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.
A Simple Model of Reverse Roll Coating
The key feature of a reverse roll coater is the fluid flow in the gap between two parallel rigid cylinders rotating with opposed surface velocities. A simplified model system studied by Greener and Middleman has the two rolls side-by-side and half-submerged in the coating liquid. Over a certain range of roll surface speed ratio, their experimental measurements of the flow rate through the gap deviated from predictions of a simple lubrication theory and recirculations were observed. This model configuration is examined experimentally and by finite element solutions of the Navier-Stokes equations in two dimensions. The results indicate that the film-transfer free surface and the recirculations under it do not significantly influence the flow rate through the gap
The Liverpool Cholera Epidemic of 1832 and Anatomical Dissection--Medical Mistrust and Civil Unrest
Asiatic cholera reached Britain for the first time in late 1831, with the main epidemic occurring during 1832. The disease caused profuse diarrhea, severe dehydration, collapse, and often death. There was widespread public fear, and the political and medical response to this new disease was variable and inadequate. In the summer of 1832, a series of "cholera riots" occurred in various towns and cities throughout Britain, frequently directed against the authorities, doctors, or both. The city of Liverpool, in the northwest of England, experienced more riots than elsewhere. Between 29 May and 10 June 1832, eight major street riots occurred, with several other minor disturbances. The object of the crowd's anger was the local medical fraternity. The public perception was that cholera victims were being removed to the hospital to be killed by doctors in order to use them for anatomical dissection. "Bring out the Burkers" was one cry of the Liverpool mobs, referring to the Burke and Hare scandal four years earlier, when two men had murdered people in Edinburgh in order to sell their bodies for dissection to the local anatomy school. This issue was of special concern to the Liverpool citizenry because in 1826, thirty-three bodies had been discovered on the Liverpool docks, about to be shipped to Scotland for dissection. Two years later a local surgeon, William Gill, was tried and found guilty of running an extensive local grave-robbing system to supply corpses for his dissection rooms. The widespread cholera rioting in Liverpool was thus as much related to local anatomical issues as it was to the national epidemic. The riots ended relatively abruptly, largely in response to an appeal by the Roman Catholic clergy read from church pulpits, and also published in the local press. In addition, a respected local doctor, James Collins, published a passionate appeal for calm. The Liverpool Cholera Riots of 1832 demonstrate the complex social responses to epidemic disease, as well as the fragile interface between the public and the medical profession.