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Research Papers

Numerical Simulation of Natural Convection in Solar Cavity Receivers

[+] Author and Article Information
James K. Yuan

Concentrating Solar Technologies Department,
Sandia National Laboratories,
P.O. Box 5800,
Albuquerque, NM 87185-0828
e-mail: jkyuan@sandia.gov

Clifford K. Ho

Concentrating Solar Technologies Department,
Sandia National Laboratories,
P.O. Box 5800,
Albuquerque, NM 87185-1127
e-mail: ckho@sandia.gov

Joshua M. Christian

Concentrating Solar Technologies Department,
Sandia National Laboratories,
P.O. Box 5800,
Albuquerque, NM 87185-1127
e-mail: jmchris@sandia.gov

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received June 1, 2012; final manuscript received November 4, 2014; published online December 23, 2014. Assoc. Editor: Markus Eck.

J. Sol. Energy Eng 137(3), 031004 (Jun 01, 2015) (10 pages) Paper No: SOL-12-1145; doi: 10.1115/1.4029106 History: Received June 01, 2012; Revised November 04, 2014; Online December 23, 2014

Cavity receivers used in solar power towers and dish concentrators may lose considerable energy by natural convection, which reduces the overall system efficiency. A validated numerical receiver model is desired to better understand convection processes and aid in heat loss minimization efforts. The purpose of this investigation was to evaluate heat loss predictions using the commercial computational fluid dynamics (CFD) software packages fluent 13.0 and solidworks flow simulation 2011 against experimentally measured heat losses for a heated cubical cavity receiver model (Kraabel, 1983, “An Experimental Investigation of the Natural Convection From a Side-Facing Cubical Cavity,” Proceedings of the ASME JSME Thermal Engineering Joint Conference, Vol. 1, pp. 299–306) and a cylindrical dish receiver model (Taumoefolau et al., 2004, “Experimental Investigation of Natural Convection Heat Loss From a Model Solar Concentrator Cavity Receiver,” ASME J. Sol. Energy Eng., 126(2), pp. 801–807). Simulated convective heat loss was underpredicted by 45% for the cubical cavity when experimental wall temperatures were implemented as isothermal boundary conditions and 32% when the experimental power was applied as a uniform heat flux from the cavity walls. Agreement between software packages was generally within 10%. Convective heat loss from the cylindrical dish receiver model was accurately predicted within experimental uncertainties by both simulation codes using both isothermal and constant heat flux wall boundary conditions except when the cavity was inclined at angles below 15 deg and above 75 deg, where losses were under- and overpredicted by fluent and solidworks, respectively. Comparison with empirical correlations for convective heat loss from heated cavities showed that correlations by Kraabel (1983, “An Experimental Investigation of the Natural Convection From a Side-Facing Cubical Cavity,” Proceedings of the ASME JSME Thermal Engineering Joint Conference, Vol. 1, pp. 299–306) and for individual heated flat plates oriented to the cavity geometry (Pitts and Sissom, 1998, Schaum's Outline of Heat Transfer, 2nd ed., McGraw Hill, New York, p. 227) predicted heat losses from the cubical cavity to within experimental uncertainties. Correlations by Clausing (1987, “Natural Convection From Isothermal Cubical Cavities With a Variety of Side-Facing Apertures,” ASME J. Heat Transfer, 109(2), pp. 407–412) and Paitoonsurikarn et al. (2011, “Numerical Investigation of Natural Convection Loss From Cavity Receivers in Solar Dish Applications,” ASME J. Sol. Energy Eng. 133(2), p. 021004) were able to do the same for the cylindrical dish receiver. No single correlation was valid for both experimental receivers. The effect of different turbulence and air-property models within fluent were also investigated and compared in this study. However, no model parameter was found to produce a change large enough to account for the deficient convective heat loss simulated for the cubical cavity receiver case.

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References

Figures

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Fig. 1

Cubical cavity (left) and cylindrical dish receiver (right) models and instrumentation [1,2]

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Fig. 2

Computational meshes in fluent (left) and solidworks (right) for cubical cavity model

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Fig. 3

Computational mesh in fluent (left) and solidworks (right) for cylindrical dish receiver

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Fig. 4

Heat losses from cubical cavity model by software package and boundary condition

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Fig. 5

Exit velocity profiles on cavity aperture. Experimental (top), isothermal wall boundary conditions, solidworks (middle left), and fluent (middle right). Constant heat flux boundary conditions, solidworks (bottom left), and fluent (bottom right).

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Fig. 6

Exit temperature profiles on cavity aperture. Experimental (top), isothermal wall boundary conditions, solidworks (middle left), and fluent (middle right). Constant heat flux boundary conditions, solidworks (bottom left), and fluent (bottom right).

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Fig. 7

Simulated wall temperatures, constant heat flux wall boundary conditions. fluent (left) and solidworks (right), with high temperatures near corners and interior edges and lower temperatures along outer edges.

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Fig. 8

Comparison of empirical correlation results for convective heat loss from a heated cubical cavity

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Fig. 9

Convective heat loss from cylindrical dish receiver model over a range of inclination angles

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Fig. 10

Empirical and average numerical convective heat loss results from cylindrical dish receiver model [7]

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Fig. 11

Convective heat loss from cubical cavity model by air specification method and wall boundary condition

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Fig. 12

Convective heat loss from cylindrical dish receiver model at 0 deg inclination by air specification and wall boundary condition

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Fig. 13

Convective heat loss from cubical cavity model by turbulence closure method and wall boundary condition

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Fig. 14

Convective heat loss from cylindrical dish receiver by turbulence closure method, inclination angle, and wall boundary condition

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Fig. 15

Representative pathlines in cubical cavity for RANS turbulence models shaded by temperature from 250 K to 700 K. Realizable k–ε shown under constant heat flux wall boundary conditions.

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Fig. 16

Representative pathlines in cubical cavity for LES over 4.75 s of solution time, shaded by temperature from 250 K to 700 K, constant heat flux boundary conditions

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Fig. 17

Representative pathlines in cylindrical dish receiver model at 0 deg and 30 deg inclination for RANS turbulence models shaded by temperature from 300 K to 750 K. Realizable k–ε shown under isothermal wall boundary conditions.

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Fig. 18

Representative pathlines in cylindrical dish receiver model for LES over approximately 3 s of solution time, shaded by temperature from 300 K to 750 K, constant temperature wall boundary conditions. 0 deg inclination (left) and 30 deg inclination (right).

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Fig. 19

Representative pathlines in cylindrical dish receiver model at 60 deg and 90 deg for RANS turbulence models, shaded by temperature from 300 K to 750 K. Realizable k–ε shown under isothermal wall boundary conditions.

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