alipainehaihdutin

An alipainehaihdutin, commonly known as a vacuum evaporator, is a device used to concentrate liquids by evaporating them under reduced pressure. By lowering the ambient pressure inside the evaporator, the boiling point of the liquid decreases, allowing operation at temperatures lower than those at atmospheric pressure. The term stems from Finnish alipaine (low pressure) and haihdutin (evaporator), and is used in Finnish technical literature to denote vacuum evaporators.

Principle and design: It consists of a feed chamber, a heating source, a vacuum system, and a condenser. The liquid is heated to its boiling point at the operating pressure, vaporizes, and the vapor is condensed and collected separately or used to preheat incoming feed in multi-effect arrangements. The design may include falling-film, rising-film, or scraped-surface configurations, depending on the liquid’s properties and the required heat transfer.

Applications: Vacuum evaporators are widely used in the food industry for concentrating fruit juices, milk, whey, and sugar solutions; in the chemical and pharmaceutical industries for heat-sensitive compounds; and in wastewater treatment to recover solvents and reduce volume. They are often part of energy-saving schemes when integrated with condensers and heat-recovery systems.

Advantages and limitations: Key advantages include operation at lower temperatures, which limits thermal degradation and preserves product quality, plus potential energy savings in multi-effect setups. Limitations include high capital and maintenance costs for vacuum equipment, the need for reliable seals and cleanability, and challenges with foaming, fouling, or corrosion. They are less suitable for highly viscous slurries without pretreatment.

Variants and related concepts: Common variants include falling-film, rising-film, and scraped-surface vacuum evaporators, as well as single-effect and multi-effect configurations. Related terms include vacuum evaporator and multi-effect evaporator.