Effect of residence-time distribution on the determination of the overall heat transfer coefficient in a flow system between a gas and heated walls

The residence-time distribution (RTD) of an inert gas in a flow-through reactor, consisting of a cylindrical conduit equipped with an axial distributor, is measured and represented in terms of the mixing cells with an exchange (MCE) flow model. In the same system, heat transfer rate measurements are carried out between the heated sides of the reactor and the air flowing through. Unusually high heat transfer coefficients characterize this system. The measured heat transfer data are evaluated in the usual plot of Nusselt number versus Reynolds number, in terms of the MCE model, incorporating the experimental RTD information, and, also, in terms of the ideal plug flow and the perfectly well mixed fluid flow models. Very great differences exist between the results obtained by the different models. The reactor used herein is compared with empty tube is longer by almost two orders of magnitude, but the viscous dissipation in the reactor is greater by about four orders of magnitude. The great difference is due to the axial distributor in the reactor.