Size analysis in gas turbine fogging systems

Mee Industries is using the Malvern Instruments Spraytec particle size analyser in the development of a measurement protocol for inlet fogging nozzles used in gas turbines

Mee Industries, a leader in high pressure fogging systems and applications, is using the Malvern Instruments Spraytec particle size analyser in the development of a measurement protocol for inlet fogging nozzles used in gas turbines.

Inlet fogging can be used to augment the power of a gas turbine by up to 20%, but in order to be able to achieve this level of augmentation a number of important parameters must be understood.

These include fog droplet size, droplet kinetics and duct behaviour of the droplets.

A major problem faced by gas turbine users considering the use of inlet fogging is that different fog nozzle manufacturers and suppliers present data in varying formats and under different operating conditions.

Mee Industries is one of several companies working with the American of Society of Mechanical Engineers (ASME) to develop a measurement protocol for such systems.

Dr Mustapha Chaker, director of research and development at Mee Industries, said: "We use the Spraytec because it employs a spatial light scattering technique and algorithm which have been proven to be precise and repeatable in several independent studies".

The Spraytec measures the intensity of light scattered from droplets passing through a laser beam.

The angle at which droplets scatter light is inversely proportional to their size, allowing the droplet particle size distribution to be directly calculated from the spray scattering pattern using an appropriate scattering model, in this case Mie Theory.

A patented multiple scattering algorithm incorporated into the Spraytec allows the accurate measurement of both dense and diffuse spray plumes.

Measurement using this technique is very fast, and the Spraytec is capable of acquiring size distributions at a rate of up to 2500 Hz.

This allows for the measurement of short-duration sprays, revealing fine temporal fluctuations in the atomizer output.

Continuous measurements over long periods are also possible at lower acquisition rates, enabling users to understand the stability of different nozzle systems and also directly track the effect of changing atomizer conditions on the delivered particle size.

"Laser diffraction is ideal for measuring particle size distribution in inlet fogging systems," said Dr Chaker.

"It is a non-invasive and fast technique that gives accurate and reliable data.

This information can be used to optimise the inlet fogging process and increase power augmentation while reducing corrosion in gas turbines.

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