1. Date of download: 7/10/2016 Copyright © ASME. All rights reserved. From: Mechanical Efficiency of Hydraulic Air Compressors J. Energy Resour. Technol. 2016;138(6):062005-062005-11. doi:10.1115/1.4033623 Schematic of a hydraulic air compressor—station 1: air inlet; station 2: compressed air outlet; station 3: water inlet; and station 4: water outlet Figure Legend:

2. Date of download: 7/10/2016 Copyright © ASME. All rights reserved. From: Mechanical Efficiency of Hydraulic Air Compressors J. Energy Resour. Technol. 2016;138(6):062005-062005-11. doi:10.1115/1.4033623 Control volume schematic of an HAC: (a) for first law analysis and (b) for analysis where gases dissolve in the water, by-pass the gas–liquid separator, and return to atmosphere via the riser Figure Legend:

3. Date of download: 7/10/2016 Copyright © ASME. All rights reserved. From: Mechanical Efficiency of Hydraulic Air Compressors J. Energy Resour. Technol. 2016;138(6):062005-062005-11. doi:10.1115/1.4033623 Calculated theoretical and overall mechanical efficiency of the reported performance of 14 historical hydraulic air compressor installations [1,9,10], plotted against the product of the mass ratio of the two-phase (water, air) bubbly flow and delivery pressure Figure Legend:

4. Date of download: 7/10/2016 Copyright © ASME. All rights reserved. From: Mechanical Efficiency of Hydraulic Air Compressors J. Energy Resour. Technol. 2016;138(6):062005-062005-11. doi:10.1115/1.4033623 Calculated HAC exergetic efficiency of the reported performance of 14 historical hydraulic air compressor installations [1,9,10], plotted against the product of the mass ratio of the two-phase (water, air) bubbly flow and delivery pressure Figure Legend:

5. Date of download: 7/10/2016 Copyright © ASME. All rights reserved. From: Mechanical Efficiency of Hydraulic Air Compressors J. Energy Resour. Technol. 2016;138(6):062005-062005-11. doi:10.1115/1.4033623 Rate of irreversibility production of 14 hydraulic air compressor installations normalized to the water mass flow rate. Mean results are presented for installations with several test conditions available (see Table 4 in the Appendix). Figure Legend: