Properties: adiabatic, not isentropic, symmetric, ![]() inlet based restrictor
 inlet based restrictor
Restrictors are discontinuous geometry changes in gas pipes. The loss factor
![]() can be defined based on the inlet conditions or the outlet
conditions. Focusing on the h-s-diagram (entalpy vs. entropy) Figure (81), the inlet conditions are
denoted by the subscript 1, the outlet conditions by the subscript 2. The
entropy loss from state 1 to state 2 is
 can be defined based on the inlet conditions or the outlet
conditions. Focusing on the h-s-diagram (entalpy vs. entropy) Figure (81), the inlet conditions are
denoted by the subscript 1, the outlet conditions by the subscript 2. The
entropy loss from state 1 to state 2 is ![]() . The process is assumed to
be adiabatic, i.e.
. The process is assumed to
be adiabatic, i.e. 
![]() , and the same relationship applies to the
total entalpy
, and the same relationship applies to the
total entalpy ![]() , denoted by a dashed line in the Figure.
, denoted by a dashed line in the Figure. ![]() denotes the
kinetic energy part of the entalpy
 denotes the
kinetic energy part of the entalpy ![]() , the same applies to
, the same applies to ![]() . Now,
the loss coefficient
. Now,
the loss coefficient ![]() based on the inlet conditions is defined by
 based on the inlet conditions is defined by
| (56) | 
and based on the outlet conditions by
| (57) | 
![]() is the entropy for zero velocity and isobaric conditions at
the inlet, a similar definition applies to
 is the entropy for zero velocity and isobaric conditions at
the inlet, a similar definition applies to 
![]() . So, for
. So, for
![]() the increase in entropy is compared with the maximum entropy
increase from state 1 at isobaric conditions. Now we have
 the increase in entropy is compared with the maximum entropy
increase from state 1 at isobaric conditions. Now we have ![]() and
 and
![]() consequently,
 consequently,
| (58) | 
and based on the outlet conditions by
| (59) | 
Using Equation (44) one obtains:
| (60) | 
| (61) | 
| (62) | 
from which [65]
|  | (63) | 
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
|  | (64) | 
Using the general gas equation (30) finally leads to (for
![]() ):
):
|  | (65) | 
This equation reaches critical conditions (choking, ![]() ) for
) for
|  | (66) | 
Similar considerations apply to ![]() .
.
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
|  | (67) | 
and
|  | (68) | 
respectively.
A long orifice is a substantial reduction of the cross section of the pipe over a significant distance (Figure 82).
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):
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.