抄録
It is well known that, in a pneumatic conveying system, electric charges accumulate on powder that is carried in a gas-solid two-phase flow. This paper presents a problem arising from the electric charges accumulating on the powder when the solid fraction in a two-phase flow is measured using a capacitance transducer. The electrified powder induces polarization charges in the tube wall by various means when it approaches to transducer tube wall, and accordingly the polarization charges cause both a number of voltage spikes and a DC voltage drift to appear on the output voltage of the capacitance meter. These voltage spikes and DC voltage drift reduce a resolution of determining solid fraction. Simplified models to explain the generations of the voltage spikes and DC drift are proposed. It is recommended to use either an alumina pipe or a glass pipe as a transducer tube to avoid the voltage spikes when less conductive powder such as silica powder is pneumatically transported, since appearance of the voltage spikes greatly depends on the relaxation times of the transducer tube material.
