Development and Validation of a Stationary Water-Spray Cleaning System for Concentrated Solar Thermal (CST) Reflectors

This study presents a novel analysis of a non-contact cleaning system for Concentrated Solar Thermal (CST) reflectors. The analysis is essentially divided in two parts, the first aims at developing a robust computational fluid dynamic model of a stationary water-spray impingement upon flat surfaces to investigate CST flat reflector cleaning techniques. An in-depth investigation on shear stress profiles obtained at different inlet pressure levels and standoff distances, with impinging angle set at 90°, has been developed with ANSYS CFX V 15.0. Findings outline that cleaning effectiveness, as determined by the generation of fluid flow shear stresses on the target surface, is improved as inlet pressure increases in the optimal standoff distance range of 5D-26D, with D as outlet nozzle diameter. Beyond 26D, the water-jet loses cleaning ability due to insufficient jet velocity whereas before 5D backward flows and turbulent eddies obstruct the central jet-flow of the cleaning system. The second part of this analysis focuses on the validation of the fluid dynamic model through the comparison of Smedley's and Young's experimental tests. A normalisation of shear stress (τ/τmax) and radial distances (r/H) has been utilised to compare flows characterised by different nozzle types, standoff distances and measures of computational domains.