Authors: Millar, DL
Show More

Citation as:   ris   bibtex   endnote   text   Zotero

The discounted (i = 10%) cost of a unit of refrigeration supplied by a coefficient of performance = 4 surfacebuilt vapour compression refrigeration mine air cooling system, with a load factor of 100%, equipped with condenser water cooling towers and underground spray chambers is approximately CAD 100/MWhr. This rises to CAD 200/MWhr for the same system when the load factor of the plant falls to 25%. These high costs motivate searches for alternative mine air cooling systems. In a reverse Brayton cycle refrigeration system, where compressed air acts both as the refrigerant and the coolant, compressed air that is aftercooled and dried on-surface is delivered to an expansion device underground whereupon it is ‘let down’ to provide a very low-temperature air stream. Cooling is delivered to hot mine intake air simply by allowing it to mix with the cold exhaust of a turbo-expander or eductor. A simplified performance model for a minimum compression work hydraulic air compressor (HAC) is presented, and the formulation is extended to include the expansion device, focusing on the use of an eductor geometry. As it pressurises the mine air that passes through it, the eductor behaves as an underground booster fan, with no moving parts, that cools and dehumidifies the mine air. For the mine, HAC plus eductor systems produce compressed air very cheaply (CAD 6.11/tonne for an open loop HAC, CAD 1.52/tonne for a run-of-river HAC) but only the latter returns a discounted cost of refrigeration supplied of CAD 27/MWhr which is 33% of the CAD 83/MWhr for the incumbent vapour compression refrigeration technology. Keywords: reverse Brayton cycle, mine refrigeration, hydraulic air compressor, eductor cooling

Keywords: reverse Brayton cycle, mine refrigeration, hydraulic air compressor, eductor cooling

Millar, DL 2017, 'A reverse Brayton cycle mine refrigeration system', in M Hudyma & Y Potvin (eds), Proceedings of the First International Conference on Underground Mining Technology, Australian Centre for Geomechanics, Perth, pp. 115-132.

ANSYS, Inc. 2017, ANSYS Fluent, version 16, ANSYS, Inc., Canonsburg, viewed 18 July 2017,
Chen, L-T & Rice, W 1982, ‘Some psychometric aspects of a hydraulic air compressor (HAC)’, Transactions of the ASME, Journal of Energy Resources Technology, vol. 104, pp. 274–276.
Chen, L-T & and Rice, W 1983, ‘Properties of air leaving a hydraulic air compressor (HAC)’, Transactions of the ASME, Journal of Fluids Engineering, vol. 105, pp. 54–57.
del Castillo, D 1988, ‘Air cycle refrigeration system for cooling deep mines’, International Journal of Refrigeration, vol. 11, no. 2, pp. 87–91.
Devonport, WJ 2001, Nozzle Applet Instructions and Source Code, Virginia Tech, Blacksburg, viewed 13 July 2016,
Eastop, TD & McConkey, A 2009, Applied Thermodynamics for Engineering Technologists, 5th edn, Pearson Education, Harlow.
Egan, AL & Ewing, SET, 1937 Conditioning Mine Air, US Patent No. US2097723A, priority date 14 December 1932,
Huang, BJ, Chang, JW, Wang, CP & Petrenko, VA 1998, ‘A 1-D analysis of ejector performance’, International Journal of Refrigeration, vol. 22, pp. 354–364.
Langborne, PL 1979, ‘Hydraulic air compression: old invention – new energy source’, Chartered Mechanical Engineer, vol. 26, no. 10, pp. 76–81.
McPherson, MJ 1993, Subsurface Ventilation and Environmental Engineering, Springer, Dordrecht, 905 p.
Millar, DL 2014, ‘A review of the case for modern-day adoption of hydraulic air compressors’, Applied Thermal Engineering, vol. 69, no. 1–2, pp. 55–77.
Pavese, V, Millar, D & Verda, V 2016, ‘Mechanical efficiency of hydraulic air compressors’, ASME Journal of Energy Resources Technology, vol. 138, no. 6, 11 p.
Rice, W 1976, ‘Performance of hydraulic gas compressors’, Transactions of the ASME, Journal of Fluids Engineering, vol. 98, no. 4, pp. 645–652.
Schulze, LE 1954, ‘Hydraulic air compressors’, United States Department of Interior Information Circular No. 7683, May 1954.
Sheer, J, del Castillo, D & Csatary, C 1986, ‘Unconventional systems for removing heat from deep mines’, The South African Mechanical Engineer, vol. 36, pp. 207–217.
Young, S 2017, Simulating Air Absorption in a Hydraulic Air Compressor (HAC), MSc Thesis, Laurentian University, Sudbury.
Young, SM, Pavese, V, Hutchison, AD, Rico, J & Millar, DL 2016, ‘Interphase mass transfers in hydraulic air compressors for production of mine compressed air’, in R Canello (ed.), Proceedings of the 3rd International Seminar Energy Management in Mining: ENERMIN2016, Gecamin, Santiago, pp. 87–97.
Youngworth, M 1937, ‘An application of the use of compressed air motor exhaust in mine air cooling’, Journal of the Chemical, Metallurgical and Mining Society of South Africa, March 1937, pp. 461–465.

© Copyright 2018, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries to or error reports to