Electrostatic charges measurement of powder flowing on a surface.
Electrostatic charges appear in powders during a flow. The apparition of these electrostatic charges is due to the triboelectric effect, which is a charge exchange at the contact between two solids. During the flow of a powder inside a device (mixer, silo, conveyor, ...), the triboelectric effect takes place at the contact between the grains and at the contact between the grains and the device. Therefore, the characteristics of the powder and the nature of the material used to build the device are important parameters.
Unfortunately, the triboelectric effect is still poorly understood, even at the fundamental level, and most instruments that claim to measure electrostatics do it indirectly. Therefore, the approach to solving practical problems due to electrostatic is mostly empirical. Moreover, reproducible electrostatic measurements are difficult to perform.
The GranuCharge was developed to fill that gap in powder characterization instruments by measuring the electric charge density of a sample with a customized Faraday cup.
GranuCharge measures automatically and precisely the quantity of electrostatic charges created in a powder during a flow in contact with a certain material. The powder sample flows inside a vibrating V-tube and falls into a Faraday cup connected to an electrometer. The electrometer measures the charge acquired by the powder during the flow inside the V-tube. To obtain reproducible results, a rotating or a vibrating feeder is used to feed the V-tube regularly.
The V-tube geometry has been selected to combine the different mechanisms leading to triboelectrification:
Therefore, the V-tube charges the powder more in comparison to a single tube geometry and reproduces more accurately industrial processes.
The GranuCharge is compatible with a large range of powders and used in many applications:
The GranuMidity controls the relative humidity (range: 0% to 100% RH) of the air before pulsing it outside. Dry compressed air is supplied: one part of this air goes through a bottle containing water to get moisture while the other part goes directly to the mixing chamber. This system allows the user to condition the relative humidity inside the GranuCharge to get relevant and repeatable results. This can also be used to study the impact of humidity.
