Falling Film Evaporator Film Thickness & HTC Calculator
Model industrial vertical tube falling film evaporators: tube periphery mass wetting rate (Γ), film Reynolds number, Nusselt liquid film thickness (δ), and Chun & Seban evaporation heat transfer coefficients.
1. Tube Bundle Geometry & Feed Loading
2. Thermal Driving Force & Fluid Properties
Falling Film & Evaporation Results
Vertical Tube Falling Film & Wetting Status
5 Fatal Engineering Traps in Falling Film Evaporator Design
1. Top Distribution Ferrule Plugging & Catastrophic Dry Patch Burnout
Falling film evaporators rely entirely on calibrated top distributor ferrules or perforated trays to split liquor evenly across hundreds of tubes. If debris, fibrous particles, or crystal scale clog even 10% of ferrules, the affected tubes starve below the minimum wetting rate (Γmin ≈ 0.08 kg/s·m). The liquid film tears, causing immediate dry patch burnout and scorched product coking.
2. Co-Current High Vapor Velocity Stripping & Entrainment
As vapor generates down the tube, linear vapor velocity accelerates, reaching over 40 m/s near the lower tube exit. Extreme interfacial shear stress strips the liquid film completely off the wall, transforming the falling liquid into an atomized mist that escapes into the overhead vapor duct, contaminating condensate.
3. Non-Condensable Gas Blanketing in the Steam Shell
Failure to continuously vent non-condensable gases (air, CO₂) from the heating steam shell causes stagnant gas pockets to accumulate around the tube bundle. Even 1% non-condensable gas in steam slashes the external condensation film coefficient by up to 60%, crippling thermal duty.
4. Overlooking Boiling Point Elevation (BPE) Stifling Effective Delta-T
In high-concentration food syrups, black liquor, or saline brine, BPE climbs to 10°C–18°C. If the evaporator is designed with a nominal steam-to-vapor delta of 15°C, an unrecognized BPE of 12°C collapses the true thermal driving force to a meager 3°C, reducing evaporation output by 80%.
5. Lower Discharge Recirculation Starvation & Viscosity Surges
As liquid concentrates near the bottom of long (10–12 m) tubes, product viscosity surges exponentially. High viscosity increases film thickness and dampens turbulent ripples, suppressing heat transfer precisely where thermal duty is most needed. Without a high-ratio bottom recirculation loop, the discharge plugs solid.
Governing Hydrodynamic & Chun-Seban Formulations
Periphery mass wetting rate (Γ) and film Reynolds number (ReΓ):
Γ = mfeed / [ Ntubes · π · Din ], ReΓ = 4 · Γ / μL
Nusselt falling liquid film thickness (δ):
δ = [ (3 · μL · Γ) / (ρL² · g) ]1/3
Chun & Seban boiling heat transfer coefficient (hevap):
Laminar Wavy (Re < 1600): hevap = 0.822 · [ (kL³ · ρL² · g) / μL² ]1/3 · ReΓ-0.22
Turbulent Wavy (Re ≥ 1600): hevap = 0.0038 · [ (kL³ · ρL² · g) / μL² ]1/3 · ReΓ0.4 · PrL0.65
Effective thermal driving force and solvent vaporization rate:
ΔTeff = Tsteam - Tboil - BPE, mevap = (U · A · ΔTeff) / λvap