Efficient and Versatile Thermoacoustic Generators

Saturday - November 18 2023, 07:30 UTC - 1 year ago

This article discusses the design and applications of thermoacoustic generators, which are increasingly efficient and versatile. It also covers the Chinese design, which offers impressive efficiency and is made of porous metal and coated with a refractory material that allows it to concentrate heat more efficiently.

The Chinese design can be used for ultraquiet submarines.Nasa’s LEW-TOPS-80 patent proposed a thermoacoustic engine paired with an alternator to generate electricity in space. NASA has not shown a prototype.NASA Glenn’s thermoacoustic power converter reshapes the conventional Stirling engine from a toroidal shape into a straight colinear arrangement. Instead of relying on failure-prone mechanical inertance and compliance tubes, this design achieves acoustical resonance by using electronic components .

In a typical Stirling engine, the acoustical wave travels around a toroid and reflects back, forming a standing wave. In Glenn’s device, by contrast, the wave instead travels in a straight plane where a transducer receives the acoustical wave and electrical components modulate the signal. A second transducer on the diametrically opposed side reintroduces the acoustic wave with the correct phasing to achieve amplification and resonance .

Glenn’s design allows the transducers to operate at high frequency while presenting a mass rather than stiffness impedance. Glenn’s magnetostrictive alternator uses stacked magnetostrictive materials under a biased magnetic and stress-induced compression. The acoustic energy from the engine travels through an impedance-matching layer (which can be formed from aerogel materials) that is physically connected to the magnetostrictive mass .

Compression bolts keep the structure under compressive strain, allowing for the micron-scale compression of the magnetostrictive material and eliminating the need for bearings. The alternating compression and expansion of the magnetostrictive material creates an alternating magnetic field that then induces an electric current in a coil wound around the stack. This alternator produces electrical power from the acoustic pressure wave and, when the resonant frequency is tuned to match the engine, can replace the linear alternator to great effect .

BenefitsEfficient: Offers very high thermal-to-electrical efficiency compared to other heat engines Reliable: Features no moving parts or bearing systems, limiting opportunities for failure Lower-cost: Reduces fabrication expense by using fewer parts and allowing wide tolerances in manufacturing Compact: Enables significantly reduced engine mass and volume Versatile: Provides flexibility in design so that any heat source can be used to provide powerApplicationsDistributed generation and residential power systems Combined heat and power systems Concentrated solar power generation Hybrid electric vehicles Refrigeration systems Heat pumps Underwater and marine power systems Auxiliary power unitsChina’s VersionThe Chinese generator was created by the Technical Institute of Physics and Chemistry (TIPC) at the Chinese Academy of Sciences (CAS) and is about 2 metres (6½ feet) in length with a dumbbell-like shape .

It operates with impressive efficiency, according to Professor Hu Jianying of the TIPC."The current thermoelectric conversion efficiency is about 28 per cent; with a hotter 600 degree thermal fluid, efficiency could reach 34 per cent," he said.Such efficiency ca be attained because the nuclear reactor core does not move inside the chamber, yet concentrates heat so efficiently that the water that surrounds it evaporates and turns to steam .

The newer dumbell-like design, with inner parts made of porous metal and coated with a refractory material, enables this process to occur even faster.