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Research Papers

Thermo-Fluid Optimization of a Solar Porous Absorber With a Variable Pore Structure

[+] Author and Article Information
P. Wang

Department of Renewable Energy,
Hohai University,
Nanjing 210029, China;
Department of Mechanical Engineering,
University of California,
Riverside, CA 92521

J. B. Li, L. Zhou

Department of Renewable Energy,
Hohai University,
Nanjing 210029, China

K. Vafai

Department of Mechanical Engineering,
University of California,
Riverside, CA 92521
e-mail: vafai@engr.ucr.edu

L. Zhao

China Electric Power Research Institute,
Nanjing 210029, China

1Corresponding author.

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 April 10, 2017; final manuscript received June 23, 2017; published online August 23, 2017. Assoc. Editor: Robert F. Boehm.

J. Sol. Energy Eng 139(5), 051012 (Aug 23, 2017) (5 pages) Paper No: SOL-17-1136; doi: 10.1115/1.4037350 History: Received April 10, 2017; Revised June 23, 2017

Optimization based on reconstruction of the velocity, temperature, and radiation fields in a porous absorber with continuous linear porosity or pore diameter distribution is carried out in this work. This study analyzes three typical linear pore structure distributions: increasing (“I”), decreasing (“D”), and constant (“C”) types, respectively. In general, the D type porosity (ϕ) layout combined with the I type pore diameter (dp) distribution would be an excellent pore structure layout for a porous absorber. The poor performance range, which should be avoided in the absorber design, is found to be within a wide range of porosity layouts (ϕi = ∼0.7 and ϕo > 0.6) and pore diameter layouts (di = 1.5–2.5 mm), respectively. With a large inlet porosity (ϕi > 0.8), the D type layout with larger porosity gradient (Gp) has a better thermal performance; however, the I type dp layout with a smaller inlet pore diameter (di < 1.5 mm) and a larger pore diameter gradient (Gdp) is recommended when considering the lower pressure drop. Different pore structure layouts (D type or I type) have a significant effect on the pressure drop, even with the same average ϕa and da, the maximum deviation can be up to 70.1%. The comprehensive performance evaluation criteria (PEC) value shows that the D type ϕ layout with a larger ϕa has an excellent thermopressure drop performance, and a part of PEC values for the I type dp layout are greater than unity.

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References

Figures

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Fig. 1

The effect of the linear variable porosity on the thermal efficiency η (dp = 1 mm)

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Fig. 2

Effect of the linear variable pore diameter on thermal efficiency η (ϕ = 0.9)

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Fig. 3

Effect of the porosity distribution on heat loss: (a) surface radiative heat loss Γs and (b) diffusive radiative heat loss Γd (dp = 1 mm)

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Fig. 4

Effect of the pore diameter distribution on heat loss: (a) surface radiative heat loss Γs and (b) diffusive radiative heat loss Γd (ϕ = 0.9)

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Fig. 5

Effect of the variable pore structure on the pressure drop of the absorber: (a) porosity (dp = 1 mm) and (b) pore diameter (ϕ = 0.9)

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Fig. 6

Effect of the variable pore structure on the PEC: (a) effect of ϕ, dp = 1 mm and (b) effect of dp, ϕ = 0.9

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