First International Workshop on Thermoacoustics

First International Workshop on Thermoacoustics

April 23-25, 2001
's-Hertogenbosch
The Netherlands

Organized by:

Technische Universiteit Eindhoven and the Acoustical Society of America

Report on the First International Workshop on Thermoacoustics April 22-25, 2001

INTRODUCTION

From 22-25 April the "First International Workshop on Thermoacoustics" has been held at the Golden Tulip Hotel Central in 's-Hertogenbosch in the Netherlands. This meeting was organized by the Eindhoven University of Technology, and in cooperation with the Acoustical Society of America.

PARTICIPANTS

In total about 80 persons participated at the workshop. They came from the USA, Canada, Mexico, Japan, Russia, Ireland, United Kingdom, France, Germany, Japan, China, Australia, and the Netherlands. About 80% of the participants had an academic background working at a university, and the other 20% were from industry, research institutes or governmental subsidy organizations. The number of participants was limited to 80 but there were at least 100 scientists who wanted to attend the workshop. Due to significant sponsoring 14 persons have received a scholarship, which gave them the opportunity to join this meeting, and present their work.

PROGRAM

The workshop started on Sunday 22 with a welcome reception and ended on Wednesday April 25 late in the afternoon. There were 63 contributions, divided in 36 oral presentations and 27 poster presentations. There were 8 presentations of 40 minutes by invited speakers and the other presentations were 20 minutes long. The posters were introduced in a short 2-minute oral preview session, which took place just after the invited presentation of the session they belonged to The workshop was split up in 6 main sessions:

A. Thermoacoustic components
B. Streaming and non-linearities
C. Driven Refrigerators
D. Transducers, drivers and outside the gas topics
E1. Spontaneous oscillators: Combustion
E2. Spontaneous oscillators: Engines
F. Visions of the Future

In session A emphasis was placed on thermoacoustic components. Here stacks, special geometries, measurement techniques and other detailed aspects of the components were discussed. In session B much emphasis was placed on streaming effects and non-linearities. This is of importance as due to these effects significant reduction in the performance of thermoacoustic machines can occur. For instance it was shown that numerical simulation models more and more predict what is occurring in the refrigerator. In session C the driven refrigerators were discussed. These driven refrigerators consist in general of an electrical driver that generates motional energy to sustain an acoustic wave in a resonator. In session D topics were discussed related to the components needed to build a thermoacoustic system. Session E was divided in two sub-sessions. In the first sub-session E1 combustion associated thermoacoustic phenomena were discussed. These occur in boilers and on flame supporting burner tiles and flame holders, and can lead to resonance problems. The second sub-session E2 dealt with engines by which sound is thermoacoustically generated with heat, and which is used to convert sound at another position into cooling power for refrigeration applications. In session F some visions for the future and opportunities for applications were given.

GENERAL OUTLINE

The workshop was a success. The organization went smoothly, and the combination of lodging and workshop presentation in one hotel has been a good choice. Participants could meet with each other in the poster sessions, and discussions were held and resumed during breakfast, lunch and dinners. This gave favourable opportunities to learn about each other's work and to make contacts. It also seems that it was the good moment of initiating this workshop, as there are already some applications of this field of science. In this context several applications can be mentioned:
* a commercially made piezoelectric driven refrigerator was shown. This cooler could for instance be used to cool electronic parts in computers or other electric equipment;
* large electrically driven refrigerators are in a stage of development. They can be used for cooling of radar equipment in ships;
* commercial available electric drivers were shown and demonstrated at the workshop. These can be used for thermoacoustic as well as pulse tube systems;
* a heat pump driven by thermoacoustically generated sound was demonstrated at the workshop. This heat pump will be upgraded for industrial applications on the order of several kilowatts;
* understanding of combustion oscillations by thermoacoustics is on its way, and numerical simulations are in reasonable agreement with experiments. Understanding of these phenomena is of high importance for boiler manufacturers;
* large-scale thermoacoustic traveling wave machines are under development. These machines are used to drive large-scale pulse-tube coolers in the kW or MW range. The technology can be used to liquefy natural gas.

In two presentations at the end of the workshop it was shown that there are favourable chances for the application of thermoacoustic technology in the near future. On the one hand use of this technology was mentioned for the liquefaction of natural gas in oil/gas wells in hostile areas where no pipe transport lines are available. On the other hand it was emphasized that thermoacoustic heat pump technology for industrial waste heat has good chances in the Netherlands. The further development and commercialization of this technology could mean much for this field of science. The development of analysis and understanding of thermoacoustic oscillations in combustion systems seems to be very relevant for the manufacturers of boilers.

An interesting aspect of the workshop was that two communities were joined here, one community of researchers out of the field of thermoacoustic cooling engines and heat-pumps, the other community being the people out of the field of combustion. The first group is interested to achieve large thermoacoustic oscillations to apply them, the other group tries to attenuate the oscillations, as they are a nuisance. So also in this respect the workshop gave the opportunity to exchange ideas between members of these two research groups.

FOLLOW UP

During the workshop, it was proposed that a follow up of this workshop is of interest. No exact date was mentioned nor is it yet known who should organize it. A follow up is certainly of interest, but it should be organized when there is really a need for it. In this case one can think of 2003 or later. The workshop could in principle take place anywhere in the world at a favourable location and setting, like we had in 's-Hertogenbosch.