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

Abstract

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.

Techno-Economic Optimization of CSP Plants with Free-Falling Particle Receivers

“…The receiver model is the most novel part of this study. The main modifications to the receiver model from [ 15 ] are the calculation of convection and radiation losses and the calculation of the initial thickness needed to achieve a certain mass flow rate (following model proposed by [ 21 ]). Moreover, the equations used to calculate curtain absorptance and transmittance have also been upgraded.…”

“…The code contains these equations dividing the curtain in 40 sections with the same length. The initial thickness is calculated with Equation (16), which is recommended by [ 21 ], where is the mass flow rate, the curtain width, the initial particle volume fraction (i.e., the volume fraction of a compact bed) and the particle diameter: …”

“…The upgrades allow to optimize some essential parameters such as the tower height and concentration, which could not be analyzed in the previous version. Moreover, special attention is paid to the receiver the particle curtain area and the thermal energy storage (TES) size since these components must have a specific design for particle systems [ 20 , 21 ]. Particle loss is also analyzed due to its importance in particle CSP systems.…”

On-Sun Performance Evaluation of Alternative High-Temperature Falling Particle Receiver Designs

“…FEBRUARY 2019, Vol. 141 / 011009-3 particle image velocimetry, and terminal velocities were found to be $0.5-0.8 m/s [24]. Thermocouples were used to measure the particle temperatures at several locations at the inlet and outlet of the receiver.…”

Spectral Radiative Properties of Ceramic Particles for Concentrated Solar Thermal Energy Storage Applications

“…Therefore, they have been investigated as the candidate materials for solar falling particle receivers, where particle flows pass open apertures and form a particle film (or curtain) that is directly subjected to concentrated solar irradiation [20][21][22]. These particles primarily consist of Al 2 O 3 , with a weight fraction over 0.75, along with other oxides such as SiO 2 , Fe 2 O 3 , and TiO 2 [23,24]. The particle temperature can reach 1000 °C or higher [5].…”