MODELING AND SIMULATION OF DIRECT STEAM GENERATION IN PARABOLIC TROUGH SOLAR COLLECTOR
The present study aims to investigate the thermo-hydrodynamics of direct steam generation (DSG) in the absorber tube of parabolic trough solar collector (PTSC) using the two-fluid modeling approach. The majority of the existing numerical investigations are based on the homogeneous equilibrium model where 1-D (onedimensional) governing equations are solved for the fluid mixture. In this study, the 3-D (three-dimensional)
simulations are performed based on the Eulerian multiphase model, where the governing equations are solved for the liquid and vapor phases separately. The steady-state governing equations are solved using commercial CFD software ANSYS Fluent 2020R1. The simulations are performed for operating pressures of 60 bar and 100 bar; mass flow rates of 0.4 kg/s and 0.6 kg/s; and DNI 750 W/m2. The non-uniform solar heat flux around the absorber surface is considered at solar noon and two hours before or after the solar noon. The absorber wall
temperature around the circumference and temperature contours at various axial positions have been plotted to analyze the circumferential temperature difference. The maximum temperature difference around the circumference varies between 14 K to 18 K under the considered boundary conditions. The circumferential
temperature difference is minimum at solar noon and increases before or after the solar noon for the same DNI. The pressure drop is lower more at higher operating pressures for the same inlet mass flow rates and DNI. The vapor volume fraction at the collector outlet varies in the range of 0.31 to 0.46. It is observed that vapor volume fraction decreases with an increase in inlet mass flow rate and operating pressure. The contours of vapor volume fraction and absorber wall temperature have been plotted. The variations in the mixture velocity and liquid-vapor relative velocity have been investigated.