Long tube climbing film evaporators are also excluded because of their fundamentally different design. Many of the first vessels in the installation studied here are of this type. It so happened that data for most of the remaining first effect vessels had to be exclude for one or other of the reasons mentioned above. The evaluation has thus been restricted to tail vessels only, that is from second to last effect. This has the further advantage that, with one exception, no vapour bleed is wihdrawa from the vessels considered and one potential source of error is thus avoided.