WOLFRAM NOTEBOOK

Part 4—Valve Example

This is part 4 of a 5 part series on modeling a fluid circuit using the Modelica Fluid library. Please go through the previous part, if you have not done it already:
In this post, I will use a valve to control the flow between two tanks.
Model to check the flow between tanks that are connected by a valve.

Steps

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  • Create a new model
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  • Drag the following components from the Modelica standard library:
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  • Fluid.Vessels.OpenTank: 2 num
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  • Blocks.Sources.Ramp
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  • Fluid.Valves.ValveIncompressible
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  • Fluid.System: Used to define system properties and default values so that you do not need to define it for every component
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  • Define the parameters of the tank (we will use the same parameters for both the tanks. Only the initial value of the fluid will be different):
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  • Medium (This parameter cannot be left blank)
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  • Select a fluid from the drop-down. Eg: “Extension of the standard water package”
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  • height
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  • Total height of the tank
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  • Change level_start (in the Initialization tab) of tank 1 to 10 m and tank 2 to 1 m.
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  • crossArea
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  • Define cross sectional area of the tank
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  • Ports (Important) : This refers to the outlet of the tank to which other components can be connected
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  • nPorts
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  • In this example as we want to connect only to the valve so we will set the nPorts to 1
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  • use_portsData
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  • set use_portsData to true
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  • portsData
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  • Provide the portsData as a list which means they need to be specified using curly braces {}.
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  • It takes a function as an argument. The function is Modelica.Fluid.Vessels.BaseClasses.VesselPortsData().
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  • You can open the function (type the name in the search field in the Class Browser) and check the inputs
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  • You can define diameter, height and other parameters
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  • For our example we want to set the port height to 1 m and diameter to 0.3 m. We will use the defaults for zeta_out and zeta_in.
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  • The input to the portsData should look like this:
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  • {Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter = 0.3, height = 1)}
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  • Define the parameters of the valve:
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  • Medium
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  • Select a fluid from the drop-down. Eg: “Extension of the standard water package”
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  • valveCharacteristic
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  • Choose a valve characteristics. Using the default setting (linear) should work for most cases.
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  • CvData
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  • Use a flow coefficient for the valve.
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  • Cv (US) flow coefficient is typically used.
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  • Cv
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  • Set the Cv value
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  • Eg: for a ball vale of size 10 inch (150 rating) Cv value is 15771 (Ref: https://www.piping-world.com/cv-flow-coefficients-of-ball-valve )
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  • dp_nominal
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  • Set nominal pressure drop across the valve
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  • m_flow_nominal
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  • Set nominal mass flow rate through the valve
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  • filteredOpening
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  • Set it to true to improve the numerics
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  • Define the parameters of the valveOpening ramp:
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  • startTime
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  • Set start time
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  • height
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  • Here, height is used as the normalized opening value of the valve
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  • Set the height of the ramp
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  • duration
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  • Set the duration for the ramp to reach the desired height from its initial value
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  • Define the parameters of the system:
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  • under the Assumptions tab
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  • Set massDynamics to FixedInitial (this priorities the use of the initial values as we want our tanks to start from their initial levels)
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  • Connect the ports of the tanks and the ramp to the valve:
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  • Provide a simulation time in the Experiment Setup and simulate:
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  • Plot the mass flow rate through the valve and the levels of the tank
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  • mass flow rate through the valve can be plotted using the following variable: valve.m_flow
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  • Flow of water starts at 2 seconds when the ramp signal starts. Water flows from tank with higher height (tank 1) to the tank with lower height (tank 2).
    • In this post, we saw how to instantiate a valve and used it to model flow between tanks. In the final post, model filling of a tank using a pipe that heats the fluid flowing through it.
    Other posts in this series can be found here:
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