INTENSIFICATION OF SECONDARY VAPOR CONDENSATION IN GRAPE JUICE CONCENTRATION UNITS THROUGH OPTIMIZATION OF PHASE HYDRODYNAMICS

Abstract

Subject. The mixing-type condensation of secondary vapor during vacuum concentration of grape juice in a barometric condenser, in which the cooling water is dispersed through atomizing nozzles of various geometries.

Purpose. To intensify heat and mass transfer and improve the energy efficiency of vacuum-evaporation units by optimizing phase hydrodynamics in a mixing-type barometric condenser through nozzle atomization of the cooling water.

Methodology. Experiments were carried out on a vacuum-evaporation unit concentrating grape juice (‘Black Kishmish’ variety, 16–18% Brix). The hydrodynamic interaction between secondary vapor and finely dispersed cooling-water droplets, produced by centrifugal-jet nozzles, was studied at condenser pressures of 15–30 kPa. Droplet size distribution and motion were recorded by high-speed photography and laser Doppler anemometry; data were processed by one-way ANOVA (p < 0.05).

Results. Replacing the traditional tray (cascade) elements of the barometric condenser with a fine-droplet nozzle-spray system fundamentally reshapes the phase hydrodynamics. At a mean droplet diameter of 1.2–1.8 mm, the specific phase-contact area reaches 162 m²/m³, shifting condensation into a highly turbulent regime. The volumetric heat-transfer coefficient increased by 52.4%. Vacuum depth stabilized at 92–94%, lowering the juice boiling temperature and preserving thermolabile components. Specific cooling-water consumption fell by 25.6%, and vacuum-pump energy consumption fell by 21.0%.

Practical value. The developed hydrodynamic scheme and operating parameters are recommended for retrofitting existing barometric condensers at food- and wine-industry plants.