Falling film vs forced circulation vs rising film
Compare liquid behaviour, thermal exposure and maintenance on one basis.
Falling film, forced circulation or rising film?
| Design | Liquid path | Strong candidate when | Check first |
|---|---|---|---|
| Falling film | Distributed liquid descends along heated tubes | Thermal exposure matters and continuous wetting can be maintained | Outlet viscosity, particles, distribution at minimum load |
| Forced circulation | Pump recirculates liquid through a heater and flash separator | Concentrate becomes viscous, fouling or crystallization needs managed circulation | Pump energy, shear, hold-up, blockage and wear |
| Rising film | Vapour generation lifts liquid through tubes | Upward flow can be sustained by vapour generation and adequate temperature driving force | Start-up conditions, operating range and product thermal history |
Effect count and TVR/MVR are heat-recovery choices; they are not alternative liquid-flow geometries. Compare at identical feed, final concentration and utility boundaries.
Principle references: GEA natural-circulation / rising-flow principle; GEA heating options, multiple effects, TVR and MVR.
Screen the application, then the final concentrate
| Material | Measurements to bring |
|---|---|
| Clarified juice | Solids basis, aroma target, final viscosity and acceptable colour change |
| Milk / whey | Protein stability, mineral deposition, heat history and hygienic acceptance |
| Sugar / glucose | Solubility, crystallization margin and viscosity across concentration |
| Plant extracts / proteins | Suspended matter, foaming, shear and heat sensitivity |
| Beer / wort | Foaming, aroma/volatile losses and thermal quality targets |
| Soy sauce / vinegar | Salt, acidity, materials compatibility and volatile loss |
| Organic solvents | Separate specialist safety, sealing, materials and recovery assessment; not a standard food-system assumption |
Illustrative mass balance only: 1,000 kg/h at 12% solids to 60% gives 200 kg/h concentrate and 800 kg/h water removed. Temperatures and achievable concentration remain product-specific. Fibrous puree, high viscosity, crystallizing or strongly fouling feeds may need forced circulation or another finishing method.
Prevent dry patches before increasing heat
Inspect the distributor, filter large particles, preheat consistently and verify minimum wetting at turndown. A partly blocked distributor can create dry tubes even when total feed flow looks normal.
Trend feed rate, vacuum, temperatures, concentration and pressure drop against a clean baseline. Where heat duty and temperature difference are known, track U = Q / (A × ΔT). A fall in normalized U is a maintenance signal, not proof of a single cause.
For CIP, isolate production, drain safely and validate chemical compatibility, return flow, temperature, concentration and contact time for the actual soil. Verify rinse completion and hygienic acceptance before release. Cleaning interval and efficiency-decay curves require site measurements; no universal cycle is claimed.
Technical basis: GEA falling-film principle and Tetra Pak cleaning handbook.