Thermal-hydraulic transient performance and dynamic characterization analysis of direct steam generation for parabolic trough solar collectors

Parabolic trough solar direct-steam-generation (PTC-DSG) technology is a low-carbon technology by combining clean energy with green energy carriers. However, abrupt variations in solar radiation (I) due to weather changes can significantly affect the DSG performance and stable operation. In this work, PTC-DSG system's optical-thermal-flow-pattern transient coupling model is developed based on the Separated Flow model, Finite Volume method and Lagrangian method. The dynamic response of the loop's transient flow law and heat transfer performance under I step-variation are analyzed, and the correlation between the DSG system's transient flow characteristics and the multiple perturbation factors is discussed. The results reveal that adding (reducing) 12.5 % and 37.5 % of I shortens (lengthens) the evaporation phase by 7.2 % and 16.5 % (10.7 % and 16 %). The superheated zone has the greatest influence on the transient response characteristics and instability relative to the preheated and evaporated zones under various step-variations, and the heat transfer recovery still needs longer time after flow state is re-stabilized. Under I step-variation, adding mass flow can effectively shorten the superheat phase but not the response time, and the system instability range increases; Increasing inlet temperature (T_in) can augments the superheat zone, but effectively shorten the response time and regulate and improve the outlet steam quality; Raising inlet pressure not only reduces the evaporation phase, which is most favorable for heat transfer, but also requires longer re-stabilization time and increases the probability of stratified flow, which should be paid more attention.