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## Ratio of solids transported vs air transport

Section summary
1. Definition of the solids load ratio in pneumatic conveying systems
3. Usual values for dilute and dense phase conveying solid to air ratio

## 1. Definition of the solids load ratio in pneumatic conveying systems

The solids load ratio is defined as the ratio of the mass of solids transported over the mass of air - or other gas - transporting the solids. Along with the air conveying velocity, the solids load ratio is very important parameter to characterize the flow of the solids in the conveying pipe and classify it as dilute phase, dense phase or intermediary.

The solids loading ratio is calculated by divided the mass flowrate of solids by the mass flowrate of conveying air.

With :

- mair = mass flowrate of transport air (kg/h)
- mmaterial = mass flowrate of conveyed material (kg/h)

Note the following : the litterature is giving various formula for the solids load ratio to cope with different units. The equation above is the most simplest way to calculate the ratio, although you may have to make intermediary calculations to be able to determine the air mass rate. It is important to have both air mass flowrate and material mass flow rate in the same units.

## 3. Usual values for dilute and dense phase conveying solid to air ratio

Every conveying line is unique and will have its specific product air ratio, however, some orders of magnitudes can be given for both dilute and dense phase. Some of the ranges given overlap as at a same loading ratio in the intermediary zone some materials will behave in denser phase than others.

Table 1 : Reference solids load ratio for dilute and dense phase conveying

Type of conveying Material / air ratio
Dilute phase
5-15
Intermediary 10-30
Dense phase
> 30

Generally speaking, the higher the solid-air ratio is, the higher the pressure drop in the conveying pipe will be.