Chemical, Process & Catalysis Engineering
Geldart Powder Fluidization Group (C, A, B, D) Classifier Formula: Size & Density Map
Classify gas-solid fluidized bed powders into Derek Geldart’s (1973) four hydrodynamic regimes — Group C (Cohesive), Group A (Aeratable), Group B (Sand-Like Bubbling), and Group D (Spoutable) — from Sauter mean diameter d_sv (um) and density difference Delta_rho.
Predict whether a powder channels, expands smoothly, bubbles immediately, or spouts — from TWO numbers!
Derek Geldart (1973, Powder Technology) discovered that ambient-gas fluidization behavior maps cleanly onto Sauter Mean Particle Diameter d_sv (um) and Solid-Gas Density Difference Delta_rho = rho_p - rho_g (kg/m^3, or Delta_rho_g = Delta_rho / 1000 in g/cm^3): Group C ultrafine powders (such as talc or flour, where interparticle van der Waals cohesion exceeds drag: Delta_rho_g * d_sv < 25) lift as solid plugs and channel; Group A aeratable powders (such as FCC cracking catalyst: 25 <= Delta_rho_g * d_sv < 225) expand homogeneously above u_mf before bubbling at u_mb > u_mf!
Crossing Delta_rho_g * d_sv >= 225 enters Group B sand-like solids (where bubbles form immediately at incipient fluidization u_mb = u_mf), until coarse inertia crosses Geldart’s B/D boundary Delta_rho_g * (d_sv^2) >= 1,000,000 (equivalent to Delta_rho * d_p^2 >= 10^-3 kg/m in SI, such as roasting coffee beans or coarse gravel), entering Group D spoutable beds!
| Geldart Group | Algebraic Criterion (Delta_rho_g in g/cm^3, d_sv in um) | Fluidization Signature & Industrial Example |
|---|---|---|
| Group C (Cohesive) | Delta_rho_g * d_sv < 25 | Channels/rat-holes; needs mechanical vibration (Flour, Cement) |
| Group A (Aeratable) | 25 <= Delta_rho_g * d_sv < 225 | Bubble-free bed expansion u_mf < u < u_mb (FCC Catalyst, 65 um) |
| Group B (Sand-Like) | Delta_rho_g * d_sv >= 225 and Delta_rho_g * d_sv^2 < 10^6 | Bubbles form right at u_mf; vigorous mixing (Silica Sand, 300 um) |
| Group D (Spoutable) | Delta_rho_g * d_sv^2 >= 1,000,000 | Slow large bubbles; operated as spouted beds (Grain, 800+ um) |
Geldart Dimensionless C/A/B Boundary Product (Delta_rho / 1000) * d_sv
Evaluates (Delta_rho_kg_m3 / 1000) * d_sv_um across particle size B2 (um) and buoyant density difference B3 (kg/m^3).
=IF(OR(B2 <= 0, B3 <= 0), "Requires Particle Diameter d_sv > 0 and Delta_rho > 0", ROUND((B3 / 1000) * B2, 2))Geldart Gas-Solid Fluidization Regime Classifier (Groups C, A, B, D)
Classifies the solid into Group C, Group A, Group B, or Group D using Kunii-Levenspiel algebraic Geldart boundaries.
=IF(OR(B2 <= 0, B3 <= 0), "Requires Particle Diameter d_sv > 0 and Delta_rho > 0", IF((B3 / 1000) * B2 < 25, "Group C: Cohesive Powder (Channeling — Needs Agitation)", IF((B3 / 1000) * B2 < 225, "Group A: Aeratable Powder (Smooth Expansion Before Bubbling)", IF((B3 / 1000) * (B2 ^ 2) < 1000000, "Group B: Sand-Like Powder (Immediate Bubbling at u_mf)", "Group D: Coarse Spoutable Solid"))))Try the example
Use the original values or change them to test your understanding.