Contributed by the Heat Transfer Division for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received by the Heat Transfer Division May 23, 2000; revision received November 13, 2000. Associate Editor: D. Poulikakos.

The Knudsen number (Kn) is defined as the ratio of the mean free path of a gas, λ, to a dimension of an object which interacts with the gas, x,
$Kn=λx.$
(1)
According to Rohsenow and Choi 1, when fluid velocities are small relative to the speed of sound, the dynamics of a gas can be loosely classified into four regimes, the boundaries of which are determined by characteristic Knudsen numbers.

When $Kn<0.01,$ the mean free path of a gas is small compared with the dimensions of the system, and the gas may be approximated as a continuous medium. This is known...

1.
Rohsenow, W. M., and Choi, H., 1961, Heat, Mass, and Momentum Transfer, Prentice-Hall, Inc.
2.
Loeb, L. B., 1934, The Kinetic Theory of Gases, Second ed., McGraw-Hill Book Company, New York and London.
3.
Kennard, E. H., 1938, Kinetic Theory of Gases, McGraw-Hill Book Company, New York and London.
4.
Knudsen, M., 1950, Kinetic Theory of Gases, Third ed., Methuen and Co., London.
5.
Schrage, R. W., 1953, A Theoretical Study of Interphase Mass Transfer, Columbia University Press, New York.
6.
Nabavian
,
K.
, and
Bromley
,
L. A.
,
1963
, “
Condensation Coefficient of Water
,”
Chem. Eng. Sci.
,
18
, pp.
651
660
.
7.
Collier, J. G., 1981, Convective Boiling and Condensation, Second ed., McGraw-Hill, Berkshire, England.
8.
Patterson, G. N., 1956, Molecular Flow of Gases, John Wiley and Sons.
9.
Chapman, S., and Cowling, T. G., 1970, The Mathematical Theory of Non-Uniform Gases, Third ed., Cambridge University Press, Cambridge.
10.
Langmuir
,
I.
,
1915
, “
The Dissociation of Hydrogen Into Atoms, Part II
,”
J. Am. Chem. Soc.
,
37
, p.
417
417
.
11.
Shankar
,
P. N.
,
1970
, “
A Kinetic Theory of Steady Condensation
,”
J. Fluid Mech.
,
40
No.
2
, pp.
385
400
.
12.
Pao
,
Y.-P.
,
1971
, “
Application of Kinetic Theory to the Problem of Evaporation and Condensation
,”
Phys. Fluids
,
14
, No.
2
, pp.
306
312
.
13.
Pao
,
Y.-P.
,
1971
, “
Temperature and Density Jumps in the Kinetic Theory of Gases and Vapors
,”
Phys. Fluids
,
14
, No.
7
, pp.
1340
1346
.
14.
Sone
,
Y.
, and
Onishi
,
Y.
,
1978
, “
Kinetic Theory of Evaporation and Condensation—Hydrodynamic Equation and Slip Boundary Condition
,”
J. Phys. Soc. Jpn.
,
44
, No.
6
, pp.
1981
1994
.
15.
Labuntsov
,
D. A.
, and
Kryukov
,
A. P.
,
1979
, “
Analysis of Intensive Evaporation and Condensation
,”
Int. J. Heat Mass Transf.
,
22
, pp.
989
1002
.
16.
Bird, G. A., 1994, Molecular Gas Dynamics and the Direct Simulation of Gas Flows, Oxford University Press.
17.
Carey
,
V. P.
,
Oyumi
,
S. M.
, and
Ahmed
,
S.
,
1997
, “
Post-Nucleation Growth of Water Microdroplets in Supersaturated Gas Mixtures: A Molecular Simulation Study
,”
Int. J. Heat Mass Transf.
,
40
, No.
10
, pp.
2393
2406
.
18.
Kang
,
S.-W.
,
1967
, “
Analysis of Condensation Droplet Growth in Rarefied and Continuum Environments
,”
AIAA J.
,
5
, No.
7
, pp.
1288
1295
.
19.
Young
,
J. B.
,
1991
, “
The Condensation and Evaporation of Liquid Droplets in a Pure Vapour at Arbitrary Knudsen Number
,”
Int. J. Heat Mass Transf.
,
34
, No.
7
, pp.
1649
1661
.
20.
Harvie
,
D. J. E.
, and
Fletcher
,
D. F.
,
2001
, “
A Hydrodynamic and Thermodynamic Simulation of Droplet Impacts on Hot Surfaces, Part I: Theoretical Model
,”
Int. J. Heat Mass Transf.
,
44
, No.
14
, pp.
2633
2642
.
21.
Harvie
,
D. J. E.
, and
Fletcher
,
D. F.
,
2001
, “
A Hydrodynamic and Thermodynamic Simulation of Droplet Impacts on Hot Surfaces, Part II: Validation and Applications
,”
Int. J. Heat Mass Transf.
,
44
, No.
14
, pp.
2643
2659
.
22.
Fletcher
,
D. F.
, and
Theofanous
,
T. G.
,
1997
, “
Heat Transfer and Fluid Dynamic Aspects of Explosive Melt-Water Interactions
,”
,
29
, pp.
129
213
.
23.
Inoue
,
A.
,
Ganguli
,
A.
, and
Bankoff
,
S. G.
,
1981
, “
Destabilization of Film Boiling Due to Arrival of a Pressure Shock, Part II: Analytical
,”
ASME J. Heat Transfer
,
103
, pp.
465
471
.
24.
,
M. L.
,
1983
, “
Modeling Film Boiling Destabilization Due to a Pressure Shock Arrival
,”
Nucl. Sci. Eng.
,
84
, pp.
196
205
.
25.
Knowles, J. B., 1985, “A Mathematical Model of Vapour Film Destabilisation,” Technical Report AEEW-R1933, United Kingdom Atomic Energy Authority, Winfrith, Dorchester, Dorset.
26.
Heideger
,
W. J.
, and
Boudart
,
M.
,
1962
, “
Interfacial Resistance to Evaporation
,”
Chem. Eng. Sci.
,
17
, pp.
1
10
.
27.
Mills
,
A. F.
, and
Seban
,
R. A.
,
1967
, “
The Condensation Coefficient of Water
,”
Int. J. Heat Mass Transf.
,
10
, pp.
1815
1827
.