Question

# What is Stefan flow? Write the expression for Stefan’s law and indicate what each variable represents.

Solution

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Stefan flow is induced convective flow that enhances mass diffusion.

Expression for Stefan's law:

\begin{align*} \overline{j_A}&= \frac{ \dot{N}_{A}}{ A}\\ &= \frac{ CD_{AB}}{ L} \hspace{1mm} \ln \hspace{1mm} \frac{ 1- y_{A, L}}{1- y_{A, 0}} \hspace{1mm} [\frac{\text{ kmol}}{\text{ s}\text{ m}^2}] \end{align*}

$\overline{j_A}= \dfrac{ \dot{N}_{A}}{ A} [\dfrac{\text{ kmol}}{\text{ s}\text{ m}^2}]$ is the total molar flux

$\dot{N} [\dfrac{\text{ kmol}}{\text{ s}}]$ is diffusion molar flow rate

A $[{\text{ m}^2}]$ is the surface

$C$ [kmol] is the average concentration of mixture

$D_{AB} [\dfrac{\text{ m}^2}{\text{ s}}]$ is binary diffusion coefficient

$L$ [m] is the height of the gas column

$y_{A, L}$ [kmol] is the molar concentration of species at $x=L$

$y_{A, 0}$ [kmol] is the molar concentration of species at $x=0$

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