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Research Papers

Numerical Investigation of Natural Convection Loss From Cavity Receivers in Solar Dish Applications

[+] Author and Article Information
S. Paitoonsurikarn, K. Lovegrove

School of Engineering, Australian National University, Canberra ACT 0200, Australiakeith.lovegrove@anu.edu.au

G. Hughes

Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia

J. Pye

School of Engineering, Australian National University, Canberra ACT 0200, Australia

J. Sol. Energy Eng 133(2), 021004 (Mar 22, 2011) (10 pages) doi:10.1115/1.4003582 History: Received April 25, 2007; Revised January 19, 2011; Published March 22, 2011; Online March 22, 2011

In open cavity receivers employed in solar paraboloidal dish applications, natural convection occurs and contributes a significant fraction of energy loss. Its characteristics hence need to be clarified so that it can be effectively minimized in order to improve the system efficiency. The investigation of natural convection loss from cavity receivers was undertaken numerically and was validated using the published experimental results for four different receiver geometries. A good agreement between experimental and numerical results was obtained. Furthermore, the numerical results of all receivers were qualitatively comparable to the predictions by other available correlations hitherto, although it was found that each correlation has a limited range of applicability arising from the particular cavity geometry and experimental conditions used to derive it. To address this shortcoming, a new correlation based on the numerical results for three of the above four receivers has been proposed. The correlation employs a new concept of an ensemble cavity length scale, to take into account the combined effects of cavity geometry and inclination. Despite a wide variety of cavity geometries and operating conditions, the proposed correlation predicts approximately 50% of the data within ±20% and 90% of the data within ±50%. This is better than any of the other correlations published to date. The new correlation is also simpler to use than the most accurate of those previously published.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Configurations of receivers used in the study

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Figure 2

Schematic diagram of flow configuration: (a) the receiver location in the entire domain and (b) the 20 m2 dish cavity receiver showing the angle of inclination

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Figure 3

Typical computational grids for (a) model receiver and (b) 400 m2 dish receiver

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Figure 4

Contour plot of velocity magnitude at symmetry plane for model receiver

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Figure 5

Profiles at aperture plane for model receiver: ((a)–(c)) normal velocity (m/s) and ((d)–(f)) temperature (K).

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Figure 6

Comparison for the case of the model receiver with varying aperture areas

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Figure 7

Comparison for the case of the model receiver with varying cavity wall temperature

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Figure 8

Comparison for the case of the McDonald receiver

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Figure 9

Comparison of free convection losses between the numerical simulation and the predictions by different correlations for the case of the model receiver

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Figure 10

Comparison of free convection losses between the numerical simulation and the predictions by different correlations for the case of the 20 m2 dish receiver

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Figure 11

Comparison of free convection losses between the numerical simulation and the predictions by different correlations for the case of the 400 m2 dish receiver

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Figure 12

Effect of the cavity wall temperature on the convective heat flux for the case of the model receiver

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Figure 13

Effect of the cavity size on the convective heat flux for the case of the model receiver

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Figure 14

Effect of the cavity aspect ratio on the convective heat flux for the case of the model receiver

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Figure 15

Denotation of cavity geometrical parameters used in the definition of the ensemble cavity length scale Ls

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Figure 16

Comparison between the prediction by Eq. 5 and the numerical results

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Figure 17

Comparison between the predicted results from various correlations Numodel and the numerical results NuCFD. (a) New model (Eq. 4), (b) Le Quere model, (c) Clausing model, (d) Siebers and Kraabel model, (e) Koenig and Marvin model, (f) Stine and McDonald model, (g) modified Clausing model, (h) modified Stine and McDonald model, and (i) Taumoefolau model.

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