Trapped Modes about Tube Bundles in Waveguides

Abstract

A possible design for a heat exchanger involves packing a rectangular array of rigid hollow cylinders in a parallel-walled duct; the transfer of heat conducted from a fluid flowing in the cylinders to a fluid flowing through the duct. It is important to identify under what conditions the configuration may be subject to resonant acoustic modes which may be generated by various means so that design parameters can be chosen to avoid this undesirable effect. These resonant modes of oscillation are associated with the occurrence of so-called trapped modes in waveguides. Trapped modes are characterised by a persistent oscillation in the vicinity of a geometric structure which does not radiate energy away to infinity. They therefore also represent a non-uniqueness in a corresponding forcing problem.