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Research Papers

# Optimization of the Mass Flow Rate Distribution of an Open Volumetric Air Receiver

[+] Author and Article Information
Nils Ahlbrink

German Aerospace Center (DLR e.V.),
Institute of Solar Research,
Linder Hoehe,
Cologne 51147, Germany
e-mail: nils.ahlbrink@dlr.de

Moritz Diehl

Professor
Principal Investigator
Optimization in Engineering Center
of Excellence (OPTEC),
Department of Electrical Engineering (ESAT),
SCD, Katholieke Universiteit Leuven,
Leuven 3001, Belgium

Robert Pitz-Paal

Professor
Head of the Solar Research Institute,
German Aerospace Center (DLR e.V.),
Cologne 51147, Germany

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received April 3, 2012; final manuscript received December 19, 2012; published online June 25, 2013. Assoc. Editor: Wojciech Lipinski.

J. Sol. Energy Eng 135(4), 041003 (Jun 25, 2013) (10 pages) Paper No: SOL-12-1087; doi: 10.1115/1.4024245 History: Received April 03, 2012; Revised December 19, 2012

## Abstract

The thermodynamical efficiency of a solar power tower power plant with an open volumetric air receiver depends among others on the operational strategy of the receiver. This strategy includes, on the one hand, controlling the distribution of irradiated power on the receiver surface via aim point optimization, and on the other hand, controlling the air mass flow rate and its distribution by choosing suitable dimensions of fixed orifices and controlling air flaps. The maximum mass flow rate of the receiver as an indication of the thermal power is commonly used as a quality function when assessing new component designs, comparing different operational strategies, or evaluating the role of aim point optimization for the open volumetric air receiver technology. In this paper, a method is presented to maximize the mass flow rate of the receiver using given technical capabilities of the receiver technology like orifices and air flaps for a desired air outlet temperature of the receiver. The method is based on dynamic programming, a general technique for solving decision making problems where a complex problem can be split up into a sequence of simpler ones. The potential of the method is demonstrated for a prototype solar thermal power tower with open volumetric air receiver technology.

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## References

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Bertsekas, D., 2005, Dynamic Programming and Optimal Control, 3rd ed., Vol. 3, Athena Scientific, Belmont, MA.
Ahlbrink, N., “Modellgestützte Bewertung und Optimierung der offenen Luftreceivertechnologie,” Dissertation, RWTH Aachen, Aachen, Germany (in press).
Schwarzbözl, P., 2009, “The User's Guide to hflcal. A Software Program for Heliostat Field Layout Calculation,” Software Release Visual hflcal VH12, Cologne, Germany.
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Ahlbrink, N., Andersson, J., Diehl, M., and Pitz-Paal, R., 2010, “Optimized Operation of an Open Volumetric Air Receiver,” Proceedings of the SolarPACES 2010 Conference, Perpignan, France, September 21–24.
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Ahlbrink, N., Belhomme, B., and Pitz-Paal, R., 2009, “Modeling and Simulation of a Solar Tower Power Plant With Open Volumetric Air Receiver,” Proceedings of the 7th Modelica Conference, Como, Italy, September 20–22.
Pitz-Paal, R., 1993, “Entwicklung eines selektiven volumetrischen Receivers für Solarturmkraftwerke—Parameter-Untersuchungen und Exergetische Bewertung,” Dissertation, Fortschrittsberichte VDI, VDI-Verlag, Düsseldorf, Germany.

## Figures

Fig. 1

Schematic setup of the open volumetric air receiver technology

Fig. 2

The complex optimization problem is split up into a sequence of simpler problems like combining the values of two absorber modules. The calculated discrete values for the first absorber module are shown on the left side and the discrete values of the second absorber module are shown in the middle. The discrete values obtained by combination of the values of both absorber modules are shown on the right. Using dynamic programming, only those values are kept, which have the highest enthalpy flow rate at a discrete mass flow rate (like C1 or C3).

Fig. 3

Determination of the maximal mass flow rate out of the optimal curves of the receiver

Fig. 4

Heliostat field setup and chosen focal lengths of the heliostats (left) and heliostat field model in stral (right)

Fig. 5

Design flux density distribution, the optimized orifice distribution, the mass flow rate distribution of the absorber modules, and the distribution of the specific enthalpies at the absorber module outlet

Fig. 6

Diagrams for the flux density per absorber module, the subreceiver pressure drop normalized using its maximum value, the subreceiver mass flow rate, and the corresponding air outlet temperature of the mass flow rate for the optimized operation (left) and the absolute or relative comparison to the results of the comparative operation (right) on 21.03. at 10:00 h

Fig. 7

Distributions of mass flow rate per absorber module and corresponding air outlet temperature of the mass flow rate for the optimized operation on 21.03. at 10:00 h

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