PERFORMANCES OF FALLING FILM EVAPORATORS ON WHOLE MILK AND A COMPARISON WITH PERFORMANCE ON SKIM MILK

The performances of falling film evaporators used in the New Zealand d airy industry for concentrating whole milk were evaluated by determini ng kg steam used/kg water evaporated, and the heat transfer coefficien t of each pass in the evaporators. A specially written computer progra m was used to calculate the results. The heat transfer coefficients va ried from 0.3 to 3.0 kW/m(2)K, and the steam consumption from 0.10 to 0.39 kg steam/kg evaporation, depending on the number of effects. The steam consumptions for whole and skim milk were similar. The momentum of the vapours passing down the tubes, the temperature difference acro ss the tubes, the viscosity of the feed and the liquid loading were fo und to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented, and other factors likely to have an influence on the per formance are discussed. The correlation is compared with that obtained for skim milk.