Effect of Pore Size and Thickness on Critical Pressure of Elastic Systems

Significant energy savings can be achieved by improving efficiency of water removal in the press section of a paper machine, rather than energy-intensive evaporative dryer cans. Impulse drying is a novel technology to remove water from the sheet in the press section by using a heated press roll. Delamination is a major challenge to be overcome before impulse drying can be implemented successfully. Delamination is caused by a region of high temperature liquid water under high pressure in the press. Upon exiting the nip, the pressure drops and the high temperature water flashes to steam. If the expansion of the steam is too strong, the bonds between the fibers will fail and a blister will form. The formation of this blister is characteristic of delamination. The goal of this project was to understand the internal mechanics of a wet web as it exits the nip of an impulse dryer. In this way, the components of the sheet can be tailored to open the operating window of impulse drying. A mathematical model, developed to describe the deflection and delamination of an elastic membrane, was utilized in this work. Three failure criteria were employed to represent delamination of this pliable membrane from the more rigid sub layers in the sheet. The experimental portion of this effort was devoted to showing the validity of these models and which was the best fit. A series of experiments were employed to validate the model. A peel test was used to determine the amount of work needed to pull a membrane from a rigid substrate. Pressurized blister experiments were conducted to find the relationship between critical pressure and initial defect size. The predictions from the mathematical model were then compared to these experimental values. Finally, work was done to understand the physics of the delamination of a porous membrane.M.S