Experimental investigation of internal air flow during slow piston compression into isothermal compressed air energy storage

摘要

Compressed air could be a solution for the future mass storage of renewable energies. The isothermal compression and expansion of air by liquid piston is a solution that offers good performance and significant power. Lengthening the compression chamber and slowing down piston displacement may be advantageous for quasi-isothermal development. Presented here is an analysis of the internal air flow during slow piston compression inside a compression chamber with a very low stroke-to-bore ratio. The existence of two consecutive flow regimes is produced repeatably by 2D PIV (particle image velocimetry) measurement. First, a highly-structured regime develops with air speeds significantly higher than the piston advance speed, and a general recirculation of the air. The symmetry of this structure is confirmed with a simple flow distribution model. A second, more disorderly, flow regime then takes over for the remainder of the compression. The transition between the two regimes observed is also described, highlighting instabilities in the high shear zones in the transition from the first regime to the second.