The indication is that total evaporation is 6% higher if last effect is twice the area of intermediate effects than the conventional situation of the same heating surface for all tail fabrication costs of a different sized vessel must be offset against this advantage. The potential to improve heating surface distribution in the case of expansion of an existing set has however been recognized (van Hegel). The final two vessels can be parallel on vapor to form a double-sized last effect and a new vessel installed (or vessels rearranged) earlier in the tail. Modifications along these lines have in fact been carried out to five of the eight evaporator trains in the huletts mills over the last 10 years. In all cases juice feed is in series between the two paired vessels. This provides a further advantage in that brix in the first vessel of the pair is well below final (syrup) brix level and thus HTC is higher. However another factor tends to negate this advantage, namely absence of flash in the second vessel of the pair. Table 3 gives HTC values for such two vessel last effects. It must be noted that most of these figures were calculated using short-cut manual methods and are thus not directly comparable with the rigorous PEST values discussed earlier.