In a multi-effect evaporator, steam is used only in the first effect. The use of vapors as a heating medium in additional effects results in obtaining higher energy-use efficiency from the system. The partially concentrated product leaving the first effect is introduced as feed into the second effect. After additional concentration, product from the second effect becomes feed for the third effect. The product from the third effect leaves at the desired concentration. This particular arrangement is called a forward feed system. Other flow arrangements used in industrial practice include backward feed systems and parallel feed systems.