Last week,  with the delivery of the pressure vessels and feedback loops at the assembling hall, the construction of the  100 kW TAP (Thermo Acoustic power) unit  is started.

The housing is build in two sections and will be filled with helium at 600 kPa. Because of the large volume the design, construction and testing of the pressure vessels takes a lot of effort and is done according to the PED 97/23/EC category IV requirements.

During the last months most parts and components like heat exchangers, regenerator, valves, pumps etc. are prepared, manufactured or ordered and are ready for assembling now.

After the build is completed the TAP will be tested functionally at low mean pressure  and low power first before transporting the system to the paper factory plant in the north of the Netherlands. There the TAP will be coupled to the flue gas heat exchanger which will be installed during the next production stop.

According to the plan we expect to have  TAP in full operation for testing by the end of May.

To be continued!

Record onset temperature difference of 31 K

Within the framework of the THATEA project (European joint project FP7-FET) Aster has designed, build and test a multistage thermoacoustic engine for low input temperature operation.

Heat is supplied and removed by the internal gas-fluid heat exchangers connected to a high and low temperature water circuit. Oscillation start when the high temperature water circuit reach 51°C and the low temperature water circuit is at 20 °C.  The setup for testing this four stage traveling wave engine is shown below.

Brief explanation

At declining temperatures thermoacoustic engines become increasingly more sensitive to imperfections such as heat exchanger temperature drop, acoustic impedance matching and dissipation. Thermoacoustic power gain is proportional with the operating temperature consequently leading to less gain at abating temperatures. Because the thermoacoustic engine is a power amplifier loop power has to be increased at lower gain to maintain the same net output power. Higher loop power however will result in higher acoustic loss. Summarizing, these two effects will increase acoustic loop power (higher loss) and reduced gain and reinforce each other in a negative sense seriously degrading overall system performance at declining operating temperatures.

One way to overcome this problem, and to allow for efficient operation at declining temperatures (< 200°C), is to increase the (thermo)acoustic power gain by using multiple regenerator units (regenerator clamped between two heat exchangers). This is not as straight forward as it seems because of the thermal and acoustic interaction between the regenerator units. In the common torus geometry, as for example used in the high temperature engine, a high and near real acoustic impedance, required to drive the thermodynamic cycle properly, can not be maintained in more than two regenerator units at the same time. In addition the standing wave resonator which is part of this configuration shows relatively high acoustic losses which becomes increasingly harmful at declining operating temperatures.

For low temperature operation therefore, a novel acoustic resonance and feedback circuit is implemented which allows for inserting an arbitrary number of regenerator units while maintaining the optimal high and real impedance in each stage

The low temperature engine is build up from four identical regenerator units which are connected acoustically in series by near traveling wave loop sections and connected thermally in parallel.

Low cost aluminum brazed louvered fin heat exchangers are used to supply and remove heat from the thermoacoustic process in the regenerator. The low temperature heat exchangers are connected to a car radiator plus fan. The high temperature heat exchangers are connected to a dedicated gas fired water heater to simulate a waste or solar heat source.  Helium at 3.1 MPa bar is used as working fluid.

Converting 100 kW waste heat at 130-150°C into electricity

This project is funded by the Dutch Economic Affairs within the framework of the Small Business Research Programme (SBIR).

Based on the four stage traveling wave concept, a 100 kW_T thermoacoustic power (TAP) generator is under construction now.

For the TAP project Aster collaborate with Huisman Innovations B.V. (www.huisman-elektro.nl) and Innoforte (www.innoforte.nl). Recently the first phase of this project which include also identification of component supplier and launching customers in industry is finished.

This project is carried out in the framework of phase two of the Dutch SBIR program. The 100 kW TAP will be installed at a paper manufacturing plant in the Netherlands for converting part of the flue gas at 130-150°C from the paper drying process into electricity. Emphasis in this project is on production and cost aspects lowering the investment per kW_e to a level competitive to ORC’s. After successful completion of this pilot, commercialization and delivery of 100kW_T to 1 MW_T thermoacoustic power generators for industrial waste heat recovery and as add-on for CHP systems is planned to begin in 2012.

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

Abstract

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

Acoustics08_kees_de_blok

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