City Research & Enterprise Review 2011
  1. Health & Wellbeing
  2. Cultural Heritage
  3. Processes & Systems Improvement
  4. Government & Society at Large
  5. Effective Use of Energy
  1. The power of positive thinking
City Research & Enterprise Review 2011

The power of positive thinking

Established in 1995, City’s Centre for Positive Displacement Compressors has become a global go-to resource for pioneering research and consultancy and is now turning its attention to green technology.


The Centre for Positive Displacement Compressors (or the Compressor Centre) evolved from parallel yet independent work that began in the 1980s on screw expanders at City University London and screw compressors at the University of Sarajevo. It was the civil war in former Yugoslavia that brought the two together, when many academics were forced to leave the country and seek new tenures abroad. Professor Nikola Stosic was one of them - he secured a research position with Professor Ian Smith at City, funded by the Engineering and Physical Sciences Research Council (EPSRC). This twist of fate proved to be the start of a long and fruitful partnership.

Compressors and expanders

Screw compressors are machines that pressurise liquid or gas in industries such as energy, water management, oil and gas, and desalination. They consist of two powered, meshing, helical screws, known as rotors. Screw expanders have a similar design, but enable gases to expand. This turns the rotors, which can then be connected to a generator to create energy. The performance and efficiency of each machine are influenced by the profile of the rotors and it is this area that became a focus for the Compressor Centre. The initial EPSRC collaboration highlighted that there was a serious lack of engineering science-based knowledge of how to design and predict the performance of these machines - something that was confirmed by discussions with industry. So it was realised that by combining their abilities and using the existing test facilities at City, Professors Smith and Stosic could offer industry advisory services that were not available elsewhere.

With the support of Holroyd - a UK-based rotor manufacturer - Professor Stosic was awarded a Royal Academy Chair to remain at City and the Compressor Centre was initiated in 1995. From the outset its aims were to advance the design and manufacture of compressors and expanders through research, while supplying consultancy services to industry in the form of analysis, design, testing and development, and training of engineers.

As part of this approach, the Compressor Centre formed a partnership with the Institution of Mechanical Engineers (IMechE) to host an international conference on compressors and their systems at City. This has been held biennially since 1999 and is now a recognised forum for advancements in the compressor industry.

Since 1995 the Compressor Centre has gone from strength to strength. It has a truly global reach, cooperating with 69 companies in 31 countries across all continents and generating approximately £8 million in research income. To support this work, five test rigs have been built and 133 research papers have been published in conference proceedings and journals. In recognition of their work, members of the Centre have received 11 awards, including the James Clayton Prize - the IMechE's most prestigious accolade - which was given jointly to Smith and Stosic in 2006.

The factors behind the success

A key to the Compressor Centre's global reputation has been the breadth of its offerings. It licenses its Scorpath/Disco software to screw compressor manufacturers to help them design and maximise the performance of their machines.

"City's advantage over others comes from our ability to optimise screw machines to give the best performance, rational investment and operation response even if made of ordinary and cost-effective elements,"
explains Professor Stosic.

In addition, customers' engineers take a course at the Compressor Centre, providing them with insight into the procedures used to programme the software as well as training to use it. The Compressor Centre also offers its own design service, most recently creating a family of oil-flooded compressors for a Chinese manufacturer.

Looking ahead to a green future

It was one such design assignment that created a new direction for the Compressor Centre, when Geodynamics - an Australian geothermal energy company - commissioned a new type of steam expander. "Geothermal energy is most apparent in areas of volcanic activity, where the tectonic plates forming the Earth's surface come into contact with each other. It is normally manifested in the form of geysers or fumaroles, where steam and hot water naturally emerge from the ground," says Professor Smith.

Geodynamics is harnessing this energy by pumping water underground, where it is heated by the hotter temperatures found at depth and from where it returns to the surface as steam. To reap the benefits of this process, the Compressor Centre has designed and manufactured a prototype expander which can then convert this steam to electricity. The Centre was the only organisation in the world that would commit to building such a machine.

A new venture

With the steam expander device completed in Spring 2011 and currently undergoing tests in Italy before it ships to Australia, a spin-out company, Heliex Power Ltd., has been formed to exploit the commercial potential of the idea. Heliex will design, manufacture and sell twin screw steam expanders. The key innovation in City's design is that it can operate with so-called 'wet steam' - steam which is at a low pressure and temperature and contains water droplets that would destroy traditional machines. This means that the expanders can be implemented in a wider array of applications. Beyond geothermal energy, this could include recovering energy from the otherwise waste steam that arises in power production and industrial processes.

Entrepreneur Dan Wright, who is leading the Heliex venture, elaborates: "Our system promises a rare combination of radical advances in industrial energy efficiency with low risk because it is based on tried and tested technology. It uses established manufacturing methods and materials.

"Heliex's technology lightens the growing burden for industry created by escalating costs by capturing energy traditionally lost in a variety of industrial processes ranging from power generation to dairy operation and marine propulsion."

Market research has indicated that the energy recoverable by the system in Europe and North America rivals the world-installed capacity of wind turbines. If this potential can be realised, then the seeds sown by Professors Smith and Stosic in the 1980s will reap an impressive harvest for generations to come.

Watch Lonelyleap's video about Heliex.