Flow regimes of air suspensions of MDF fibres in vertical flow

The flow regimes of wood fibres suspended in air were studied. This knowledge is of importance for process design in the panelboard and pulp and paper industries. It is also an important tool for determining the validity of mathematical models for the flow of fibre-air suspensions. Flow regime maps for two different types of MDF fibres (pine and aspen) in vertical flow were determined in the velocity range 7-27 m/s (Re=90000-340000) and the fibre concentration range 25175 g/m(3). Two different flow regimes were identified: flocculated and homogeneous. The flow regime maps were made independent of fibre length, fibre diameter and channel dimensions by depicting them in a diagram where the x- and y-axis were the Reynolds number and crowding factor, respectively. The boundary between flocculated and homogeneous flow is not sharp; there is a transition region. The experimental results indicate that, for the Reynolds numbers considered in this study, the flow regime boundary can be described by a straight line in the said diagram.