Selection and experimental evaluation of low-cost porous materials for regenerator applications in thermoacoustic engines

This paper aims at evaluating three selected low-cost porous materials from the point of view of their suitability as regenerator materials in the design of thermoacoustic travelling-wave engines. The materials tested include: a cellular ceramic substrate with regular square channels; steel " scourers" ; and stainless steel " wool" Comparisons are made against a widely used regenerator material: stainless steel woven wire mesh screen. For meaningful comparisons, the materials are selected to have similar hydraulic radii. One set of regenerators was designed around the hydraulic radius of 200 μm. This included the ceramic substrate, steel " scourers" , stainless steel " wool" and stacked wire screens (as a reference). This set was complemented by steel " scourers" and stacked wire screens (as a reference) with hydraulic radii of 120 μm. Therefore six regenerators were produced to carry out the testing. Initial tests were made in a steady air flow to estimate their relative pressure drop due to viscous dissipation. Subsequently, they were installed in a looped-tube travelling-wave thermoacoustic engine to test their relative performance. Testing included the onset temperature difference, the maximum pressure amplitude generated and the acoustic power output as a function of mean pressure between 0 and 10. bar above atmospheric. It appears that the performance of regenerators made out of " scourers" and steel " wool" is much worse than their mesh-screen counterparts of the same hydraulic radius. However cellular ceramics may offer an alternative to traditional regenerator materials to reduce the overall system costs. Detailed discussions are provided.