Flow instability in bulk solids handling can quickly undermine even the most carefully designed material handling system. When a material flows smoothly one moment and stalls the next, the consequences ripple through storage, discharge, and processing operations. Production slows, feed rates fluctuate, and equipment can experience unnecessary stress. These issues may appear unpredictable, but they are typically the result of how a material responds to its handling environment. Understanding the material’s behavior during handling is essential for achieving stable flow.
Jenike & Johanson offers bulk material testing services to determine the physical causes of flow instability. The resulting data from such tests pinpoints the flow behavior responsible, offering a clear basis for diagnosing unstable flow, guiding corrective action, and restoring reliable performance.
What Drives Flow Instability in Bulk Solids
Bulk solids are highly sensitive to seemingly minor changes in their physical properties. Key flow attributes such as cohesion, wall friction, compressibility, aeration behavior, and segregation tendency can shift as moisture, temperature, or storage duration vary. Even small differences in particle size or humidity can alter how the material shears or moves against equipment surfaces. As these characteristics evolve, the material’s flow behavior changes as well, often leading to instability.
Flow instability cannot be diagnosed reliably through observation. Two batches of the same material may look identical yet behave very differently in a silo or hopper. Determining why flow becomes unstable necessitates the direct measurement of the material’s critical properties, allowing engineers to compare its actual behavior with the conditions the equipment was designed to accommodate.
Why Material Testing Is Vital for Understanding Instability
Troubleshooting flow instability without material testing often leads to slow and costly trial-and-error. Equipment adjustments may offer temporary relief, but they rarely address the underlying cause. Material testing provides quantitative flow data that can diagnose an issue accurately. It can:
- Identify the specific behavior driving the instability by measuring key flow properties
- Reveal whether a material’s behavior aligns with equipment design limits, such as required outlet size or wall friction conditions
- Prevent repeated adjustments by replacing speculation with measured performance
- Guide targeted corrective actions that directly address the root cause.
Together, the insights gathered from material testing offer a clear path to resolving flow instability.
Identifying the Root Causes of Flow Instability Through Jenike & Johanson’s Material Testing Services
1. Assessing Cohesive Strength as a Cause of Blockages or Erratic Flow
Unexpected increases in cohesive strength are a common cause of blockages and erratic flow. If a material arches, ratholes, or stops discharging intermittently, excessive interparticle attraction is typically responsible. Shear cell testing quantifies the stress at which the material begins and continues to move, showing whether the outlet can overcome the material’s cohesive strength. When it cannot, the data will demonstrate that the cohesive strength of the material surpasses the outlet’s available stress, identifying it as the source of flow instability.
2. Evaluating Wall Friction and Its Impact on Discharge Stability
Wall friction strongly influences how a material moves against equipment surfaces. Surface changes such as wear, corrosion, roughness, or build-up increase friction, which can interrupt slip behavior and hinder the development of mass flow. Engineers can use wall friction testing to measure the stress that initiates sliding on specific surfaces and identify whether elevated friction is contributing to flow instability and resulting in erratic or inconsistent discharge.
3. Diagnosing Flow Instability Linked to Density and Compressibility
Some materials compact during storage or become highly aerated during handling, causing their bulk density to shift rapidly. These changes can trigger flow instability, often seen as surging, feeder pulsing, or uncontrolled flooding at the outlet. Compressibility and aeration tests capture how density evolves under vibration, consolidation, or airflow (fluidization), ensuring engineers can confirm if density fluctuations are the mechanism driving the unstable flow.
4. Investigating Segregation as a Driver of Variable Discharge
Segregation occurs as particles separate according to size, density, or shape, forming zones of varying compositions within a vessel. Such shifts in composition can alter how the material moves during filling or discharge, generating flow instability, variable feed rates, or product inconsistency. Segregation testing characterizes how a material stratifies under handling conditions and indicates if composition differences are causing the variability in discharge. By showing how segregation affects discharge performance, this type of testing highlights when targeted interventions are needed to restore stable flow.
5. Identifying Environmental or Time-Dependent Changes Behind Intermittent Instability
Some flow issues develop only after the material has been stored, exposed to humidity, or subjected to temperature swings. Over time, changes such as moisture uptake, strength gain, or caking can emerge and influence how the material responds during discharge. Time-dependent storage time at rest and environmental testing tracks how these behaviors evolve and identifies if their progression coincides with the onset of flow instability. Because such shifts often mirror weather patterns or extended storage, the testing also clarifies why instability may appear only intermittently or at certain times of the year.
From Instability to Insight: The Value of Material Testing
Flow instability is never random. It stems from a material’s physical properties and how they evolve during handling. When those properties shift, equipment that once performed reliably can behave very differently. Material testing offers clarity should changes occur, showing not only what has been altered but why it matters for flow. Jenike & Johanson offers detailed bulk material testing services that can identify the behavior responsible for flow instability and support engineers in defining measures that restore stable, predictable performance. Contact our specialists today for additional information on our bulk material testing services.
