Investigation on Thermodynamic Mechanisms of Brine Evaporation in Air-Carried Evaporating Separation Cycle Coupling with Process-Heat-Supplied (PHS)

Process-heat-supplied (PHS) technology has been proven effective in accommodating low-grade solar energy and reduces the necessary supply temperature for traditional air-carried evaporating separation (ACES) cycles, enabling complete separation of brine at temperatures around 50℃. Nevertheless, the thermodynamic mechanism underlying the ACES cycle coupled with PHS remains unelucidated, particularly the fundamental relationships between exergy and entropy. Regarding aforementioned issues, a redesigned experimental system capable of measuring internal temperature variations is employed. Furthermore, comprehensive thermodynamic analysis of the PHS-coupled evaporating separation process is conducted in conjunction with simulations based on the second law of thermodynamics. The results demonstrate that PHS effect essentially transforms the 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, the beneficial effects of PHS prove to be universal. Even under conditions involving high-humidity and milk-drying conditions, experimental system consistently achieves separation and maintains favorable 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=2.04kg/(m2·h), ηex=139.7%).