Spray cooling technique in liquid piston gas compression and impact of air dissolution on efficiency evaluation at different pressure levels

Abstract

For a compressed air-based energy storage, the integration of a spray cooling method with a liquid piston air compressor has a great potential to improve the system efficiency. To assess the actual applicability of the combination, air compressions with and without the spray were performed from different pressure levels of 1, 2, and 3 bars with the pressure ratio of 2. Under the testing conditions, compressions with the spray technique showed about 98–98.5 % isothermal efficiencies for all the three pressure levels, which are huge improvement from the efficiencies of 83–88 % without the spray. Droplet properties that are critical to determining the heat transfer were quantified to estimate how they were affected by a pressure level. Considering the spray work input, the overall efficiency drops at a higher pressure. In addition, the impact of air dissolution on the compression efficiency was estimated, and a suggestion for adjusting the conventional efficiency evaluation method is made. With the newly suggested approach, at a higher initial pressure, the actual efficiency is even lower than the conventionally calculated efficiency.