Liquid Piston Compression Heat Transfer Prediction via Thermal-Resistance Network: Simulation, Experimental Validation, and Liquid Carryover Evaluation

Liquid piston compressors gain attention due to their potential for more efficient and isothermal compression compared to traditional solid piston compressors. Liquid piston compressors use a liquid column instead of a solid piston, allowing for innovative mechanisms to enhance heat transfer and achieve near-isothermal compression. However, a validated analytical model for heat transfer in liquid piston compressors is still needed to understand the exhaust phase within a liquid piston. In this work, a thermal network model, able to predict the polytropic index to within 8% of the experimental results, is proposed. Moreover, thorough experimentation is conducted to measure the amount of liquid carried over to better understand the exhaust phase. In the results, it is revealed that the piston carries over 13-21 mL of liquid within the exhaust gas for 10-23 s of stroke. Notably, the difference in liquid carried over for the three-stroke times is not statistically significant, indicating that the liquid carried over is a function of liquid piston design and not stroke time. Finally, most liquid piston applications consider only water; hence, for the first time, this research assesses the stability of a cycle using a nonflammable hydraulic fluid (Fuchs 46 M red) to enhance compressor longevity and material compatibility. A thermal network model for liquid piston compressors, accurate within 8% of experiments, is presented. Extensive testing reveals liquid carryover during exhaust is independent of stroke time, highlighting piston design importance. Also, in this study, a nonflammable hydraulic fluid is evaluated to improve compressor durability and material compatibility for future applications.image (c) 2024 WILEY-VCH GmbH