T. A. Aldugman, M Cui, A. Alzailaie, A. Alhareth, K.Langley, L. Alfilfil, K. Almajnouni, J. Gascon, S. Thoroddsen and P. Castaño. Chem. Eng. J. Adv. (2024). Comparative analysis of counter-current and co-current downer reactors using particle image velocimetry and computational particle-fluid dynamics.