As the name suggests, contra-rotating mixers consist of agitators rotating in opposite direction. Contra mixers consists of two impellers, both of which rotate around the same axis, in opposing directions at differential speeds. It is common to have a slow moving anchor operating near the vessel walls, and a relatively higher speed impellers such as pitched blade turbine, hydro foil producing axial flow of material. In jacketed vessels, the anchor reduces the buildup of stagnant material near the vessel walls, and promotes heat transfer. Scrapers or wipers can be provided remove material deposited on internal walls of the vessel, further enhancing the transfer of heat. The material after mixing is discharged through special flush bottom valves.