CFD assessment of mixing uniformity in a 100 NB static mixer

01 / THE CHALLENGE

Assess mixing at the point that matters

Graphler Technology Solutions evaluated how a sodium hypochlorite solution mixed with water through a static mixer and its downstream pipe. The simulation predicted a more uniform distribution at the outlet, showing why the assessment location matters.

A dosing system can deliver the specified flow rate while distributing the added solution unevenly across the pipe. For this project, the engineering question was how the mixture developed through the static mixer and farther downstream.

We examined several sections along the flow path to distinguish the distribution just beyond the mixing elements from the distribution reached at the model outlet. This gave the assessment a clear spatial context.

02 / OUR APPROACH

Follow the complete flow path

The model represented a 100 NB static mixer within a 3.4 m pipe arrangement. The operating case combined a water stream with a smaller dosing stream of sodium hypochlorite solution.

GTS reviewed velocity and solution volume fraction along the model and across selected sampling planes. These included a section upstream of the mixer, sections downstream, and the outlet.

A numerical measure alongside the contours

The assessment used the coefficient of variation (CoV) to describe the relative variation in solution volume fraction across a sampled section. A lower value indicates a more uniform distribution.

A concentration average alone cannot show whether the solution is concentrated in one part of the pipe. Reviewing CoV alongside the contour plots reveals both the amount of variation and its spatial pattern.

03 / THE FINDINGS

Uniformity continued to develop downstream

At 100 mm beyond the mixer, the concentration contour showed variation across the pipe. At the model outlet, the distribution was substantially more uniform. The reported CoV values reflected that difference.

100 mm beyond the mixerPLANE 04

At the model outletOUTLET

FIGURES 02–03Original solution volume-fraction contours. Both use the same colour scale, from 0 to 0.00150. *Mixing classifications are those used in the project report.

04 / ENGINEERING VALUE

Include the downstream pipe in the assessment

The study established how concentration uniformity developed along the evaluated flow path. Checking only the section immediately after the mixer would have missed the more uniform distribution predicted farther downstream.

For engineering teams, this provides a basis for assessing mixing at the process location that matters. A sampling connection, branch, or downstream component may sit before the model outlet. Its location should therefore be included explicitly when defining the CFD assessment.

The result supports the geometry and operating case evaluated. Changes to the flow rates, dosing arrangement, or available pipe length would require further assessment.