Helical static mixer

A helical static mixer is a static mixer with twisted elements inside a pipe. In the classic design each element is twisted through half a turn. The direction of twist alternates from one element to the next. Each element is also turned at a right angle to the previous one. As the flow passes, it is divided, rotated and reversed at every element. There are no moving parts, and the mixing energy comes from the pressure drop of the flow. STRIKO Helical is the universal mixer in the STRIKO range. Dutch Valve Vision supplies it as exclusive STRIKO agent for the Benelux.

The alternation is what turns a flow divider into a mixer. Each element rotates the flow around the pipe axis in one direction. At the transition to the next element, the rotation is reversed abruptly. That reversal adds shear and prevents the flow from settling into a stable pattern. Because each element is also set at a right angle to the previous one, it cuts across the layers already formed. The number of layers doubles with every element in laminar flow. After ten elements there are more than a thousand layers. That repeated folding is what produces a homogeneous mixture.

The number depends on the mixing task and the flow regime. In laminar flow, more elements mean finer division and a more homogeneous result. Large viscosity differences or small dosing ratios require more elements. In turbulent flow, vortices help, so fewer elements may be sufficient for the same task. More elements also mean more pressure drop. The design therefore balances mixing quality against the available pressure. We determine the number of elements on the basis of your process data. Please include the required mixing quality at the outlet in your request.

A helical design works in laminar flow, which is typical for viscous products. Each element divides the flow further, so a thick product can be blended with enough elements. For very high viscosities or extreme viscosity ratios, a dedicated geometry may reach the result in a shorter length. STRIKO offers the STX series specifically for viscous liquids, ideal for thick and syrupy media. STRIKO specialises in mixers for (highly) viscous media. We compare Helical and STX for your specific product. The decision depends on viscosities, flow rates and the available pressure drop. Send us the data and we will advise which series fits.

The helical geometry has a relatively open flow path, with each element dividing the pipe into two channels. That tends to keep pressure drop moderate compared with more intricate geometries. The actual value depends on flow rate, viscosity, diameter and the number of elements. In laminar flow, pressure drop rises roughly in proportion to velocity. Under turbulent conditions the increase is steeper, roughly with velocity squared. A more intricate geometry may mix a difficult blend in a shorter length at a higher pressure drop. The right balance depends on the task. We calculate the expected pressure drop as part of our advice.

Helical is the universal starting point for general blending and dosing. STX is the better choice for thick and syrupy liquids, where STRIKO’s viscous media specialism counts most. STV is optimised for gases, which behave very differently from liquids. EREstat is designed for food processing and hygienic processes. When a medium clearly belongs to one of those categories, the dedicated series is usually the better fit. When it sits between categories, the process data decide. We often start with Helical and check whether the medium pushes the selection elsewhere. You receive a clear recommendation with the reasoning behind it.

A helical static mixer has no moving parts, so wear is virtually ruled out. Regular mechanical maintenance is therefore unnecessary. For cleaning or inspection, a STRIKO unit can be taken apart without difficulty. They also support inline sterilisation and steam cleaning. The relatively open geometry makes visual inspection of the elements straightforward. Some products leave deposits over time, so an inspection interval matched to the medium is sensible. A rising pressure drop across the mixer can indicate that inspection is due. We advise on a practical interval for your process.

We need the viscosity of each component and the volume flows at minimum and maximum load. Temperature and operating pressure come next. The required mixing quality at the outlet determines the number of elements. Chemical compatibility decides the material. The available pressure drop and the pipe size define the hydraulic and mechanical limits. With these data we confirm whether Helical is right or whether another STRIKO series fits better. We then configure diameter, length and elements. Mail your request to sales@dutchvalvevision.com and you will hear from us shortly.