Thermal transfer characteristics and thermoelasticity analysis of direct-steam-generation parabolic trough collector

Parabolic trough solar direct-steam-generation technology integrates clean energy with green carriers and is one of the favorable low-carbon technologies. However, the non-uniform heat flow distribution and flow stratification of collectors are susceptible to variations in climatic conditions, causing dry spots and raising the failure risk, and there are fewer studies on their influence laws based on three-dimensional two-fluid modeling. Therefore, the three-dimensional optical-thermal-stress-hydrodynamic model of the collector is built in this work based on Monte Carlo Ray Tracing method, finite volume method, finite element method and Eulerian two-fluid modeling method, and the model validation results agree with the experimental results. The impacts of direct solar radiation (I) and inlet pressures (Pin) on heat transfer performance and thermoelasticity characteristics of the three flow stages are analyzed. The results revealed that heat transfer performance in two-phase flow is better than single-phase flow at the same working conditions. The elevation of I effectively improves the Nusselt number and collector efficiency, but also dramatically raises the circumferential temperature difference (CTD) and thermal stresses. Especially, the CTD, maximum deformation, and maximum equivalent stresses in the superheated stage are as high as 54.37 K, 32.82 mm, and 38.23 MPa at Pin = 3 MPa and I = 1000 W m−2, similarly the maximum equivalent stress is also as high as 32.96 MPa in the stratified flow. The results serve as a reminder to pay particular attention to the superheated stage and the laminar flow, particularly at low Pin and high I. Furthermore, the lower the Pin, the higher the deformation and equivalent stresses in the stratified flow phase and the higher the risk of induced failure. Therefore, this implies that higher operating pressures are more appropriate for stratified flow, but this may be limited by high heat loss and low collector efficiency.