The mixing of solids in tumbling mixers—I

Abstract Work on the measurement of mixedness in mixtures of solid particles is reviewed. Results on the rate of mixing of sands differing only in colour are given for simple experimental mixers. A suitable index of mixing has been obtained from the variance of a number of small samples to which a correction has to be applied for the random variance owing to the small sample size. Mixing occurs at different rates in different directions to the plane of particle circulation and the resultant rate curve can be approximated by addition of the directional variances. The sampling was mostly done by taking from 40 to 60 samples of from 40 to 60 grains of sand in each sample and gave reliable enough results for an exploratory investigation.