Thermohydraulic management coupled with flow pattern distinction for concentrating solar direct-steam-generation technology

Abstract

Concentrating solar direct-steam-generation (DSG) technology is favored for tying solar energy and water to directly power the energy loop, which is positive in achieving a zero-carbon future. Whereas, the external intermittence of the meteorological irradiation and internal instability of flow boiling pose challenges to the thermohydraulic operation and management. Herein, a light-heat-flow-pattern transient coupled analysis model of parabolic trough collector direct-steam-generation (PTC-DSG) loop was established to figure out the action among the irradiance, thermohydraulic and two-phase flow pattern. The transient flow patterns along the loop were investigated under different irradiance (I), mass flowrate (min) and inlet temperature (tin) of the loop. The results showed that increasing I and tin temporarily reduces the probability of stratified flow and increasing tin permanently reduces the probability of stratified flow. In all cases, the proportion of intermittent flow to evaporation stage remains almost unchanged (about 11%.), and the heat transfer in superheating stage still needs a long time (253s ∼ 3646s) to recover after the flow stages distribution is stable. More importantly, a quantified management strategy for irradiance -thermohydraulic-flow pattern is built. To achieve a favorable operating state, the inlet mass flow rate min should be lower than the superheated line ((1.25·I – 6.25)✕10−3 kg s−1) to obtain the superheated steam, and higher than 0.35 kg s−1 to get out of the stratified flow in evaporation stage. When the irradiation is lower than 285 W m−2 for a long time, the start-up and operation is not recommended.