The rheological properties of fibre-water suspensions are of critical importance in many of the papermaking processes from stock preparation (beating, screening, fractionation, cleaning) through transport and distribution (pumping, pipe flow, headbox flow), to the actual forming process (dispersion in headbox and forming zone, dewatering).
The limitations of existing techniques for measuring velocity and turbulence as well as concentration and flocculation in pulp suspensions are discussed.
The major recent fundamental investigations of fibre suspension flow in pipes are critically reviewed within the framework of the three basic flow mechanisms (plug, mixed and turbulent flow) and the three basic study levels (empirical, network and fibre). It is concluded that the varied and complex flow phenomena exhibited by the suspensions, from plug flow through to turbulent flow, are controlled by the same variables at the fibre level : the volumetric concentration, aspect ratio and modulus of elasticity of the fibres.
Recent investigations of flocculation and turbulence are critically reviewed, and it is found that no reliable measurements of turbulence in fibre suspensions have been reported.
A new investigation of elongational pipe flow is presented.
Finally a new method for the simultaneous noncontact measurement of turbulence and flocculation is described. It is a combination of laser doppler anemometry and light reflection measurement, and offers many new possibilities in the fundamental study of pulp suspension flow.