Thermo-Hydrodynamic Modeling of Direct Steam Generation in Parabolic Trough Solar Collector

Direct steam generation (DSG) in the parabolic trough solar collector (PTSC) has the potential to improve the thermal efficiency and minimize the investment cost for solar thermal power generation. In the present work, three-dimensional (3-D) numerical simulations of DSG in the absorber tube have been performed using computational fluid dynamics (CFD) approach to predict the fluid flow and heat transfer phenomena for uniform wall heat flux condition. Wall boiling model under Eulerian multi-phase flow has been used in this study and it includes modeling of turbulence, mass transfer, and wall heat flux partition. The numerical modeling of DSG has been performed in CFD software ANSYS Fluent 19.0 and the results have shown good agreement with the available experimental results. Two-phase flow boiling pressure drop, volume fraction of vapor, liquid temperature, and variation of fluid velocity in axial direction have been studied for various operating pressures and inlet mass flow rates. It is observed that pressure drop is more at lower operating pressure for the same mass flow rate and wall heat flux. Contours of volume fraction of vapor at different positions along the length of absorber tube have been predicted. It is found that vapor phase moves upward due to gravity and the upper section of the tube gets dried.