Thermal Performance of the Solar Expanding Vortex Receiver (SEVR)

Abstract

A novel windowless configuration of the Solar Expanding Vortex Receiver (SEVR) has been proposed to heat particles used in industrial applications, such as particle heaters, mineral-processing devices, and air heaters. Understanding the influence of different parameters on the thermal performance of the SEVR is essential for the success of the integration of the receiver for the generation of industrial process heat in potential applications such as the Bayer process in alumina production. However, there is a lack of understanding of the effects of some key dimensionless parameters and flow regimes on the thermal performance of the SEVR. Furthermore, most studies on the SEVR have been conducted under isothermal conditions, and there is a lack of analysis and understanding of the thermal performance of the SEVR, which is critical for the operational requirements in any industrial process. This project aims to provide a new understanding of the thermal performance of the windowless vortex-based solar receiver under high-flux solar radiation by demonstrating the influence of critical parameters and flow regimes in single and two-phase flow conditions using both experimental and numerical methods. More specifically, the objective of the current study is to assess the thermal performance with an aerodynamic control strategy within a windowless SEVR under single-phase conditions. Meanwhile, the two-phase flow study seeks to characterise the essential influencing dimensionless parameters (particle loading, Froude and Stokes number) of initial inflow conditions on the reactor's thermal efficiency and heat transfer. In the single-phase flow study, a proof-of-concept experimental study was conducted to assess the effects of overventilation on the thermal performance of the receiver by employing a 5- kWel single-lamp Xenon arc solar simulator. A primary aerodynamic control strategy was developed based on the application of suction to the outlet section of the device. It was utilized to prevent particle egress from the device through the windowless aperture. The influence of the air inlet mass flowrate and suction level on the thermal performance (thermal efficiency, heat losses and wall temperature distribution) was investigated. It was found that the trade-off between the suction level and thermal efficiency needs to be cautiously considered to prevent exergy destruction in the reactor. In the two-phase flow study, the systematic research assesses the coupled influence of particle loading, Froude, and Stokes numbers through variation of the inlet volumetric flowrate, particle size and loading on the performance of the SEVR under steady-state conditions. The experiments employ polydisperse CARBO CP ceramic particles heated with an 18-kWel Metal Halide three-lamp solar simulator. A numerical study was also performed using computational fluid dynamics (CFD) software ANSYS/CFX 2019 R1. It was found that the volumetric particle loading and Froude number have primary controlling influence, while the Stokes number has a secondary impact on the thermal performance for these conditions. Overall thermal efficiency of 67% was obtained under high particle loading and Froude numbers.