A Self‐Circulating Heat Exchanger for Use in Stirling and Thermoacoustic‐Stirling Engines

A major technical hurdle to the implementation of large Stirling engines or thermoacoustic engines is the reliability, performance, and manufacturability of the hot heat exchanger that brings high‐temperature heat into the engine. Unlike power conversion devices that utilize steady flow, the oscillatory nature of the flow in Stirling and thermoacoustic engines restricts the length of a traditional hot heat exchanger to a peak‐to‐peak gas displacement, which is usually around 0.2 meters or less. To overcome this restriction, a new hot heat exchanger has been devised that uses a fluid diode in a looped pipe, which is resonantly driven by the oscillating gas pressure in the engine itself, to circulate the engine’s working fluid around the loop. Instead of thousands of short, intricately interwoven passages that must be individually sealed, this new design consists of a few pipes that are typically 10 meters long. This revolutionary approach eliminates thousands of hermetic joints, pumps the engine’s working fluid to and from a remote heat source without using moving parts, and does so without compromising on heat transfer surface area. Test data on a prototype loop integrated with a 1‐kW thermoacoustic engine will be presented.