TABLE OF CONTENTS Piston flow is a convenient approximation of a real tubular reactor. The design equations for piston flow are relatively simple and are identical in mathematical form to the design equations governing batch reactors. The key to their mathematical simplicity is the assumed absence of any radial or tangential variations within the reactor. The dependent variables a, b, ,T, P, change in the axial, down-tube direction but are completely uniform across the tube. This allows the reactor design problem to be formulated as a set of ordinary differential equations in a single independent variable, z. As shown in previous chapters, such problems are readily solvable, given the initial values a in , b in , , T in , P in.
Piston flow is an accurate approximation for some practical situations. It is usually possible to avoid tangential ( ?-direction) dependence in practical reactor designs, at least for the case of premixed reactants, which we are considering throughout most of this book. It is harder, but sometimes possible, to avoid radial variations. A long, highly turbulent reactor is a typical case where piston flow will be a good approximation for most purposes. Piston flow will usually be a bad approximation for laminar flow reactors since radial variations in composition and temperature can be large.
Chapters 8 and 9 discuss design techniques for real tubular reactors. By real, we mean reactors for which the convenient approximation of piston flow is so inaccurate that a more...
