Pilot-scale investigation of effectiveness of evaporation of skim milk compared to water

Abstract

As evaporation is an energy-intensive process, it is important that evaporators operate efficiently at their maximum capacity. The aim of this study was to compare the effectiveness of a pilot-scale, single-stage falling-film evaporator in the evaporation of water and skim milk. The solutions were fed at a boiling temperature of 60 °C, and a mass flow rate of 50.0 ± 0.7 kg·h−1. There was no significant variation (p < 0.05) in the evaporation rate or in the energy efficiency for the experiments with skim milk at two different initial concentrations, but these values were higher than those obtained with the experiments with water. The heat transfer coefficient did not differ according to the product, and this result does not explain why the evaporation of skim milk was more effective than that of water. Flow behavior was modified according to the product: a thicker and slower film was obtained at the end of the skim milk concentration process compared to water. Increasing the concentration of a product would lead to an increase in residence time, which would modify the evaporation rate. The behavior of a product during the evaporation process cannot be predicted by the overall heat transfer coefficient alone, and a wide range of information is required to understand the evaporation process, such as residence time distribution, product viscosity, and surface tension.