An investigation on the falling film thickness of sheet. The nikon d70 digital slr camera was operated in the manual shooting mode. In charge of major work fof the major department for the graduyne college. Cfd, horizontal tubes, falling film, falling film thickness, vof. Measurement of liquid film thickness around horizontal tube. Pdf an investigation on the falling film thickness of sheet. The thickness of the falling film of liquid around a taylor. In the first stage, process liquid enters the falling film evaporator through the inlet feed pipe and is directed to the top liquid distributor. Film and wave data are available for falling film flow in the presence of a gas stream. This nonintrusive measurement method is based on the visualization of the falling film flowing around the horizontal tube and uses the laser induced fluorescence and image processing techniques. The beta type fallingfilm evaporators operate with an independent juice circulation system. An investigation on the falling film thickness of sheet flow. Brotz1964 used the experimental drainage technique to estimate film thickness by.
How to design a falling film reactor for sulfonation posted in student. Theoretical and experimental analysis of absorptioncondensation in a combined power and cooling cycle by nitin goel december 2005 chair. The distributor then delivers the liquid to the tube sheet. The falling film model developed is based on applying momentum balance on the liquid film. 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. Fallingfilm evaporator plant for a cane sugar factory. We present the results of laboratory experiments that quantify the physical controls on the thickness of the falling film of liquid around a taylor bubble, when liquidgas interfacial tension can be neglected. Instantaneous film thickness measurements of falling annular films were. Introduction condensers, evaporators, distillation columns, chemical reactors, and nuclear reactor cores are all important examples of applications demanding a good understanding of falling liquid film hydro dynamics. The liquid flows as a thin film on the inside of heated vertical tubes, driven by gravity. Astm d plastic film impact resistance free falling drop dart equipment validating the specifications, value and safety of your raw materials, products and assets. These design and operational parameters have a significant influence on the hydrodynamic of the liquid film eg. Predictions based on 2 are more sensitive to the accuracy of the eddy viscosity distribution in the.
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 liquidgas systems has been proposed. 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. Pdf the thickness of the falling film of liquid around a. A plot of nusselt number against film reynolds number can be used to correlate data. An optical method for the nonintrusive measurement of falling film thickness on the perimeter of the horizontal tube is described. It is itself equipped with many drip points to ensure the generation of an even and calm static liquid height outside the tubes. Falling film evaporation on horizontal tubes with smooth. However, they are different in practical industrial application. Process modelling and optimization of design parameters in. The corresponding effects on heat transfer have also been estimated. It is itself equipped with many drip points to ensure the generation of.
Figures 7 to 10 show the effect of film reynolds number re f on the film thickness. The circumferential thickness of a falling liquid film is inversely proportional to the local heat transfer coefficient. The technique uses a highspeed digital video camera to capture the images of the liquid interface that are illuminated by a laser sheet, with the contrast enhanced by a fluorescent powder in the fluid. Theoretical and experimental study on the fallingfilm. Falling film evaporation on horizontal tubes with smooth and structured surfaces by mingchien chyu a dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of doctor of philosophy major.
The numerical investigation was performed to analyze the film thickness characteristics over fully wetted horizontal round tube in a falling film evaporator using commercial cfd code fluent 6. Nov 16, 2001 the film thickness, flow regimes, and flooding points for the countercurrent annular flow of corn oil mazola and carbon dioxide at 338 k and pressures between 7. We find that the dimensionless film thickness the ratio of the film thickness to the pipe radius is a function only of the dimensionless parameter, where. Investigation into falling film outside horizontal tube. Measurement of falling film thickness around a horizontal tube using laserinduced fluorescence technique. A new optical method for the nonintrusive measurement of falling film thickness on the perimeter of horizontal tubes is described. Knowledge of temperature distribution alnog the reactor is important for the product quality control, since for highly exothermic reactions under certain conditions degredation of the products may occur. The main advantage of the rising film evaporator is the low residence time of the liquid feed in the evaporator compared to other evaporator designs like platetype evaporators. The reason of this deviation is because of the liquid film rotation in coil which causes some deletion.
Additionally, it is a process of falling film flow with heat and mass transfer between the start and end of falling film. The thickness of the falling film of liquid around a taylor bubble. Falling film evaporation an overview sciencedirect topics. The high performance evaporators are important for process industries such as food, desalination and refineries. In falling film evaporators, the liquid product usually enters the evaporator at the head of the evaporator. How to design a falling film reactor for sulfonation.
Fallingfilm evaporation has an essential method for desalination. The relationship between the film thickness and the calculated heat transfer coefficient was. Establishment of the falling film evaporation model and correlation of the overall heat transfer coefficient abstract in order to study the heat transfer of the falling film evaporator with phase change on both sides, in this paper we built the mathematical model and the physical model where the liquid film inside the tube is laminar and turbulent. Keywords falling films, probability density, correlation, spectral analysis 1. Statistical characteristics of free falling water film. Falling film condensation and evaporation are impor tant heat transfer processes in shell. Measurement of falling film thickness around a horizontal.
The result shows there is an optimization that the film thickness at the bottom of the tubes amounts to that of boundary layer of velocity. This paper presents a computational modelling of water falling film flowing over horizontal tubes. Film thickness measurements in falling annular films. For higher r values r 50, region iii may not be present. The heat transfer area is the key parameter in designing of an evaporator and many correlations are available to estimate the size of. Llewellin and elisabetta del bello and jacopo taddeucci and piergiorgio scarlato and sharrah lane, journalproceedings of the royal society a. The heat transfer tube is the core component of falling film evaporator. The objective of this study is to use numerical predictions for comparing the film thickness along circumferential direction of tube on 2d cfd models. This is crucial because it allows the usage of the evaporator in higher operating temperatures and gives assurance of high product quality despite the product being heat. The falling film evaporators have many advantages over flooded and vertical tubes that make them best candidate for processes industries application. A falling film evaporator is an industrial device to concentrate solutions, especially with heat sensitive components. These evaporators are being used in many countries to produce black liquor slurry with up to 80% solids content for firing in the recovery boiler vakkilainen and holm, 2000. Equations for the calculation of local velocities in the film with respect to cross curvature of wetted surface have been established.
