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Next: Energy conservation Up: Assumptions implicit in the Previous: Mass conservation   Contents   Index

Momentum balance

The most important assumption is that the correct momentum of, say, the liquid phase is approximated in the following way

\begin{displaymath}
\mbox{$<\!{(1-\alpha)A_c\rho_\ell u_\ell^2}\!>$} \approx
\...
...\!{u_\ell}\!>$}_\ell ^2\rho_\ell(1-\mbox{$<\!{\alpha}\!>$})A_c
\end{displaymath} (6.28)

and this assumption is not very accurate according to Ishii and Mashima6.3. In fact, it is necessary to introduce a correlation coefficient $C_{v \ell}$ defined by

\begin{displaymath}
C_{v \ell} \;\hbox{$=$\kern-0.68em\raise1.1ex
\hbox{$\scri...
...\!>$})A_c}{\mbox{$<\!{(1-\alpha) A_c\rho_\ell
u_\ell^2}\!>$}}
\end{displaymath} (6.29)

in order to account for the non-uniform profiles. The same comment applies to the vapor phase momentum equation.

Furthermore, the axial change of the cross-sectional average of the laminar and turbulent zz-stress ($\tau_{zz}$) is neglected--an acceptable assumption since we have a large $\mbox{\bf Re}$ in the reactor core.

 
 

 
 
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