Abstract—This work explores the use of thermo-acoustic coolers as alternative technology for refrigeration. A valid experimental evidence on the influence of the geometry of the honeycomb ceramic stack on the performance of thermos- acoustic refrigerators is described. Sixteen cordierite honeycomb ceramic stacks with square cross sections having four different lengths of 26 mm, 48 mm, 70 mm and 100 mm are considered. Measurements are taken at six different locations of the stack hot ends from the pressure antinode, namely 100 mm, 200 mm, 300 mm, 400 mm, 500 mm and 600 mm respectively. Measurement of temperature difference across the stack ends at steady state for different stack geometries are used to measure the performance of the device. The results with atmospheric air demonstrates the influence of the stack geometry on the cooling power and shows that some its geometrical parameters are interdependent. Index Terms— Thermo-acoustic refrigerator, Stack, honeycomb ceramic, sound wave. 1 INTRODUCTION Thermo-acoustic refrigerators offer a solution to the current search for alternative refrigerants and alternative technologies (such as absorption refrigeration, thermoelectric refrigeration and pulse-tube refrigeration) necessary to reduce harsh environmental impact [1]. Thermo-acoustics is a field of study that combines both acoustic waves and thermodynamics. The interaction of the temperature oscillation accompanied by the pressure oscillation in a sound wave with solid boundaries initiates an energy conversion processes. In ordinary experience, this interaction between heat and sound cannot be observed. But it can be amplified under suitable conditions to give rise to significant thermodynamic effects such as convective heat fluxes, steep thermal gradients and strong sound fields. Thermo-acoustic refrigerators (TARs) use acoustic power to cause heat flow from a low temperature source to high temperature sink [2]. Thermo-acoustic refrigerators (Fig. 1) consist mainly of a loudspeaker (a vibrating diaphragm or Thermo- acoustic prime mover) attached to a resonator filled with gas, a stack usually made of thin parallel plates, and two heat exchangers placed at either side of the stack. The stack forms the heart of the refrigerator where the heat-pumping process takes place, and it is thus a critical element for determining the performance of the refrigerator [3]. For the temperature gradient along the stack walls to remain steady, the material selected should have higher heat capacity and lower thermal conductivity than the gas; otherwise the stack won’t be affected by the temperature oscillations of the nearby gas. In addition, a material of low thermal conductivity should be chosen for the stack and the resonator to prevent leaking from the hot side of the resonator back to the cold side and to withstand higher pressure [4]. Fig. 1: Schematic diagram of a typical Thermo-acoustic refrigerator Using a sound source such as a loudspeaker, an acoustic wave is generated to make the gas resonant. As the gas oscillates back and forth within the chamber, the standing sound wave creates a temperature difference along the length of the stack. This temperature change is a result of compression and expansion of gas by sound pressure and thermal interaction between the oscillating gas and the surface of the plate. Heat is exchanged with the surroundings through heat exchangers at the cold and hot side of the stack [2]. The basic mechanics behind Thermo- acoustics are already well-understood. A detailed explanation of the way Thermo-acoustic coolers work is given in Refs [3] and [5]. Recent research focuses on improving the performance of the devices so that Thermo- acoustic coolers can compete with commercial refrigerators. One way to improve the performance of current devices is by understanding interactions between design parameters experimentally. Due to the critical nature of the interaction between the gas and solid material forming the stack, there have been a number of studies focused on the selection and optimisation of the stacks for standing-wave refrigerators. Typically, stacks with regular geometrical configurations, for example parallel-plate type [2], offer excellent performance. However, such stacks are too costly and too difficult to make, especially when the channel size goes down into tens of microns range. Similarly, there seem to be very few commonly available materials for such stacks. Therefore, a common practice in Thermo-acoustics is to use ceramic substrate with square pores. The idea behind A sustainable solution for refrigeration using Thermo-acoustic technology (March 2016) L.K. Tartibu L.K. Tartibu, Mechanical Engineering Technology Department, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa (e-mail: ltartibu@uj.ac.za).