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Turbines for Heat Recovery and low-Carbon Power

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December 2014 to December 2019

PI: Andy Wheeler, University of Cambridge

Transforming heat-recovery system performance by exploiting multi component turbine flows

Funded by: EPSRC / GE Global Research

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Introduction

The project is exploring how the behaviour of complex fluids can be used to increase turbine performance for use in heat recovery systems and low-Carbon Power. The work involves developing methods to simulate complex fluids within turbines. We use a combination of experiments and computational techniques to model these flows and use the results from this work to improve current computational methods. The project is aiding the development of turbine performance models which can be used for the design of future systems.

Summary

All industrial and power generation processes produce heat which is often released into the environment in the form of high temperature exhaust products. New technologies are being developed to recover this otherwise wasted energy for use elsewhere, such as electricity, heating or cooling. Heat-recovery technologies are also used for renewable power from biomass, geothermal, solar-thermal sources and in de-centralized power generation. The development of heat recovery technology is therefore important in terms of cutting our carbon footprint as well as increasing UK energy security.

Heat recovery systems work by transferring heat into a high-pressure working-fluid, using a heat exchanger. In order to produce electricity, the working fluid drives a turbine which is connected to an electrical generator. Heat recovery systems often use working fluids which are refrigerants or long-chain hydrocarbons. The properties of these working fluids differ greatly from those which have traditionally been used within turbines and can be made up of several components including mixtures of gases and liquids. There is very little known about the behaviour of these unconventional working fluids within turbines largely due to a lack of experimental data with which to test current theories. This is important because turbine designers require accurate models in order to develop high performance machines, and uncertainties in the modelling can have a detrimental impact on both the development costs and the overall performance of a heat recovery system. There is also a potential to exploit the unusual behaviour of these working fluids, such as their ability to change from liquid to gas across the turbine, which can be exploited to increase system power to size ratios (power density) in ways not possible using normal working fluids like water.

We have developed a unique experimental test facility for testing independently working-fluid and turbine design. We have also used experimental data to validate current computational methods for simulating these flows, as well as developing our own reduced-order models to predict the influence of these effects on turbine performance.  We find that a key parameter affecting loss is the isentropic exponent, which varies significantly for gases at high pressure levels and temperatures. Our results show that this parameter can alter turbine loss by between 20%-35%, depending on turbine design. The results are important for future turbines used for heat recovery systems as well as turbines used at high gas temperatures and pressures (such as future advanced cycles and future propulsion systems).

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