Moisture analysis is the determination of the amount of water in a substance Usually, moisture analysis is reported as a percent of moisture on a weight basis. This measurement is important in many manufacturing and industrial applications for many reasons.
Care must be taken when preparing samples for moisture analysis. The water in the sample will tend to evaporate if the ambient humidity is lower than the sample conditions or if the temperature is warmer. Similarly, water may condense in the sample if either the ambient humidity or the temperature is high relative to the sample. Collection containers must be impermeable and sealed to the atmosphere, and have little headroom.
Thermogravimetric analysis is commonly used to determine moisture content. The weight loss due to water is calculated by weighing the sample before and after heating, drying, and cooling. As long as the sample collection is good and there are no low-molecular-weight volatile compounds in the sample, this is a standard and accurate technique.
In many industrial processes, moisture is a critical property that must be known prior to further processing. In the combustion of coal, moisture affects the ability of the ground coal to be transported, the heat required to burn the coal, and the energy derived from the coal. When the coal feed is slurry, or a mixture of very finely ground coal and water, the moisture content must be determined in real time to achieve the proper combustion conditions. The moisture analysis is performed across a moving conveyor belt, which is also a dewatering station. A microwave receiver, placed above the belt, calculates the percentage of water based on the percentage of the original microwave energy received compared to that transmitted from below the conveyor belt and through the layer of coal slurry sludge.
The water content of natural gas is important for gas suppliers. Natural gas, as drilled, is saturated with water and various hydrocarbons that must be removed. A moisture analysis is performed continuously on the production stream of natural gas. As the natural gas stream passes by the analyzer, water passes into a water-attractive layer between two electrical plates. The subsequent changes in conductance is calibrated to report the moisture content.
Soil moisture is measured by farmers and scientists to predict crop yield, prevent plant disease, and evaluate irrigation or other farming technologies. While thermogravimetric techniques may be used, simple probes can measure the conductivity of the soil and thus the moisture content. Measurements of soil moisture over time help scientists understand drought cycles and long-term effects on forests.
Beginning bakers are often told to pay attention to the humidity in the room when making bread. The addition of flour into the dough will be directly related to the moisture in the air. Large-scale bakeries also test for moisture at the dough stage to ensure their products taste good and have a pleasing texture and an acceptable shelf life. Thermogravimetric techniques are generally used in these production lines.