Study of Slip Effects in Reverse Roll Coating Process Using Non-Isothermal Couple Stress Fluid

The non-isothermal couple stress fluid inside a reverse roll coating geometry is considered. The slip condition is considered at the surfaces of the rolls. To develop the flow equations, the mathematical modelling is performed using conservation of momentum, mass, and energy. The LAT (lubrication approximation theory) is employed to simplify the equations. The closed form solution for velocity, temperature, and pressure gradient is obtained. While the pressure and flow rate are obtained numerically. The impact of involved parameters on important physical quantities such as temperature, pressure, and pressure gradient are elaborated through graphs and in tabular form. The pressure and pressure gradient decreases for variation of the couple stress parameter and velocity ratio parameter K. While the variation of the slip parameter increases the pressure and pressure gradient inside the flow geometry. Additionally, flow rate decreases for the variation of the slip parameter as fluid starts moving rapidly along the roller surface. The most important physical quantity which is responsible for maintaining the quality of the coating and thickness is flow rate. For variation of both the couple stress parameter and the slip parameter, the flow rate decreases compared to the Newtonian case, consequently the coating thickness decreases for the variation of the discussed parameter.

Innovative High-Visibility Protective Clothing Development

Technical clothing with light-responsive features for outdoor sports practiced in environments with low visibility is extremely important for athletes’ safety. Lack of signaling by users and visibility for drivers is one of accidents causes, namely run overs, which can leave serious consequences. The products available on the market lack efficiency and their design is not appealing which makes the development of these new materials a compelling need. Therefore, fluorescent and phosphorescent functional finishings with ability to provide illuminant signalization without compromising the design and/or color of clothing as well as comfort and ergonomics, were developed and applied in the textile structure by knife over roll coating technology. The greatest challenge is to integrate the high visibility materials without compromising the design of the garment and accomplish the European Standard of Protective clothing: Enhanced visibility equipment for medium risk situations and test methods and requirements—EN 17353 (that supersedes EN1150:1999 and allows more freedom in the design of the apparel) published in 2020. Phosphorescent materials were evaluated by luminance decay according to DIN 67510, before and after fastness to wash tests. Results obtained regarding high visibility functional finishings and the integration of the materials developed in the final sports collection will be presented.

Forward Roll Coating of a Williamson’s Material onto a Moving Web: A Theoretical Study

This paper presents a mathematical model for the thin film roll coating process of an incompressible Williamson material, passing through a closed passage between a rotating roll and a web. In light of lubrication approximation theory, the flow equations are nondimensionalized. The regular perturbation approach is used to provide solutions for the velocity profile, pressure gradient, flow rate per unit width, and shear stress at the roll surface. Important engineering quantities such as coating thickness, maximum pressure, separation point, roll/sheet separating force, and roll-transmitted power to the fluid are also obtained. The effects of several factors are graphically projected. The study shows that the material factors that are involved determine the operating variables. Coating thickness and separation point are controlled by Weissenberg’s number, therefore acting as a controlling parameter for the rate of flow, thickness in coating, power contribution, pressure, roll separating force, and separation point. In comparison to the existing results in the literature, the current results are broader and zero-order results are more accurate.