Thermoacoustic analysis of a pulse tube refrigerator

Abstract

Abstract. Thermoacoustic devices use acoustic gas oscillations in place of pistons. They execute mutual energy conversion between work flow and heat flow through the heat exchange between the gas and the channel walls. Understanding of the acoustic field is necessary to control the resulting energy flows in thermoacoustic devices. We will present from experimental point of view the physical mechanism of a pulse tube refrigerator that is one of the travelling wave thermoacoustic heat engines. IntroductionSimplifying heat engine's hardware design while maintaining the highest possible efficiency has been a longstanding desire since the 19th century. One way to achieve this is to eliminate solid pistons from heat engines. A thermoacoustic device uses acoustic gas oscillations in place of pistons and hence it operates essentially with no moving parts.Wheatley [1], Swift [2] and Tominaga [3] proposed work flow I and heat flow Q from a viewpoint of thermodynamics, and successfully gave a framework for understanding the thermoacoustic device working as a prime mover or a cooler. The work flow I is equivalent to the acoustic intensity used in acoustics, and the heat flow Q is the energy flow associated with the hydrodynamic transport of entropy. Thermoacoustic effects such as production and strong damping of I by the temperature gradients [4], and occurrence of Q against the temperature gradient take place in narrow channels where sound wave propagates. Such effects are governed by two factors; one is a nondimensional parameter ωτ [3], a product of an angular frequency ω of the sound wave and a thermal relaxation time τ for a gas to equilibrate with the channel walls, and the other is the acoustic field expressed by the acoustic pressure and the axial acoustic particle velocity.We will present the propagation of acoustic waves in narrow channels [5] and show the physical mechanism of a pulse tube refrigerator that is one of the thermoacoustic devices. Measurements of pressure and velocity oscillations show that pulse tube refrigerator controls the phase difference between them to enhance heat flow through the regenerator [6].