Modelling the Simultaneous Heat and Mass Transfer in Paper Calendering Process

Paper is calendered in order to improve its surface properties when demanding
print quality is desired. Calendering operation is performed by passing the paper
web through nip(s) formed by rotating rolls pressed against each other. To achieve
the optimal surface properties over paper bulk relationship, temperature-gradient
and moisture-gradient calendering techniques have been developed and
implemented on most calender machines.

Furthermore, the extended soft nip concept, which can significantly save bulk by
reducing the compression pressure, has also been subject of extensive research
works. Traditionally, paper is treated as semi-infinite slab when solving the
problem of heat transfer to paper in the nip. This is valid especially for a hardnip
where the dwell time is too short for the heat to penetrate through the total paper
thickness. This assumption is, however, no longer valid for a calender with an
excessively long nip.

The objective of the thesis is a mathematical model comprehensive enough to be
applicable to the simultaneous heat and mass transfer occurring in the paper
calendering process. Moreover, the model is also able to predict the possible
thermal shock to the thermal roll. Such a model can certainly deepen our insights
and contribute to the knowledge base.