Solids loading ratio is a useful way to describe how much bulk material is transported relative to the mass of conveying air. It helps engineers compare test runs, evaluate how heavily a pipeline is loaded and connect the required air supply with the target solids throughput. It is not, however, a complete pneumatic conveying design method or a universal definition of dilute and dense phase.
The Mass-Based Definition
When the solids and air mass flow rates are expressed in the same units, the relationship is:
Here, is the dimensionless solids loading ratio,
is the solids mass flow rate and
is the conveying-air mass flow rate. If solids flow is stated in tonnes per hour and air flow in kilograms per second, the units must be converted before the ratio is calculated.
Mass flow is used because gas volume changes as pressure and temperature change. In a leak-free line, air mass flow can remain nearly constant while actual volumetric flow and velocity increase toward the receiver as pressure falls.
What the Ratio Can Tell a Buyer
The ratio provides a compact comparison between material rate and conveying-air demand. It can help identify whether a proposed duty is lightly or heavily loaded, compare alternative test points and reveal how a change in feeder output affects the air-to-solids balance.
It is especially useful when accompanied by:
- Material flow rate and bulk properties.
- Air mass flow or a volumetric flow with clearly stated reference conditions.
- Conveying-line inlet pressure and temperature.
- Pipe bore, route and elevation.
- Measured or predicted total pressure loss.
- Observed flow regime and pressure stability.
Two systems can have the same loading ratio and very different behavior. One may carry particles in high-velocity suspension, while another moves a permeable product in low-velocity plugs. The ratio does not state particle velocity, local concentration, bed depth, plug length or blockage margin.
Why There Is No Universal Phase Boundary
Dilute-phase and dense-phase capability depends on particle size, density, distribution, permeability, air retention, moisture, wall friction and the available pressure gradient. A numerical threshold that works for one powder may be unsafe for another grade of the same product.
Reducing airflow increases the calculated loading ratio only if the material continues to move at the required rate. If velocity falls below the stable range, particles can deposit, feeder pressure can rise and throughput can decline. A high calculated ratio is therefore not automatically a high-performance result.
Leakage and Additional Air Matter
The air delivered by a roots blower is not always the same as the air entering the conveying pipe. A rotary airlock can leak air back toward the supply hopper. Auxiliary fluidizing air, purge air or downstream injection can increase gas mass flow after the main feed point. Pipeline leaks can also change the balance.
For this reason, the ratio should be defined at a stated system boundary. The calculation must identify whether the air value represents blower inlet flow, total package flow or effective conveying-line flow after known losses and additions.
Using the Ratio in a Pasifik Blower Enquiry
A useful enquiry states the required solids throughput, material properties, expected ratio or test data, effective conveying airflow, total pressure requirement and operating cases. Pasifik Blower can then check whether a two-lobe or three-lobe positive-pressure roots blower can meet the duty within the selected model’s flow, speed, motor-power and discharge-temperature limits.
The published portfolio limit of up to 1,000 mbar is a product boundary, not proof that a requested loading ratio is achievable. Final selection requires a material-specific conveying calculation or representative test data for the complete feeder, pipeline and receiver system.
Glossary
Air mass flow rate: Mass of conveying air passing a defined system boundary per unit time.
Effective conveying airflow: Air that actually enters and travels through the conveying line after identified leakage and auxiliary flows are considered.
Loading ratio boundary: Defined point in the system at which solids and gas mass flows are compared.
Mass flow rate: Quantity of mass passing a location per unit time.
Phase density: Alternative industry term sometimes used for the solids-to-gas mass flow ratio.
System boundary: Stated physical limits across which flow quantities are measured or calculated.