Operating Window

u_mf — m/s

u_op — m/s

u_t — m/s

Fixed bed Bubbling Turbulent Transport

— Geldart: —

Operating velocity exceeds terminal velocity — particles will be entrained!

Aspect ratio L/D > 2 and u > u_ms — slugging may occur. Consider a wider, shallower bed.

Geldart C particles are cohesive and difficult to fluidize. Consider vibration or mechanical agitation.

Geldart D particles — consider spouted bed design instead of conventional fluidized bed.

Velocities

u_mf (selected)—

u_op = N_f * u_mf—

u_t (Haider-Lev.)—

u_t (iterative drag)—

u_mb (Abr. & Geldart)—

u_ms (slugging onset)—

Regime—

Dimensionless Numbers

Archimedes Ar—

Re_mf—

Re_op (at u_op)—

Re_t (at u_t)—

Fluidization # u/u_mf—

Richardson-Zaki n—

Bed Behaviour

Bed expansion L/L_mf—

Expanded bed height—

Expanded voidage eps—

Bed dP (fluidized)—

TDH (freeboard min.)—

Min. vessel height—

Aspect ratio L/D—

Moist Air Properties

Relative humidity—

Humidity ratio x—

Dew point T_dp—

Sat. pressure p_sat—

Dry air density—

Moist air density—

Density correction—

Gas Flow & Fan Sizing

Gas density rho_g (moist)—

Gas viscosity mu_g—

Bed cross-section A—

Volume flow (actual)—

Volume flow (Nm3/h)—

Mass flow (dry air)—

Drying Duty — Mass & Energy Balance

Dry solids throughput—

Evaporation rate—

Product output rate—

Inlet humidity ratio x_in—

Outlet humidity ratio x_out—

Outlet relative humidity—

Required dry air flow—

Specific air consumption (SAC)—

Specific energy consumption (SEC)—

Heater duty (ambient → inlet)—

Heat rate for drying—

Thermal efficiency—

Initial moisture must be greater than final moisture for drying.

Outlet air is near or above saturation — reduce feed rate or increase inlet temperature.

SEC is high (> 6000 kJ/kg). Consider heat recovery or higher inlet temperature.

Adiabatic dryer assumption (h_in ≈ h_out). Heat losses typically add 5–15%. Ref: Mujumdar, "Handbook of Industrial Drying", 4th ed., Ch. 3.

u_mf Correlation Comparison

Correlation	Constants	Notes	u_mf [m/s]
Ergun (1952)	Full equation	Needs eps_mf, phi	—
Wen & Yu (1966)	C1=33.7, C2=0.0408	Most widely used	—
Grace (1982)	C1=27.2, C2=0.0408	Geldart B/D	—
Chitester (1984)	C1=28.7, C2=0.0494	High pressure	—

Spread between correlations indicates uncertainty. For final design, validate with experiments or CFD.

References: Ergun (1952) Chem. Eng. Prog. 48(2):89; Wen & Yu (1966) CEP Symp. Ser. 62:100; Grace (1982) Can. J. Chem. Eng. 60:353; Chitester et al. (1984) CES 39:253; Haider & Levenspiel (1989) Powder Tech. 58:63; Richardson & Zaki (1954) Trans. IChemE 32:35; Darton et al. (1977) Trans. IChemE 55:274; Horio et al. (1980) AIChE Symp. Ser. 76(196):136; Kunii & Levenspiel, "Fluidization Engineering", 2nd ed. (1991); Mujumdar, "Handbook of Industrial Drying", 4th ed. (2014), Ch. 3, 8; Buck (1981) J. Appl. Meteorol. 20:1527 (saturation pressure); Hyland & Wexler (1983) ASHRAE Trans. 89(2A):520 (enhancement factor); Alduchov & Eskridge (1996) J. Appl. Meteorol. 35:601 (dew point inversion); Keey, R.B. (1992) "Drying of Loose and Particulate Materials", Ch. 2 (mass/energy balance); Perry's Chemical Engineers' Handbook, 9th ed., Ch. 12 "Psychrometry" (enthalpy, SEC).

Fluidized Bed Dryer — Quick Sizing Calculator

Inputs

Drying Duty