- Difficulties are encountered sometimes with new chemical products during manufacturing, handling, or marketing due to lack of knowledge in the particle technology area. The major problem discussed in this article is that, in most cases, this is due to the neglect of the mutual interactions between different unit operations during manufacturing and conveying in the design phase of these new products. Unlike the case with most other materials, it is not sufficient to know the present thermodynamic state of bulk powdery materials in order to determine their attributes since their “history” also affects the material's properties and behavior, often dramatically. The mutual effects between different operations such as bulk material handling, conveying, milling, and drying, as well as the property changes that occur during these processes, are discussed by presenting several case studies from the authors’ own work and previous experiences. These include such properties as effective thermal conductivity, size distribution, flowability, caking, and surface activation in such operations as fluidized bed drying, pneumatic conveying, granulation, and tabletting. Finally, a flow sheet containing unit operations with powders is optimized using experience gained from these case studies.