A Computational Fluid Study of Falling Film Behavior on Flat Plate

2014 ◽  
Author(s):  
Yiqi Yu
Keyword(s):  
Shear Stress ◽  
Surface Wave ◽  
Film Thickness ◽  
Flat Plate ◽  
Film Flow ◽  
Theoretical Data ◽  
Water Film ◽  
Reynolds Numbers ◽  
Falling Film ◽  
Liquid Shear

In this paper, the 3D numerical simulations on falling film behaviour on flat plate with and without interfacial gas-liquid shear stress are carried out. The film thickness and velocity distribution of water film flow with different Reynolds numbers are studied. The results agree well with the experimental and theoretical data. The influence of the surface wave on film velocity is revealed. The calculations also investigate the effect of gas-liquid shear stress on solitary waves of falling film.

Theoretical Analysis on Film Thickness of Intertube Falling-Film Flow With a Countercurrent Gas Flow

2011 ◽  
Author(s):  
Binglu Ruan ◽  
Huan Li ◽  
Qiuwang Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Film Thickness ◽  
Gas Flow ◽  
Film Flow ◽  
Falling Film ◽  
Two Phase ◽  
Flow Effects

In falling–film type of heat exchangers, gas/vapor usually exists, and its effect on falling-film mode transitions and heat transfer could not be neglected. It could impact the film thickness, which is an important parameter to determine the thin-film heat transfer performance, or even destroy falling-film modes and significantly deteriorate the heat transfer. However, there have been very few studies of countercurrent gas flow effects on the film thickness. In this paper, the falling-film film thickness with and without liquid-gas interfacial shear stress due to the countercurrent gas flow was studied. A two-phase empirical correlation is used to solve the momentum equation. Calculation results were compared with available experimental data in literatures for validation. Reasonable agreement was achieved. Thus, the two-phase correlation for predicting shear stress of a thin film flow inside a vertical rectangular channel has been extended to a new type of flow. Effects of film Reynolds number, gas velocity, and gas-channel equivalent hydraulic diameter on the film thickness were studied. It is shown that the countercurrent gas flow thickened the falling film. The increased film thickness can shift the mode transitional Reynolds number and reduce the heat transfer coefficient, corroborating the conjecture in our earlier work.

Linear stability of a cylindrical falling film

1987 ◽  
Vol 183 ◽  
pp. 365-377 ◽  
Author(s):  
Francisco J. Solorio ◽  
Mihir Sen
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Numerical Computation ◽  
Linear Stability ◽  
Weber Number ◽  
Perturbation Technique ◽  
Reynolds Numbers ◽  
Falling Film ◽  
Fully Developed Flow ◽  
Long Cylinder

The problem of a cylindrical falling film, descending vertically outside an infinitely long cylinder is considered. The linear stability of the fully developed flow is studied, first with a perturbation technique for small wavenumbers, and then by direct numerical computation. The numerical results are in agreement with other published values for the cylindrical jet and flat plate limits. The study shows that the cylindrical falling film is unstable for all Reynolds numbers, Weber numbers and radius ratios. Stability and amplification curves are calculated for different values of the parameters. With increasing curvature of the film the range of unstable wavenumbers and the wavenumber of the most amplified wave increase. For low curvature the wavenumber of the most amplified wave decreases with Reynolds number or Weber number, while for high curvatures it increases.

Heat Transfer of Water Film Outside the Vertical Helix Tube with Hydrophilic Nanolayer

2009 ◽  
Vol 87-88 ◽  
pp. 339-344
Author(s):  
Yong Yan Wang ◽  
Ze Rong Zhang
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Mathematical Models ◽  
Smooth Surface ◽  
Film Flow ◽  
Flow Behavior ◽  
Water Film ◽  
Surface Geometry ◽  
Physical And Mathematical Models ◽  
Transfer Properties

The purpose of this study is to investigate the formation of water film and its flow behavior on the surface of a vertical helix tube with hydrophilic nanolayer. The physical and mathematical models for single ingredient fluid are established and the effects of the surface geometry of the vertical helix tube on the water film flow are studied. The film thickness goes up at the trough and becomes thinner at the crest. The film thickness on the vertical helix tube with hydrophilic nanolayer is more uniform and has better heat transfer properties than the classical smooth surface tube.

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.

Falling film flow of ionic liquid–MEA solution on vertical cooling flat plate and channel

2015 ◽  
Vol 88 ◽  
pp. 334-340 ◽  
Author(s):  
Xun Zhu ◽  
Fang-Fang Zhang ◽  
Yu-Dong Ding ◽  
Zhong-Hai Liu ◽  
Qiang Liao
Keyword(s):  
Ionic Liquid ◽  
Flat Plate ◽  
Film Flow ◽  
Falling Film

Measurement of Liquid Film Thickness around Horizontal Tube Bundle by Optical Technique for Optimizing Evaporator Design and Manufacturing

2014 ◽  
Vol 974 ◽  
pp. 220-224
Author(s):  
Karim Bourouni ◽  
Ali L. Taee
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Liquid Film ◽  
Film Flow ◽  
Tube Bundle ◽  
Horizontal Tube ◽  
Falling Film ◽  
Optical Technique ◽  
Design And Manufacturing ◽  
Liquid Film Flow

This paper proposes the improvement of design and manufacturing of Falling Film Horizontal Tube Evaporators (FFHTE) through optimizing different parameters such as tubes pitch, tubes diameter and material and liquid film flow rate. These design and operational parameters have a significant influence on the hydrodynamic of the liquid film (eg: wetability of the tubes, scale deposition, heat transfer coefficient, etc.). Due to the complexity of the liquid film flow around the horizontal tube bundle, the experimental approach is preferred than modeling because it gives a better understanding of the phenomena occurring in the heat exchanger. In this paper one experiment was carried out to investigate liquid film flow around a single horizontal tube. A particular attention was taken for the measurement of liquid film thickness around the tube using a novel optical technique based on light reflection. The influence of the tubes pitch, tube diameter, height of the liquid distribution system and the liquid mass flow on the transitions between falling-film modes and film thickness is investigated and the results are compared to other data obtained from the literature. It was found that tubes wetability and heat transfer increased with increasing the vertical tube pitch. To account for fouling and heat transfer performance, a tube spacing value of 1.3 was recommended.

scholarly journals FENOMENA HYDRAULIC JUMP LOOK LIKE DAN ONSET OF FLOODING DALAM PIPA VETIKAL

2012 ◽  
Vol 12 (2) ◽  
pp. 182
Author(s):  
MAHMUDDIN MAHMUDDIN ◽  
SAMSUL KAMAL ◽  
INDARTO INDARTO ◽  
PURNOMO PURNOMO
Keyword(s):  
Wave Propagation ◽  
Film Thickness ◽  
Pressure Gradient ◽  
Hydraulic Jump ◽  
Film Flow ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Countercurrent Flow ◽  
Air Inlet

Experiments have been conducted on countercurrent flow of air and water in pipe of 24 mm diameter. Flow patterns observations, measurement of the pressure gradient and film thickness conducted at water Reynolds numbers (ReL) are varied 322, 465, 630 and 709 combined to injectedair with velocity from 1.845 m/s to 6.148 m/s at a distance of 400 mm, 1600 mm and 2200 mm from the water inlet. The data showed that the pressure gradient and film thicknessdid not increase appreciably until just before the onset of flooding. Otherwise, when flooding conditions wave propagation in surface the film flow from the bottom of air inlet, increasing film thickness gradually and pressure gradient also increase quickly. Increasing film thikcness gradually indicated as phenomenon hydraulic jump look like.

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