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### Restrictor, Long Orifice

Restrictors are discontinuous geometry changes in gas pipes. The pressure loss is characterized by [44]

| (16)

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

| (17)

if refers to the second section (e.g. for a contraction or an entrance). and are the total pressure and Mach number in section one, and are the total pressure and Mach number in section two, is the loss coefficient and 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

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):

- reduced cross section .
- full cross section .
- hydraulic diameter defined by where is the perimeter of the cross section.
- Length of the orifice.

A restrictor of type long orifice MUST be preceded by a restrictor of type user with . This accounts for the reduction of cross section from to .

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