Moisture analysis

Moisture analysis covers a variety of methods for measuring moisture content in both high level and trace amounts in solids, liquids, or gases. Moisture in percentage amounts is monitored as a specification in commercial food production. There are many applications where trace moisture measurements are necessary for manufacturing and process quality assurance. Trace moisture in solids must be controlled for plastics, pharmaceuticals and heat treatment processes. Gas or liquid measurement applications include dry air, hydrocarbon processing, pure semiconductor gases, bulk pure gases, dielectric gases such as those in transformers and power plants, and natural gas pipeline transport.

Moisture Dewpoint (the temperature at which moisture condenses out of a gas) and moisture content (how many molecules of water as a fraction of the total) are inherently related. Both can be used as a measure of the amount of moisture in a gas. They are inherently related and one can be calculated from the other fairly accurately.

Unfortunately, both terms are sometimes used interchangeably. It is important to note that these two parameters (e.g. water dewpoint and water content) are NOT the same thing. They are completely different, though related measurements. There are a number of methods to measure water content as listed below. However, to measure the water dewpoint, there is only one class of methods: Chilled-mirrors (needs a reference to an article on chilled-mirrors).

The classic laboratory method of measuring high level moisture in solid or semi-solid materials is loss on drying (LOD). In this technique a sample of material is weighed, heated in an oven for an appropriate period, cooled in the dry atmosphere of a desiccator, and then reweighed. If the volatile content of the solid is primarily water, the LOD technique gives a good measure of moisture content. Because the manual laboratory method is relatively slow, automated moisture analyzers have been developed that can reduce the time necessary for a test from a couple hours to just a few minutes. These analyzers incorporate an electronic balance with a sample tray and surrounding heating element. Under microprocessor control the sample can be heated rapidly and a result computed prior to the completion of the process, based on the moisture loss rate, known as a drying curve.

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