Static mixer (inline pipe mixer)

01

Pick the element type for your flow regime

NOV's Kenics brochure explains that in its KM mixer a helical element directs flow radially to the pipe wall and back to the centre, with alternating right- and left-hand elements adding flow division and velocity reversal so radial gradients in temperature, velocity and composition are removed. KM mixers are used for laminar, transitional and turbulent flow, liquid–liquid and gas–liquid dispersion, heat transfer and promoting plug flow in place of laminar flow's parabolic profile. [1]

For turbulent flow NOV describes its HEV mixer, whose tabs generate counter-rotating vortices, limiting mixer length to less than 1.5 pipe diameters with, by NOV's account, 75% lower pressure loss than conventional static mixers; and the UltraTab with an upstream injector, which it says produces a 0.05 coefficient of variation in as little as two pipe diameters downstream. For laminar mixing with extreme viscosity or volume ratios it describes the KMX-V, with intersecting blades and elements about one pipe diameter long. [1]

Editorial note: coefficient of variation (CoV) is the standard deviation of concentration divided by the mean across the pipe; ask suppliers to state the CoV their design achieves at your flow, viscosity ratio and additive ratio, and how it was determined.

Give the supplier the fluids and their viscosities, flow rates (minimum and maximum), additive ratio, required uniformity (CoV) and distance, allowable pressure drop, line size and connections, temperature, pressure and materials, and whether elements must be removable for cleaning.

02

Size the mixer for viscosity and pressure drop

NOV's Kenics KM quick-selection guide (Bulletin 825) lists models by flow range (0.5 to 40 gpm), line size (0.5 to 3 in) and viscosity (1, 10, 100 and 500 cP). For a 1 in line at 0.5–2 gpm, the model moves from 1-KMS-4 at 1 cP to 1-KMS-6 at 10 cP, 1-KMS-12 at 100 cP and 1-KMS-18 at 500 cP; combinations where pressure drop would exceed 10 psi are marked instead of a model, and these marks cluster at higher viscosity and flow in small lines. [2]

The brochure offers fixed (KMS), removable (KMR), element-assembly (KMA) and edge-sealed (KME) designs, in carbon and stainless steels, high alloys, titanium, zirconium and plastics such as PVC, PTFE and PVDF, with options including ASME B31.3 certification, design pressures above 10,000 psi, polished finishes down to 8 microinches and jackets. [1]

An independent 2025 review in ACS Omega (10(45):53746–53759, Luo and co-authors) compares element families for viscous duties. It reports that helical elements have a laminar friction factor about 5–6 times that of an empty tube, while intensive cross-blade (SMX-type) elements can reach pressure drops tens of times the empty pipe. Its comparison table gives about 0.3–0.5 bar per metre and 0.01–0.2 kW/t for helical mixers, against about 1–2 bar per metre and 0.5–1 kW/t for SMX or interfacial-surface-generator mixers, which it recommends where components have large viscosity or density contrasts. It cites a hybrid of crossover-disc and SMX elements reaching about 2–3% concentration variance in a polymer system, and jacketed SMX elements for temperature control in viscous polymer processes. [3]

Editorial calculation: on those per-metre figures, a 2 m mixer section adds about 0.6–1.0 bar with helical elements and 2–4 bar with SMX-type elements; ask the supplier to calculate pressure drop for your viscosity, flow and element count rather than relying on per-metre ranges. [3]

Editorial calculation: 10 psi is about 0.69 bar (69 kPa); use the guide as a first check and ask for a calculated pressure drop at your maximum flow and viscosity.

03

Check the cross-blade option for laminar, high-viscosity blending

Sulzer describes its SMX™ plus static mixer as "the reference for homogenization and dispersing tasks in laminar flow", including dosing a small amount of low-viscous additive into a high-viscous main stream, with mixing under minimal shear stress. It states "SMX plus with 50% lower pressure drop compared to a standard SMX mixer". SMX plus is offered from 15 mm to 200 mm diameter in stainless steel 1.4404, and the standard SMX from 3.2 mm to 200 mm in 316 stainless steel; standard housings follow DIN or ANSI code, with ASME or AD2000 design possible. [4]

The review by Luo and co-authors on this page gives pressure drop of about 0.3–0.5 bar/m for helical elements against about 1–2 bar/m for SMX-type elements [3]. Sulzer's 50% claim compares SMX plus with its own standard SMX [4], so on those review figures SMX plus would still be in a different range from a helical mixer. Ask each supplier for the calculated pressure drop at your flow, viscosity and pipe size, and for the number of elements and the mixing quality (CoV) that pressure drop buys.

Kenics recommends selecting by flow, line size and viscosity, and marks combinations where pressure drop exceeds 10 psi [2]. Sulzer's 3.2 mm minimum diameter for standard SMX [4] reaches smaller lines than the 0.5 in (12.7 mm) bottom of the Kenics guide [2]; for small-bore dosing lines, ask which element types are offered at that size.

Editorial calculation: halving 1–2 bar/m gives about 0.5–1 bar/m, which on the review's figures would still be above the 0.3–0.5 bar/m given for helical elements; the review's ranges and Sulzer's claim come from different sources and conditions. [3] [4]

Values are from Sulzer's SMX plus product page; Sulzer's brochures were not reviewed.

04

Who lists metal and plastic inline mixers

Listings include stainless, carbon-steel and plastic static mixers and replacement elements for liquid–liquid, gas–gas and oil blending.

05

Parts of a mixer section, from end connections to element mounting

06

Flow, viscosity and allowable pressure drop to send for sizing

Fill the viscosity and flow rows first: the Kenics guide picks the element model from them, and the pressure-drop row then shows whether that choice stays under the 10 psi mark the guide uses. [2]

07

Send the fluids, flow and uniformity target together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Fluids: [main; additive; viscosities; ratio]
Flow: [minimum; maximum; regime]
Target: [CoV; distance]
Line: [size; connections; pressure; temperature]
Limits: [allowable pressure drop; length]
Construction: [material; removable elements; certification]

See manufacturer records Send an enquiry through CNFX