Multi-Effect Evaporators. Evaporation thermally removes a liquid from a solution, suspension, or emulsion. In evaporator technology, each evaporator is referred to as an effect. When several connected evaporators or “effects” are use in one system, it is called a multi-effect evaporator. In these systems, the product output from one effect is the feed for the next effect. The high temperature vapor that is removed from one effect is used to heat the lower temperature product in the next effect, with considerable efficiency gains. There are two feed operations: backward and forward. In backward feeds, the raw feed enters the last (coldest) effect, and the discharge from this effect becomes a feed for the next to last effect. This feed is used when the feed is cold, as much less liquid must be heated to the higher temperature of the early effects. In backward feeds, the raw feed is introduced in the first effect, and passed from effect to effect parallel to steam flow. The product is withdrawn from the last effect. This feed is used when the feed is hot.