The so-called static mixer refers to a device that does not have a rotating element inside, but uses fixed elements fixed in the tube to make the fluid reach the mixing device.
Some people abroad have defined static mixers as "fluid pipeline structures that can mix fluids over a wide range without the use of mechanical rotation" by virtue of the different structures of the fluid pipeline.
When the fluid flows through the static mixer, it is constrained by the mixing element to generate divergence, confluence and rotation, so that the fluid can be fully mixed.
For different flow states such as laminar and turbulent flow, the mechanism of the static mixer is different. In laminar flow, the static mixer and the device repeatedly perform the "splitting-displacement-rejoining" regular function of the fluid to achieve mixing. In turbulent flow, in addition to the above effects, the fluid is generated on the flow section. The violent vortex causes the fine parts of the fluid to be further divided to achieve mixing.
Take a unit of the Kenics static mixer as an example, it is divided into two parts, left-handed and right-handed, each part of the spiral plate rotates 180 ° around the axis, and the adjacent two parts of the plate cross 90 °. The length of each unit is about the tube 1.5 times the diameter. The Kenics static mixer consists of several such mixing units. The fluid is divided into two strands from the entrance, and each strand flows along a circular channel. After rotating through 180 °, it is divided into two strands, rotating in opposite directions, and then flowing out of the first unit. Obviously, after passing through the unit, the fluid is divided and rotated 2n times, and finally it is fully mixed.
In terms of heat transfer between fluids, heat transfer is enhanced because the internals of the static mixer can cause turbulence. Compared with the empty tube, the enhanced heat transfer effect of SMK type is about 4 times; the heat transfer effect of SMX type, SMH type and SMV-2.3 type is about 8-10 times that of empty tube.
In terms of mass transfer between fluids, it is due to the effect of "splitting-displacement-reconvergence", which makes the fluids fully mixed, the interface is constantly updated, and fresh liquid is continuously brought from the inside to the surface. Liquid effective contact area Before they return to their original positions, fresh liquids contact gas for mass transfer, which accelerates mass transfer.
If the movement of the fluid is laminar, the mass transfer between adjacent fluids is purely due to molecular diffusion. When the fluid in which mass transfer occurs is in a turbulent state, the mass transfer will be carried out in a turbulent diffusion mode. At this time, the rate is relatively fast. . For most gases, it is over 100 times higher than the molecular diffusion coefficient. For liquids, it is 100,000 times or more higher than the molecular diffusion coefficient.
It can be seen from Figure 1 that compared with the empty tube, the static mixer can provide a larger interphase interface area under the same energy input conditions.