An experimental study of heat transfer from a cylinder in low-amplitude zero-mean oscillatory flows

This is the report of an experimental study on the convective heat transfer behavior from a cylinder in an intense acoustic field which is representative of a strong zero-mean oscillatory flow. The measurements are based on a steady state technique in which, at equilibrium, a predetermined rate of heat dissipation in the cylinder is balanced by the convective cooling action of the acoustic field. Only low-amplitude cases have been treated for which the particle displacement amplitude in the oscillatory flow is small on the scale of the cylinder diameter. Two distinct flow regimes have been identified. The first regime, consistent with theory, is the laminar attached flow regime which shows the expected square root dependence of the Nusselt number, Nu, on the appropriate Reynolds number, which in this case is the streaming Reynolds number, Rs. The second regime, which is less well understood, is predicted to be an unstable regime in which vortex shedding is prevalent, contributing to higher heat transfer rates. Suitable correlations have been provided for both regimes for the case of air, and suggestions have been included to extend them to other Prandtl number gases for which they are likely to be used. This work could find application in the design of heat exchangers for thermoacoustic engines.