Experimental heat exchanger performance in a thermoacoustic prime mover

Abstract

The effectiveness of heat transfer between the thermoacoustic stack and a typical copper fin heat exchanger is determined by the detailed gas motion and thermal diffusion, and the fin geometry. This effectiveness depends strongly on acoustic amplitude and heat load, as does the ability of the copper to conduct the heat. These and other nonlinear effects contribute to limiting the amplitude of a prime mover. A modular prime mover experiment has been built so that the limiting amplitude can be measured with a variety of heat exchanger geometries, with the goal of finding the best geometry. The liquid nitrogen temperature experiment uses a heavier gas, such as neon, at a low pressure in order to minimize the heat load, and the temperature defects associated with copper conduction, while allowing large Mach numbers and gas particle displacements. In preliminary measurements, peak pressure amplitudes are in access of 20% of the mean pressure and the peak‐to‐peak acoustic displacements are comparable to the stack length. Such large displacements take the study of prime movers into a poorly explored region. [Work supported by the Naval Research Laboratory and the Office of Naval Research.]