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@PHDTHESIS{Tiddens:689803,
author = {Tiddens, Arne},
othercontributors = {Hoffschmidt, Bernhard and Kemna, Andreas},
title = {{M}easurement methods for investigating the air return
ratio of open volumetric receivers at solar power towers},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2017-04595},
pages = {1 Online-Ressource (VI, 130 Seiten) : Illustrationen,
Diagrammme},
year = {2017},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, RWTH Aachen University, 2017},
abstract = {Cost reduction plays a significant role in the field of
concentrated solar thermal energy. It is therefore essential
to quantify all factors that influence the energy conversion
efficiency. The air return ratio is a key factor for the
overall efficiency of the open volumetric receiver. It is
the fraction of the blown out air which is sucked in again
through the solar receiver. To achieve a high receiver
efficiency it is therefore important to increase the air
return ratio. Many variables such as wind speed and
direction, geometry of the receiver design and operational
mode influence the air flow in front of the receiver. This
in turn influences the air return ratio. It is therefore of
vital importance to be able to measure the air return ratio
and furthermore visualize the air flow in front of the
receiver. The air return value was prior to this work
unknown on a large scale and under concentrated solar
irradiation.The development of a measurement technique for
the quantification of the air return ratio with maximum
accuracy is the main objective of this thesis. The second
objective lies in the visualization of the returned air.
This improves the understanding of the occurring flow
phenomena which govern the air return ratio. The measurement
methods were developed at a lab scale, tested under
operating conditions and successfully demonstrated at the
solar tower Jülich. In order to measure the air return
ratio, three variants of a novel circular tracer gas
measurement technique have been developed. The tracer gas is
injected either continuously or intermittently into the open
air system. The tracer gas is diluted by the imperfect air
return ratio. The mole fraction of the injected noble gas
helium is measured with a mass spectrometer within the air
system, from which the air return ratio is determined. A
temporal resolution of 0.5 s has been achieved. A maximal
air return ratio of (68.6 ± $0.7)\%$ with $95\%$ confidence
interval has been measured during irradiation with
concentrated sunlight at the solar tower power plant
Jülich. This is higher than thepreviously assumed air
return ratio of $60\%.$ This difference corresponds to a 4
− $5\%$ higher overall system efficiency. The return air
in front of the receiver was visualized for the first time
with the newly developed Induced Infrared Thermography.
Hereby, carbon dioxide is added to the return air. This
induces a larger amount of radiationbeing given off in the
infrared region. This radiation from the return air is
visualized using an infrared camera.},
cin = {421010},
ddc = {620},
cid = {$I:(DE-82)421010_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2017-04595},
url = {https://publications.rwth-aachen.de/record/689803},
}
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