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Research Papers

Granular Flow and Heat-Transfer Study in a Near-Blackbody Enclosed Particle Receiver

[+] Author and Article Information
Janna Martinek

National Renewable Energy Laboratory (NREL),
15013 Denver West Parkway,
Golden, CO 80401
e-mail: janna.martinek@nrel.gov

Zhiwen Ma

National Renewable Energy Laboratory (NREL),
15013 Denver West Parkway,
Golden, CO 80401

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 February 13, 2015; final manuscript received June 19, 2015; published online July 23, 2015. Assoc. Editor: Prof. Nesrin Ozalp.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Sol. Energy Eng 137(5), 051008 (Jul 23, 2015) (9 pages) Paper No: SOL-15-1034; doi: 10.1115/1.4030970 History: Received February 13, 2015

Concentrating solar power (CSP) is an effective means of converting solar energy into electricity with an energy storage capability for continuous, dispatchable, renewable power generation. However, challenges with current CSP systems include high initial capital cost and electricity price, and advances are needed to increase outlet temperature to drive high-efficiency power cycles while simultaneously maintaining stability of the heat-transfer medium and thermal performance of the receiver. Solid-particle-based CSP systems are one alternative projected to have significant cost and performance advantages over current nitrate-based molten salt systems. NREL is developing a design that uses gas/solid, two-phase flow as the heat-transfer fluid (HTF) and separated solid particles as the storage medium. A critical component in the system is a novel near-blackbody (NBB) enclosed particle receiver that uses an array of absorber tubes with a granular medium flowing downward through channels between tubes. Development of the NBB enclosed particle receiver necessitates detailed investigation of the dimensions of the receiver, particle-flow conditions, and heat-transfer coefficients. This study focuses on simulation and analysis of granular flow patterns and the resulting convective and conductive heat transfer to the particulate phase using Eulerian–Eulerian two-fluid modeling techniques. Heat-transfer coefficients in regions with good particle/wall contact are predicted to exceed 1000 W/m2 K. However, simulations predict particle/wall separation in vertical flow channels and a resultant reduction in heat transfer. Particle-flow visualization experiments confirm particle/wall separation, but also exhibit complex periodic behavior and flow instability that create intermittent side-wall contact and enhance heat transfer above that predicted by the theoretical simulations.

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Figures

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Fig. 1

Schematic of the FB-CSP system with a NBB enclosed particle receiver, integrated FB heat exchanger, and solid-particle TES

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Fig. 2

NBB particle receiver and conceptual absorber design

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Fig. 3

Computational domain and boundary conditions

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Fig. 4

Solids volume fraction contours at t = 0.025, 0.05, 0.075, 0.1, 0.125, and 0.15 s for: (a) first solution iteration and (b) second solution iteration

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Fig. 5

Profiles of: (a) solids volume fraction, (b) solids velocity (m/s), and (c) solids temperature (K) for the baseline dimensions and ms = 333 kg/s m2

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Fig. 6

(a) Solids volume fraction across the center vertical flow channel and (b) solids volume fraction and velocity at the centerline of the vertical flow channel for ms = 333 kg/s m2 (solid lines) and ms = 500 kg/s m2 (dashed lines)

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Fig. 7

Profiles of solids volume fraction for modified tube geometry: (a) gb/gt = 0.5, (b) β = 120 deg, (c) rounded upper corners, and (d) with a fin extending 7 mm below the upper vertex

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Fig. 8

Snapshots of experimental particle-flow patterns

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