SPECIAL ISSUE PAPER Design and experimental evaluation of a travelling‐wave thermoacoustic refrigerator driven by a cascade thermoacoustic engine Isares Dhuchakallaya 1 | Patcharin Saechan 2 1 Department of Mechanical Engineering, Faculty of Engineering, Thammasat University, Klong‐Luang, Pathumthani 12120, Thailand 2 Department of Mechanical and Aerospace Engineering, Faculty of Engineering, King Mongkut's University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand Correspondence Patcharin Saechan, Department of Mechanical and Aerospace Engineering, Faculty of Engineering, King Mongkut's University of Technology North Bangkok, Bangsue, Bangkok 10800, Thailand. Email: patcharin.s@eng.kmutnb.ac.th Funding information King Mongkut's University of Technology North Bangkok, Grant/Award Number: KMUTNB‐ART‐60‐097 Summary A travelling‐wave thermoacoustic refrigerator driven by a cascade thermoacoustic engine is evaluated experimentally in this paper. A prototype is developed under the constraint of a low‐cost and less complicated device. In order to reduce the total budget, commercial materials and standard parts are selected, and air at atmospheric pressure is used as working fluid in the system. The thermoacoustic coupled engine‐refrigerator system consists of 1 standing‐ wave unit, 1 travelling‐wave unit, and 1 travelling‐wave refrigerator arranged in a linear configuration. A resonator‐tube is connected at each end of the thermoacoustic core. The effects of the length and hydraulic radius of the regenerator in the refrigerator on the cooling performance are investigated at different levels of input power. In the experimental results, the maximum temperature difference of 17.6°C was realised at the no‐load condition. The maximum coefficient of performance relative to Carnot (COPR) of 2.4% was accomplished at the cooling load of 13 W. KEYWORDS cascade, engine, linear configuration, refrigerator, thermoacoustic 1 | INTRODUCTION Thermoacoustic technologies deal with the conversion between thermal and acoustic energies of working fluids within the vicinity of a solid boundary. The interaction between the oscillating fluid and solid surface under an appropriate phase relationship between pressure and velocity oscillations is so‐called “thermoacoustic effect” which is capable of either producing work or offering a heat‐pumping effect. Thermoacoustics is a novel type of technology because of its reliability, low maintenance cost, and environmental friendliness. In the thermoacoustic devices, inert gases or air can be used as the working fluids. They are environmentally friendly and do not contain any toxic, flammable, or ozone depleting substances. In addition, the structure of such devices is simple and has no moving parts, which makes them attractive because of high reliability and low cost of manufacture and maintenance. 1 Furthermore, the cooling capacity can be adjusted straightforwardly by varying the level of sound pressure, unlike the compressor Nomenclature: A cross‐sectional area (m 2 ); a speed of sound (m/s); _ E acoustic power (W); P pressure (Pa); _ Q load cooling load, (W); _ Q SWU heating power supplied to SWU, (W); _ Q TWU heating power supplied to TWU, (W); r radius, (m); T a absolute temperature of the AHX (K); T c absolute temperature of the CHX (K); x distance Greek letters: Δ difference; δ penetration depth (m); γ ratio of isobaric to isochoric specific heats; η cooling cooling efficiency; ρ mean density (kg/ m 3 ); σ Prandtl number; μ viscosity (Pa‐s); ω angular frequency (s -1 ) Subscripts: a ambient; c cold; ν viscous Special symbols: Im[-] imaginary part of; Re[-] real part of; | | magnitude of complex number; ∇ spatial gradient,; ∂ partial derivative; Overdot time derivative; Tilde complex conjugate Received: 25 June 2017 Revised: 20 August 2017 Accepted: 29 August 2017 DOI: 10.1002/er.3897 Int J Energy Res. 2017;1–9. Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/er 1