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This thesis represents the first systematic description of the
two-phase flow problem. Two-phase flows of volatile fluids in
confined geometries driven by an applied temperature gradient play
an important role in a range of applications, including thermal
management, such as heat pipes, thermosyphons, capillary pumped
loops and other evaporative cooling devices. Previously, this
problem has been addressed using a piecemeal approach that relied
heavily on correlations and unproven assumptions, and the science
and technology behind heat pipes have barely evolved in recent
decades. The model introduced in this thesis, however, presents a
comprehensive physically based description of both the liquid and
the gas phase. The model has been implemented numerically and
successfully validated against the available experimental data, and
the numerical results are used to determine the key physical
processes that control the heat and mass flow and describe the flow
stability. One of the key contributions of this thesis work is the
description of the role of noncondensables, such as air, on
transport. In particular, it is shown that many of the assumptions
used by current engineering models of evaporative cooling devices
are based on experiments conducted at atmospheric pressures, and
these assumptions break down partially or completely when most of
the noncondensables are removed, requiring a new modeling approach
presented in the thesis. Moreover, Numerical solutions are used to
motivate and justify a simplified analytical description of
transport in both the liquid and the gas layer, which can be used
to describe flow stability and determine the critical Marangoni
number and wavelength describing the onset of the convective
pattern. As a result, the results presented in the thesis should be
of interest both to engineers working in heat transfer and
researchers interested in fluid dynamics and pattern formation.
This thesis represents the first systematic description of the
two-phase flow problem. Two-phase flows of volatile fluids in
confined geometries driven by an applied temperature gradient play
an important role in a range of applications, including thermal
management, such as heat pipes, thermosyphons, capillary pumped
loops and other evaporative cooling devices. Previously, this
problem has been addressed using a piecemeal approach that relied
heavily on correlations and unproven assumptions, and the science
and technology behind heat pipes have barely evolved in recent
decades. The model introduced in this thesis, however, presents a
comprehensive physically based description of both the liquid and
the gas phase. The model has been implemented numerically and
successfully validated against the available experimental data, and
the numerical results are used to determine the key physical
processes that control the heat and mass flow and describe the flow
stability. One of the key contributions of this thesis work is the
description of the role of noncondensables, such as air, on
transport. In particular, it is shown that many of the assumptions
used by current engineering models of evaporative cooling devices
are based on experiments conducted at atmospheric pressures, and
these assumptions break down partially or completely when most of
the noncondensables are removed, requiring a new modeling approach
presented in the thesis. Moreover, Numerical solutions are used to
motivate and justify a simplified analytical description of
transport in both the liquid and the gas layer, which can be used
to describe flow stability and determine the critical Marangoni
number and wavelength describing the onset of the convective
pattern. As a result, the results presented in the thesis should be
of interest both to engineers working in heat transfer and
researchers interested in fluid dynamics and pattern formation.
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