 
 
 
 
 
 
 
  
Restrictors are discontinuous geometry changes in gas pipes. The pressure loss is characterized by [63]
|  | (17) | 
if  is defined with reference to the first section (e.g. for an
enlargement, a bend or an exit) and
 is defined with reference to the first section (e.g. for an
enlargement, a bend or an exit) and
|  | (18) | 
if  refers to the second section (e.g. for a contraction or an entrance).
 refers to the second section (e.g. for a contraction or an entrance).  and
 and  are the total pressure and Mach
number in section one,
 are the total pressure and Mach
number in section one,  and
 and  are the total pressure and Mach
number in section two,
 are the total pressure and Mach
number in section two,  is the loss coefficient and
 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 if they are used for
compressible fluids.
 the ratio
of the heat capacity at constant pressure to the heat capacity at constant
volume. These formulae apply to all restrictors if they are used for
compressible fluids.
Restrictors can be applied to incompressible fluids as well, though, by specifying the parameter LIQUID on the *FLUID SECTION card. In that case the pressure losses amount to
|  | (19) | 
and
|  | (20) | 
respectively.
A long orifice is a substantial reduction of the cross section of the pipe over a significant distance (Figure 80).
There are two types: TYPE=RESTRICTOR LONG ORIFICE IDELCHIK with loss coefficients according to [33] and TYPE=RESTRICTOR LONG ORIFICE LICHTAROWICZ with coefficients taken from [42]. 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):
 .
.
 .
.
 defined by
 defined by  where
 where  is the
  perimeter of the cross section.
 is the
  perimeter of the cross section. 
 of the orifice.
 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
. This accounts for the reduction of cross section from
 to
 to  .
.
By specifying the parameter LIQUID on the *FLUID SECTION card the loss is calculated for liquids. In the absence of this parameter, compressible losses are calculated.
Example files: restrictor, restrictor-oil.
 
 
 
 
 
 
