Statistical characteristics of free falling water film. 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. In the head, the product is evenly distributed into the heating tubes. Brotz1964 used the experimental drainage technique to estimate film thickness by. Falling film evaporator design our falling film evaporator is the simplest and most commonly used type of film evaporator. The heat transfer area is the key parameter in designing of an evaporator and many correlations are available to estimate the size of. 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. 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.
In falling film evaporators, the liquid product usually enters the evaporator at the head of the evaporator. The falling film model developed is based on applying momentum balance on the liquid film. Process modelling and optimization of design parameters in a. 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. Thus a hydrodynamically or thermally fully developed flow cannot be truly main tained in falling films. 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.
A falling film evaporator is an industrial device to concentrate solutions, especially with heat sensitive components. Cfd, horizontal tubes, falling film, falling film thickness, vof. Comparison between the experimental data and the model predictions shows a maximum absolute average discrepancy of 22. Keywords falling films, probability density, correlation, spectral analysis 1. The evaporator is a special type of heat exchanger. Measurement of falling film thickness around a horizontal tube using laser induced fluorescence technique.
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 distributor then delivers the liquid to the tube sheet. 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. Film thickness measurements in falling annular films. 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.
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. 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. 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. Falling film evaporation an overview sciencedirect topics. Evaluation of cross curvature influence on the film thickness is presented. Falling film evaporators are used much like conventional evaporators, except the mechanism of evaporation in each stage is different. 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. Falling film evaporation on horizontal tubes with smooth. Measurement of falling film thickness around a horizontal tube. Gourdon author for correspondence division of industrial energy systems and technologies, department of energy and environment chalmers university of technology, goteborg, 412 96, sweden.
Introduction a falling liquids film flow over a surface of a horizontal tube has been widely used as a configuration of heat exchanger. Theoretical and experimental analysis of absorptioncondensation in a combined power and cooling cycle by nitin goel december 2005 chair. A falling film is the gravity flow of a continuous liquid film down a solid tube having one free surface. Investigation into falling film outside horizontal tube. Establishment of the falling film evaporation model and. Based on the numerical simulated results, it is found that the average values of water film thickness for each model are 0. The resulting vapor normally flows cocurrently with the liquid, in the centre of the tubes. The thickness of the falling film of liquid around a taylor. Presentation of the concept and operating results vapour and 4th effect vapour. Equations for the calculation of local velocities in the film with respect to cross curvature of wetted surface have been established.
An optical method for the nonintrusive measurement of falling film thickness on the perimeter of the horizontal tube is described. 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. Design of industrial falling film evaporators intechopen. Theoretical and experimental study on the fallingfilm. 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. Measurement of falling film thickness around a horizontal tube using laserinduced fluorescence technique. The liquid flows as a thin film on the inside of heated vertical tubes, driven by gravity. 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. He derived the following expression for the thin film thickness shown in eq. Modeling of falling film in vertical downward twophase pipe. Predictions based on 2 are more sensitive to the accuracy of the eddy viscosity distribution in the. 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. In the first stage, process liquid enters the falling film evaporator through the inlet feed pipe and is directed to the top liquid distributor. 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.
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. 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. The statistical description of the film thickness is complicated by the fact. 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. Wave evolution on a falling film university of notre dame. Llewellin and elisabetta del bello and jacopo taddeucci and piergiorgio scarlato and sharrah lane, journalproceedings of the royal society a. 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 heat transfer tube is the core component of falling film evaporator. These design and operational parameters have a significant influence on the hydrodynamic of the liquid film eg. Falling film evaporation on a tube bundle with plain and. A comprehensive design of 2d models have been developed.
Falling film condensation and evaporation are impor tant heat transfer processes in shell. Instantaneous film thickness measurements of falling annular films were. Additionally, it is a process of fallingfilm flow with heat and mass transfer between the start and end of fallingfilm. In charge of major work fof the major department for the graduyne college.
Measurement of liquid film thickness around horizontal tube. 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 falling film evaporators have many advantages over flooded and vertical tubes that make them best candidate for processes industries application. The thickness of the falling film of liquid around a taylor bubble. 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. Brauner1987, studied the effect of velocity and turbulence on film thickness in the fully developed regions. Film thickness, flow regimes, and flooding in countercurrent. Measurement of falling film thickness around a horizontal. 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 film thickness is evaluated from 2, and mass conservation. 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. 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 difference is that the thickness of the film begins from a limited thickness for falling film evaporation. Process modelling and optimization of design parameters in.
Astm d plastic film impact resistance free falling drop dart equipment validating the specifications, value and safety of your raw materials, products and assets. 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 corresponding effects on heat transfer have also been estimated. The circumferential thickness of a falling liquid film is inversely proportional to the local heat transfer coefficient. 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. It is itself equipped with many drip points to ensure the generation of. Falling film evaporation is the same as the process of falling film condensation essentially, but the different generating direction is reversed. 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. An investigation on the falling film thickness of sheet flow.
How to design a falling film reactor for sulfonation. The use of a numerical simulation tool on water falling film has resulted in a detailed investigation of film thickness. Other geometries and conditions are possible variables, 1 but normal practice is with a vertical tube and countercurrent gas flow. The relationship between the film thickness and the calculated heat transfer coefficient was. Mass and momentum transport in smooth falling liquid films. Falling film thickness measurement using aircoupled. Falling dart impact is a traditional method for evaluating the impact strength or toughness of a plastic film.
The beta type fallingfilm evaporators operate with an independent juice circulation system. Pdf an investigation on the falling film thickness of sheet flow over. The results are compared to those predicted by the nusselt. This paper presents a computational modelling of water falling film flowing over horizontal tubes. The numerical modelling of falling film thickness flow on. 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. Even if the clear juice feed rate should fluctuate, correct operation of the different. The results are then validated with a theoretical result in previous literatures. Measurement of liquid film thickness around horizontal. Pdf the thickness of the falling film of liquid around a. However, they are different in practical industrial application. Additionally, it is a process of falling film flow with heat and mass transfer between the start and end of falling film. An investigation on the falling film thickness of sheet.
Fallingfilm evaporator plant for a cane sugar factory. The wave spectra from localized probes at the four regions are also shown. It is itself equipped with many drip points to ensure the generation of an even and calm static liquid height outside the tubes. 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. Distribution characteristics of falling film thickness around. The thickness of the falling film of liquid around a. The high performance evaporators are important for process industries such as food, desalination and refineries. 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 result shows there is an optimization that the film thickness at the bottom of the tubes amounts to that of boundary layer of velocity.
Pdf an investigation on the falling film thickness of sheet. How to design a falling film reactor for sulfonation posted in student. For higher r values r 50, region iii may not be present. Local heat transfer coefficient in wavy freefalling. I mass flow rate per unit film width for a planar film.
A new optical method for the nonintrusive measurement of falling film thickness on the perimeter of horizontal tubes is described. Figures 7 to 10 show the effect of film reynolds number re f on the film thickness. A plot of nusselt number against film reynolds number can be used to correlate data. 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. Numerical study of falling film thickness on horizontal circular tube. The nikon d70 digital slr camera was operated in the manual shooting mode. The objective of this study is to use numerical predictions for comparing the film thickness along circumferential direction of tube on 2d cfd models. The reason of this deviation is because of the liquid film rotation in coil which causes some deletion. Falling films are used in industry for distillation, absorption, reactions, condensation, etc. Pdf an investigation on the falling film thickness of.
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