About Static Inline Mixing

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What is inline mixing?

Mixquip Static Inline mixers can be applied to a wide range of process operations including blending, dosing, dispersion and emulsion formation, laminar flow heat exchange, mass transfer and as an inline plug-flow reactor. These processes can be broadly grouped into the following mixing classifications. The principles of operation of the motionless mixer vary according to each mixing classification. 

Principle of Operation

The main mechanism in laminar flow in static mixers is flow division. Mixquip Static elements are either helical or pseudo-helical and are arranged in a series of alternating left and right hand 180° twists. The leading edge of an element, which is on a diameter, is at 90° to the trailing edge of the upstream element.

In flow division, the leading edge of the first element splits the fluids entering the mixer into 2 streams, which are then rotated through 180°. The second element splits the flow again, this time into 4 streams, followed by a further rotation, in the opposite direction, through 180°. The third element repeats the process by splitting into 8 streams, and so on. As the number of streams or layers increases, the layer thickness decreases. Typically, 12 to 24 elements are required to provide a complete mix.

Mixture quality is a function only of mixer diameter and number of elements and, in laminar flow, is independent of flowrate and viscosity

At higher Reynold’s numbers, much greater than 2000, a second mixing mechanism, acting simultaneously with flow division, becomes important to the overall mixing process:

In general terms, the fluid viscosity in turbulent flow is lower than in laminar flow. The element shape is now able to impart a rotational spin to the fluids, which changes direction with each succeeding element. Fluids are constantly moved from the pipe centre to the pipe wall and back again, with the interface between elements a particularly active zone. This mechanism is called radial mixing, which dominates the flow division mechanism in turbulent flow. It very rapidly eliminates radial differences in, for example, composition, colour, pH, temperature and velocity.

The number of mixing elements required to achieve a fully homogeneous mix in turbulent flow applications is much less than in laminar flow and is typically 1.5 to 4 elements.

The radial mixing mechanism is important in reducing radial differences in velocity and therefore shear rate. The even shear history results in a predictable average droplet size where approximately 80% of the dispersed phase is within ±20% of the average droplet size. An open pipe, without controlled mixing, provides a huge range of droplet sizes with far less surface area of contact between phases.

The average droplet size is velocity dependent, with the terminal droplet size approached after 4 elements.

As with Liquid/Liquid immiscible systems, Gas/Liquid systems operate with a similar principle. The gas is dispersed throughout the liquid continuous phase to produce a uniform terminal bubble size, which helps to increase the rate of mass transfer between the phases.

The even shear history results in a predictable average bubble size where approximately 80% of the dispersed gas phase bubbles are within +- 20% of the average bubble size. Once again, the terminal bubble size is approached after 4 elements.

In engineering terms, gases are low viscosity fluids. The Mixquip Static Mixer behaves in the same manner as in the Liquid / Liquid turbulent flow classification.

Both flow division and radial mixing mechanisms are fundamental to the mixing of free flowing particulates. However, this classification is complex due to the large number of parameters affecting flow and mixture quality and is an area requiring further study.

Advantage of Static Inline Mixing:

Highly efficient mixing results in low energy consumption – low pressure drip on pipes or low headloss in channels. Mixquip Static Inline mixers are invariably installed in existing systems without reducing the capacity of existing pumps and, in most cases, can be installed on gravity flow systems. The Static Inline mixers reduce power consumption by up to 90% compared with dynamic mixers in stirred tanks. 

Mixquip Static Inline mixers have been carefully designed, for both pipes and channels, to provide a highly efficient mixing process. Our static inline mixers feature the highest degree of mix in the shortest time and with the lowest energy consumption. 

Inline static mixers have no moving parts and are virtually maintenance free. 

Efficient mixing and high mixture quality reduces the consumption of dosed chemicals by eliminating the need to overdose to compensate for poor mixing. 

The energy required for mixing is efficiently extracted as pressure drop from the fluid flows through the elements. No electric motors and associated equipment are required. 

All Mixquip Static Inline mixers for pipe systems are totally enclosed and without the need for shaft seals which are necessary on stirred tanks. This eliminates the risk of contamination both from and into the system. This feature is especially important when mixing dangerous and corrosive fluids and in the food and pharmaceutical industries where any amount of contamination cannot be tolerated. 

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