Thermoacoustic prime movers and refrigerators: Thermally powered engines without moving components

Velocity measurement in pulsating flows is more difficult than that in steady flows. One problem follows from the necessity to synchronize the measuring instrument with the characteristic of the flow which is not required for steady-flow measurements. The second challenge is high frequency response of the measuring device which is required for high frequency pulsating flow measurements. Because of development of more advanced measurement devices, there has recently been a growing interest in pulsating velocity measurement and the number of papers in this field has increased significantly in recent years. In this review, the most frequently-used advanced techniques for velocity measurement in pulsating flows are surveyed. The characteristics of different pulsating flows as well as the advantages and limitations of the developed techniques are discussed.

http://iopscience.iop.org/article/10.1088/0957-0233/21/4/042002/pdf

A critical review on advanced velocity measurement techniques in pulsating flows

The impact of gas blockage on the performance of a thermoacoustic refrigerator

Magnetic refrigeration is a fascinating superior choice technology as compared with traditional refrigeration that relies on a unique property of particular materials, known as the magnetocaloric effect (MCE). This paper provides a thorough understanding of different magnetic refrigeration technologies using a variety of models to evaluate the coefficient of performance (COP) and specific cooling capacity outputs. Accordingly, magnetic refrigeration models are divided into four categories: rotating, reciprocating, C-shaped magnetic refrigeration, and active magnetic regenerator. The working principles of these models were described, and their outputs were extracted and compared. Furthermore, the influence of the magnetocaloric effect, the magnetization area, and the thermodynamic processes and cycles on the efficiency of magnetic refrigeration was investigated and discussed to achieve a maximum cooling capacity. The classes of magnetocaloric magnetic materials were summarized from previous studies and their potential magnetic characteristics are emphasized. The essential characteristics of magnetic refrigeration systems are highlighted to determine the significant advantages, difficulties, drawbacks, and feasibility analyses of these systems. Moreover, a cost analysis was provided in order to judge the feasibility of these systems for commercial use.

Magnetic Refrigeration Design Technologies: State of the Art and General Perspectives

Thermoacoustic oscillations have been one of the most exciting discoveries of the physics of fluids in the 19th century. Since its inception, scientists have formulated a comprehensive theoretical explanation of the basic phenomenon which has later found several practical applications to engineering devices. To date, all studies have concentrated on the thermoacoustics of fluid media where this fascinating mechanism was exclusively believed to exist. Our study shows theoretical and numerical evidence of the existence of thermoacoustic instabilities in solid media. Although the underlying physical mechanism exhibits some interesting similarities with its counterpart in fluids, the theoretical framework highlights relevant differences that have important implications on the ability to trigger and sustain the thermoacoustic response. This mechanism could pave the way to the development of highly robust and reliable solid-state thermoacoustic engines and refrigerators.

Thermoacoustics of solids: A pathway to solid state engines and refrigerators

Thermoacoustic effect, as a subprocess of the photoacoustic effect, can also convert heat to acoustic wave by a thermoacoustic prime mover, and can also pump heat by acoustic wave in a thermoacoustic refrigerator. The present study focuses on a thermoacoustically driven pulse tube refrigerator, utilizing sound from a thermoacoustic prime mover to drive a pulse tube refrigerator. Experiments emphasize on the characteristics of both the thermoacoustic prime mover and the combined refrigeration system, including resonant frequency, onset temperature, pressure amplitude, and refrigeration temperature, etc. A cryogenic temperature lower than 120 K has been achieved from the present system. Much effort is also devoted to the influence of some working gases, such as helium–argon mixture, on the performance of the system.

Application of thermoacoustic effect to refrigeration

The energy flow inside a thermoacoustic regenerator of fluid-filled porous media is analyzed. Based on Biot’s acoustic propagation theory of porous materials, a theoretical model is proposed to consider dynamic solid–fluid interaction, which was generally neglected in traditional models of regenerators. Theoretical expressions for the energy flux and critical temperature gradient are given.

Analysis of energy flow in regenerator of thermoacoustic engines

The selection of operating frequencies is a key step to optimize the performance of thermoacoustic systems, and a minor frequency mismatch can cause a serious drop of the efficiency. Generally, the characteristic frequency of the resonance pipe is a significant factor to determine the operating frequency, however, in a thermoacoustic refrigerator driven by an electrodynamic loudspeaker, the match between the loudspeaker and resonance pipe cannot be ignored. The two-microphone method is used to determine the operating frequency of a thermoacoustic system, meanwhile, the proper position for the stack is also determined. It is demonstrated that the two-microphone method, which can be used to obtain the sound pressure, particle velocity and acoustic impedance distributions in the pipe, is proper to determine the working conditions of a thermoacoustic system driven by an electrodynamic loudspeaker.

Ben-ren Wang

Papers

Application of thermoacoustic effect to refrigeration

Analysis of energy flow in regenerator of thermoacoustic engines

Performance optimization of thermoacoustic systems by measurement with two-microphone method