Measurement of liquid film thickness around horizontal. Experimental and statistical investigation of hydrodynamics of a falling liquid film masters thesis within the double master programme energietechnik university of stuttgart sustainable energy systems chalmers university of technology, sweden christoph karl ambros department of energy and environment. The liquid enters the heating tube and forms a thin film on the tube wall where it flows downwards at boiling temperature and is partially evaporated. A comprehensive design of 2d models have been developed. In general evaporation takes place inside vertical tubes, but there are also applications where the process fluid evaporates on the outside of horizontal or vertical tubes. Introduction a falling liquids film flow over a surface of a horizontal tube has been widely used as a configuration of heat exchanger. Numerical study of falling film thickness on horizontal circular tube. The technique was applied to measure the horizontal tube falling film thickness for falling film reynolds number ranging from to 350, at different circumferential angles ranging from 40 to. Presentation of the concept and operating results vapour and 4th effect vapour. The resulting vapor normally flows cocurrently with the liquid, in the centre of the tubes.
I mass flow rate per unit film width for a planar film. The difference is that the thickness of the film begins from a limited thickness for falling film evaporation. The film thickness is evaluated from 2, and mass conservation. Falling film evaporation on a tube bundle with plain and. Process modelling and optimization of design parameters in a. Pdf an investigation was performed to analyze the liquid film distributions of sheet flow on the surface of a horizontal round tube in a falling. In order to study the heat transfer of the falling film evaporator with phase change on both sides, in this paper we built the mathematical model and the physical model where the liquid film inside the tube is laminar and turbulent. Pdf an investigation on the falling film thickness of sheet flow over. Measurement of falling film thickness around a horizontal tube. The film flows down a stainless steel rod with a diameter of 10 mm and a length of mm that is inserted in a glass tube with an internal diameter of 15 mm, yielding an annulus of 2.
He derived the following expression for the thin film thickness shown in eq. The film thickness of the crest increases as the re number increases, and the liquid film spreads along the circumferential direction at the wave crest under the force of gravity. Modeling of falling film in vertical downward twophase pipe. The thickness of the falling film of liquid around a. Measurement of falling film thickness around a horizontal tube using laser induced fluorescence technique. Pdf an investigation on the falling film thickness of. Distribution characteristics of falling film thickness around. Local heat transfer coefficient in wavy freefalling. Establishment of the falling film evaporation model and. Brauner1987, studied the effect of velocity and turbulence on film thickness in the fully developed regions.
Mass and momentum transport in smooth falling liquid films. Even if the clear juice feed rate should fluctuate, correct operation of the different. Falling dart impact is a traditional method for evaluating the impact strength or toughness of a plastic film. Gourdon author for correspondence division of industrial energy systems and technologies, department of energy and environment chalmers university of technology, goteborg, 412 96, sweden. Falling film evaporators are used much like conventional evaporators, except the mechanism of evaporation in each stage is different. In the head, the product is evenly distributed into the heating tubes.
The evaporator is a special type of heat exchanger. The wave spectra from localized probes at the four regions are also shown. The use of a numerical simulation tool on water falling film has resulted in a detailed investigation of film thickness. Experimental results for the film thickness distribution, the mean film thickness, the film wave frequency and celerity are presented and further compared to other theoretical and experimental results in the existing literature. An investigation on the falling film thickness of sheet flow over a completely wetted horizontal round tube surface qinggang qiu school of energy and power engineering, dalian university of technology, dalian 116024, china, tel.
Falling film evaporator design our falling film evaporator is the simplest and most commonly used type of film evaporator. Information on more detailed characteristics of the film thickness variations and information on the velocity profile within the film and wall shear stress are much less common. The results are compared to those predicted by the nusselt. Falling film evaporation is the same as the process of falling film condensation essentially, but the different generating direction is reversed. Astm d test for plastic film impact resistance and free falling drop dart cover the determination of the energy that causes plastic film to fail under. Comparison between the experimental data and the model predictions shows a maximum absolute average discrepancy of 22. The thickness of the falling film of liquid around a references downloaded from the thickness of the falling film of liquid around a taylor bubble. The thickness of the thin liquid film and its effects have always been a research hotspot in nuclear power applications and operating nuclear power plants, because the flow phenomenon of the liquid film is extremely common in multiphase flow research. Evaluation of cross curvature influence on the film thickness is presented. The statistical description of the film thickness is complicated by the fact. The re number is an important factor in the liquid film distribution process, but the tube spacer has a minor impact on the liquid film distribution when the re. The film thickness, flow regimes, and flooding points for the countercurrent annular flow of corn oil mazola and carbon dioxide at 338 k and pressures between 7. Falling film thickness measurement using aircoupled.
This test method can be used for films whose impact resistances require masses of about 50 g or less to about 6 kg to fracture them. Falling films are used in industry for distillation, absorption, reactions, condensation, etc. Film thickness, flow regimes, and flooding in countercurrent. Other geometries and conditions are possible variables, 1 but normal practice is with a vertical tube and countercurrent gas flow.
Wave evolution on a falling film university of notre dame. Additionally, it is a process of fallingfilm flow with heat and mass transfer between the start and end of fallingfilm. Thus a hydrodynamically or thermally fully developed flow cannot be truly main tained in falling films. Design of industrial falling film evaporators intechopen.
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