High capillary number withdrawal from viscous Newtonian liquids by flat plates
TL;DR: In this article, the authors proposed a new theory for withdrawal from viscous Newtonian liquids by vertical plates, and the thickness of the liquid layer on the withdrawn plate was determined experimentally by a light adsorption method.
About: This article is published in Chemical Engineering Science.The article was published on 1970-01-01. It has received 59 citations till now. The article focuses on the topics: Capillary number & Newtonian fluid.
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TL;DR: In this article, the rationale of using edible coatings on fresh and minimally processed produce, the challenges in developing effective coatings that meet the specific criteria of fruits and vegetables, the recent advances in the development of coating technology, the analytical techniques for measuring some important coating functionalities, and future research needs for supporting a broad range of commercial applications.
Abstract: One of the major growth segments in the food retail industry is fresh and minimally processed fruits and vegetables. This new market trend has thus increased the demands to the food industry for seeking new strategies to increase storability and shelf life and to enhance microbial safety of fresh produce. The technology of edible coatings has been considered as one of the potential approaches for meeting this demand. Edible coatings from renewable sources, including lipids, polysaccharides, and proteins, can function as barriers to water vapor, gases, and other solutes and also as carriers of many functional ingredients, such as antimicrobial and antioxidant agents, thus enhancing quality and extending shelf life of fresh and minimally processed fruits and vegetables. This review discusses the rationale of using edible coatings on fresh and minimally processed produce, the challenges in developing effective coatings that meet the specific criteria of fruits and vegetables, the recent advances in the development of coating technology, the analytical techniques for measuring some important coating functionalities, and future research needs for supporting a broad range of commercial applications.
522 citations
TL;DR: In this article, the authors discuss the thickness of the liquid layer entrained by a solid drawn out of a bath, focusing on the case where the solid is a fiber or a wire.
Abstract: ▪ Abstract We discuss the thickness of the liquid layer entrained by a solid drawn out of a bath, focusing on the case where the solid is a fiber or a wire. Slow withdrawals out of a pure or a complex fluid are described as well as quick coatings. We specify the general laws of entrainment and stress the cases where the fiber curvature plays a role. We finally give an overview on the further evolution of the coated film.
496 citations
TL;DR: In this paper, a new theoretical treatment is presented which predicts accurately the relationship between the dimensionless thickness parameter, T0, and the Capillary Number, Ca, up to a value of Ca of 2.
147 citations
TL;DR: In this paper, a partially hydrolysed solution of tetraethoxysilane was used to prepare thin glassy films on glass microscope slides by dipping and the thickness of these films after heat treatment to 500 °C was determined as a function of the withdrawal speed and the properties of the coating solution, such as viscosity, density and surface tension.
Abstract: A partially hydrolysed solution of tetraethoxysilane was used to prepare thin glassy films on glass microscope slides by dipping. The thickness of these films after heat treatment to 500 °C was determined as a function of the withdrawal speed and the properties of the coating solution, such as viscosity, density and surface tension. The results were fitted to available theories of dip coating and acceptable agreement was obtained for coating solution viscosities below around 8 mPas and withdrawal speeds in the range 5 to 15 cm/min. In addition, the thickness of selected coatings were obtained at a range of heat treatment temperatures. Differences in the thickness of coatings prepared after different maturing times of the solution are also discussed.
142 citations
TL;DR: In this paper, a flat plate dip-coating in low-capillary-number Newtonian liquids was used to measure the internal oxygen and carbon dioxide of apples, and the results indicated that coating thickness varied with viscosity, concentration, density and draining time of the biopolymer solution.
Abstract: Hydroxypropyl methylcellulose solutions were used as coating systems in this study and solution concentrations, viscosity, densities, and surface tensions were characterized. Fuji apples were coated by dipping and stored 4 d at room temperature, after which the internal oxygen and carbon dioxide were measured. Results indicated that coating thickness varied with viscosity, concentration, density, and draining time of the biopolymer solution. Coating thickness relates to the square root of viscosity and the inverse square root of draining time, which agrees with the theoretical approach for flat plate dip-coating inlow-capillary-number Newtonian liquids. These results indicate the possibility of controlling coating thickness and internal gas composition based on coating solution properties. Keywords: coating thickness, viscosity, fruits, vegetables, modified atmosphere
129 citations
Cites background or methods from "High capillary number withdrawal fr..."
...Different theoretical approaches have been used to estimate the film thickness from these properties (Levich 1962; Groenveld 1970; Scriven 1988; Derjaguin 1993)....
