Forced convection effects on desiccant evaporation and energy consumption assessment in liquid desiccant dehumidification systems

Desiccant regeneration through saline evaporation is critical and major energy consumer in liquid desiccant dehumidification systems (LDDS) for indoor air conditioning. This study investigated the coupled heat and mass transfer behavior of saline droplet evaporation under forced convection, focusing on the enhancement effects of sweeping air (SA) and Marangoni effect. In-situ measurements and numerical simulations were performed, developing semi-empirical equations correlating evaporation rates with desiccant conditions and SA flowrates. By employing the equations considering SA’s impact on regeneration temperature, EnergyPlus simulation was conducted to evaluate the energy consumption of a typical office building in Guangzhou equipped with a temperature-humidity-independent control system incorporating LDDS. Results showed that SA significantly lowered the temperature required for high evaporation rates. At desiccant temperature of above 70 °C, a strong thermal Marangoni effect resulted in enhanced evaporation, which increased with SA flowrates. At lower temperatures, forced convection still facilitates evaporation, though to a lesser extent, while also helping to prevent desiccant crystallization. EnergyPlus simulations revealed that if SA was incorporated into regeneration, substantial annual energy savings of up to 18.30% for LDDS can be achieved, with hourly savings ranging from 7.83 to 8.40 kW, peaking in August. Optimizing the SA flowrate is crucial, with ideal rates of around 3.5 m/s in high-humidity and 2.5 m/s in low-humidity conditions. This study deepens the understanding of non-isothermal droplet evaporation under forced convection, and establishes a significant bridge between saline evaporation and LDDS energy consumption assessment in practical buildings.