Laboratory study of co-axial stock mixing

A model thick stock co-axial jet mixer was investigated to elucidate the im portant factors for the dispersion of 3% consistency pulp suspensions into a dilute white water stream. The jet breakup was characterized by simultane ous radial sampling and by stepwise axial sampling. A combined axial and ra dial concentration profile for the jet breakup was obtained to characterize the mixing behaviour. The criterion for 'good mixing' was defined as the d istance from injection where the range in radial samples was less than 5% o f the mean. The mixing behaviour of the pulp jets differed significantly fr om the electrolyte jet mixing. The pulp required a longer mixing zone to ac hieve 'good mixing' with the fibre length identified as a key factor in the dispersion. The resistance to jet dispersion exhibited by the pulp was att ributed to the flocs present in the system and interlocked fibres promoting jet cohesion.