Abstract
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.
Highlights
In thermoacoustic engines, thermal energy is directly converted to an acoustic wave as a result of heat interaction between a solid material and adjacent gas, within the so-called “thermal penetration depth”
Setting the input power directly to the required power rate is more practical because a quick engine start-up is favourable for any practical thermoacoustic engines
The motivation behind the current research is to identify the low cost regenerators with a possible comparable performance to those widely used in the thermoacoustic practice
Summary
Thermal energy is directly converted to an acoustic wave (mechanical energy) as a result of heat interaction between a solid material and adjacent gas, within the so-called “thermal penetration depth”. A detailed theoretical analysis of standing wave systems, based on the linear acoustics model was performed by Swift [6], who provided some examples of the early developments at Los Alamos National Laboratory. Zhou and Matsubara [9] studied the performance of a standing wave engine as a function of gas properties, frequency, mean pressure, stack length and the hydraulic radius of the mesh used to fabricate the stack They expressed the engine performance in terms of the normalised input power, hot heat exchanger temperature and measured pressure amplitudes
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