.ThermoPower.Water.BaseClasses.ValveBase

Information

This is the base model for the ValveLiq, ValveLiqChoked, and ValveVap valve models. The model is based on the IEC 534 / ISA S.75 standards for valve sizing.

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.

An optional heat loss to the ambient can be included, proportional to the mass flow rate; Qnom specifies the heat loss at nominal flow rate.

Modelling options

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

• CvData = ThermoPower.Water.ValveBase.CvTypes.Av: the flow coefficient is given by the metric Av coefficient (m^2).
• CvData = ThermoPower.Water.ValveBase.CvTypes.Kv: the flow coefficient is given by the metric Kv coefficient (m^3/h).
• CvData = ThermoPower.Water.ValveBase.CvTypes.Cv: the flow coefficient is given by the US Cv coefficient (USG/min).
• CvData = ThermoPower.Water.ValveBase.CvTypes.OpPoint: the flow coefficient is specified by the nominal operating point: pnom, dpnom, wnom, rhonom, thetanom (in forward flow).

The nominal 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; it can be replaced by functions taken from Functions.ValveCharacteristics, or by any suitable user-defined function extending Functions.ValveCharacteristics.baseFun.

Contents

Revisions

• 17 Jul 2012 by Francesco Casella:
  Added heat loss to ambient (defaults to zero).
• 5 Nov 2005 by Francesco Casella:
  Moved replaceable characteristics to Function.ValveCharacteristics package.
• 29 Sep 2005 by Francesco Casella:
  Re-introduced valve sizing by an operating point.
• 6 Apr 2005 by Francesco Casella:
  Enumeration-type choice of CvData.
• 16 Dec 2004 by Francesco Casella:
  Standard medium definition added.
• 18 Nov 2004 by Francesco Casella:
  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.
• 1 Jul 2004 by Francesco Casella:
  Valve models restructured using inheritance.
  Adapted to Modelica.Media.
• 1 Oct 2003 by Francesco Casella:
  First release.