modelCheckValve
Extends from BuildingSystems.Fluid.BaseClasses.PartialResistance, BuildingSystems.Fluid.Actuators.BaseClasses.ValveParameters.
Information
Implementation of a hydraulic check valve. Note that the small reverse flows can still occur with this model.
Main equations
The basic flow function
ṁ = sign(Δp) k √ Δp ,
with regularization near the origin, is used to compute the pressure drop. The flow coefficient
k = ṁ ⁄ √ Δp
is increased from l*KV_Si to KV_Si,
where KV_Si is equal to Kv but in SI units.
Therefore, the flow coefficient k is set to a value close to zero for negative pressure differences, thereby
restricting reverse flow to a small value.
The flow coefficient k saturates to its maximum value at the pressure dpValve_closing.
For larger pressure drops, the pressure drop is a quadratic function of the flow rate.
Typical use and important parameters
The parameters m_flow_nominal and dpValve_nominal
determine the flow coefficient of the check valve when it is fully opened.
A typical value for a nominal flow rate of 1 m/s is
dpValve_nominal = 3400 Pa.
The leakage ratio l determines the minimum flow coefficient,
for negative pressure differences.
The parameter dpFixed_nominal allows to include a series
pressure drop with a fixed flow coefficient into the model.
The parameter dpValve_closing determines when the
flow coefficient starts to increase,
which is typically in the order of dpValve_nominal.
Implementation
The check valve implementation approximates the physics
where a forward pressure difference opens the valve such that
the valve opening increases, causing a growing orifice area
and thus increasing the flow coefficient.
Near dp=dpValve_closing, the valve is fully open and the flow coefficient saturates
to the flow coefficient value determined by dpValve_nominal and m_flow_nominal.
For typical valve diameters, the check valve is only fully open
near nominal mass flow rate. Therefore, the model sets dpValve_closing=dpValve_nominal/2
by default.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Real | l | 0.001 | Valve leakage, l=Kv(y=0)/Kv(y=1) |
| Real | kFixed | if dpFixed_nominal > Modelica.Constants.eps then m_flow_nominal/sqrt(dpFixed_nominal) else 0 | Flow coefficient of fixed resistance that may be in series with valve, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2). |
| Nominal condition | |||
| Modelica.Units.SI.PressureDifference | dpFixed_nominal | 0 | Pressure drop of pipe and other resistances that are in series |
| Modelica.Units.SI.PressureDifference | dpValve_closing | dpValve_nominal/2 | Pressure drop when the check valve starts to close |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Real | k | Flow coefficient of valve and pipe in series in allowed/forward direction, k=m_flow/sqrt(dp), with unit=(kg.m)^(1/2). |
Revisions
-
February 3, 2023, by Michael Wetter:
Corrected grahpical annotation. -
September 16, 2019, by Kristoff Six and Filip Jorissen:
Implementation of a hydraulic check valve. This is for issue 1198.