Real-time controlling particle distribution in pneumatic conveyance by electrical capacitance tomography with airflow injection system (ECT-AIS)

Abstract

Electrical capacitance tomography with airflow injection system (ECT-AIS) has been developed for controlling particle distribution in pneumatic conveyance in order to maintain homogeneous downstream particle distribution εndot+τ with a delay time τ even under inhomogeneous upstream particle distribution εnupt. ECT-AIS is composed of two ECT sensors for monitoring εnupt and for evaluating εndot+τ after injecting airflow. The airflow is injected to the conveyance pipe by activating a solenoid valve of airflow injection system (AIS) to control the homogeneous εndot+τ in the case that the spatial standard deviation of permittivity distribution at the upstream ECT sensor εSDupt which is calculated from εnupt and the spatial mean permittivity 〈εnup〉t is greater than the threshold value δ. With this developed ECT-AIS, three different experiments are performed under different particle loading ratios (ϕ = 0.25, 0.50 and 0.75) with air flow rate Qa = 0.75 kg/s, 0.50 kg/s and 0.25 kg/s. As εnupt is homogeneous, εndot+τ is also homogeneous. While εnupt was inhomogeneous, εndot+τ was homogeneously distributed due to airflow injection. To evaluate the homogeneity of εndot+τ, the spatial mean permittivity 〈εnup〉t in upstream sensor is compared with 〈εndo〉t+τ in downstream sensor and the two results were evaluated with the measured pressures pnupt and pndot. As a results, εSDdot+τ is less than or equal to δ so that 〈εndo〉t+τ is homogeneous after airflow injection. Based on Darcy–Weisbach equation, as the particles are homogeneous, the pressure is lower than that in inhomogeneous distribution. According to the relationship between mean permittivity and pressure, εndot+τ is successfully controlled in homogeneous conditions by ECT-AIS.