Pore network simulation of imbibition into paper during coating: I. Model development

A novel imbibition model of a coating fluid in a paper was developed. The microstructure of the paper was represented by a network of interconnected channels or throats formed between the paper's fibers. Geometrical characteristics of the channels, such as effective radius and length, were selected from representative statistical distributions. The interconnectivity of the channels was characterized by an average coordination number treated as a parameter of the model, and its effect on the imbibition process was studied. The study dealt with a dynamic (time-dependent) boundary condition, in which a convection-driven pressure was applied to the coating fluid on the external surface of the paper or driven only by capillary forces. The flow parameters used in the model represent a high-speed coating process. Extensive computer simulations were carried out to study the effect on the imbibition process of three distinct sets of parameters: microstructural parameters of the paper; the fluid's properties; and the dynamic boundary condition. The mean coordination number and average throat size of the paper's pore space, the coating fluid's viscosity, and the dynamic boundary condition all strongly influenced imbibition of the coating fluid.