In this paper, a new model for the below-boiling point evaporation process with a meshfree collocation method is developed. In order to capture the phase change process, two different approaches are proposed: multi-phase and single-phase. First, a multi-phase approach is considered, where a novel mass transfer model assumes that the diffusion driven by the vapor concentration gradient in the air phase near the interface is the primary driving force for the mass transfer between phases as both the liquid water and air/vapor phases are simulated. Then, a water-only single-phase approach is also proposed, in which only the liquid water phase is simulated. For this, appropriate free surface boundary conditions are developed based on the convective mass transfer theory to model evaporation and incorporate airflow effects without explicitly simulating the air phase. In order to validate the proposed models, a series of experiments with varying air temperature, relative humidity, and airflow rate is conducted. The numerical results show a good agreement with the evaporation rate measured in the experiments. The multi-phase simulations agree better with the experiments, while the single-phase simulations also produce good results with a much lower computational effort.

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