City Research Online

Abstract

Flashing boiling is a phase-changing process that takes place under abrupt pressure decrease and manifests when a liquid reaches a superheated state.
As a phenomenon, flash boiling is present in many industrial and technical applications. Flashing can be observed in the case of nozzle, orifice and valve flows, in cooling applications of cryogenic fluids, in internal combustion engines for fuel spray atomisation purposes or upon failure and rapture of pressurised vessels or pipes that contain liquefied gases.
The present work focuses on flash boiling in aerospace and automotive applications. To study the phenomenon two different numerical approaches have been implemented. First, a compressible, transient, explicit, density-based solver, on which tabulated thermodynamic properties have been implemented, was developed within the OpenFOAM framework and has been executed for URANS simulations. Secondly, a compressible, transient, implicit, coupled, pressure-based solver, was used within the framework of ANSYS Fluent software. A mass transfer model has been developed and tested with said pressure-based solver using URANS, DES and LES turbulence modelling.
A wide range of experimental conditions that are of relevance to space applications has been investigated to study flash boiling using cryogenic liquids, namely liquid oxygen and nitrogen, and traditional fuels like isooctane as the operating fluids. The numerical results highlight that flash boiling is a process of high uncertainty due to its inherent features, namely metastability effects and transient phenomena that may occur upon its development. Although an assumption of thermal equilibrium can not always be valid, in the case of injection under steady conditions, the results can be sufficiently accurate. The methodology presented in this work can be applied without any calibration for any range of conditions that have been tabulated, regardless of the boundary conditions or the involved geometry. Although flash boiling in aerospace and automotive applications has been the focus of this work, the proposed methods can be applied to a broad spectrum of engineering problems, ranging from gasoline direct injection (GDI) and aerospace engine optimisation to industrial cooling and nuclear safety.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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