Gas residence time distribution studies of beds of 3 mm glass ballotini provide evidence for an explanation of the anomalous heat transfer results reported in the literature for moving bed equipment. The gas maldistribution in moving beds is such that the gas flow cannot be modelled by plug flow nor by plug flow plus axial dispersion. This discrepancy from plug flow has caused misinterpretation of experimental heat transfer data. The RTD experiments confirm that the flow of solids in a moving bed can be stopped, producing a frozen bed, without altering the structure developed in the solid packing. This phenomenon will be exploited in future studies of moving beds.