.ThermoPower.Gas.Valve

Information

This model is based on the IEC 534/ISA S.75 standards for valve sizing, compressible fluid.

The model optionally supports reverse flow conditions (assuming symmetrical behaviour) or check valve operation, and has been suitably modified to avoid numerical singularities at zero pressure drop.

The model operating range include choked flow operation, due to sonic conditions in the vena contracta.

The flow characteristic can be customised.

Modelling options

The actual gas used in the component is determined by the replaceable Medium package. In the case of multiple component, variable composition gases, the start composition is given by Xstart,whose default value is Medium.reference_X.

The following options are available to specify the valve flow coefficient in fully open conditions:

• CvData = 0: the flow coefficient is given by the metric Av coefficient Av (m^2).
• CvData = 1: the flow coefficient is given by the metric Kv coefficient Kv (m^3/h).
• CvData = 2: the flow coefficient is given by the US Cv coefficient Cv (USG/min).
• CvData = 3: the flow coefficient must be specified by an additional initial equation (e.g. w=0.5); the start value given by Av is used to initialise the numerical solution of the equation.

The nominal inlet pressure pnom and pressure drop dpnom must always be specified; to avoid numerical singularities, the flow characteristic is modified for pressure drops less than b*dpnom (the default value is 1% of the nominal pressure drop). Increase this parameter if numerical instabilities occur in valves with very low pressure drops.

If CheckValve is true, then the flow is stopped when the outlet pressure is higher than the inlet pressure; otherwise, reverse flow takes place.

The default flow characteristic FlowChar is linear; this can be replaced by any user-defined function (e.g. equal percentage, quick opening, etc.).

The product Fk*xt is given by the parameter Fxtnom, and is assumed constant by default. The relative change of the xt coefficient with the valve opening can be specified by customising the xtfun function.

Contents

Name	Description
Medium
FlowChar	Flow characteristic
xtfun	Critical ratio characteristic

Revisions

• 15 Mar 2005 by Francesco Casella:
  Rewritten with sqrtReg.
• 19 Nov 2004 by Francesco Casella:
  Adapted to Modelica.Media.

Avnom removed, Av can now be set directly. Kvnom and Cvnom renamed to Kv and Cv.
CvData=3 no longer uses dpnom,wnom and rhonom, and requires an additional initial equation to set the flow coefficient based on the initial working conditions.
• 5 Mar 2004 by Francesco Casella:
  First release.