Modeling evaporation with a meshfree collocation approach

Abstract

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.

Water Evaporation CFD Method with the Meshfree Volume-Volume-Coupling Approach for Wet Automotive Component Dry-Out Time Prediction

“…The mathematical and computational models used for this current study to resolve multi-phase evaporation phenomenon is explained in this section. In order to keep a stable phase coupling condition for arbitrary free surface formation in the meshless approach, the volume-volume-coupling [9,13] instead of the surface-surface-coupling [11] is adopted.…”

“…For the coupling, Brinkman model is used [9,13]. This modeling approach replaces the surface-surface-coupling since it shows considerably more stable phase coupling conditions for arbitrary geometry and free surface formations based on the studies carried out [11]. An example of initial point cloud organization of the surface-surface-coupling, where no overlap is allowed, and the volume-volume-coupling with phase overlapping is depicted in Fig.…”

“…The transition of liquid water mass into vapor occurs due to the vapor concentration gradient in the vicinity of the interface within the air phase [12]. Hence, the local mass transfer rate or local mass flux (𝑚 water ) can be calculated as [11]:…”

“…During the mass transfer process, the latent heat is consumed at the interface. Hence, thermal energy at the interface should be balanced with the following thermal balance equation proposed [11]: where Δℎ evap is the evaporation enthalpy or latent heat of the water evaporation, 𝜆 water is the thermal conductivity of water, 𝒏 water,interface is the derivative of water temperature at the interface in inward normal direction, 𝑞 air to water , 𝑞 radiation are the heat flux from air to water and due to solar radiation, respectively. In the current study, solar radiation is not considered, i.e., 𝑞 radiation 0.…”

“…A two-phase mass transfer model is developed with GFDM to numerically resolve the free water surface evaporation phenomenon at the water-air interface. To keep stable phase interface for any arbitrary geometry and frees surface formation in a meshless approach, volume-volume-coupling is used [9] as it shows much stable coupling conditions compared to the surface-surface-coupling approach [11]. Here, by using the Brinkman model, only water phase models the free surfaces whereas the air phase is overlapping the more complex phase.…”