Mass flow silos are generally for coal or other materials with segregation problems. With the mass flow pattern, the first materials in are the last materials out. This is important with materials like coal, when you need to keep the coal moving within the silo to minimize the risk of spontaneous combustion.
The mass flow pattern allows for the materials to move down the silo as a column with no flow channels. This eliminates stagnant, non-moving materials and/or the effects of segregation of materials stored within the silo. The cone angle will be between 68-72 degrees depending on the material being stored.