This work deals with all aspects of mixing solids, liquids and gases in single and multi-phase fl... more This work deals with all aspects of mixing solids, liquids and gases in single and multi-phase flow and therefore reflects the modern use of non-intrusive methods and simulations by computational fluid dynamics.
YesTensioned web-roll coating is widely used but has surprisingly received little research attent... more YesTensioned web-roll coating is widely used but has surprisingly received little research attention. Here, a new semi-empirical model that predicts film transfer from applicator roller to web is developed and tested against data collected from a pilot coating line. The film transfer is found to vary linearly with web to applicator speed ratio S. Flow stability investigations revealed three types of defects: rivulets, air entrainment due to dynamic wetting failure and cascade, occurring at different values of S and capillary number Ca. Rivulets occurred at Ca 0.71-0.81, air entrainment at Ca>0.4 and S>0.71-0.83 and cascades at S>1.1 for Ca up to 6. Web speeds at which dynamic wetting failure occurred were, for the same Ca, comparatively higher than those that occur in dip coating. The data show that such hydrodynamic assistance is due to the coating bead being confined, more so with increasing web wrap angle β.The authors acknowledge the support of the Films R&D Centre of Toyobo Co. Ltd., Otsu, Japan and of the Thin Liquid Films Research Group of the University of Bradford, UK.The full-text of this article will be released for public view at the end of the publisher embargo on 26th March 2022
Three-dimensional CFD simulations of turbulent flow in baffled stirred tanks - an assessment of t... more Three-dimensional CFD simulations of turbulent flow in baffled stirred tanks - an assessment of the current position CFD to fluidmixing needs realistic physical data the influence of rotation on the atmospheric mixing of a buoyant plume from a tall stack resistance tomography imaging of stirred vessel mixing dispersed phase distribution in liquid-liquid mixing in an agitated tank. (Part contents).
Abstract A mathematical model of the reverse and metering roll coating flow of Newtonian fluids i... more Abstract A mathematical model of the reverse and metering roll coating flow of Newtonian fluids is presented. It is based on the lubrication approximation and simple physical notions regarding the separation region. These physical notions discard the effect of surface tension on the dynamics of the system. The results of this model give the dimensionless net flux through the nip, λL, as a function of the speed ratio, rs and the radius ratio rr. This function is a weak one over the range of rr and rr normally encountered in reverse and metering roll coating operations and is in good agreement with experimental data[1] obtained previously. The results of this present study have also been related to the findings from a previous analysis of forward roll coating[2].
An experimental investigation of the effect of fluid rheology on air entrainment in plunging tape... more An experimental investigation of the effect of fluid rheology on air entrainment in plunging tape experiments (dip coating) was carried out. The critical velocity at which the dynamic wetting line breaks up, allowing air to entrain into the liquid, was measured for a range of viscoelastic polymer solutions in glycerin/water mixtures. Variations of the critical velocities with various solutions were found to be unexpectedly small in comparison with the large viscosity variations. The results suggest that dynamic wetting failure and subsequent air entrainment are governed by nonhydrodynamic phenomena occurring at the molecular scale at the wetting line. It was also found that fluid elasticity gives rise to flow instabilities that may lead to a different, hydrodynamic mechanism of air entrainment.
Abstract Experimental measurements are reported for the flow of Newtonian liquids through the nip... more Abstract Experimental measurements are reported for the flow of Newtonian liquids through the nip of two co- and counter-rotating rolls of various size and speed ratios. Results are presented in a dimensionless form for the total volumetric flux through the nip and for the distribution of this flux between the two rolls. Simple correlations have been developed and these should be useful in the design and analysis of roll coating equipment. Some preliminary data are also presented for a shear thinning inelastic non-Newtonian liquid. The forms of the correlating equations developed for the Newtonian systems are still applicable but the constants in the equations are slightly modified.
This work deals with all aspects of mixing solids, liquids and gases in single and multi-phase fl... more This work deals with all aspects of mixing solids, liquids and gases in single and multi-phase flow and therefore reflects the modern use of non-intrusive methods and simulations by computational fluid dynamics.
YesTensioned web-roll coating is widely used but has surprisingly received little research attent... more YesTensioned web-roll coating is widely used but has surprisingly received little research attention. Here, a new semi-empirical model that predicts film transfer from applicator roller to web is developed and tested against data collected from a pilot coating line. The film transfer is found to vary linearly with web to applicator speed ratio S. Flow stability investigations revealed three types of defects: rivulets, air entrainment due to dynamic wetting failure and cascade, occurring at different values of S and capillary number Ca. Rivulets occurred at Ca 0.71-0.81, air entrainment at Ca>0.4 and S>0.71-0.83 and cascades at S>1.1 for Ca up to 6. Web speeds at which dynamic wetting failure occurred were, for the same Ca, comparatively higher than those that occur in dip coating. The data show that such hydrodynamic assistance is due to the coating bead being confined, more so with increasing web wrap angle β.The authors acknowledge the support of the Films R&D Centre of Toyobo Co. Ltd., Otsu, Japan and of the Thin Liquid Films Research Group of the University of Bradford, UK.The full-text of this article will be released for public view at the end of the publisher embargo on 26th March 2022
Three-dimensional CFD simulations of turbulent flow in baffled stirred tanks - an assessment of t... more Three-dimensional CFD simulations of turbulent flow in baffled stirred tanks - an assessment of the current position CFD to fluidmixing needs realistic physical data the influence of rotation on the atmospheric mixing of a buoyant plume from a tall stack resistance tomography imaging of stirred vessel mixing dispersed phase distribution in liquid-liquid mixing in an agitated tank. (Part contents).
Abstract A mathematical model of the reverse and metering roll coating flow of Newtonian fluids i... more Abstract A mathematical model of the reverse and metering roll coating flow of Newtonian fluids is presented. It is based on the lubrication approximation and simple physical notions regarding the separation region. These physical notions discard the effect of surface tension on the dynamics of the system. The results of this model give the dimensionless net flux through the nip, λL, as a function of the speed ratio, rs and the radius ratio rr. This function is a weak one over the range of rr and rr normally encountered in reverse and metering roll coating operations and is in good agreement with experimental data[1] obtained previously. The results of this present study have also been related to the findings from a previous analysis of forward roll coating[2].
An experimental investigation of the effect of fluid rheology on air entrainment in plunging tape... more An experimental investigation of the effect of fluid rheology on air entrainment in plunging tape experiments (dip coating) was carried out. The critical velocity at which the dynamic wetting line breaks up, allowing air to entrain into the liquid, was measured for a range of viscoelastic polymer solutions in glycerin/water mixtures. Variations of the critical velocities with various solutions were found to be unexpectedly small in comparison with the large viscosity variations. The results suggest that dynamic wetting failure and subsequent air entrainment are governed by nonhydrodynamic phenomena occurring at the molecular scale at the wetting line. It was also found that fluid elasticity gives rise to flow instabilities that may lead to a different, hydrodynamic mechanism of air entrainment.
Abstract Experimental measurements are reported for the flow of Newtonian liquids through the nip... more Abstract Experimental measurements are reported for the flow of Newtonian liquids through the nip of two co- and counter-rotating rolls of various size and speed ratios. Results are presented in a dimensionless form for the total volumetric flux through the nip and for the distribution of this flux between the two rolls. Simple correlations have been developed and these should be useful in the design and analysis of roll coating equipment. Some preliminary data are also presented for a shear thinning inelastic non-Newtonian liquid. The forms of the correlating equations developed for the Newtonian systems are still applicable but the constants in the equations are slightly modified.
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