Dynamic and thermodynamic characterization of a resonance tube-coupled free-piston Stirling engine-based combined cooling and power system

Abstract

This paper proposes a novel resonance tube-coupled free-piston Stirling engine-based combined cooling and power (FPS-CCP) system for future application in scavenging unconventional natural gas from coal mines and oil fields. Unlike the traditional duplex Stirling system, the proposed system employs a resonance tube to couple an engine and a cryocooler. In addition, a linear alternator is introduced to facilitate startup and meet multiple demands, resulting in flexible adjustments and even higher exergy efficiency. A novel time-domain unsteady model based on thermoacoustic theory was developed to investigate the onset behavior of the (FPS-CCP) system. The proposed model successfully predicted the onset temperature and onset frequency. Results indicated that within the calculation range, the resonance tube with either a larger diameter or a shorter length leads to a lower onset temperature. Furthermore, the system performance under the steady-oscillating state was studied in terms of the typical operation characteristics and energy flow distribution. When the heating temperature is 833 Kand the mean pressure of helium gas is 5 MPa, the proposed system can provide a cooling capacity of 1000 W at 110 K and an electric power of 800 W with a global exergy efficiency of 29.4%, demonstrating an efficient power matching among the subsystems.