In the study of a participate process, one of the most important subjects to consider is what mean particle diameter to employ. In this study, an experimental value is divided into two terms, one with some interaction between particles and the other without such interaction (the linear term). The mean particle diameter is defined only in terms of the latter, that is the linear term. It is shown that the scattering in previously published data for the particulate process, is attributable to the fact that the mean diameter is not determined correctly. Further, if such a diameter as determined in this study is used, a satisfactory result with little scattering in the data is achieved. In connection with the definition, the practical method for determining the mean particle diameter and suggestions as to its use are given, and the relation between the process variables observed when the distribution is log-normal, is also discussed
