Experimental investigation of a single plate thermoacoustic refrigerator

Thermoacoustic refrigeration was developed during the past two decades as a new, environmentally safe refrigeration technology. The operation of thermoacoustic refrigerators employs acoustic power to pump heat from a cold to a hot temperature reservoir. The disadvantage of such devices is that, because of the poor performance of their individual components, the acoustic driver and heat exchangers, the efficiencies achieved up to date are lower when compared to commercially available refrigerators. The poor performance of the heat exchangers can be attributed to the fact that in thermoacoustic refrigerators the physical situation is characterized by oscillating flow with zero mean velocity. For such situations heat transfer has not yet been completely understood, and conventional heat exchanger design methods are not applicable.; One objective of the present thesis was to gain better insight into the heat transfer in oscillatory flows. In order to achieve this goal the oscillating temperature fields and time averaged heat fluxes in a thermoacoustic refrigerator model were measured applying holographic interferometry (HI) combined with high-speed cinematography. To apply HI to temperature measurements in an acoustic field two new evaluation procedures that account for acoustic pressure variations were developed. The procedures were verified by comparing temperature measurements obtained with the new evaluation procedures to theory. The temperature and heat flux measurements revealed unexpected heat transfer behavior: heat flow from the colder working fluid to a heated plate at the edge of the plate was detected. Through the energy balance this heat transfer into the plate could be related to the thermoacoustic effect. In addition to revealing this unexpected behavior, the thermoacoustic effect was visualized through the temperature measurements.; Additionally, a design optimization algorithm for thermoacoustic refrigerators was developed. Through a first law analysis four main modules of the refrigerator were identified: (i) acoustic driver, (ii) resonance tube, (iii) heat exchangers and thermoacoustic core. To find a global performance maximum of the thermoacoustic refrigerator, viewed as a thermodynamic system, the analysis suggests separate optimization of these four main modules. From the linear theory 19 independent design parameters, relevant for the optimization of the thermoacoustic core, were identified. By introducing new scaling arguments it was possible to reduce the number of parameters to 10. Performance calculations of the thermoacoustic core predict limiting values of 40% to 50% of Carnot's efficiency.; With the two new evaluation procedures for HI this dissertation provides a novel contribution to the field of metrology, and with the measurements of the temperature fields and heat fluxes as well as with the design algorithm and the optimization scheme new contributions to the field of thermoacoustics.