This thesis is dedicated to the study of the interaction between a gas jet and a liquid film on a moving surface. This flow configuration corresponds to the gas-jet wiping technique, which is widely used in the coating industry to reduce and control the thickness of a liquid film dragged by a moving substrate. For that purpose, a turbulent slot jet impinges on the liquid surface, involving a runback flow and consequently a lower coating thickness downstream wiping. The different process parameters (nozzle pressure, nozzle to substrate standoff distance, slot width, substrate speed) allow controlling the final film thickness. This metering technique is very common in coating processes, such as the application of gelatin layers on photographic films. The first part of this thesis deals with the prediction of the mean jet wiping flow, i.e. the film thickness distribution in the wiping region. A lubrication model is developed for that purpose, which is simplified to a zero-dimensional model giving directly the final thickness In the second part, the prediction of splashing occurrence in jet wiping is addressed. The splashing phenomenon in jet wiping is featured by the ejection of droplets from the runback flow, and it constitutes a physical limit to the process. An experimental investigation is conducted on a water model facility, and based on a phenomenological description, a dimensionless correlation in terms of film Reynolds number and jet Weber number is derived for splashing occurrence. The latter is perfectly well validated with observations on industrial lines. The last part of this thesis is dedicated to the study of the unsteady phenomena occurring on the free surface of the liquid film downstream wiping. This phenomenon has never been understood nor characterized up to now. In the present research, undulation is investigated both theoretically and experimentally. Two model test facilities with dedicated measurement techniques have been designed and constructed. They allow performing parametric studies of the undulation characteristics (amplitude, wavelength, wave velocity), and analyzing the jet/film interaction.

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Film flow measurements at several axial positions in round pipes with variousaxial power distributions are presented for conditions corresponding to normaloperation of a BWR. It is confirmed that the film flow rate approaches zero atthe onset of dryout. Selected phenomenological models of annular two-phaseflow are shown to reasonably reproduce the measurements. It is concluded thatmodels are in better agreement with measurements if terms corresponding topossible boiling induced entrainment are excluded. A method to perform film flow analysis in subchannels as a post-processto a standard two-field subchannel code is suggested. It is shown that thisapproach may yield accurate prediction of dryout power in rod bundles to alow computational cost and that the influence of the power distribution is wellpredicted by the model. / QC 20100618

<p>Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions.</p>

Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions. / QC 20101108

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21764号 / 工博第4581号 / 新制||工||1714(附属図書館) / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 横峯 健彦, 教授 村上 定義 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This diploma thesis deals with an application of the finite element method on elastohydrodynamic (EHD) lubrication simulations. Commercially available software COMSOL is used for the computation, while two different modules for modeling EHD lubrication are described in a detail. Firstly, a new approach using the module Thin-Film Flow is developed, considering and describing some limitations of this approach. This is the very first published work dealing complex with EHD simulation in Thin-Film Flow module. In the second part of the thesis, there was created a model of line contact using the module for the introduction of partial differential equations (PDE). The model is partially verified with available works for different values of the input parameters. Subsequently, the velocity effect of the contact surfaces on the pressure and the lubricant thickness in contact is analyzed. Finally, the last part is examines the influence of the values of some parameters on the final value of the contact pressure and the lubricant thickness, as well as on numerical stability of the entire model.

This thesis is dedicated to the study of the interaction between a gas jet and a liquid film on a moving surface. This flow configuration corresponds to the gas-jet wiping technique, which is widely used in the coating industry to reduce and control the thickness of a liquid film dragged by a moving substrate. For that purpose, a turbulent slot jet impinges on the liquid surface, involving a runback flow and consequently a lower coating thickness downstream wiping. The different process parameters (nozzle pressure, nozzle to substrate standoff distance, slot width, substrate speed) allow controlling the final film thickness. This metering technique is very common in coating processes, such as the application of gelatin layers on photographic films.<p><p>The first part of this thesis deals with the prediction of the mean jet wiping flow, i.e. the film thickness distribution in the wiping region. A lubrication model is developed for that purpose, which is simplified to a zero-dimensional model giving directly the final thickness<p><p>In the second part, the prediction of splashing occurrence in jet wiping is addressed. The splashing phenomenon in jet wiping is featured by the ejection of droplets from the runback flow, and it constitutes a physical limit to the process. An experimental investigation is conducted on a water model facility, and based on a phenomenological description, a dimensionless correlation in terms of film Reynolds number and jet Weber number is derived for splashing occurrence. The latter is perfectly well validated with observations on industrial lines.<p><p>The last part of this thesis is dedicated to the study of the unsteady phenomena occurring on the free surface of the liquid film downstream wiping. This phenomenon has never been understood nor characterized up to now. In the present research, undulation is investigated both theoretically and experimentally. Two model test facilities with dedicated measurement techniques have been designed and constructed. They allow performing parametric studies of the undulation characteristics (amplitude, wavelength, wave velocity), and analyzing the jet/film interaction.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Evaporation is a key process for the water exchange between soil and atmosphere, it is controlled by the internal water fluxes and surface vapor fluxes. The focus of this thesis is to visualize and quantify the multiphase flow processes during evaporation from porous media. The retained liquid films in surface roughness (thick-film flow) and angular corners (corner flow) have been found to facilitate and dominate evaporation. Using the representative 2D micromodels (artificial pore networks) with different surface roughness and pore structures, this thesis gives visualizations of the corner and thick-film flow during the evaporation process, presents the enhanced hydraulic continuity by corner and thick-film flow, and tests the validity of the SSC-model which assumes corner flow is dominant for the mass transport during evaporation. Surface roughness and wettability are proved both experimentally and theoretically to play a key role for the time and temperature behaviors of the evaporation process, besides, this thesis shows that for a consistent description of the time-dependent mass loss and the geometry of the corner/thick-film flow region, the fractality of the evaporation front must be taken into account.