Sample dryers are used to remove liquids from a sample through techniques such as freeze drying, spray drying, and evaporation. Drying or dehydration is a mass transfer process that causes the removal of water. There are many types of sample dryers. Examples include freeze dryers and spray dryers. A spray dryer consists of a feed pump, atomizer, air heater, air disperser, drying chamber, and systems for exhaust air cleaning and powder recovery. Spray drying is the process of mixing and drying slurry to form a homogeneous mixture of powders. The powders are mixed with a solvent, and then the mixture is sprayed into the air, so that the solvent evaporates leaving the mixed powders. By contrast, a freeze dryer freezes the material and then reduces the surrounding pressure. Freeze drying allows the frozen water in the material to sublimate directly from the solid phase to gas.

Selecting Sample Dryers

Selecting sample dryers requires an analysis of drying methods and application requirements. Some sample dryers use a two-stage process which drops the sample's temperature twice, removing moisture in two individual trap assemblies. Drying can also be done by using evaporators to apply of dry, heated air. This causes the evaporation of surface water, which is replaced by water internally. The process of extreme drying is called desiccation. Desiccators create a dry environment with electronically controlled storage. Lyophilization technology uses the principle of freeze drying in preserving a perishable material. Operating conditions and sample dryer design are selected according to the drying characteristics of the product and powder specification. 

Differences

Sample dryers differ in terms of performance specifications, physical dimensions, and optional features. Volume or capacity, the number of chambers, and temperature range are the most important performance parameters to consider. Physical dimensions for sample dryers include the length, width, and height of the sample dryer. In terms of features, sample dryers may provide electrostatic discharge (ESD) protection or block ultraviolet light (UV). Both ESD and UV can damage sensitive materials and equipment. Sample dryers with shelves provide individual platforms for samples during drying.

Applications

Sample dryers are designed and manufactured to meet most industry specifications. They are used in many applications. Examples include pharmaceuticals, chemical synthesis, food preservation, semiconductor wafers, and obtaining absolute alcohol. Sample dryers should adhere to various food processing standards specified by the International Standards Organization (ISO).