Voids are important regions in some industrial processes,particularly in the iron-making process,because a void is a zone in which gas-solid heat transfer and reactions occur.This paper presents a 3D experimental study of void formation measurement with 2D projection in a packed bed using an optical method.By developing an experimental laser-attenuation scanning method,invisible voids that form in a packed bed can be detected and identified as relatively stable ellipsoids.The effects of various operational parameters on void formation are analyzed in terms of the resulting void sizes and shapes.The results show that the void shape that forms in the packed bed is close to an ellipsoid and is relatively stable.The void size is positively correlated with the blast volume rate and is negatively correlated with the blowpipe diameter.The blowpipe depth has no significant effect on either the void formation or size.The blast angle affects the void location strongly;when this angle is increased,the void moves upward.The information and methods obtained in this experiment are significant in aiding understanding of the mechanism of void formation in gas-solid reactors.