Zhao, S: Modelling the Simultaneous Heat and Mass Transfer i

Paper is calendered in order to improve its surface properties when demandingprint quality is desired. Calendering operation is performed by passing the paperweb through nip(s) formed by rotating rolls pressed against each other. To achievethe optimal surface properties over paper bulk relationship, temperature-gradientand moisture-gradient calendering techniques have been developed andimplemented on most calender machines.Furthermore, the extended soft nip concept, which can significantly save bulk byreducing the compression pressure, has also been subject of extensive researchworks. Traditionally, paper is treated as semi-infinite slab when solving theproblem of heat transfer to paper in the nip. This is valid especially for a hardnipwhere the dwell time is too short for the heat to penetrate through the total paperthickness. This assumption is, however, no longer valid for a calender with anexcessively long nip.The objective of the thesis is a mathematical model comprehensive enough to beapplicable to the simultaneous heat and mass transfer occurring in the papercalendering process. Moreover, the model is also able to predict the possiblethermal shock to the thermal roll. Such a model can certainly deepen our insightsand contribute to the knowledge base.