A method has been developed by which the process engineer will be able to
design continuous mixing systems and to explore mixing strategies, thus
enabling him to take advantage of the benefits of the continuous mixing of
The method is based on the prediction of the degree of smoothing out of
periodic fluctuations in composition from a knowledge of the residence time
distribution of the mixer and the nature of the fluctuations.
Experimental verification of the method has been carried out in a ribbon
blade continuous mixer using both free flowing sand and cohesive chalk. The
residence time distributions were measured by adding an impulse of coloured
tracer and measuring the outgoing composition, continuously, by a
reflectivity device. Models involving a proportion of piston flow and of
simple (or perfect) mixers in series were found to fit the experimental
Periodic fluctuations were approximated by a Fourier Series and the
amplitude reduction of rectangular periodic impulses were computed and
compared with the measured amplitude reduction. With few exceptions the
agreement was satisfactory for engineering purposes.
It is claimed that the method can be used for designing continuous mixing
systems and it is shown how a minor ingredient can be added in periodic
impulses rather than a continuous stream to produce a satisfactory
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.
The present work formed part of the Warren Spring Laboratory Mixing
Cooperative Project jointly financed by the Chemical and Minerals
Requirements Board of the Department of Industry and the following
companies: Associated Portland Cement Company Ltd., Foseco International
Ltd., General Foods Ltd., I.C.I. Ltd., Polycell Products Ltd., Sturtevant
Engineering Ltd. and Unilever Ltd.