Air Cycle Refrigeration



Refrigeration is a world wide multi-billion pound business, with applications ranging from food processing to air conditioning.This industry is under massive pressure to develop new ideas, technologies and methods of work that will meet the demands of an ever changing world.

One major driver for the industry is the impending legislation resulting from the Kyoto and Montreal Protocols, which will outlaw the use of the most common chlorofluorocarbon (CFC) and hydrofluorocarbon (HFC) refrigerant gases currently being used in the world today, in an attempt to reduce global warming and its effects.

CFCs and HFCs are toxic and have large global warming and ozone depletion potentials; consequently an environmentally-friendly alternative is urgently required.  A solution to this problem has been designed in the form of an air cycle refrigeration system for blast freezing applications, which uses air as the refrigerant in place of CFCs and HFCs.


Air cycle refrigeration manipulates the fact that when air expands, there is an associated drop in its temperature.

Before the air can be expanded to produce a cooling effect, it must first be compressed; this is achieved by passing the air through two stages of turbomachinery compressors.  The compression of the air results in its temperature rising, so to provide very cold air at the end of the cycle, it is necessary to remove heat from the air; this is achieved by passing the air through heat exchangers immediately after each stage of compression.  The final stage of the cycle is to expand the air using a turbine, yielding an instantaneous drop in the temperature of the air to around -60oC, dependent upon necessary cooling requirements.

The primary compressor is driven by a high speed electric motor, operating at a speed of up to 25,000 rpm, whilst the combined secondary compressor and turbine module, arranged in the ‘bootstrap’ configuration, is powered completely by the flow of the air through it, eliminating the need for further power input.  To maximise mechanical efficiency, the design utilises the latest magnetic bearing technology.  Losses due to non-isentropic processes have been minimised by designing optimised components using Computational Fluid Dynamics (CFD) software.


The air cycle refrigeration system for blast freezing applications offers the following main benefits:

  • The system is immune to the impending phase out of CFCs and is environmentally friendly
  • It is relatively leak free, eliminating the need for costly refills and potnetial fines associated with refrigerant leaks
  • Air cycle refrigeration systems offer better performance at off-design conditions than existing systems
  • The lower temperatures offered by the system lead to shorter freezing times and hence improved process throughput, whilst also reducing moisture loss and improving food quality

Queen's Project Number

Air Cycle Refrigeration

Lead Institution

Queen's University Belfast


Project Funding

We have access to a range of potential funding mechanisms to support your business collaborate with this project including

ktp Knowledge Transfer Partnerships are based on partnerships between academic groups and companies who need access to skills and knowledge in order to innovate. The academic and industrial partners jointly devise and manage a two or three year programme to achieve the advances the company needs. This programme of work is carried out in the company by a KTP Associate and the resulting relationship can be very challenging and rewarding to all parties
4k-vouchers Innovation Vouchers are designed to enable small Northern Ireland enterprises to access knowledge and expertise to develop innovative solutions to business issues. The programme provides a voucher of up to £4000 to enable small enterprises to engage with one of the 41 universities, colleges and other publicly funded research organisations throughout Northern Ireland and the Republic of Ireland
If you are interest and would like to find out more including potential funding mechanisms, please complete your details below