Comparative Analysis of Transient Thermodynamic Performance for the Parabolic-Trough Photothermal Conversion Technology

The intermittent nature of solar energy poses a great challenge to the parabolic trough collector (PTC) technology. Although PTC technology is mature in application, its thermodynamic performance in transient processes is in need of a more comprehensive understanding. Here, a transient photothermo-hydraulic model of a parabolic-trough collector loop (600 m) was established with the finite volume method (FVM). A comprehensive comparative analysis for the transient photo-to-thermal characteristics (transient entropy generation and thermal-exergy efficiency) of PTC loop under a main weather disturbance [direct normal irradiance (DNI)], main control parameter (the mass flow rate of the heat transfer fluid mHTF), and geometry-dependent parameters (the collector width a and the absorber tube diameter douter) was carried out. The research shows that increasing DNI increases the entropy generation rate of each part of the absorber tube (up to 45.52%) and decreases the energy and exergy efficiency during the transient process, and vice versa. Transient entropy generation can be reduced by regulating the operating parameters (increase mHTF rapidly) and changing the geometric parameters (a or douter) of PTC (up to 87.58%, 38.03%, and 32.92%, respectively). Moreover, the influencing mechanism of mHTF (a or douter) on the transient entropy generation of the absorber tube is different from that in steady state. The transient thermodynamic response analysis is of great significance to the control and design optimization of PTC loop in the actual system.