Optimization of thermoacoustic refrigerators using second law analysis

In this paper a simplified two-dimensional computational method for studying the entropy generation characteristics inside the core porous structures of a thermoacoustic refrigerator is presented. The model integrates the equations of the standard linear thermoacoustic theory into an energy balance-based numerical calculus scheme. The numerically computed spatial distributions of the time-averaged entropy generation rate within a channel of the stack and adjoining heat exchangers (HXs) evidence as the stack-HXs junctions act as strong sources of thermal irreversibility. The study also shows as, for a fixed refrigerating output level and temperature span, minimum in entropy generation can be effectively used as a suitable design criterion for optimizing simultaneously the stack length, the stack position and the plates interspacing. The same method, when applied to the optimization of the HXs, reveals that the length of the HXs along the direction of the acoustic vibration should be comprised between x1 (the amplitude of the acoustic displacement) and 2x1, the optimal value resulting an increasing function of the fin interspacing and of the drive ratio.

► The entropy generation affecting a thermoacoustic refrigerator is studied.
► The investigation involves a 2D numerical model based on linear thermoacoustics.
► Entropy generation minimization allows for the optimization of the device.
► The stack-heat exchanger junctions act as strong sources of thermal irreversibility.
► The heat exchangers length is of the order of the particle oscillation amplitude.