Доступ предоставлен для: Guest
Портал Begell Электронная Бибилиотека e-Книги Журналы Справочники и Сборники статей Коллекции
Multiphase Science and Technology
SJR: 0.124 SNIP: 0.222 CiteScore™: 0.26

ISSN Печать: 0276-1459
ISSN Онлайн: 1943-6181

Выпуски:
Том 32, 2020 Том 31, 2019 Том 30, 2018 Том 29, 2017 Том 28, 2016 Том 27, 2015 Том 26, 2014 Том 25, 2013 Том 24, 2012 Том 23, 2011 Том 22, 2010 Том 21, 2009 Том 20, 2008 Том 19, 2007 Том 18, 2006 Том 17, 2005 Том 16, 2004 Том 15, 2003 Том 14, 2002 Том 13, 2001 Том 12, 2000 Том 11, 1999 Том 10, 1998 Том 9, 1997 Том 8, 1994 Том 7, 1993 Том 6, 1992 Том 5, 1990 Том 4, 1989 Том 3, 1987 Том 2, 1986 Том 1, 1982

Multiphase Science and Technology

DOI: 10.1615/MultScienTechn.v9.i3.10
pages 205-327

MOLECULAR-FLOW EFFECTS IN EVAPORATION AND CONDENSATION AT INTERFACES

Tor Ytrehus
Department of Applied Mechanics, Thermo- and Fluid-Dinamics, Norwegian University of Science and Technology, 7034 Trondheim, Norway

Краткое описание

Using the kinetic theory approach to molecular motion, the fluid- and thermodynamics aspects of a vapor next to its dense-phase boundary is studied under conditions of arbitrarily strong interphase transfer processes in single component systems. Typical non-rarefied global flow conditions are considered, such that the molecular mean free path in the vapor is very small compared to geometrical length scales for the interphase surface, and a kinetic boundary layer known as the Knudsen layer, may thus be treated separately beneath the macroscopic, continuum flow field. Although vanishingly thin on the global scale of the problem, the Knudsen layer may still adapt changes to leading order in basic variables like velocity and temperature between their values at the surface and in the external field. The coupling of values of the variables across the vapor Knudsen layer is reminiscent of the Rankine-Hugoniot relations across a normal shock wave, except that the state at the surface is at translational and thermodynamic nonequilibrium and must be described in terms of some non-Maxwellian molecular distribution function. It is shown that these Knudsen layer jump conditions determine most of the quantities of practical interest, like mass and energy fluxes, the temperature jump across the interphase surface, and the thermodynamic state of the vapor. We provide some general background for the gas dynamics description on the level of the Boltzmann equation, then give some elements from the rational linear theory for weak evaporation and condensation, before we discuss in detail an approximate moment solution for strong and moderately strong interphase rates. The classical Hertz-Knudsen and Schrage formulas are reinterpreted in the context of our results, and major improvements are suggested. We emphasize the influence of a poorly known element in the gas-kinetic boundary conditions: the evaporation/condensation coefficient, upon many of the results. The coupling of the Knudsen-layer results to the description of the external continuum flow is demonstrated by means of specific examples. Our findings are discussed with reference to other available theoretical and computational results in an attempt to define the current state of the art of this rapidly expanding field on the crossroad between microscopic and conventional fluid mechanics.