E. Tsioli’s research while affiliated with The Cyprus Institute and other places

The Cyprus Institute’s Pentakomo Field Facility (PFF) is a major infrastructure for research, development and testing of technologies relating to concentrated solar power (CSP) and solar seawater desalination. It is located at the south coast of Cyprus near the sea and its environmental conditions are fully monitored. It provides a test facility specializing in the development of CSP systems suitable for island and coastal environments with particular emphasis on small units (<25 MWth) endowed with substantial storage, suitable for use in isolation or distributed in small power grids. The first major experiment to take place at the PFF concerns the development of a pilot/experimental facility for the co-generation of electricity and desalinated seawater from CSP. Specifically, the experimental plant consists of a heliostat-central receiver system for solar harvesting, thermal energy storage in molten salts followed by a Rankine cycle for electricity production and a multiple-effect distillation (MED) unit for desalination.

This chapter will elaborate upon the fundamental flow behaviour associated with vortex-rings and jets issuing from nozzles, where the nozzle trailing-edges or lips are physically modified with selected geometries. This technique represents a passive but robust form of manipulating the underlying vortex-ring and jet circulation, such that improvements to their entrainment and mixing characteristics can be achieved. Implementations of simple inclined, hybrid inclined, notched, crown-shaped, chevron and stepped nozzles, as well as some of their implementations in circular and noncircular jets, single-stream or dual-stream coaxial jets, will be discussed as part of the overall understanding. In particular, recently observed influences of trailing-edge modifications upon the axis-switching behaviour of noncircular jets, as well as their relationships with coaxial jet flow parameters such as the velocity- and area-ratios will be presented. On top of key flow physics insights in terms of how the nozzle trailing-edge geometry will confer distortionary effects upon the basic vortex structures, the impact of such nozzles upon jet mixing efficacies will be discussed as well.

This chapter will elaborate upon the fundamental flow behaviour associated with vortex-rings and jets issuing from nozzles, where the nozzle trailing-edges or lips are physically modified with selected geometries. This technique represents a passive but robust form of manipulating the underlying vortex-ring and jet circulation, such that improvements to their entrainment and mixing characteristics can be achieved. Implementations of simple inclined, hybrid inclined, notched, crown-shaped, chevron and stepped nozzles, as well as some of their implementations in circular and noncircular jets, single-stream or dual-stream coaxial jets, will be discussed as part of the overall understanding. In particular, recently observed influences of trailing-edge modifications upon the axis-switching behaviour of noncircular jets, as well as their relationships with coaxial jet flow parameters such as the velocity- and area-ratios will be presented. On top of key flow physics insights in terms of how the nozzle trailing-edge geometry will confer distortionary effects upon the basic vortex structures, the impact of such nozzles upon jet mixing efficacies will be discussed as well.

An experimental study was carried out on 45° and 60° inclined coaxial jets, where secondary-to-primary jet area- and velocity-ratios were 4.0 and ranged from 0.5 to 2.0 respectively. Results reveal that the use of a relatively larger area-ratio here is able to suppress self-excited jet oscillations seen earlier in comparatively smaller area-ratio jets when velocity-ratio is 1.0. Flow visualization and PIV measurements demonstrate that this is due to the physically wider annular gap associated with a larger area-ratio. This reduces the extent to which primary and secondary ring-vortices can undergo vortex-pairing and merging seen in the previous study. Near-field centerline flow characteristics clarify the impact of area-ratio upon the flow fields, as well as its relationships with velocity-ratio and incline-angle. Unlike relatively smaller area-ratio jets, the effects of the velocity-ratio are found to be insignificant in the lower cases of 0.5 and 1 examined here. Correspondingly, primary jet deflections are found to be comparatively smaller for relatively larger area-ratio jets and significant only when velocity-ratio reaches 2.0. Lastly, jet velocity profile developments reveal that within the present measurement range, the two jet-streams in relatively larger area-ratio jets do not merge as rapidly as smaller area-ratio counterparts, particularly at a velocity-ratio of 2.0.

An experimental study on inclined coaxial jets using laser-induced fluorescence and particle image velocimetry is presented here. The Reynolds numbers of the inner primary jet and outer secondary jet were Re=2,500 and between Re=500 and 2,000 (based on gap size), respectively, which corresponded to secondary-to-primary jet velocity ratios (VR) of VR=0.5–2.0. The secondary-to-primary jet area ratio was 2.25, and 45° and 60° incline-angles were studied. Flow visualizations show that relatively independent inclined primary and secondary jet vortex roll-ups were formed at VR=0.5. At VR=1.0, regular pairings and mergings between primary and secondary jet vortex roll-ups led to large-scale entrainment of secondary jet and ambient fluids into the primary jet column and conferred a “serpentile”-shaped outline upon it. While the “serpentile”-shaped outline continued to exist at VR=2.0, it was a result of stronger secondary jet inner vortex roll-ups which “pinched” the primary jet column regularly. These flow behaviours are observed to intensify with an increase in the incline-angle used. Velocity measurements demonstrate that inclined coaxial nozzles promoted vectoring of the primary jet momentum towards the longer nozzle lengths when velocity-ratio and/or incline-angle were increased. Lastly, peak velocity and higher turbulence intensity levels due to augmented vortical interactions are also detected along shorter nozzle lengths.