Acoustic Forming for Enhanced Dewatering and Formation

Abstract

and key words:The next generation of forming elements based on acoustic excitation to increase drainage and enhances formation both with on-line control and profiling capabilities has been investigated in this project. The system can be designed and optimized based on the fundamental experimental and computational analysis and investigation of acoustic waves in a fiber suspension flow and interaction with the forming wire. 2 PROJECT TITLE: ACOUSTIC FORMING FOR ENHANCED DEWATERING AND FORMATIONPRINCIPAL INVESTIGATOR: Cyrus K. Aidun, Professor, School of Mechanical Engineering, Georgia Institute of Technology, 500 10th St. NW, Atlanta, GA 30332-0620, (404) 894-6645, Fax 4778, cyrus.aidun@me,gatech.edu, Georgia 5th Congressional District. RESEARCH AREA(S) IN THE SOLICITATION TO WHICH THIS WORK IS FOCUSED: ENERGY PERFORMANCE, Area 1: New Approaches to Drying and Water Removal I. Executive SummaryWhen ultrasonic waves are applied to pulp fibers in a liquid suspension, the fibers move away from the source due to the acoustic force acting on the fibers. The acoustic force consists of three major forcing mechanisms acting on a fiber. These are acoustic radiation, acoustic streaming, and capitation bubble-induced force. These mechanisms are inter-dependent and nonlinear as well as frequency-dependent. It is the combination of all three forces that contributes to the manipulation of pulp fibers suspended in liquid. In this project we use this effect at the early stages of the forming table to generate controlled normal force on the fiber mat in the forming section to: (a) re-fluidize the fibers in the fiber mat to increase the drainage rate, (b) generate controlled activity on the forming wire to enhance formation, and (c) through sectional excitation, profile the sheet for more uniform moisture profile. The results have had limited success, as a large portion of the acoustic energy is dampened while crossing the porous wire. We have done substantial evaluation of acoustic transmission through the actual forming wires and have compiled a substantial data set from the experiments, as presented in the appendix. Through this project we have been able to develop a technology for enhanced dewatering and formation improvement in some grades of specialty paper where the value of the final product is large enough for a favorable cost-benefit process. II. IntroductionIn the forming section, foils and suction boxes are used for dewatering of the pulp suspension delivered from the headbox. As soon as the forming jet impinges on the forming board, a layer of concentrated fiber mat forms on the forming wire. It has been demonstrated that by re-fluidizing the fiber mat at the early stages of the forming table, the dewatering rate increases resulting in additional drainage capacity along the same length of the forming section. Furthermore, it is demonstrated that this action enhances formation of the sheet by generating additional activity on the wire with benefits in quality and fiber savings (1). This application is currently...