Acoustic waves generated by a TA (ThermoAcoustic) laser pair Wongee Chun a , Seung Jin Oh a , Yoon Joon Lee a , Sang Hoon Lim c , Rohit Surathu b , Kuan Chen b, * a Department of Nuclear and Energy Engineering, Jeju National University, Jeju 690-756, Republic of Korea b Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA c New and Renewable Energy Research Division, Korea Institute of Energy Research, Daejeon 305-343, Republic of Korea article info Article history: Received 23 August 2011 Received in revised form 19 February 2012 Accepted 20 February 2012 Available online 22 March 2012 Keywords: Acoustic energy Focusing and synchronization Phase difference Sound wave Thermoacoustic laser pair abstract Sound waves and acoustic energy generated by two identical TA (ThermoAcoustic) lasers were analyzed and studied. SPL (Sound Pressure Level) meters and microphones were employed to measure and study the sound waves at different distances from the openings of the TA laser pair for different laser position arrangements. The sound waves of the two TA lasers at or near the focusing point were found to be almost 180  out of phase when the distance between the openings of the two lasers was within about two tube diameters and the angle between the laser axes did not exceed 135  . As the distance increased, it became difficult to control the two TA lasers in synchronized operation. For separation distances greater than three times tube diameter, the sound wave amplitudes and the phase difference between the two laser outputs varied periodically with time. With the openings of the two TA lasers touching each other, the frequency of the sound waves increased when the angle between the laser axes was very close to 180  . In this case, the glass tube opening was no longer a pressure anti-node and the wavelength of the fundamental mode reduced to approximately twice the tube length. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Thermoacoustics is a field that studies the conversion of heat to acoustic energy. Research on thermoacoustics can be dated back to the late 19th century. Lord Rayleigh discussed the possibility of pumping heat with sound in 1878 [1]. For power generation, heat should be pumped into the working gas of a TA converter during or after compression, and removed from the gas during or after expansion of the gas. A TA heat pump or refrigerator operates on a thermodynamic cycle in the direction opposite to that of the power cycle. Using sound waves to replace a mechanical compressor in heat engine operations has recently being tested in advanced propulsion systems. In a pulse -detonation engine the pressure rise in the power cycle is solely due to the shock waves generated by explosion. Theories and models have been developed and reviewed for thermoacoustic phenomena and devices [1e 7]. The interest in thermoacoustics has been increased in recent years due to its applications to power generation and refrigeration. Researches on heat-generated acoustic oscillations in Sondhauss and Rijke tubes were reviewed in Bisio and Rubatto’s paper [8]. Actual and possible applications of these acoustic oscillations were also described in this paper. The TA engine is one of the thermofluidic oscillators in which thermodynamic oscillations are generated and sustained by steady external temperature differences [9]. Various TA converter designs and different forms of input energy have been tested to generate sound waves of high amplitude and/or high frequency. Simple solar-powered, ¼ -wavelength TA lasers can generate sound waves with an amplitude greater than 120 db at a distance 1 m away from the laser opening [10]. Symko and students at the University of Utah have recently developed TA lasers for the generation of sound waves in the kHz range [11]. Symko’s team has also developed miniature TA engines and TA array energy converters for the generation of electricity [12e14]. Element interaction in TA engines and optimizations of TA system compo- nents or geometries were studied in [15e17]. Spoor and Swift [18,19], McDonald and Symko [20], and Chen et al. [21] have investigated the coupling effects of TA devices. TA converters powered by engine waste heat (e.g [22]), concentrated solar fluxes (e.g [23]), or even candles (e.g [24]) have been developed and tested. In the past two decades, applications of the thermoacoustic effect to refrigeration (e.g [25,26]) and heat pumping seemed to be more popular and successful than power generation. Commercial TA coolers for gas liquefaction and other cooling and cryogenic applications are now available (e.g [27]). Recent developments in TA engines (e.g [28]) and converters, as * Corresponding author. E-mail address: chen@mech.utah.edu (K. Chen). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2012.02.047 Energy 45 (2012) 541e545