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`.

Name | Description |
---|---|

Medium | |

FlowChar |

*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.

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