Abstract
Refrigerators are widely used for cooling. However, vapour compression refrigerators use chemicals which are harmful to the environment. Thermoacoustic refrigeration (TAR) can replace the current vapour compression refrigeration because they are not harmful to the environment. In addition, they have a simple design which does not require moving parts. Thermoacoustic refrigerators use sound in order to induce cooling. They are currently not in use because of their inherent inefficiency as compared to Vapour compression refrigerators. Getting an insight into the geometrical configuration of thermoacoustic refrigerators could potentially provide clarity on the aspect of the systems that can enhance their performance. A typical TAR is made of an acoustic driver, a porous medium (stack) and a resonator tube. This study has considered two configurations of the TAR: a closed resonator and an opened resonator. Two approaches were considered in this study namely numerical modelling and an experimental investigation. The modelling approach of TAR using DeltaEC and the experimental investigation conducted on the standing wave thermoacoustic refrigerator was explained in chapter 4. Firstly, a model of a simple thermoacoustic refrigerator was built using the Design Environment for Low-amplitude ThermoAcoustic Energy Conversion (DeltaEC). This study examined the influence of the position, the length and the porosity of the stack on performance indicators such as the cooling power, the COP and the temperature difference. The geometrical configuration of the stack was adjusted to analyse the trends of the results and get clarity on the designing of TAR The geometry and the position that are susceptible to enhancing the performance indicators were identified. A COP of approximately 80% corresponding to a resonant frequency of 590 Hz was achieved with the stack positioned relatively further away from the acoustic driver. Secondly, experimental testing was conducted on a loudspeaker-driven TAR to identify the best stack (among a sample of stacks having different porosities and lengths) geometry as well as its position in the resonator in order to determine the highest temperature difference. This indicator was adopted to analyse the trends of the results. Temperature difference at different five (5) positions of the resonator using different stacks in a simple thermoacoustic refrigerator was tested and analysed. The resonance frequency was assumed to be constant at 130 Hz. With the device closed, a highest temperature difference of 13.808 K was achieved. The longer stack with the smallest porosity yielded better results at the closest position to the acoustic driver. This shows that a better position of performance is the one closer to the acoustic driver.