Heat transfer in packed-tube reactors.

Radial heat transfer was investigated for three tubes packed with alumina spheres, cylinders, or rings. Overall heat-transfer coefficients, determined from the average gas temperature for different packed heights, were used with expressions for the effective thermal conductivity to calculate wall-film heat-transfer coefficients. The Nusselt number for the wall film increased with Dp/Dt as well as with the particle Reynolds number, but the effective thermal conductivity decreased with Dp/Dt for a given Reynolds number. These trends led to a fairly broad maximum in the curve of overall coefficient versus Dp/Dt, with the maximum shifting to lower values of Dp/Dt at higher flow rates. For the same size packing, the overall coefficients for the different shapes were nearly the same over a 10-fold range of flow rates.