Abstract
Pressure-swirl atomizers are used in a wide range of industrial applications, e.g.: combustion, cooling, painting, food processing etc. Their spray characteristics are closely linked to the internal flow which predetermines the parameters of the liquid sheet formed at the discharge orifice. To achieve a better understanding of the spray formation process, the internal flow was characterised using Laser Doppler Anemometry (LDA) and high-speed imaging in a transparent model made of cast PMMA (Poly(methyl methacrylate)). The design of the transparent atomizer was derived from a pressure-swirl atomizer as used in a small gas turbine. Due to the small dimensions, it was manufactured in a scale of 10:1. It has modular concept and consists of three parts which were ground, polished and bolted together. The original kerosene-type jet A-1 fuel had to be replaced due to the necessity of a refractive index match. The new working liquid should also be colourless, non-aggressive to the PMMA and have the appropriate viscosity to achieve the same Reynolds number as in the original atomizer. Several liquids were chosen and tested to satisfy these requirements. P-Cymene was chosen as the suitable working liquid. The internal flow characteristics were consequently examined by LDA and high-speed camera using p-Cymene and Kerosene-type jet A-1 in comparative manner.
Highlights
Pressure-swirl (PS) atomizers are easy to manufacture and provide good atomization
The pumped liquid is injected via tangential ports into a swirl chamber where it gains a swirl motion, under which it leaves the exit orifice as a conical liquid sheet which breaks up into small droplets due to aerodynamic forces
The results are divided into two main parts: The air core shape based on the high-speed visualization and the velocity profiles based on the Laser Doppler Anemometry (LDA) measurements
Summary
Pressure-swirl (PS) atomizers are easy to manufacture and provide good atomization. They are frequently used in various applications where a large surface area of droplets is needed or a surface must be coated by a liquid e.g. combustion, fire suspension or air conditioning. The pumped liquid is injected via tangential ports into a swirl chamber where it gains a swirl motion, under which it leaves the exit orifice as a conical liquid sheet which breaks up into small droplets due to aerodynamic forces. The centrifugal motion of the swirling liquid creates a low-pressure zone in the centre of the swirl chamber and generates an air core along the centreline. There is a strong link between the internal flow conditions and the resulting spray characteristics; not all aspects of the internal flow are well understood
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