Simulation of coating -visco-elastic liquid in the Micro-nip of metering size press
For a set of operating conditions and coating color formulations, undesirable phenomena like color spitting and coating ribs may be triggered in the Micro-nip during the coating process. Therefore, our interest in this work focus on another parameter affect on the undesirable phenomena as the vortices in the Micro-nip. The problem deals with the flow through the Micro-nip of metering size press. The flow enters and exits at a tangential velocity of 20 m/s between two rollers with diameter 80 cm and 60 mum apart. In the upper and bottom part of the domain the angular velocity is 314 rad /s. It has one sub-domain. Previous studies focus on the Micro-nip without considering the inertia and the viscoelasticity of the material. Roll coating is a technique commonly used in the coating industry to meter a thin fluid film on a moving substrate. During the film formation, the fluid is subjected to very high shear and extensional rates over a very short period of time. The fluid domain changes as a function of the hydrodynamic pressure within the nip as a result of the deformable cover usually used on one of the rolls. The free surface also adds more complexity to the flow due to the force equilibrium in the fluid gas interface. Last of all, the rheological behavior of the coating fluid is usually non-Newtonian, so the metering flow hydrodynamics is finally very difficult to describe. It is concluded that the normal forces of micro-nip increases with increasing the inhibitors. Therefore, it affects on the smoothness and creates defects. On the other hand, it can be concluded that the creation of big vortex in the middle of micro-nip affects on the coating liquid behavior.
Reverse roll coating of non‐Newtonian liquids
The essence of reverse roll coating is the rapid high‐shear flow in a small gap between two rigid cylinders rotating with opposed surface speeds. The flow field established in this gap, including the free surface locations and flow rate, is determined mainly by the balance of viscous and surface tension forces, as measured by the capillary number. Non‐Newtonian rheological behavior can strongly affect both the steady, uniform flow and the instabilities to which it is susceptible. Computed solutions of the governing equations indicate that flows of purely viscous liquids differ little from those of Newtonian liquids at the same capillary number, provided that the dimensionless force ratio is defined with the viscosity at the appropriate shear rate. Experiments with shear thinning but relatively inelastic algin solutions confirm this, with the exception that ribbing is strongly exaggerated, presumably by slight elasticity of the liquid. Experiments with highly elastic polyacrylamide solutions show that the coating thickness and the nature of the instabilities can be dramatically altered.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.