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ABSTRACT
Droplet evaporation has great scientific significance in industrial and agricultural production as well as natural meteorological processes. Among many factors that affect evaporation, wettability and wall temperature are among the most important. The Lattice Boltzmann Method (LBM) was used to explore the effects of evaporative wall wettability and wall temperature on the Constant Contact Angle (CCA) model. We constructed a dual-distribution gas–liquid phase transition model and found that the higher the wall temperature, the more rapid the evaporation; however, nucleate boiling was more likely to occur at high temperatures, making the CCA (and thus evaporation) unstable. Compared to hydrophobic surfaces, hydrophilic surfaces have larger droplet spreading area, and generally higher evaporation rate; as the contact diameter decreased, droplet diffusion occurred and evaporation to dryness was observed. Droplets on hydrophobic surfaces tended to form nucleus of boiling, thus generating bubble and gas films. After the droplets shrunk and stabilized, the contact diameter reduced and evaporation slowed. Droplet evaporation can be regulated to improve energy efficiency depending on different applications.
Nomenclature
| = | Discrete lattice velocity vectors | |
| c | = | Discrete lattice velocity vectors |
| cv | = | Specific heat capacity (J kg−1 K−1) |
| cs | = | Grid speed of sound |
| D | = | Droplet diameter (m) |
| E | = | Internal energy (J) |
| e | = | Discrete speed |
| fi | = | Distribution function for velocity |
| fieq | = | Equilibrium distribution function for velocity |
| Gs | = | Force coefficients |
| gi | = | Distribution function for energy |
| gieq | = | Equilibrium distribution function for energy |
| H | = | Height of droplet (m) |
| i | = | Velocity vector’s discrete direction |
| L | = | Length of droplet contact to wall (m) |
| p | = | Pressure (Pa) |
| R | = | Gas constant (J/(kg K)) |
| T | = | Temperature (K) |
| Tw | = | Temperature of the wall (K) |
| u | = | Velocity (m s−1) |
| x | = | Position lattice vectors (m) |
Greek symbols
| α | = | Thermal diffusivity (m2 s−1) |
| θ | = | Contact angle (°) |
| ν | = | Kinematic viscosity (m2 s−1) |
| ρ | = | Macroscopic density (kg m−3) |
| ρw | = | Density of the wall (kg m−3) |
| σ | = | Surface tension (mN/m) |
| τ0 | = | Dimensionless relaxation time for fi |
| τT | = | Dimensionless relaxation time for gi |
| Ф | = | Source term of the phase variable |
| χ | = | Properties at the gas-liquid interface |
| ωi | = | Weight coefficient |
Disclosure statement
No potential conflict of interest was reported by the author(s).
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