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...The transformation of withdrawal speed (U) to draining time is given as (Groenveld 1970; Toledo 1991): U = z/t (3) The objective of our study was to apply the physical principles of the dip coating process to apple fruits and to define the relationship between the coating thickness, the properties…...
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...In both cases, the proportionality constant K can be experimentally determined (Groenveld 1970; Scriven 1988; Guglielmi and Zenezini 1990; Guglielmi and others 1992)....
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...K values have been reported to be in the order of 0.8 (Scrivens 1988), 0.66 (Groenveld 1970) and 1.0 (Jeffrey 1930, Derjaguin 1993) for high capillary numbers (for example, Ca > 1)....
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References
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TL;DR: In this article, a theoretical relationship for estimating the film thickness and flow rate at which a liquid is dragged out of a bath by a moving flat plate is given by the integration of the Navier-Stokes equation for flow in films on solid supports given by Levich and by consideration of the linearized form of this equation and a similar simpler one derived by Landau and Levich.
154 citations
01 Apr 1930
TL;DR: In this article, a thin film of liquid clings to the inside and gradually drains down to the bottom under the action of gravity, and the curvature of the surface in a horizontal direction may be ignored.
Abstract: When a vessel of liquid has been emptied and put aside, a thin film of liquid clings to the inside and gradually drains down to the bottom under the action of gravity. The layer being thin, the motion is very nearly laminar flow, and the curvature of the surface in a horizontal direction may be ignored. Thus the problem for a cylindrical vessel is reducible to that of a wet plate standing vertically.
102 citations
TL;DR: In this article, the authors compared the results of experiments reported in literature and of their own experiments and compared with theory in the case of single-and continuous-lifting of a viscous and wetting liquid.
Abstract: When an object is withdrawn from a bath of a viscous and wetting liquid, a liquid film adheres to its surface and liquid is thus lifted out of the bath. The simplest case is that in which the liquid is lifted by means of a plane vertical plate emerging from the liquid. In part I the “single-lift” process is treated where the thickness of the film lifted by the plate is a function of location on the plate and time. Results of experiments reported in literature and of our own experiments are correlated and compared with theory. Part II deals with the “continuous-lift” process in which the liquid is continuously lifted, e.g. by an endless belt and removed at some height above the bath, thus forming a most primitive type of pump. In the stationary state the flux lifted and film thickness are constant. Theory for this case is incomplete and experiments have been carried out in order to determine what flux and film thickness can be expected under certain conditions.
73 citations
TL;DR: The relationship existing between the average film thickness, the speed of withdrawal, and the kinematic viscosity of the liquid is the subject dealt with in this article, where an experimental apparatus was designed to test the theory and found that within the range of speeds used the theory does not correctly predict the film thickness.
Abstract: When a solid body is immersed in a bath of liquid and withdrawn, a film of the liquid adheres to the solid surface and gradually drains back into the bath when the motion ceases. The relationship existing between the average film thickness, the speed of withdrawal, and the kinematic viscosity of the liquid is the subject dealt with in this paper. According to the generally accepted theory the film thickness varies with the square root of the product of the speed and the kinematic viscosity. It was noticed that corrections based on this relationship and used in the calibration of a gas-measuring standard were not satisfactory. Therefore an experimental apparatus was designed to test the theory. Analysis of the data revealed that within the range of speeds used the theory does not correctly predict the film thickness, and an empiricaJ equation of the form t=k (vs)n was employed, in which t is the average film thickness, v is the kinematic viscosity of the liquid, s is the speed of withdrawal of the surface, k and n are quantities varying slightly with the liquid used. The approximate values of k and n found by experiment are 0.015 and 0.63, respectively. Nine liquids were tested, including mineral, vegetable, and animal oils, and synthetic organic compounds of oily nature. ' CONTENTS Pal:1l
41 citations
TL;DR: In this paper, the effect of surface tension on the curvature of the outer surface of the liquid layer was studied and the change of the coating thickness with height was shown to be relatively small at places well above the main surface of a liquid bath.
Abstract: Prediction of the thickness of the liquid film during draining of the liquid on a vertical surface has considerable importance in various practical cases such as in lubrication, in drainage and in estimation of the amount of liquid adhering to walls of pipetes, burettes, and capillary viscometers after emptying. The thickness of the liquid film draining from a vertical surface depends upon the interrelationship among surface tension, the gravitational force, and the viscous force. The effect of surface tension depends upon the curvature of the outer surface of the liquid layer which can be expressed as the change of the coating thickness h with height. For the case of a flat plate which is partially immersed in the liquid, the change of thickness with distance from the top will be relatively small at places well above the main surface of the liquid bath. However, near the bath surface the
31 citations