Tube ◽  
Flow Density ◽  
Falling Film ◽  
Film Distribution ◽  
Simulation Results

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.

Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas

2015 ◽  
Author(s):  
Zezhi Zeng ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Film Thickness ◽  
Liquid Film ◽  
Direct Contact ◽  
High Speed ◽  
Small Diameter ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Coolant

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.

Measurement of Liquid Film Thickness for Annular Two-Phase HFC134a Gas-Liquid Ethanol Flow in the Vertical Tube

2021 ◽  
Author(s):  
Huacheng Zhang ◽  
Tutomo Hisano ◽  
Shoji Mori ◽  
Hiroyuki Yoshida
Keyword(s):  
Film Thickness ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Atmospheric Condition ◽  
Heating Surface ◽  
Operating Conditions ◽  
Liquid Film Thickness ◽  
Two Phase ◽  
Disturbance Waves ◽  
Analytical Approaches

Abstract Annular gas-liquid two-phase flows, such as the flows attached to the fuel rods of boiling water reactors (BWR), are a prevalent occurrence in industrial processes. At the gas-liquid interface of such flows, disturbance waves with diverse velocity and amplitude commonly arise. Since the thin liquid film between two successive disturbance waves leads to the dryout on the heating surface and limits the performance of the BWRs, complete knowledge of the disturbance waves is of great importance for the characterized properties of disturbance waves. The properties of disturbance waves have been studied by numerous researchers through extensive experimental and analytical approaches. However, most of the experimental data and analyses available in the literature are limited to the near atmospheric condition. In consideration of the properties of liquids and gases under atmospheric pressure which are distinct from those under BWR operating conditions (7 MPa, 285 °C), we employed the HFC134a gas and liquid ethanol whose properties at relatively low pressure and temperature (0.7 MPa, 40 °C) are similar to those of steam and water under BWR operating conditions as working fluids in a tubular test section having an inside diameter 5.0mm. Meanwhile, the liquid film thickness is measured by conductance probes. In this study, we report the liquid film thickness characteristics in a two-phase HFC134a gas-liquid ethanol flow. A simple model of the height of a disturbance wave was also proposed.

Measuring Water Film Thickness in a Wet Gas Compressor Diffuser: Design, Calibration, and Testing of Electromagnetic Probes

2017 ◽  
Author(s):  
Craig Nolen ◽  
Melissa Poerner
Keyword(s):  
Film Thickness ◽  
Water Level ◽  
Water Film ◽  
Probe Design ◽  
Two Phase ◽  
Water Film Thickness ◽  
Wet Gas ◽  
Flow Phenomena ◽  
In Series ◽  
Electromagnetic Probes

The distribution of water in the diffuser of a wet gas compressor is not well understood. Measurements of water film thickness across the diffuser surface would improve the understanding of two-phase flow phenomena in wet gas compressors. Electromagnetic probes were designed in order to measure water film thickness in the diffuser of a SwRI-designed wet gas compressor. The probes consisted of two electrode foils plated on a thin insulating substrate, allowing them to be bonded in place without drilling through the diffuser. An AC signal was passed between the electrodes, and the voltage across a resistor in series with the electrodes was recorded. As the water level covering the electrodes increased, the recorded voltage increased. A method of calibrating the probes was developed and used prior to installation in the diffuser. Testing showed the probes to be effective at detecting the presence of water in the diffuser and indicating the general water level. Improvements in probe design, calibration, and installation are needed to provide more precise water film thickness data.

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