Freeze Drying vs. Thermal Water Evaporation in Engineering Applications

With thermal water evaporation, a product stored in a hot area, causing water inside to evaporate. As water vapour is lost, the volume of the product decreases and the system tries to replace these molecules by shifting the system equilibrium to create more gaseous water molecules. Evaporative cooling occurs due to energy lost from the open system that the gaseous molecules "take" with them as they leave; so the system absorbs energy from the surroundings. This product is then vacuum sealed after dehydration, forming hypothetical boundaries for a closed system. This means that the product will remain dry - this is the process by which dehydrated meals can be manufactured.

Freeze drying is a popular in industry, used in many products ranging from space food, to extending the shelf life of foods and pharmaceuticals. For this process, rather than the product being initially exposed to a hot environment, it is frozen and dehydrated by lowering pressure and utilising sublimation (solid to vapour phase) to remove the ice.

Thermal Water Evaporation Analysis:

- Completely removing the water by evaporation is difficult since the water is not exposed to air directly. The typical dehydration of food removes between 90 - 95% of water.

- The evaporation process significantly alters the food's shape, texture and composition. Thermal energy causes chemical reactions in the food that changes these characteristics.

How Freeze Drying Compares:

- Freeze drying allows for the preservation of the characteristics of foods such as their taste and freshness

- In food, bacteria and enzyme activity are slowed but not completely stopped.