Optimal design of operating frequency for the ionic liquid compressor applied in hydrogen storage

The ionic liquid compressor developed in recent decades shows a prospective application in hydrogen storage. The gas flow and the movement of the metal piston cause a complex two-phase interaction problem. Both this gas-liquid interaction and the structure dimension are significantly influenced by the operating frequency, which is not reported in the public literature. Therefore, this paper proposed a design method to identify the optimal operating frequency of the compressor. The dynamic flow characteristics at different operating frequencies with the same liquid height or the same liquid volume were studied by computational fluid dynamics (CFD) and image process methods. The result showed that the smallest fluctuation in the liquid level stability was obtained at the frequency of 3 Hz with the same liquid height. The maximum mass flow rate for delivering hydrogen and the minimum mass flow rate for delivering ionic liquids were achieved at 2.88 g/s and 14.02 g/s, respectively under the frequency of 3 Hz. The maximum isothermal efficiency of 60.19 % was obtained at the frequency of 3 Hz with the same liquid volume. Therefore, the operation frequency of 3 Hz was recommended considering the liquid level stability, the delivered mass flow rate and the specific energy consumption.