Design and evaluation of two-stage travelling wave thermoacoustic cooler

The overall aim of this research is to investigate the underpinning science behind constructing a practical travelling-wave thermoacoustic refrigerator. At the outset, this was defined as a demonstrator that could be further developed into a means of thermal management of various enclosures – for example weather proof enclosures containing heat generating electronics, popular across the process industries. The practical requirements were set as 400 to 500 W of cooling power at 25 K temperature difference between the inside of the enclosure and the ambient. The initial research addressed issues of coupling the linear motors to such a refrigerator. This included analytical solutions of equations governing the electrodynamic behaviour of the motors, which lead to obtaining preferred acoustic conditions for their optimum performance. Meanwhile, a series of DeltaEC simulations was conducted to investigate possible configurations of the acoustic network that provide the required acoustic impedance matching. The project had the practical limitations of using two existing Q-drive linear motors. As a result, a refrigerator network has been developed which required a compliance and inertance matching a twin-alternator excitation and a two-stage looped-tube travelling-wave refrigerator. The second part of the research was concerned with engineering a practical demonstrator of the above refrigerator concept. DeltaEC simulations have been used to design a practical build and predict its performance characteristics. A prototype, based on helium pressurised at 40 bar and operating frequency of 60 Hz, has been subsequently built and commissioned. A number of experiments have been conducted to evaluate its performance “as built” followed by improvements including, in particular, the use of elastic membranes to supress Gedeon streaming. The prototype achieved a maximum temperature difference of 40ºC, minimum cold temperature of -7.5ºC, maximum COP of 2.05, highest COPR of 21.72% and total cooling power of 283W. Good overall agreement was found between modelling and experiments.