The combination of a liquid piston gas compressor and a solid metal insert can achieve a near-isothermal compression process, which can greatly contribute to improving the system efficiency of a compressed-air energy storage system. To examine the effectiveness of the insert at various pressure levels, compressions were performed in a liquid piston compressor with and without copper wire mesh inserts at three different pressures of 1, 2, and 3 bars. The use of inserts increased isothermal compression efficiencies by 8–10% from the baseline isothermal efficiencies about 83–87%, while the compromised air volume due to the inserts was minor. In addition to the solid insert-based technique analysis, a comparative study with other proven liquid-based heat transfer enhancement techniques, spray injection and aqueous foam, was performed. Not only was a quantitative analysis made comparing the isothermal efficiency values but the pros and cons of each technique’s distinctive working mechanisms were also compared.

The acceleration of climate change and increasing weather-related disasters require more active utilization of renewable energy. To maximize the use of renewable energy, energy storage is an essential part. Liquid piston gas compressors have recently drawn attention because of their applicability to compressed air-based energy storage. Aqueous foam can be used to enhance the efficiency of liquid piston gas compression by boosting heat transfer. To validate the effectiveness of the combination of liquid piston and aqueous foam in a multi-stage compression system, which can contribute to higher efficiency, the present work performed experimental study at various pressure levels. Compressions were performed with and without aqueous foam at three different initial pressure levels of 1, 2, and 3 bars. For each cycle of compression, a pressure ratio of 2 was used, and the impact of pressure levels on compression efficiency was measured. With the use of foam, isothermal efficiencies of 91.4, 88.2, and 86.6% were observed at 1, 2, and 3 bar(s), which improved by 2.2, 2.1, and 1.3% compared to the baseline compressions. To identify the cause of the effectiveness variations, the volume changes in the foam at the different pressure levels were visually compared. In higher-pressure tests, a significant reduction in the foam amount was observed, and this change may contribute to the decreased effectiveness of the technique.