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Restrictor, Long Orifice

Restrictors are discontinuous geometry changes in gas pipes. The pressure loss is characterized by [45]

$\displaystyle \frac{p_{t_1}}{p_{t_2}} = \left( 1 + \frac{\kappa -1}{2} M_1^2 \right) ^{\zeta \frac{\kappa}{\kappa-1}}$ (16)

if $ \zeta$ is defined with reference to the first section (e.g. for an enlargement, a bend or an exit) and

$\displaystyle \frac{p_{t_1}}{p_{t_2}} = \left( 1 + \frac{\kappa -1}{2} M_2^2 \right) ^{\zeta \frac{\kappa}{\kappa-1}}$ (17)

if $ \zeta$ refers to the second section (e.g. for a contraction or an entrance). $ p_{t_1}$ and $ M_1$ are the total pressure and Mach number in section one, $ p_{t_2}$ and $ M_2$ are the total pressure and Mach number in section two, $ \zeta$ is the loss coefficient and $ \kappa$ the ratio of the heat capacity at constant pressure to the heat capacity at constant volume. These formulae apply to all restrictors.

A long orifice is a substantial reduction of the cross section of the pipe over a significant distance (Figure 51).

Figure 51: Geometry of a long orifice restrictor
\begin{figure}\epsfig{file=Long_orifice.eps,width=11cm}\end{figure}

There are two types: TYPE=RESTRICTOR LONG ORIFICE IDELCHIK with loss coefficients according to [22] and TYPE=RESTRICTOR LONG ORIFICE LICHTAROWICZ with coefficients taken from [29]. In both cases the long orifice is described by the following constants (to be specified in that order on the line beneath the *FLUID SECTION, TYPE=RESTRICTOR LONG ORIFICE IDELCHIK or TYPE=RESTRICTOR LONG ORIFICE LICHTAROWICZ card):

A restrictor of type long orifice MUST be preceded by a restrictor of type user with $ \zeta=0$. This accounts for the reduction of cross section from $ A_2$ to $ A_1$.


next up previous contents
Next: Restrictor, Enlargement Up: Fluid Section Types: Gases Previous: Gas Pipe   Contents
guido dhondt 2008-07-31