Blog — Conveying · 6 min read
Dense phase vs
dilute phase conveying
Why one damages fragile product and the other doesn't, and where the crossover sits.
In short
Dilute phase conveying suspends powder in a fast air stream (15–30 m/s) at low pressure; dense phase pushes powder as slugs at low velocity (1–8 m/s) and higher pressure. Dilute is simpler and cheaper; dense protects friable product and abrasive-duty pipework. The choice turns on what velocity does to your powder — and what your powder does to the pipe.
The post
The physics in one paragraph
Every pneumatic system balances air velocity against particle behaviour. Above a powder's saltation velocity, particles stay suspended — that is dilute phase, and it needs speed. Below it, material gathers along the pipe and must be pushed as slugs by pressure — that is dense phase, and it needs air pressure rather than air volume. Same pipe, opposite regimes.
The post
What velocity does to product
At 25 m/s a milk powder agglomerate hitting a bend experiences an impact it was never engineered to survive. The result is attrition: fines, changed bulk density, worse solubility, downgraded product. At dense-phase velocities the same particle arrives intact.
The same mechanics govern wear in reverse: at dilute velocity an abrasive powder machines the outer radius of every bend. Dense phase multiplies bend life because wear scales steeply with velocity.
The post
Cost, honestly
Dilute phase wins on capital: a blower, rotary valve and filter receiver against dense phase's pressure vessel, valves and controls. Dense phase claws back on operating cost per tonne (higher pressure but far less air) and on everything downstream — bag weights that stay honest as bulk density holds, bends that stay on the wall, product that stays in spec.
The post
The crossover
A working rule of thumb:
- Robust, non-abrasive powder, cost-driven → dilute phase
- Friable, agglomerated or blended product → dense phase
- Abrasive material at any duty → dense phase
- Very long distances at high rate → dilute (or staged dense)
- In doubt → convey a trial batch; material tests beat rules of thumb
Common questions
Frequently asked questions.
- What is the difference between dense phase and dilute phase?
- Velocity and pressure. Dilute phase suspends powder in a high-volume air stream at 15–30 m/s and low pressure. Dense phase pushes powder as slugs at 1–8 m/s using higher pressure from a pressure pot. Dilute is the simpler system; dense is gentler on product and pipework.
- When should you use dense phase conveying?
- When the powder is friable (dairy powders, agglomerates, coffee), when a blend must not segregate, or when the material is abrasive enough to wear dilute-phase bends. Engineers specify it where product quality and pipeline life outweigh the simpler system.
Related
Related pages.
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