AbstractThis thesis presents a compendium of work on superheated liquid releases. Superheated liquid releases are often subject to flashing. Nucleation has been identified as an important process in the early stage of flashing. The presence of strong nucleation and therefore flashing depends on the output of the balance of the promoting forces and dissipation forces inside the fluid released. A one dimensional model to classify the type of jet to be formed after the release has been developed based on the balance of these forces. The analysis is based on the assumption that the nucleation process can be modelled as a second order damped system. The model parameters are defined as a function of the pressure, temperature, fluid properties and geometric characteristic of the system. The results obtained have good agreement with the experimental results available for releases of different fluids, including both hydrocarbons and water.
The calculation of the velocity discharge, void fraction and mass flow of a flashing jet generated after the release is made based on the thermodynamics jump formulation approach. Due to the nature of the nucleation process, the assumptions of adiabatic flow with non reversible work for the surface tension forces are made. Those considerations are found to be more realistic that the isentropic condition used until now by different authors.
Numerical techniques are only applied after the flashing jet is formed, no droplets generation or vapour generation are included. Droplets are imposed as part of the boundary conditions of a gas jet. Droplets transport mechanics and momentum exchange with the gas current is made using Droplet Disperse Model (DDM) on the commercial code Fluent ®. DDM determines the distribution of the disperse phase over the continuous phase using a Lagrangian Eulerian approach. The influence of velocity, the dimension of the nozzle and mass flow used in the CFD modelling were analysed. Nozzle dimensions have a large impact on the core region length of the velocity profile. The k −e turbulent model was used. As expected, the numerical results do approach experimental values in the far region, suggesting that the momentum of the two phase jet is conserved. The one dimensional model thus provides the necessary boundary conditions for the application of numerical methods to superheated liquid releases including flashing.
|Date of Award||2008|
- fluid dynamics
- superheated liquids
- liquefied gas