Last Monday, the Sound Energy team, jointly with the installer and contractor Rouweler Installatietechniek Zelhem, installed their thermoacoustic cooler (THEAC) on the roof of the new school building IKC Magenta in Delden (Netherlands).This THEAC is a heat-powered heat pump intended to provide solar-assisted cooling to the building climate system. For that purpose, the THEAC cold output is connected via a fluid circuit to the cold buffer in the technical room.

The THEAC installed on this building is a version with increased safety for use on schools and public buildings. In this special version of the THEAC, solar energy (from the PV panels) is transferred via electricity to the internal heat exchangers of the THEAC, avoiding the use of hot liquids such as thermal oil or hot water / steam.

Read more on the soundenergy website

The THEAC-25 convert solar heat or industrial waste heat directly into cold for building, utility or process cooling based on thermoacoustic energy conversion as underlying technology.

Market introduction of the THEAC-25 will be performed by Soundenergy B.V. (soundenergy.nl an award winning start-up established in 2015.  Aster is co-founder and shareholder and is taking care of the R&D activities for Soundenergy B.V.  This year focus was on the build and test of de pre-production prototype, providing up to 25kW of cooling power when solar or waste heat with a temperature the range 100-200°C is applied.

The THEAC-25 is based on Aster’s multi-stage traveling wave technology and is assembled from two thermoacoustic heat engine stages and two thermoacoustic heat pump stages sharing an common acoustic traveling wave resonance and feedback loop.

From the application point of view, the THEAC is a waste or solar heat driven heat pump, requiring three external circuits to be connected to the application. For one of the possible applications, which is solar heat powered cooling of a building in combination with vacuum tube solar collectors as heat source, this is depicted schematically below.

The dashed box represent the hardware and functionality of the THEAC-25. The actual prototype of a heat driven 25kW cooling system currently under test is shown below.

In this test rig all pressure vessels, containing the thermoacoustic core (heat exchangers and regenerator), are equipped with flanges and vessels are positioned vertically for reason of simple access and experimenting.

In the commercial version these flanges are obsolete and removed for saving weight and cost. Furthermore all vessels will be positioned horizontally by default to reduce system height. Finally  the THEAC-25 will fit into a box of 4.5m x 4.5m x 0.6m.

This commercial version will be pre-assembled in a frame, including all internal piping and subsystems, providing the customer with the three connections for heat supply, heat sink and cold.

Production of the THEAC-25 by Soundenergy B.V. is planned to  start early 2018 for  solar heat driven cooling in and waste heat recovery applications in industry.

During the 3th International Workshop on Thermoacoustics held on October 26-27 at the Twente University in the Netherlands, Aster had presented some results of ongoing work on bi-directional turbines and the interface to thermoacoustic engines.

Since introduction on the Aster website by the end of 2012, and more recently as presented at the 2014 Pamir Conference, held in Riga,  the thermoacoustic community has recognized the concept of bi-directional turbines as an alternative for linear alternators in particular when power levels goes up. Experimental results are encouraging and had proven that

• bi-directional turbines can be scaled up in power unlimited
• efficiency raise with gas density.

In addition, emplacement of multiple stages in series is found to be a way to match the turbine circumferential speed to the available acoustic gas velocity and generator parameters.

Based on these results a design procedure is in progress allowing to characterize, scale and match bi-directional turbines to any type of thermoacoustic heat engine.

Some details may be found in the presentation

Beyond acoustic to electric conversion limits (Keynote)

Bi-directional turbines for the conversion of acoustic power into electricity as they were  introduced by Aster early 2012, has turned out be a successful approach both in scaling up in power levels and in reduction of complexity and manufacturing cost.

To demonstrate the simplicity of the concept you may have a look at the video below, which shows a small bi-directional turbine plus generator, driven by the periodic acoustic flow from a loudspeaker.

What is interesting to see, is that the electric output (light) is hardly dependent of the acoustic frequency. This is an additional benefit of the bi-directional turbine concept because of the oscillation frequency of thermoacoustic engines varies with temperature which in case of resonant linear alternators could lead to detuning and performance degradation.

Since the first experiments a lot of progress is made in the understanding, design, modelling and construction(e.g. 3D-printing) of this type of A-E conversion and at present a full scale bi-directional turbine operating in 3.6 MPa helium is under construction to be applied in a 14kWe thermoacoustic power generator.

Last year some details and intermediate results on this A-E conversion concept were presented during the 9th International Pamir conference and Summer School, both held on June 16-20,2014 in Riga, Latvia. The paper and presentation may be viewed  here.

Paper Bi-directional turbines

Presentation Acoustic to electric conversion

Thermoacoustics is a conversion technology in which the compression, expansion and displacement of the working gas is driven by acoustic wave motion rather than by pistons, valves  and displacers. Using acoustic wave motion eliminates mechanical friction and wear and therefore drastically increase lifespan and minimize maintenance. Because of the lack of moving mechanical parts in the thermodynamic process the construction tolerances and material requirements are relaxed allowing for (potential) low production and investment costs. These properties makes thermoacoustics not only a second generation energy conversion technology but also a candidate for low cost, small scale conversion technology for rural and developing areas.

These opportunities were recognized in, for example, the Score project in England (www.score.uk.com) and by initiatives supported  by the  FACT Foundation in the Netherlands (www.fact-foundation.com). The aim of these projects, started a few years ago, is to develop low cost thermoacoustic devices generating electricity combined with wood stoves for cooking or heating water.  These projects also address the social and economic aspects involving charities and local communities. This type of devices could  contribute to improving local living conditions by the use of small scale air operated multi-purpose devices for preparing hot water, cooking and generating some electricity. It could also stimulate  labour related to local production installation and maintenance of these devices.

The document below describes the design approach and underlying physics of a pre-production version of a small scale near atmospheric air operated  thermoacoustic generator and provide a blueprint for the further (local) development and production of such generators in and for rural areas and developing countries.  To make this happen, background information and construction drawings are available from Aster as input for local projects, students, scientist and construction companies who will intend to do experimenting and furthering this technology.

Design and build of a 50W thermacoustic generator(2)