The hopper is the bottom part of the silo, responsible for discharging the bulk solids. The angle of the walls and the opening of the hopper define its geometry. Regardless of what hopper geometry suits the needs of the user better, all designs should result in mass flow of the bulk solids.

For practical silo models, equations or diagrams derived by Jenike (1964) are commonly used to define the opening and angle of the hopper walls. The calculations of Jenike refer to conical hoppers and wedge-shaped hoppers. For these basic hopper forms, we need to determine the hopper's opening and the maximum angle slope of its walls to achieve mass flow.

Even though there are many types of hoppers, the majority of silos are designed with a conical bottom hopper, as seen in the first image:

Figure: Types of hopper.