Archive for the ‘ Solar or waste heat powered thermoacoustic cooling (SOTAC / THEAC) ’ Category

THEAC-25

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.

 

theac-schematics

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.

theac-testlab

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 3.5m x 3.5m x 0.6m.

theac-final-version

 

 

 

 

 

 

 

 

 

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.

The first tests showed an onset input temperature less than 50°C. Above this onset temperature, acoustic loop power and cooling power rise proportional with input temperature difference applied to the heat engine stages.

However, within the design and test temperature of 160°C applied,  a cooling power of 25kW is not reached yet due to the under performance of the heat exchangers (aluminium brazed finned tube) exchangers in combination with thermal oil, causing the TA process effectively runs at less than 120°C.

For that reason the commercial versions will make use of 2-phase heat transfer (looped heat pipe) reducing the temperature loss between heat source and thermoacoustic process drastically.

Production of the THEAC-25 by Soundenergy B.V. is planned to  start mid 2017 for  industrial waste heat recovery applications in industry, followed by solar heat driven cooling in 2018 for more southern countries.

Solar powered thermoacoustic cooling

Solar powered thermoacoustic cooling is presumably one of  the first commercial application of thermoacoustics on short term. To day onset and operating temperatures of multi-stage traveling wave thermoacoustic engines are at such a level that heat from vacuum tube solar collectors (120°C-160 °C) can be utilized effectively to power thermoacoustic (heat driven) heat pumps for cooling in domestic and rural applications. Main assets of the concept are the lack of environmental issues, absence of mechanical moving parts and the linear relation between cooling power and solar irradiation.

Market introduction is in preparation by a joint venture together with Solar collector manufacturer Watt Sp. z o.o and Thermo Acoustic Solutions Sp. z o.o both established in Poland. One of the activities within the framework of this collaboration is the build of two prototypes. (1) a representative prototype equipped with fluid-gas heat exchanger for testing in combination with vacuum tube collectors under realistic conditions and (2) a transportable device  for demonstration purposes. The demonstration prototype is completed by last week and is depicted below.

demo_nf_web

For simplicity this demonstrator operates without any fluid circuit and is externally powered by cartridge heaters keeping the hot heat exchanger at 160ºC (simulating  input heat from the vacuum tube collectors) and is cooled by forced convection keeping the cold heat exchanger around 40ºC, which both are representatives temperatures for our applications.

Ice_webTo allow visual inspection of the construction, no isolation is applied at all. Nevertheless the temperature lift of the cooler section is  more than 40ºC and ice is formed quickly at the refrigerator cold heat exchanger as is shown at the left.

The working gas in the demonstration set-up is helium at a mean pressure of 1 MPa, the pressure amplitude is 35 kPa and the oscillation frequency 138 Hz.  Net cooling power at -5ºC is about 50W at a net heat input of 380W at 160ºC. After correction for the absence of any isolation the exegetic efficiency of both the engine section and the refrigerator section is found to be in the order of 0.35 .