Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Experimental data, flashing jets, small-scale

The work was dedicated to the design of the experimental facility to perform laboratory-scale liquid-flashing tests. Preliminary tests were performed with conventional and novel laser-based measurement techniques. These tests allowed:

- To design the instrumented lab-scale liquid-flashing source, which resembles as much as possible a true hazardous situation in the case of accidental release of pressurized liquids caused by equipment or operator failure.
- To evaluate the applicability of standard and novel laser-based measurement techniques such as standard Particle Image Velocimetry (PIV), Multi-Intensity Layer Particle Image Velocimetry (MIL-PIV), Particle Tracking Velocimetry and Sizing (PTVS), Phase-Doppler Anemometry (PDA) and Global Rainbow Thermometry (GRT). Standard PIV, MIL-PIV and PDA are applicable to a flashing two-phase jet, except for regions of extremely high droplet density. GRT and PTVS are being further developed in order to make them suitable for the harsh flashing environments. Measurements were also performed by thermocouples, showing the problem of ice formation on this intrusive instrument, leading to erroneous measurements. This had a feedback on the design of the flashing facility, which should allow operation at 0% humidity, thus preventing the ice formation.

It is expected that the results of the FLIE project will lead to an improved understanding of the governing phenomena, and thus improve the safety of existing and future industrial plants. The present work on small-scale experiments addressed the influence of the initial parameters of the flashing liquid jet on the two-phase characteristics downstream of the orifice exit in case of a sudden release of pressurized liquefied R134a (refrigerant). Due to the non-equilibrium nature of the near field regions, conducting accurate data measurements for droplet size and velocity is a challenging task.

Laser-based optical techniques like Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) were used to obtain information for particle diameter and velocity evolution in this harsh environment. Moreover, high-speed video photography presented the possibility to understand the break-up patterns of the R134a liquid jet as function of driving pressure, superheat level, and discharge nozzle characteristics. Temperature measurements with an intrusive technique such as thermocouples, and non-intrusive measurements with Infrared Thermography were also performed. Cases for different initial pressure, temperatures and orifice diameters were studied. The break-up pattern, droplet size, velocity distribution and temperature evolution along the radial and axial directions have been presented as function of initial parameters.

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