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@PHDTHESIS{Hoffmann:708050,
author = {Hoffmann, Alexander},
othercontributors = {Pitz-Paal, Robert and Hampel, Uwe},
title = {{N}umerical and {E}xperimental {I}nvestigation of
{T}ransient {T}wo-phase {F}low {P}henomena in {C}oncentrated
{S}olar {P}ower {P}lants with {D}irect {S}team {G}eneration},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2017-09613},
pages = {1 Online-Ressource (xvi, 184 Seiten) : Illustrationen,
Diagramma},
year = {2017},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2017},
abstract = {The direct steam generation process in parabolic trough
collectors of CSP plants heats and evaporates water to
obtain steam that is subsequently superheated to feed a
steam turbine. Recently, this process was proven in economic
and operational perspectives in the once-through mode to be
a promising option for large-scale commercial plants.
Nevertheless, knowledge gaps about the two-phase flow could
deter the deployment of this type of power plant. The
once-through mode implies temperature oscillations at the
transition region from two-phase flow to superheated steam
that induces thermal stresses in the receiver and could
reduce the receiver's lifetime. The uncertainties complicate
a reliable economic analysis. The thesis aims to enrich the
existing pool of knowledge about the two-phase flow under
specific conditions in state-of-the-art parabolic trough
facilities with direct steam generation. The objective is to
state the relevance of intermittent flows and wavy flows,
severe slugging, and flow instabilities regarding the
implications at the end of the two-phase flow region by
means of advanced numerical and experimental tools. The
numerical simulations use the capabilities of a
one-dimensional two-fluid model that gives a deeper insight
into the two-phase flow compared to the previously used
homogeneous equilibrium models. The unique experiments are
performed with a single wire-mesh sensor, which measures the
local instantaneous void fraction and has been installed in
the low-quality region of the DISS test facility at the
Plataforma Solar de Almería in Spain for the first time. It
is analytically shown that the two-fluid model can identify
unstable liquid-gas interfaces in certain conditions that
would initiate the transition to a non-stratified flow. The
numerical results of intermittent and wavy flow are
validated by wire-mesh sensor experiments, suggesting that
thermal oscillations at the end of the two-phase flow are
linked to the transient two-phase flow pattern in the
evaporator. The wire-mesh sensor measures slug flow, roll
waves, wavy flow, and stratified-wavy flow in the horizontal
receiver pipes within pressures of 30 to 80 bar.In the
simulation, severe slugging could not be observed in the
U-shaped connection pipes under typical operating conditions
- this can mainly be ascribed to high-pressure conditions.
The obtained findings enhance the understanding of the
evaporation process in the receiver pipes and improve the
confidence in this technology. Subsequent research should
increase the number of experiments in the low-quality region
and extend the measurements towards the high-quality region.
These efforts will yield a full collection of reliable and
reproducible data for the investigated system that is
affected by many and various influencing parameters.},
cin = {412910},
ddc = {620},
cid = {$I:(DE-82)412910_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2017-09613},
url = {https://publications.rwth-aachen.de/record/708050},
}
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