Abstract
We analyzed the drainage of a fibre suspension through a wire screen and the simultaneous capture of fine particles in the forming fibrous mat as a simplified model for papermaking in static systems such as the British handsheet mold. The drainage process is modeled as an incompressible cake filtration and the retention of low loading fine particles is modeled as depth filtration. Analytical solutions for both drainage and retention problems are obtained. The model predicts the fine particle concentration to be maximum at the wire side and minimum on the top side in line with practical experience. The cause of this skewed distribution is the fact that the bottom layers of the fibre mat are formed earlier during the drainage process. As a consequence, they are exposed to the deposition of fine particles for the longest duration whereas the top layers which are formed at later stages are hardly, if ever, exposed to deposition. Results for retention show that the distribution of fine particles in the z-direction becomes greater even as the retention level increases. An analytical form of retention rate of fine particles in the mat is also provided and is used to extract the capture coefficient from the experimental retention rate. The calculated fine particle profiles agree well with experimental data in Ref. [1] for low and very high retention rates.