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Heat and mass transfer through a vapor film in view of the motion of liquid-vapor interface and the rise of temperature at the interface

“…These assumptions are valid if the duration of unsteady-state process found as a result of this solution turns out to be short enough for the film thickness and liquid temperature not to vary. Different methods were used in solving the problem: for Knudsen number values of Kn > 0.005, a numerical solution of the kinetic Boltzmann equation was used (see, for example, [4]); for lower values of Kn, a simultaneous numerical solution of the Navier-Stokes and Boltzmann equations was used [5]. It follows from the results given in [4,5] that, for a vapor film which does not communicate with space above the surface of liquid, in the investigated range of values of its thickness (up to 30 μm for helium at a liquid temperature of 2 K), the vapor condenses when the heater temperature increases, and the steady state is characterized by zero mass flux.…”

“…Different methods were used in solving the problem: for Knudsen number values of Kn > 0.005, a numerical solution of the kinetic Boltzmann equation was used (see, for example, [4]); for lower values of Kn, a simultaneous numerical solution of the Navier-Stokes and Boltzmann equations was used [5]. It follows from the results given in [4,5] that, for a vapor film which does not communicate with space above the surface of liquid, in the investigated range of values of its thickness (up to 30 μm for helium at a liquid temperature of 2 K), the vapor condenses when the heater temperature increases, and the steady state is characterized by zero mass flux. The duration of the investigated unsteady- state process is so short (of the order of several microseconds) that, in analyzing various applications, one can treat the state of vapor in the film as being quasisteady-state and use steady-state kinetic relations with zero mass flux for its description.…”

“…The macroparameters of vapor are defined as its moments, i.e., integrals of the distribution function multiplied by the respective function of molecular velocity, over the velocity space (calculation formulas are given, for example, in [6], and in the foregoing notation -in [4]). …”