THESIS
2016
vii, 125 pages : illustrations ; 30 cm
Abstract
This thesis applies the recently developed dynamic van der Waals theory to perform two-dimensional numerical simulations for two-phase, one-component, non-isothermal, liquid-vapour
systems. This model has recently been utilised to produce physically reasonable
semi-quantitative results in systems where complicated dynamics restrict alternative
methods. Two types of boiling are studied; where problematic features, such as non-uniform
temperature and phase transition, are principal characteristics: (i) The effects of
substrate wettability in pool boiling: (ii) The applicability of the lubrication approximation
to Leidenfrost drops, and the similarities between coalescing non-wetting drops and
Leidenfrost drops. Experimental study of these problems is challenging due to the small
l...[
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This thesis applies the recently developed dynamic van der Waals theory to perform two-dimensional numerical simulations for two-phase, one-component, non-isothermal, liquid-vapour
systems. This model has recently been utilised to produce physically reasonable
semi-quantitative results in systems where complicated dynamics restrict alternative
methods. Two types of boiling are studied; where problematic features, such as non-uniform
temperature and phase transition, are principal characteristics: (i) The effects of
substrate wettability in pool boiling: (ii) The applicability of the lubrication approximation
to Leidenfrost drops, and the similarities between coalescing non-wetting drops and
Leidenfrost drops. Experimental study of these problems is challenging due to the small
length scales involved, while numerical simulations can resolve the necessary detail.
In pool boiling, bubble growth rate on non-wetting surfaces is seen to be larger than
that on wetting surfaces. This is explained by noting that the factors contributing to the
rate of bubble growth include not only the strong evaporation at the thermal singularity
but also the evaporation from a portion of interface close to the substrate. Based on this,
an expression is derived for the contact line speed, showing good agreement with the simulation
results. The solutions derived from the lubrication approximation for Leidenfrost
drops are found to generally compare well to the simulation results. The robustness of
the lubrication approximation is attributed to the common features found in the pressure
variation through \he vapour layer, although it breaks down as the evaporative region
near the interface is approached. Numerical studies of Leidenfrost drop coalescence find
a build-up of vapour in the common space under both drops causing a short-range repulsion.
This is achieved through a pressure change that scales in a similar manner to that
under a single drop. A threshold drop size exists in order for a horizontal body force to
overcome the repulsion.
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