Investigation on Thermodynamic Mechanisms of Brine Evaporation in Air-Carried Evaporating Separation Cycle Coupling with Process-Heat-supplied

Process-Heat-Supplied (PHS) technology has been proven effective in accommodating low-grade non-concentrating solar thermal energy and reduces the necessary supply temperature for traditional Air-Carried Evaporating Separation (ACES) cycles, enabling complete separation of brine at temperatures around 50 °C. Nevertheless, the thermodynamic mechanism underlying the ACES cycle coupled with PHS remains unelucidated, particularly the fundamental relationships between Gibbs free energy and entropy. Accordingly, this investigation conducts experiments on internal temperature variations of the redesigned system and performs simulation analysis of PHS-coupled evaporating separation process based on thermodynamic second-law. The results demonstrate that PHS effect essentially transforms binary Gibbs free energy model (air and droplets) of traditional processes into a tripartite model (PHS source, air, and droplets). The abundant free energy supplied by PHS source compensates for the inherent irreversible evaporation losses. This novel thermodynamic mechanism not only reduces the necessary temperature but also effectively enhances the exergy efficiency (ηex = 58.85%). Meanwhile, advantages of PHS have been demonstrated to extend beyond the brine. In feasibility milk drying experiment, this system continued to achieve separation whilst maintaining considerable evaporation efficiency. Furthermore, the solar-driven double-stage PHS-ACES system developed through this mechanism enables the cascaded utilization of energy and overcomes thermodynamic limitation of traditional evaporation (me-solar = 2.04 kg/(m2 h), GOR = 139.7%).