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Title: Investigation of thermoacoustic processes in a travelling-wave looped-tube thermoacoustic engine
Author: Abduljalil, Abdulrahman S. Ahmed
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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Abstract:
In thermoacoustic devices, thermal energy is directly converted to an acoustic wave (mechanical energy) or an acoustic input is converted into thermal energy. This is a result of heat interaction between a solid material and adjacent gas, within the so-called ‘‘thermal penetration depth” of the compressible oscillatory flow. Thermoacoustic technology is receiving growing interest in research for its many advantages, such as having no moving parts, being environmentally friendly and the possibility of using renewable energy for its operation (Adeff and Hofler, 2000). However, this technology is still at the development stage and needs more research to produce feasible and practical devices that are ready for domestic and industrial applications. A looped-tube travelling-wave thermoacoustic engine was designed using DELTAEC (Design Environment for Low-amplitude ThermoAcoustic Energy Conversion). The device was equipped with a ceramic regenerator, which is commonly used in catalytic converters for automotive applications, with square channels. The results of preliminary testing of the device were compared with theoretical values estimated from the numerical model. Very close agreement was observed at the qualitative level and reasonable agreement was observed at the quantitative level. After the validation stage, the device was equipped with three selected low-cost porous materials for performance testing and studies. In addition to the ceramic regenerator that was tested before, regenerators made from stainless steel scourers, stainless steel wool and wire mesh screens were tested. This last type is widely available and commonly used in this application. To facilitate meaningful comparison, the regenerators were made in two sets: one having a common hydraulic radius of 200 μm and the other of 120 μm. In total, six regenerators were successfully tested. Before the performance experiments, all of the regenerators were tested in a steady air flow rig that was built for this purpose, to estimate their relative pressure drop due to viscous dissipation. The relative performance of the regenerators was then investigated. The testing focused on the onset temperature difference, the maximum pressure amplitude generated and the acoustic power output as a function of mean pressure as it varied from 0 to 10 bar gauge pressure. This comparative testing revealed a poor relative performance for the regenerators made of scourers and steel wool, while the cellular ceramic regenerator- 10 -seems to offer an alternative for traditional regenerator materials, which may reduce the overall system cost. The literature reports many different observations of nonlinear phenomena by various researchers, a fact which drove the candidate to carefully monitor the behaviour of the device at all stages and led to an interesting finding of a number of nonlinear behaviours during the start-up of the device. These behaviours included an “on-off” effect and “fishbone-like” oscillations in addition to the normal smooth start-up process. The new findings and the detailed observations are reported in chapter 6 of this thesis. The existence of these phenomena focused attention on identifying the key parameters affecting the existence and type of behaviour, which were found to be the mean pressure and the input power, in addition to the material of the regenerator. An attempt was also made to study the phenomena quantitatively. The observations suggest that there are strong interactions between the acoustic and temperature fields within the regenerator, which may be responsible for the reported quasi-periodic unsteady behaviour of the engine.
Supervisor: Jaworski, Artur. Sponsor: University of Bahrain
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.554178  DOI: Not available
Keywords: Thermoacoustic ; travelling-wave ; regenerators
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