Triboelectricity: A parameter for solids flow measurement
Electrostatic phenomena are well known and easily demonstrated. It is generally less well known that triboelectricity [frictional electrification] is the cause. Triboelectricity occurs when two materials collide or are rubbed together, causing a transfer of charge from one material to another. Though the magnitude of the charge is minute, it is measurable as current. Because the current is related to particulate flow activity, triboelectricity presents a novel means of monitoring dry solids flow. This article discusses the historical research and practical use of triboelectric technology as a dry solids flow measurement parameter.
Most engineers will remember the effect of passing a hard rubber comb through hair or the rubbing of a glass rod with fur. These actions create a small charge on the comb or rod that attracts small bits of paper. Frequently, a release of energy in spark form will result from the discharge of voltage buildup. This is known as static electricity, which depends on an excess or imbalance of charge polarity. This imbalance of charge can be produced by one of three phenomena:  by direct contact with an electrical source -- as in the charging of a capacitor,  by the disruption of polarized liquid films, which leads to spray electrification -- as can be found in the mists above waterfalls, and  by the transfer of charge that takes place when two materials collide or are rubbed together.