This study investigates the dehumidification performance and the gas-liquid flow of a falling film liquid desiccant dehumidifier with different plate configurations: vertical smooth, vertical rough, and inclined rough. Utilizing ANSYS Workbench 2020 R1, the Re-Normalization Group (RNG) k-ε turbulence model has been utilized to simulate the gas-liquid flow, and the volume of fluid model is employed to track the interface patterns between the gas and liquid phases. This model takes into account the effects of the two-dimensional turbulent flow which is performed for various plate configurations under situations of unstable gas-liquid flow. The 30% LiCl solution is used as an absorbent and hence, the performance has been evaluated using a constant mass transfer rate of 50 mol/s. Furthermore, the LiCl solution’s mass concentration is taken into account as 30%, 33%, 36%, 40%, and 44%, respectively, for the justification of the influence of various concentrations of LiCl solution. The study analyzes the fields of mass fractions and the mechanisms that lead to the enhancement of dehumidification. The research examines the influence of inlet desiccant concentration and air velocity on mass transfer properties, revealing that an inclined ribbed plate significantly enhances dehumidification up to 10.8% compared to the smooth plate particularly at 1.5 m/s inlet air velocity by generating liquid film waves and increasing contact time between the liquid desiccant and moist of air. Lower inlet air velocities and higher inlet desiccant concentrations resulted in a decreased outlet mass percentage of water vapor. The optimal LiCl concentrations for water vapor absorption are 30-40%, with efficiency stable above 36%, though benefits may plateau beyond a certain level. The study concludes that the inclined rough plate enhances mass transfer performance at various inlet air velocities and desiccant concentrations by increasing the contact time between the liquid desiccant and moist air, increasing the rate of water vapor absorption. These findings provide valuable insights for researchers and engineers aiming to optimize liquid desiccant dehumidification systems for various applications, especially in the hybrid liquid desiccant-vapor compression systems.