MechChem Africa February 2017

⎪ Innovative engineering ⎪

moving parts

ronmental friendliness. These systems also have the potential to utilise low-quality heat sourcessuchasindustrialwasteheat,solaren- ergy or flue gases fromcombustion processes for energy recovery. From acoustics to cooling Acoustic waves are longitudinal waves made up of alternating high-pressure and low-pres- sure zones. At a micro level, the temperature of the gas in a high-pressure zone is raised, while that in the lowpressure zone is lowered. By locating these different zones precisely via resonance, it is possible to use heat exchang- ers to extract heat and to create increasingly hot and cold temperature zones. q reduces the temperature for TAoscillations and improves cooling performance.” Following the successful development of the prototype thermoacoustic refrigerator system, the next step in this research at Tokai University is the development of practical TA engines with a primary goal of contributing to overcoming environmental problems. q References 1. Esmatullah Maiwand Sharify; Shinya Hasegawa: Travelling-wave thermoacous- tic refrigerator driven by a multistage travelling-wave thermoacoustic engine: Applied Thermal Engineering , November 2016. DOI: http://dx.doi.org/10.1016/j. applthermaleng.2016.11.021 2. Mariko Senga; Shinya Hasegawa: Design and experimental verification of a cascade wave- wave thermoacoustic amplifier: Journal of Applied Physics (JAP), 119, 204906 (2016). DOI: http://dx.doi.org/10.1063/1.4952983 3. ShinyaHasegawawebsite(inJapanese)http:// www.ed.u-tokai.ac.jp/thermoacoustic/index. html 4. Video, Thermoacoustic refrigerator. http:// www.ed.u-tokai.ac.jp/thermoacoustic/VIDEO. zip Password: thermoacoustic.

of the cooling power to the total input heating power, that is, the sum of the heating power of each engine. Results The COP increased as the temperature of the heat exchangers in the primer loop was increased and the maximum value of COP was 0.029 at 260 °C, with corresponding cooling power of 35.6W. Furthermore, the researchers obtained gas oscillations at 85 °C – that is lower than the boiling point of water – thereby opening up pos- sibilities for applications of this technology for refrigeration and power generation using low temperature waste heat in factories and auto- mobile engines. Also, refrigeration at -42.3 °C was achieved using input heat at 90 °C. Next steps “The addition of multiple regenerators in the vicinity of the ‘sweet spot’ of the prime mover loop is a major advance in travelling-wave TA engines,” says Hasegawa. “This configuration

Thermoacoustic refrigeration Thermoacoustic (TA) engines use a steep tem- perature gradient to induce high-amplitude sound waves and/or they use high-amplitude sound waves to pump heat from one place to another.

Thermalenergyappliedtotheprimemover generates a temperature gradient along a porous regenerator. At a specific temperature gradient, self-sustained acoustic waves are generated inside an acoustic resonator. The acousticwave canbe used to generate power via a piezoelectric diaphragm, placed at the end of the resonator, which converts the acoustic vibration directly into electrical energy. Also,though,theresonatingacousticvibra-

tions can be used to produce a heat pump/refrigeration ef- fect, via separate hot and cold heat exchangers. Compared to vapour refrigerators, thermoa- coustic refrigerators have no ozone-depleting or toxic cool- ant and fewor nomovingparts. They therefore require no dynamic sealing or lubrication. The technology is also very attractivebecause of its simple low-cost construction, low maintenance cost and envi-

A schematic representation of a thermoacoustic hot-air engine/ prime mover. The alternately hot and cold zones cause self-sustained acoustic waves to be generated inside the acoustic resonator.

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