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Matteo Cantiello edited Convective Velocities.tex
over 9 years ago
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\subsection{Convective Velocities}
We can calculate the accelaration of a convective fluid element
\begin{equation}
\ddot{r} = - g - \frac{1}{\rho} \frac{\partial \P}{\partial
r},
\end{equation}
which expanded at first order around the equilibrium state leads to an estimate of the total net force (buoyant minus gravitation) $f=-g \Delta \rho$. Along the distance $\Delta r$ a convective fluid element experience the force $f(\Delta r) = - g \Delta \rho (\Delta r)$. Here the variation of $g$ with height is considered negligible. The work done per unit volume over the distance $\Delta r$ is therefore
\begin{equation}
W (\Delta r) = \int_{0}^{\Delta r} f(x) \D x = - g \int_{0}^{\Delta r}
\Delta \rho (x) \D x = - \frac{1}{2} g \Delta \rho (\Delta r) \Delta r,
\end{equation}