ValveDiscrete

Valve for water/steam flows with linear pressure drop

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

This very simple model provides a (small) pressure drop which is proportional to the flowrate if the Boolean open signal is true. Otherwise, the mass flow rate is zero. If opening_min > 0, a small leakage mass flow rate occurs when open = false.

This model can be used for simplified modelling of on-off valves, when it is not important to accurately describe the pressure loss when the valve is open. Although the medium model is not used to determine the pressure loss, it must be nevertheless be specified, so that the fluid ports can be connected to other components using the same medium model.

The model is adiabatic (no heat losses to the ambient) and neglects changes in kinetic energy from the inlet to the outlet.

In a diagram animation, the valve is shown in "green", when it is open.

Parameters (10)

allowFlowReversal

Value: system.allowFlowReversal

Type: Boolean

Description: = true to allow flow reversal, false restricts to design direction (port_a -> port_b)

dp_start

Value: 0.01 * system.p_start

Type: AbsolutePressure (Pa)

Description: Guess value of dp = port_a.p - port_b.p

m_flow_start

Value: system.m_flow_start

Type: MassFlowRate (kg/s)

Description: Guess value of m_flow = port_a.m_flow

m_flow_small

Value: if system.use_eps_Re then system.eps_m_flow * system.m_flow_nominal else system.m_flow_small

Type: MassFlowRate (kg/s)

Description: Small mass flow rate for regularization of zero flow

show_T

Value: true

Type: Boolean

Description: = true, if temperatures at port_a and port_b are computed

show_V_flow

Value: true

Type: Boolean

Description: = true, if volume flow rate at inflowing port is computed

dp_nominal

Value:

Type: AbsolutePressure (Pa)

Description: Nominal pressure drop at full opening=1

m_flow_nominal

Value:

Type: MassFlowRate (kg/s)

Description: Nominal mass flowrate at full opening=1

k

Value: m_flow_nominal / dp_nominal

Type: HydraulicConductance (kg/(s┬ĚPa))

Description: Hydraulic conductance at full opening=1

opening_min

Value: 0

Type: Real

Description: Remaining opening if closed, causing small leakage flow

Connectors (3)

port_a

Type: FluidPort_a

Description: Fluid connector a (positive design flow direction is from port_a to port_b)

port_b

Type: FluidPort_b

Description: Fluid connector b (positive design flow direction is from port_a to port_b)

open

Type: BooleanInput

Components (3)

system

Type: System

Description: System wide properties

state_a

Type: ThermodynamicState

Description: state for medium inflowing through port_a

state_b

Type: ThermodynamicState

Description: state for medium inflowing through port_b

Used in Examples (4)

ControlledTanks

Modelica.Fluid.Examples.ControlledTankSystem

Demonstrating the controller of a tank filling/emptying system

BatchPlant_StandardWater

Modelica.Fluid.Examples.AST_BatchPlant

TankWithEmptyingPipe1

Modelica.Fluid.Examples.AST_BatchPlant.Test

Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient

TanksWithEmptyingPipe2

Modelica.Fluid.Examples.AST_BatchPlant.Test

Demonstrates a tank with one constant top inlet mass flow rate and a bottom outlet into the ambient