Cylindrical heat conduction models for enclosed thermophones

Abstract

The efficiency of enclosed thermophones is governed by the time-dependent heat transport between the heating element and the enclosure gas. Efficiency gains have been made by reducing the heat capacitance of the heating elements so that a maximum amount of energy is available for transport. However, efficiency is still limited when there is poor conduction into and out of the enclosure gas. An analytical model for the conduction in an enclosed thermophone with a heating element composed of a regularly spaced linear array of conducting fibers will be presented. The model considers interaction between the individual fibers and treats the enclosure wall as a heat sink. The conduction model will be incorporated into a device model which can calculate steady-state acoustic output. The results are compared against experimental data. In addition, the device model can be used to explore the optimal fiber spacing for enclosed thermophones with regularly spaced linear array heating elements. [Work funded by the Naval Research Laboratory.]