Archive for the ‘ Publications ’ Category

15th International Green Energy Conference (IGEC-XV)

A personal review of >40 years research and product development

On-line presentation held on July 13th 2023, Glasgow, UK at the  15th International Green Energy Conference


Progress made on bi-directional turbines

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)

Aster Thermoacoustics announced as one of the winners of the GE Ecomagination Innovation Challence

During a ceremony held on February 3th 2015 at the GE innovation Centre in Calgary,  Aster Thermoacoustics was announced as one of four winners of the first phase of General Electric’s two phase  “Ecomagination Innovation Challenge” with winning submissions addressing alternative uses for waste heat from SAGD (Steam Assisted Gravity Drainage), ultimately reducing greenhouse gas(GHG) emissions in Canadian oil sands.

in Calgary, Alberta, February 3, 2015. Photograph by Todd Korol               in Calgary, Alberta, February 3, 2015. Photograph by Todd Korol

Image credits: Todd Korol

During the ceremony  Kees de Blok received the challenge award from Elyse Allan, President and CEO of GE Canada and John Rice, vice chairman of GE.

Beside a cash prize of $25,000 Aster Thermoacoustics and the other winners get an offer for another $100,000 in co-development funding to bring their idea’s to application in the oils sands.

Details and background of the challenge and of the other winners may be found on

The  event also get large attention of the press as can be read for example in this copy from an article in the Daily Oil Bulletin and links to the COSIA newsletter and Benelux press release

Waste or combustion heat driven gas liquefaction

The concept of thermoacoustic heat driven gas liquefaction has been brought back on  stage by a joint experiment of Qdrive and Aster-Thermoacoustics, combining a high performance pulse tube and a multi-stage traveling wave feedback thermoacoustic engine.

At a cold head temperature of -160°C the engine input temperature was reduced from 900°C down to less than 300°C which allows for extracting more heat from the combustion, prior to exhausting,  and for the use of ordinary construction materials.

While initially the concept was intended for liquefaction of natural gas from oil wells, nowadays small and medium scale liquefaction of locally produced biogas for storage and transportation  could be the main application.

The results of the experiments were presented on the “Second Workshop on Thermoacoustics” held on May 23 -25, 2014, at the Sendai  Tohoku university in Japan.

The abstract and presentation may be found by the links below

Thermoacoustic heat driven cooling

Heat driven cooling(1)

Blue print for a simple, reliable and low cost heat driven thermoacoustic generators for rural areas producing 20-50W electric power.

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 ( and by initiatives supported  by the  FACT Foundation in the Netherlands ( 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)

Acoustic loss, a key factor in overall performance of TA systems

Since the early days of thermoacoustics, research en development had its focus on the thermodynamic process in the regenerator and heat exchangers. Thanks to this effort, nowadays the thermoacoustic process in itself is well understood and many publications can be found reporting thermoacoustic engines and heat pumps showing exegetic efficiencies over 40%.

However, overall or integral system performance, defined as the ratio between acoustic power delivered to a useful load and engine thermal input power is still far from that. In most experiments published, at least about one third of the net engine output power is dissipated in the acoustic circuitry or resonator and therefore is not available to the load, consequently degrading the overall performance proportionally.

Read more about this  in the paper and presentation given on the ICSV19 in Lithuania

Multi-stage traveling-wave feedback thermoacoustics in practice (Kees de Blok)

Presentation_Multi-stage traveling wave feedback

2010 ASME, Montreal, Canada

Novel 4-stage Traveling Wave Thermoacoustic Power Generators


Utilizing low temperature differences from solar vacuum tube collectors or waste heat in the range 70-200 °C seems to be the most promising and commercial interesting field of applications for thermoacoustic systems. Recently a novel 4-stage “self matching” traveling wave engine is developed and tested. Beside the low acoustic loss and compactness, due to traveling wave feedback, all components per stage are identical which is beneficial from (mass) production point of view. Based on this concept a 100 kWT thermoacoustic power (TAP) generator is under construction. This project is carried out in the framework of phase two of the Dutch SBIR program. The 100 kWT TAP will be installed at a paper manufacturing plant in the Netherlands for converting part of the flue gas at 150°C from the paper drying process into electricity. Emphasis in this project is on production and cost aspects lowering the investment per kWe to a level competitive to ORC’s. After successful completion of this pilot, commercialization and delivery of 100kW to 1 MW thermoacoustic power generators for industrial waste heat recovery and as add-on for CHP systems is planned to begin in 2012. The same concept of the 4-stage traveling wave engine is also implemented in an atmospheric pressure operated thermoacoustic cooking device for developing countries which generate beside hot water up to 50 W electricity. Details, ongoing work and experimental results of these projects will be presented.

Read the full article:

Novel 4-stage thermoacoustic power generators

Acoustics08, Paris, France

Low operating temperature integral thermo acoustic devices for solar cooling and waste heat recovery


Utilizing low temperature differences from solar vacuum tube collectors or waste heat in the range 70-200 °C seems to be the most promising field of applications for thermo acoustic systems.At these reduced temperatures overall system performance is increasingly affected by the ratio between amplified (useful) power and acoustic power in the resonance circuitry.Well known is that this ratio can be improved by deploying multiple regenerator units (hex-reg-hex).However, in commonly used torus or coaxial bypass configurations the correct timing (real and high acoustic impedance) is hardly to realize inside more than two regenerator units (soft spot).Acoustic losses in the standing wave resonator together with a high regenerator impedance account for another fundamental limitation because of the relatively low transferred and loop power at a given pressure amplitude.Therefore a novel acoustic geometry will be presented in which a near real impedance can be maintained in even more than two regenerator units and in which acoustic feedback is performed by a near traveling wave.This approach improves the overall performance of low operating temperature thermo acoustic systems.

Read the full article

Low operating temperature integral thermoacoustic devices for solar cooling and waste heat recovery

or view the presentation


Patent list

C.M. de Blok. “Multistage traveling wave thermoacoustic engine with phase distributed power extraction”. PCT/NL2010/050057

C.M. de Blok. “Meertraps thermoakoestische warmtemotor met fase gedistribueerde vermogensuitkoppeling”, 2009, NL 1036630

C.M. de Blok. “Multi stage heat driven thermoacoustic engine” . PCT/NL2004/000405, WO2005/001269 A1

C.M. de Blok, N.A.H.J. van Rijt. Thermo acoustic system, 1997, WO 99/20957, US 6,314,740 B1.

C.M. de Blok, N.A.H.J. van Rijt. “Device for utilizing heat via via conversion into mechanical energy, in particular cooling device”. PCT/NL89/00012, WO1989NL0000012

Measuring technology

In the beginning we at Aster realized that representing and measuring acoustic components was essential to understand the physics and to be able to develop and optimize the  acoustic configuration and interaction of thermoacoustic engines and  heat pumps or other loads like linear alternators.

The first article describes the representation of acoustic components based on N-ports and scattering (S) parameters.  The second paper deals with the design and construction of direct reading 1-port acoustic network analyzer for measuring complex acoustic reflection in the range of 1-100 Hz.

Characterization of acoustic networks

Acoustic network analyzer