For certain types of chemical reactor whose catalyst decays rapidly but reversibly

continuous operation is possible by the use of a moving bed radial flow reactor. There is an upper limit on the flowrate of gas imposed by the mechanical phenomenon of "pinning" and the formation of cavity. The dimensionless pressure drop for cavity initiation can be predicted by using the theories of particulate media mechanics

with the gas stream flowing outward radially. The theoretical results agree very well with the experimental data.