Abstract: In a closed-loop flash dryer, hot gas is introduced through a horizontal or downwardly directed nozzle. This configuration is especially adapted for drying heat-sensitive materials. The use of a single nozzle eliminates damage to equipment which results from differential expansion.

Abstract: Significant improvement in the sharpness with which particles are classified by size in a recirculating jet mill is achieved by the provision of an elongated, flexible barrier strip located adjacent the outermost part of the wall of the classifier section. The positions of both ends of the strip are adjustable for controlling classification. The cross-section of the classifier section is pear-shaped, the narrow portion of the cross-section being toward the outside of the classifier section, and the barrier strip being within said narrow portion. An auxiliary outlet for large particles can be provided behind the barrier strip.