Abstract
A transition from a d^{2} to a d law is observed in molecular dynamics (MD) simulations when the diameter (d) of an evaporating droplet reduces to the order of the vapor's mean free path; this cannot be explained by classical theory. This Letter shows that the d law can be predicted within the Navier-Stokes-Fourier (NSF) paradigm if a temperature-jump boundary condition derived from kinetic theory is utilized. The results from this model agree with those from MD in terms of the total lifetime, droplet radius, and temperature, while the classical d^{2} law underpredicts the lifetime of the droplet by a factor of 2. Theories beyond NSF are also employed in order to investigate vapor rarefaction effects within the Knudsen layer adjacent to the interface.
Highlights
A sound knowledge of the evaporation of nanodroplets is of great importance to many applications, such as combustion and spray drying [1], and the design of next-generation evaporative cooling nanodevices [2]
A transition from a d2 to a d law is observed in molecular dynamics (MD) simulations when the diameter (d) of an evaporating droplet reduces to the order of the vapor’s mean free path; this cannot be explained by classical theory
This Letter shows that the d law can be predicted within the Navier-Stokes-Fourier (NSF) paradigm if a temperature-jump boundary condition derived from kinetic theory is utilized
Summary
A sound knowledge of the evaporation of nanodroplets is of great importance to many applications, such as combustion and spray drying [1], and the design of next-generation evaporative cooling nanodevices [2]. For an isothermal drop below the critical temperature, the NSF equations without temperature-jump boundary conditions predict the time rate of change of the square of the droplet radius (or diameter) to be constant, known as the d-squared (d2) law of evaporation [5].
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