Evaporative Cooling

What is evaporative cooling? Evaporative cooling is accomplished by pulling a vacuum on moisture-enriched products within a vessel. An increase in vacuum results in a lowering of the boiling point of the moisture, causing rapid evaporation. During evaporation, the latent heat is given up – thereby reducing the temperature of the product. Processing food products under a vacuum is common, such as freeze drying and milk and juice evaporation and concentration.

Why evaporative cooling?

Cycle Time: Evaporative cooling reduces the product temperature faster than mechanical/refrigeration and other methods.
Product Shelf Life: During evaporative cooling, deaeration occurs, retarding bacterial growth and thus enhancing shelf life and product quality.
Reduced Handling: Eliminates transporting product to refrigerated air blast areas. Product can be cooked and cooled in the same vessel and then transferred directly to packaging.
Maintenance-Free and Environmentally Friendly: No moving parts; no chemical refrigerants, simplicity of operation

Evaporative Cooling in a Retort

Evaporative cooling is also used for solid foods such as potatoes, chick peas, or diced vegetables, etc. Products in baskets or trays are placed in Retorts and then pressure cooked by injecting live steam into the Retort. After the cooking cycle is completed, the product is vacuum cooled using a multi-stage ejector system as shown. A typical unit can cool from 200°F to 35°F in 15 – 20 min, depending on ejector sizing.

This schematic shows baskets of cooked potatoes in a retort vessel cooled by a three stage vacuum system.

Evaporative Cooling in a Jacketed Vessel

(Soups, Sauces, Jellies etc.)

<p”>Foods that are cooked in agitated, jacketed vessels such as soups, sauces, jellies, and slurries can be rapidly cooled in the same vessel with Fox vacuum systems. Contents could be cooled by flowing cold water through the jacket but that takes time­ lots of time. Cooling can be significantly faster by use of a Fox vacuum system.

Agitation is required, especially for viscous fluids, to expose as much product to the vacuum environment. A typical system with an agitated, jacketed vessel, with a three stage Fox ejector system as shown, can cool 50 to 1000 gallons of product from 230°F to 40°F in 30-40 min.

This schematic shows the contents of an agitated, jacketed vessel being cooled by a skid-mounted, 3-stage ejector system.

What does Fox need to design your system?

  1. Available steam pressure, psig
  2. Cooling water temperature, °F
  3. Product description; quantity (gallons or lbs.)
  4. Required cooling range, ΔT °F