2024 AIChE Annual Meeting
(631a) Mathematical Model Validation Using Solar Volumetric Receiver Datasets: Enhancing High-Temperature Heating through Obtaining Absorber Thermophysical Properties
Authors
Melhim, A. - Presenter, Texas A&M University at Qatar
Kakosimos, K. E. - Presenter, Texas A&M University at Qatar
Salih, F., Texas A&M University at Qatar
Concentrated solar technologies (CST) emerge as a sustainable solution through volumetric receivers in CST plants, utilizing reflector systems to concentrate solar radiation onto solid receivers for electricity generation or thermal storage. The ability of CST systems to achieve high temperatures and efficiencies enables them to compete with photovoltaics. Photovoltaics, with their intermediate energy conversion steps, tend to hinder energy efficiency. CSTs convert the light into thermal energy directly, achieving higher thermal efficiencies. Multiple solar receiver designs were suggested to improve the volumetric effect, therefore minimizing the radiation losses, and improving the thermal efficiency. However, the criteria for achieving volumetric behavior differ, and available experimental datasets are limited to validate modeling works. Therefore, the first objective of this work is the generation of an open experimental dataset for the validation of numerical models. The second objective, still in progress, is to further validate the computational predictions with improved and new experimental data, while building in parallel a 1D-model to capture the apparent phenomena and dimensionless correlations. In brief, the experiments were conducted using a 6 kWe powered xenon arc lamp with an ellipsoidal reflector, with irradiance fluxes ranging from 256 – 456 kW/m2 and ambient air flowed from front to back into the receiver with varying flow rates of 4 – 18 lpm. The receiver was simulated twice, initially, as a single channel, then as a full receiver with additional alterations to represent the momentum and heat transfer phenomena occurring in the experimental set up more accurately. The 1D model was employed to simulate the entire receiver, aiming to achieve steady-state conditions across the 15 experimental sets. This involved fine-tuning the model to match experimental steady-state temperatures by optimizing parameters such as the heat transfer coefficient and the solid's thermophysical properties, utilizing the NLOpt optimization package within the Julia coding language. Upon achieving the steady state temperatures, the focus will shift to capturing transient states. The tested receivers comprise ceramic components commercially available i.e., 19x19 mm2 SiC particle filter, 20mm in ID Al2O3 tube, and 19mm in ID SiC tube. Transient temperature profiles were collected at three different axial positions at the center of the receiver and on the side walls, including the inlet and exit gas temperatures. Finally, the irradiance levels on the receiver were collected using a calibrated heat flux gauge. The initial aim of this study was successfully achieved through model verification, wherein temperature profiles were reproduced to match experimental data sourced from literature. As the first objective of collecting an experimental dataset was met, the focus now is to achieve the second objective, in which the model is being verified through the new experimental results. After successfully validating the 3D-model, optimization of the receiver is expected to take place to ensure that the highest possible E_vol ratio and thermal efficiency are met through using the appropriate receiver geometry (length-diameter ratio and porosity-radius pair).