RESEARCH PAPERS: Jets, Wakes, and Impingment Cooling

Numerical and Experimental Investigation of a Multiple Air Jet Cooling System for Application in a Solar Thermal Receiver

[+] Author and Article Information
M. Röger, R. Buck, H. Müller-Steinhagen

Institute of Technical Thermodynamics, German Aerospace Centre (DLR), Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany

Work supported by the German Ministry of Education and Research, Contract No. 0329695 and the German Ministry of Economy and Technology, Contract No. 0329695A/4.

Work supported by the European Commission under the 5th Framework Program, Contract No. ENK5-CT-2000-00333.

J. Heat Transfer 127(8), 863-876 (Mar 04, 2005) (14 pages) doi:10.1115/1.1928910 History: Received March 04, 2004; Revised March 04, 2005

The transparent quartz glass window of a high temperature solar receiver (1000°C air outlet temperature, 15bars) has to be protected from overheating. The window is an axially symmetric part that can be approximated by a hemisphere with a cylindrical extension (diameter 0.31m, height 0.42m). The cooling is accomplished by impinging several air jets onto the concave window surface. Due to concentrated solar radiation, the air supply nozzles can only be installed at the circumference of the cylindrical extension. Symmetric configurations with six or nine nozzles, equally distributed around the window circumference, are examined. A second configuration generates a swirl in the window cavity by inclining the nozzles. In a third, asymmetric configuration, only nozzles on one side are simultaneously charged with mass flow, while a spatial homogenization of heat transfer is reached by periodically modulating the air flows with time. Computational fluid dynamics (CFD) calculations and laboratory measurements of the heat transfer have been carried out. In the performed 3-D simulations, the realizable k-ε model, the k-ω model, and the SST-k-ω model are compared. For measuring the heat transfer coefficient, a periodic-transient measurement technique with high spatial resolution is used. For the application of cooling of the solar receiver window, the jet cooling system with periodically modulated air flows is identified as the best solution.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

Solar air heating system of combined cycle

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Figure 2

Pressurized volumetric receiver (REFOS type)

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Figure 3

Examined cooling schemes

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Figure 4

Coordinate system for window surface, nozzle orientation, and dimensionless variables

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Figure 5

Mesh and boundary conditions

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Figure 6

Maximum (left) and mean (right) Nusselt number of the window surface versus number of grid cells

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Figure 7

Mean Nusselt number over the window surface versus maximum dimensionless wall distance

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Figure 8

Periodic-transient measurement principle

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Figure 9

Characteristic curves for different modulation frequencies

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Figure 10

Simulated contours of z velocity in m/s

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Figure 11

Contours of measured Nusselt numbers

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Figure 12

Mean heat transfer on window surface, symmetric case with six nozzles

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Figure 13

Maximum and mean Nusselt numbers, symmetric case with six nozzles

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Figure 14

Measured and simulated contours of Nusselt numbers, symmetric case with six nozzles

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Figure 15

Contours of measured Nusselt numbers, swirled case with six nozzles

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Figure 16

Measured and simulated contours of Nusselt numbers, asymmetric case with five jets (T→∞s)

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Figure 17

Contours of measured Nusselt numbers, asymmetric case with five jets, modulated (T=22s)

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Figure 18

Mean heat transfer on window surface, asymmetric case with five jets, modulated



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