This invention relates to a mixing element for mixing two or more fluids and a motionless mixer using the same.
Motionless mixers (trademark: Static Mixers) have no mechanical moving parts and are so designed that fluids are mixed as they are passed through passages in a tube having a helical blade therein. The motionless mixers of this type are used in various fields, such as chemical plants, food industry, environmental pollution prevention technology, etc. In a prior art motionless mixer, as shown in FIGS. 1 to 3, a plurality of helical blades 1 and 2 formed by twisting sheets left- or right-handed respectively at an angle of 180 degrees are arranged in a passage tube 3. The blades 1 and 2 are coupled and fixed so that the facing end edges of each two adjacent blades cross at right angles. Two fluids flow individually through regions in the passage tube 3 partitioned by the blades 1 or 2, and are divided and joined at the junction of the blades. Then, the fluids flow helically, and are divided and joined at the next junction. After such division, joining, and transfer are repeated, the two fluids are mixed thoroughly.
Conventionally, the helical blades 1 and 2 are manufactured by casting, and each two helical blades 1 and 2 are fixedly coupled by welding or brazing so that their facing end edges cross at right angles. Helical blades fixedly coupled are inserted into the hollow cylindrical passage tube 3. Thus, the manufacture of the motionless mixer is not easy, and the fluids may often stagnate at the junctions where the adhesive agent is swollen. Owing to working errors, moreover, narrow gaps are formed between the helical blades 1 or 2 and the passage tube 3. These gaps reduce the efficiency of fluid mixing. As shown in the sectional view of FIG. 4 taken along line IV--IV of FIG. 3, the surface of the blade 1 and the inner peripheral surface of the passage tube 3 cross at substantially right angles, so that acute-angled dead spaces 4 are formed at four corner portions of the inside regions of the passage tube 3 partitioned by the blade 1. The fluids may stagnate at the dead spaces 4. Moreover, the flatness of an end edge 1a of the blade 1 increases the flow resistance.
FIG. 5 shows a motionless mixer with helically twisted fluid passage tubes. As shown in FIG. 6, the fluid passage of each of passage tubes 5a and 5b has a semicircular cross section. The pair of passage tubes 5a and 5b are twisted helically, and are coupled so that their boundary between passage tubes 5a and 5b crosses the boundary between their adjacent pair of similar passage tubes 6a and 6b at right angles at the longitudinal end portions. Since it is difficult to manufacture a pair of helically twisted tubes, the manufacturing cost of this motionless mixer is high.