Helical ribbon impellers are designed especially axial movement of the liquid (in the process of ‘replacement of liquids’). Such an impeller can be designed with an additional inner helix used to pumping in the opposite direction. This is needed for the mixing of high viscosity materials. These impellers can also have two outer helixes. The quality of the final mixed product in these applications can be very important economically.
Wall scrapers can be mounted on the impeller blades to improve heat transfer and homogeneity in sticky products.