Source terms models for superheated releases of hazardous liquefied chemicals such as LPG have been developed, governing both upstream and downstream conditions. Water was utilised as the model fluid, not least for reasons of safety, but also for its ability to be stored at conditions that ensure it is superheated on release to atmosphere. Several studies have found that at low superheat jet break-up is analogous to mechanical break-up under sub-cooled conditions. Hence, a non-dimensionalised SMD correlation for sub-cooled liquid jets in the atomisation regime has been developed, based on data measured using a Phase Doppler Anemometry (PDA) system, for a broad range of initial conditions. Droplet SMD has been found to correlate with the nozzle aspect ratio and two non-dimensionalised groups i.e. the liquid Reynolds number and Weber number. An adaptation of the Rossm-Rammler distribution has been proposed for jets undergoing mechanical break-up. Through a high-speed photographic study (1000fps), three distinctive break-up regimes of superheated jets have been identified. Mechanical break-up has been confirmed to dominate jet disintegration at low superheat. Criteria for transition between regimes have been established based on the liquid Jakob number and Weber number. Using a PDA system, droplet SMD data has been produced for fully flashing jets at two sets of initial conditions and three axial downstream locations, with radial measurements performed at each position. Droplet SMD has been found to increase with nozzle diameter. An adaptation of the Rossm-Rammler distribution has been proposed for fully flashing jets. The proposed correlation for sub-cooled break-up, the PDA data for superheated releases and the established transition criteria have been compiled to produce a complete SMD model governing transition from mechanical break-up to full flashing. The model has been validated against three previous studies of flashing jets. An additional high speed photographic study (up to 50,000fps) of the upstream flow structure of superheated jets has been performed using Perspex nozzles. The downstream break-up regime has been found to depend on both the upstream bubble growth rate and concentration.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:584338 |
| Date | January 2008 |
| Creators | Cleary, Vincent Martin |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/54737/ |
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