Here are the dimensionless equations of a packed bed reactor with radial temperature and concentration gradients, assuming constant physical properties, plug flow, and first-order kinetics:
1) ,
2) ,
with the boundary conditions
3) at ,
4) , at ,
and the initial conditions
5) , at .
Reference: B. A. Finlayson, "Packed Bed Reactor Analysis by Orthogonal Collocation," Chemical Engineering Science, 26(7), 1971 pp. 1081–1091.