Design and Operating Principles of Rotor-Stator Mixers

14. Commissioning and Diagnostic Measurements for Rotor-Stator Equipment

Commissioning and diagnostic measurements verify that hydraulic, mechanical, and operating conditions meet the specified process requirements for obtaining the desired product quality.

14.1 Measured Parameters and Energy Balances

For inline mixers, the essential measurements include shaft rotational speed, torque, volumetric flow rate, inlet and outlet pressures, and process fluid temperature. Batch installations additionally require measurements of batch mass or volume, liquid level, and bulk circulation. Investigations of periodic flow forcing or cavitation also require time-resolved pressure measurements and high frequency vibration data.

Measured torque ($M$) and rotational frequency ($N$) yield shaft power according to Equation (9.6). Pressure difference and flow rate determine useful hydraulic power, while the thermal balance estimates conversion of mechanical energy into heat. All measurements must be assigned to a defined control volume. Discrepancies can arise from external heat exchange, bearing or seal losses, energy accumulation, or inappropriate averaging of torque and flow.

14.2 Diagnostics of Cavitation Regimes

Verification of cavitation requires simultaneous measurement of absolute static pressure and fluid temperature. Dynamic pressure sensors must resolve the frequencies of interest. The sampling frequency must exceed twice the highest measured frequency, as required by the Nyquist sampling theorem; hardware anti-aliasing filters and adequate measurement bandwidth are essential. Pressure peaks should be interpreted as physical events only after documenting sensor resonance characteristics, the internal geometry of pressure lines, and the overall uncertainty of the measurement system.

14.3 Monitoring and Analysis of Product Properties

Performance evaluation must focus on the actual target properties for which the equipment was selected:

• Particle and droplet size distribution: A complete size distribution is more informative than a single average diameter. Breakup of agglomerates must be distinguished from the destruction of primary solid particles.

• Physicochemical properties: Changes in rheology, interfacial tension, temperature, and gas content must be recorded sufficiently to explain the hydrodynamic response and reproduce successful operating conditions.

14.4 Commissioning Test Protocol

The following commissioning sequence is recommended to reduce process and mechanical risks:

1. Initial functional check with process-compatible liquid: Verify shaft rotation direction, vibration level, mechanical seal integrity, and pressure sensor response before adding the principal process ingredients.

2. Establish operating range: Increase rotor speed in controlled steps while recording torque, throughput, pressure, and acoustic or vibration spectra.

3. Identify regime transitions: Determine changes in power number, pressure spectra, or cavitation onset before introducing costly or hazardous ingredients.

4. Test with actual product: Process representative batches and sample them according to defined specific energy input or pass count rather than operating time alone.

5. Define the process endpoint: Establish the lowest energy input that achieves product quality while respecting thermal and mechanical constraints.

6. Check after maintenance: Repeat diagnostic tests after wear or scheduled repair to detect changes in clearance geometry, head versus flow characteristics, and cavitation thresholds.

Table 14.1. Proposed commissioning protocols and acceptance criteria

Recorded parameter	Purpose	Acceptance criterion
Rotor and stator identification; measured gap	Establishes actual working element configuration.	Matches the approved assembly and manufacturer requirements.
Speed, torque, flow, and differential pressure	Separates kinematics, power, and hydraulics.	Stable and reproducible operating range.
Temperature history and cooling duty	Quantifies thermal exposure and energy balance.	Product-specific thermal exposure remains within allowable limits.
Absolute inlet pressure and gas conditions	Necessary for interpreting cavitation and gas entrainment.	Specified inlet and pressure control conditions are met.
Product distribution or final dissolution criterion	Directly tests the required transformation.	Product specification is met with reproducible sampling.
Wear, residues, and cleaning results	Assesses equipment limitations not directly reflected by product quality.	Acceptable mechanical integrity and validated application-specific cleaning.

Application specific acceptance limits should be defined before commissioning. The parameters listed are recommended measurements, not universal numerical limits, and do not replace manufacturer instructions. Tests should be repeated after changes to rotors, stators, seals, formulations, or cleaning procedures because even minor changes may alter hydrodynamic exposure and system hydraulics.