Experiments in a cylindrical model silo were carried out with different initial densities of sand and silo wall roughness. Solid concentration changes during granular flow in the model silo were measured with electrical capacitance tomography (ECT) sensors. During silo flow, strong dynamic effects connected with booming sound occurred. Local one-dimensional (ID) and cross-sectional 2D evolutions of solid concentrations in dry sand during silo discharge were observed. The I D phenomena were estimated from the raw data and the 2D phenomena were obtained from the reconstructed data by solving an inverse problem with a linear back projection algorithm. (c) 2008 Elsevier Ltd. All rights reserved.