Single-phase flows

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Next: Two-phase flows Up: Sudden expansion Previous: Sudden expansion Contents Index

Single-phase flows

In single-phase flow it is most accurate to calculate the pressure change, $\Delta p_{\mbox{\protect\scriptsize SP,exp}}$ [Pa], by the expression

$\begin{displaymath} \Delta p_{\mbox{\protect\scriptsize SP,exp}} \;\hbox{$=$\ke... ...t\scriptsize exp}}] \frac{\mbox{$<\!{G}\!>$}_1^2}{2\rho_\ell} \end{displaymath}$

(5.27)

where indices 1 and 2 refer to quantities upstream and downstream the expansion respectively, $\mbox{$<\!{G}\!>$}$ [kg/( ${\mbox{m}}^2\cdot$ s)] is the mass flux, $\rho_\ell$ [kg/ ${\mbox{m}}^3$ ] is the liquid density, $K_{\mbox{\protect\scriptsize exp}}$ [--] is the expansion loss coefficient and $\sigma$ [--] is the flow area ratio defined by

$\begin{displaymath} \sigma \;\hbox{$=$\kern-0.68em\raise1.1ex \hbox{$\scriptscriptstyle\triangle$}}\;\frac{A_{c,1}}{A_{c,2}} \end{displaymath}$

(5.28)

The expansion loss coefficient is a function of the flow area ratio, $\sigma$ , and the Reynolds number, $\mbox{\bf Re}$ , and may be found in standard fluid mechanics text books (for instance [43]). The values of $K_{\mbox{\protect\scriptsize exp}}$ are given in Table 5.1.

$\begin{table} % latex2html id marker 20277\rule{\textwidth}{0.8mm} \refstepcou... ...\\ 0.8 & 0.04 \\ 1.0 & 0.00\\ \hline \end{tabular*}\end{minipage}\end{table}$

According to Weismann [11, p. 196] the values in Table 5.1 corresponds to a high Reynolds number $\mbox{\bf Re}>10^5$ which is normally encountered in BWR designs.

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