The performances of falling film evaporators used in the New Zealand
dairy industry for concentrating whole milk were evaluated by determining
kg steam
used/kg water evaporated, and the heat transfer coefficient of each
pass in the
evaporators. A specially written computer program was used to calculate
the results.
The heat transfer coefficients varied from 0·3 to
3·0 kW/m2K, 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
across
the tubes, the viscosity of the feed and the liquid loading were
found 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 performance are discussed. The correlation is compared
with that
obtained for skim milk.