Research Papers

Characterization of Particle Flow in a Free-Falling Solar Particle Receiver

[+] Author and Article Information
Clifford K. Ho

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

Joshua M. Christian, Julius Yellowhair

Concentrating Solar Technologies Department,
Sandia National Laboratories,
Albuquerque, NM 87185-1127

David Romano, Laura Savoldi, Roberto Zanino

Dipartimento Energia,
Polytechnic University of Turin,
Corso Duca degli Abruzzi, 24,
Torino 10129, Italy

Nathan Siegel

Mechanical Engineering Department,
Bucknell University,
701 Moore Avenue,
Lewisburg, PA 17837

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 September 18, 2015; final manuscript received November 8, 2016; published online December 22, 2016. Assoc. Editor: Carlos F. M. Coimbra. 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 139(2), 021011 (Dec 22, 2016) (9 pages) Paper No: SOL-15-1312; doi: 10.1115/1.4035258 History: Received September 18, 2015; Revised November 08, 2016

Falling particle receivers are being evaluated as an alternative to conventional fluid-based solar receivers to enable higher temperatures and higher efficiency power cycles with direct storage for concentrating solar power (CSP) applications. This paper presents studies of the particle mass flow rate, velocity, particle-curtain opacity and density, and other characteristics of free-falling ceramic particles as a function of different discharge slot apertures. The methods to characterize the particle flow are described, and results are compared to theoretical and numerical models for unheated conditions. Results showed that the particle velocities within the first 2 m of release closely match predictions of free-falling particles without drag due to the significant amount of air entrained within the particle curtain, which reduced drag. The measured particle-curtain thickness (∼2 cm) was greater than numerical simulations, likely due to additional convective air currents or particle–particle interactions neglected in the model. The measured and predicted particle volume fraction in the curtain decreased rapidly from a theoretical value of 60% at the release point to less than 10% within 0.5 m of drop distance. Measured particle-curtain opacities (0.5–1) using a new photographic method that can capture the entire particle curtain were shown to match well with discrete measurements from a conventional lux meter.

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Fig. 1

Falling particle receiver prototype

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Fig. 2

Measured mass flow rate (kg/s) versus VFD frequency (Hz) in Olds Elevator using CARBO Accucast ID50K ceramic particles with median diameter of 280 μm

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Fig. 3

Dimensions (mm) for the 9.53 mm aperture discharge plate

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Fig. 4

Falling particle curtain released through 11.1 mm (7/16 in.) discharge slot aperture

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Fig. 5

Measured and modeled mass flow rates as a function of different discharge slot apertures for 280 and 697 μm particle sizes

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Fig. 6

ansys fluent simulation of the falling particle-curtain velocity with a 9.53 mm (3/8 in.) slot aperture. Left: front view of particle traces colored by velocity magnitude. Right: side view of entrained air velocity.

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Fig. 7

Successive high-speed images of the falling particle curtain (280 μm median particle size) with a 9.53 mm (3/8 in.) slot aperture used to determine particle velocities. Each image was taken 1/200 s apart.

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Fig. 8

Measured, simulated (ansys fluent), and analytically modeled particle velocities

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Fig. 9

Side view of particle-curtain thicknesses for 280 μm particles falling through three different slot apertures: 6.35 mm (left), 9.53 mm (middle), and 11.1 mm (right). Hash marks are 1 cm apart.

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Fig. 10

Measured and simulated particle-curtain thickness as a function of drop distance

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Fig. 11

Measured and simulated particle volume fraction as a function of drop distance for different slot apertures and a median particle size of 280 μm

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Fig. 12

Top: raw image without particle curtain. Middle: raw image with particle curtain (9.53 mm aperture, 280 μm particles). Bottom: ratio of images with and without particle curtain yielding transmittance (one minus opacity), cropped over the particle curtain.

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Fig. 13

Measured particle-curtain opacity (one minus transmittance) as a function of drop distance for different slot apertures and 280 μm particles




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