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A condition describing the law of motion of the boundary between two different phases of matter and expressed as a law of energy conservation under phase transformation. For example, the boundary between the solid and liquid phases of matter in a solidifying process (or a melting process) can be described in the one-dimensional case by a function <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875901.png" />, connected to the temperature distribution <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875902.png" /> by means of the Stefan condition:
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A condition describing the law of motion of the boundary between two different phases of matter and expressed as a law of energy conservation under phase transformation. For example, the boundary between the solid and liquid phases of matter in a solidifying process (or a melting process) can be described in the one-dimensional case by a function $\xi=\xi(t)$, connected to the temperature distribution $u(x,t)$ by means of the Stefan condition:
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875903.png" /></td> </tr></table>
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$$\lambda\rho_1\frac{d\xi}{dt}=k_1\frac{\partial u(\xi(t)-0,t)}{\partial x}-k_2\frac{\partial u(\xi(t)+0,t)}{\partial x},\quad t>0$$
  
 
(for the significance of the symbols, see [[Stefan problem|Stefan problem]]).
 
(for the significance of the symbols, see [[Stefan problem|Stefan problem]]).
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The mass
 
The mass
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875904.png" /></td> </tr></table>
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$$\rho_1\Delta\xi=\rho_1[\xi(t+\Delta t)-\xi(t)]$$
  
solidifies (or melts) in the course of time <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875905.png" />. The amount of heat <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875906.png" /> thus required is equal to the difference between the amounts of heat passing through the boundaries <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875907.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875908.png" />:
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solidifies (or melts) in the course of time $\Delta t$. The amount of heat $\lambda\rho_1\Delta\xi$ thus required is equal to the difference between the amounts of heat passing through the boundaries $\xi(t)$ and $\xi(t+\Delta t)$:
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s0875909.png" /></td> </tr></table>
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$$\lambda\rho_1\Delta\xi=\left[k_1\frac{\partial u(\xi(t)-0,t)}{\partial t}-k_2\frac{\partial u(\xi(t+\Delta t)+0,t+\Delta t)}{\partial x}\right]\Delta t.$$
  
Hence, when <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s08759010.png" />, the Stefan condition is obtained. Moreover, the temperature on the boundary between the two phases <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/s/s087/s087590/s08759011.png" /> is assumed to be continuous and its value is taken equal to the known temperature of melting.
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Hence, when $\Delta t\to0$, the Stefan condition is obtained. Moreover, the temperature on the boundary between the two phases $\xi=\xi(t)$ is assumed to be continuous and its value is taken equal to the known temperature of melting.
  
 
Similar conditions on unknown boundaries which arise in studies on certain other processes and which follow from conservation laws are also called Stefan conditions (see [[Differential equation, partial, free boundaries|Differential equation, partial, free boundaries]]).
 
Similar conditions on unknown boundaries which arise in studies on certain other processes and which follow from conservation laws are also called Stefan conditions (see [[Differential equation, partial, free boundaries|Differential equation, partial, free boundaries]]).

Latest revision as of 10:46, 10 August 2014

A condition describing the law of motion of the boundary between two different phases of matter and expressed as a law of energy conservation under phase transformation. For example, the boundary between the solid and liquid phases of matter in a solidifying process (or a melting process) can be described in the one-dimensional case by a function $\xi=\xi(t)$, connected to the temperature distribution $u(x,t)$ by means of the Stefan condition:

$$\lambda\rho_1\frac{d\xi}{dt}=k_1\frac{\partial u(\xi(t)-0,t)}{\partial x}-k_2\frac{\partial u(\xi(t)+0,t)}{\partial x},\quad t>0$$

(for the significance of the symbols, see Stefan problem).

The mass

$$\rho_1\Delta\xi=\rho_1[\xi(t+\Delta t)-\xi(t)]$$

solidifies (or melts) in the course of time $\Delta t$. The amount of heat $\lambda\rho_1\Delta\xi$ thus required is equal to the difference between the amounts of heat passing through the boundaries $\xi(t)$ and $\xi(t+\Delta t)$:

$$\lambda\rho_1\Delta\xi=\left[k_1\frac{\partial u(\xi(t)-0,t)}{\partial t}-k_2\frac{\partial u(\xi(t+\Delta t)+0,t+\Delta t)}{\partial x}\right]\Delta t.$$

Hence, when $\Delta t\to0$, the Stefan condition is obtained. Moreover, the temperature on the boundary between the two phases $\xi=\xi(t)$ is assumed to be continuous and its value is taken equal to the known temperature of melting.

Similar conditions on unknown boundaries which arise in studies on certain other processes and which follow from conservation laws are also called Stefan conditions (see Differential equation, partial, free boundaries).

References

[1] A.N. Tikhonov, A.A. Samarskii, "Equations of mathematical physics" , Pergamon (1963) (Translated from Russian)


Comments

The derivation of the heat balance condition at the liquid-solid interface was for long time attributed to J. Stefan [a1], [a2]. However, it appeared for the first time in a much earlier work by B.D. Clapeyron and G. Lamé [a3]. A classical illustration of the Stefan condition and of related problems can be found in [a4].

Many generalizations of the Stefan condition have been considered in the literature. For instance, the coefficients may depend on space and time, or higher-order derivatives of may appear on the right-hand side, even in a non-linear way (see e.g. [a5], [a6]).

References

[a1] J. Stefan, "Über einige Probleme der Theorie der Wärmeleitung" Sitzungsber. Akad. Wiss. Berlin Math. Kl. , 98 (1889) pp. 473–484
[a2] J. Stefan, "Über die Theorie der Eisbildung, insbesondere über die Eisbildung in Polarmeere" Ann. Physik Chemie , 42 (1891) pp. 269–286
[a3] G. Lamé, B.D. Clapeyron, "Mémoire sur la solidification par refroidissement d'un globe liquide" Ann. Chimie Physique , 47 (1831) pp. 250–256
[a4] L.I. Rubinstein, "The Stefan problem" , Amer. Math. Soc. (1971) (Translated from Russian)
[a5] A. Fasano, M. Primicerio, "Free boundary problems for nonlinear parabolic equations with nonlinear free boundary conditions" J. Math. Anal. Appl. , 72 (1979) pp. 247–273
[a6] M. Primicerio, "Classical solutions of general two-phase parabolic free boundary problems in one dimension" A. Fasano (ed.) M. Primicerio (ed.) , Free boundary problems: theory and application , 2 , Pitman (1983) pp. 644–657
How to Cite This Entry:
Stefan condition. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Stefan_condition&oldid=11786
This article was adapted from an original article by F.P. Vasil'ev (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article