1980 Volume 13 Issue 4 Pages 318-323
A great improvement in mixing performance by the additional up-and-down motion of rotating impellers was confirmed from measurements of mixing time tM and power requirement P in a 5 l vessel. Of five impellers tested, the best mixing time was obtained with a cross-paddle consisting of two pairs of inner and outer blades pitched at opposite angles to each other. In a typical case, the mixing time was reduced to 1/3 of that for the conventional helical ribbon while the power remained unchanged, i.e. the energy for mixing completion was reduced to less than 10%. The double-stage arrangement of two impellers with spacing equal to stroke distance is preferable to the single stage, providing much improvement in mixing time in spite of the doubling of power required. The results are compared with those for conventional agitators in terms of the characteristic parameters of ntM, tM√Pv/μand√Pv/μn2. The mechanics of simultaneous rotary and vertical motion of the impeller by a single-drive motor is also mentioned.
