Presets
Playback
Air, grains and batch
Air velocity u above the minimum fluidization velocity u_mf lifts and mixes the bed; below it the bed is packed and dries slowly, far above (about 2.65 u_mf) fines are carried out. Changing the charge or the initial moisture restarts the batch.
Model checks
The science
What is modelled
A lumped bed with one temperature and one moisture inventory. Hot air transfers heat to the bed with a coefficient that grows with mixing; evaporation is limited by the drying kinetics, the heat available and the moisture capacity of the exhaust air. The fluidization state follows from the air velocity compared with the minimum fluidization velocity of the grains.
Equations
- Minimum fluidization (Wen and Yu):
Remf = √(33.7² + 0.0408 Ar) - 33.7,Ar = g d³ ρg(ρs - ρg) / μ². - Bed energy:
(m c)bed dT/dt = Qconv - ṁevap hfg - Qloss. - Water balance:
dW/dt = -ṁevap. - Fan power:
ΔP Q / η.
Checks run in the page
- Wen and Yu against an independent Ergun solution.
- Water mass balance over a whole batch.
- Saturation pressure against steam tables.
- Heater and latent power bookkeeping.
Honest simplifications
This is a lumped-parameter surrogate, not computational fluid dynamics or a discrete-particle model: the bubble animation is illustrative, the heat transfer and drying constants are empirical, and the carryover is a simple loss term. Not a process-design tool.
What to try
- Press Packed-bed overload: with too little air the bed never fluidizes and drying is slow.
- Press High airflow: watch the carryover regime and the lost fines.
- Press Gentle low-temperature and compare the batch time with Balanced production.