Helical ribbon impellers are designed especially axial and overall movement of the liquids. Such an impeller can be designed with an additional inner helix or auger used to pumping in the opposite direction. This is needed for the mixing of high viscosity materials. These impellers can also have one or two start helix. The quality of the final mixed product in these applications are very critical. Wall scrapers can be mounted on the impeller blades to improve heat transfer and homogeneity in sticky products.