Mean particle diameters are important for the science of particulate systems because they provide information on particlesize distributions in such a way that they can be related to physical or physiological processes or product properties. There are different notation systems for such mean diameters which may cause much confusion. This equally applies to their nomenclature. The present paper is concerned with comments on the “Moment‐Ratio” and German (DIN) notations. The Moment‐Ratio notation is recommended for standardization. A more extensive contribution of statistics to the science of particulate systems is recommended.

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In the science of particulate systems, existing nomenclature systems are not always consistent with each other. The same is true for their physical relevance. A coherent nomenclature system for denoting mean particle diameters is recommended and its physical relevance demonstrated. Comments have been 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1991 0934-0866/91/0309-0237 $3.50 + .25/0

The Rosin‐Rammler particle size distribution is used for a broad range of applications. Physical and statistical properties of the Rosin‐Rammler distribution and its parameters were investigated to evaluate their suitability in the particulate area. The Rosin‐Rammler volume density distribution is identical to the Weibull density distribution describing material failure and fatigue phenomena. The physical meaning of the Rosin‐Rammler location parameter depends on the value of its spread parameter. This makes the location parameter physically uninterpretable and less suitable for development of physical models. The distribution can still be used for, e.g., production control purposes. Rosin‐Rammler distributions with spread parameter values less than three cannot exist. They can at most give a rough description of size distributions within the measured particle size range. They should not be expected to describe correctly the quantity of small particles outside the measured size range. Their parameters are unsuitable for model development aiming at estimating parameters explaining/predicting physical product or process parameters. Two data sets were used for validation. Mean particle diameters (Moment‐Ratio notation) and the Rosin‐Rammler parameters are mathematically related, but the relationship is not valid for mean parameter values of a set of size distributions. It is not possible to predict a type of mean particle diameter showing a behavior close to that of the Rosin‐Rammler location parameter. For both data sets, the quality of the relationship of physical product property with proper mean particle diameter type is better than that with the Rosin Rammler location parameter. For process control applications a replacement of the Rosin‐Rammler location parameter by a mean particle diameter (Moment‐Ratio) should be considered. The type of mean particle diameter to be chosen depends on the values of the Rosin‐Rammler spread parameter occurring in the process. Two steps in the migration path are identified.

Mean particle diameters may be used to describe and to model physical, chemical or physiological properties of products or materials containing dispersed phases. An empirical method was developed to select the proper type of mean diameter from experimental data, if this mean diameter is not known a priori from theoretical reasoning. The present method uses mean diameters, D̄p, q, defined according to the Moment‐Ratio (M‐R) definition system. They are expressed as the 1/(p‐q)‐th power of the ratio of the p‐th and the q‐th raw moment of the number density distribution of the particle sizes. After calculation of the mean diameters, D̄p, q, the relationships between the product property and these mean diameters are investigated statistically. The selection method has been illustrated by four examples, three of which stem from a high shear granulation experiment in the field of detergent processing. The fourth example is concerned with a visual ranking of bubble size distributions of chocolate mousse samples. The data set of each example consists of a set of particle size distributions and the corresponding physical product properties that are influenced by the particle sizes. Hypotheses are formulated to explain the types of selected mean diameters. Application of the selection method gives mean diameters, D̄p, q, a clear physical look and identity, replacing their anonymity. Sharing worldwide results of applications of the newly developed selection method, will lead to a build‐up of knowledge of physical meanings and application areas for the types of the mean particle diameters. This will support decision‐making in product development. The examples used to develop the selection method clearly demonstrate the physical relevance of the previously developed nomenclature system for mean particle diameters, D̄p, q.