A PROPOSED MODEL IN THE ANALYSIS OF IMPULSE DRYING OF PAPER

摘要

Understanding the mechanisms of heat and mass transfer along with the Theological behaviour of paper within the impulse nip has been a matter of exhaustive study over the last three decades. Insight into the consolidation of paper using this high-intensity process may be gained by modeling and simulation of the transport phenomena involved in such process. Transport phenomena in paper are sometimes complex because the fibre network does not remain inert. For instance, water and water vapour interact with fibres; absorption of water in fibres leads to swelling that changes the porous structure of the fibrous network; water also influences the thermal conductivity and other physical properties of paper; and permeability is another relevant property that greatly depends on the structure of the porous material under study. In addition, sheet permeability is seen as an important factor controlling the development of internal vapour pressure. In this work a mathematical model is presented, which describes heat and mass transfer during impulse drying of unsatu-rated paper webs, taking into account the visco/elastoplastic behaviour of paper as well. The role of simultaneous gas-liquid flows in the fibrous web during high-intensity drying is of special interest, as liquid flow in paper is one of the most fundamental properties that need to be considered in almost every paper grade. This approach results in a three-dimensional unsteady-state problem, which is solved using a finite differences scheme for the discretization of spatial variables, and the resulting set of ordinary equations is solved using an appropriate ODE solver.