Gate Valve Parametric Study

AIM: CHALLENGE FOR GATE VALVE SIMULATION

Gate Valve:

A gate valve, also known as a sluice valve, is a valve that opens by lifting a barrier (gate) out of the path of the fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened. The gate faces can be parallel but are most commonly wedge-shaped.

Gate valves are widely used for all types of applications and are suitable for both above-ground and underground installation. Not least for underground installations, it is paramount to choose the right type of valve to avoid high replacement costs.

Use of Gate Valve:

• Gate valves are used to shut off the flow of liquids rather than for flow regulation. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low flow resistance. The size of the open flow path generally varies in a nonlinear manner as the gate is moved. This means that the flow rate does not change evenly with stem travel. Depending on the construction, a partially open gate can vibrate from the fluid flow.
• Gate valves are mostly used with larger pipe diameters (from 2 "to the largest pipelines) since they are less complex to construct than other types of valves in large sizes.
• Gate valves without an extra sealing ring on the gate or the seat are used in applications where minor leaking of the valve is not an issue, such as heating circuits or sewer pipes.

Different types of gate valves:

1. Wedge Gate Valves
2. Plug-Disk Gate Valves
3. Subsea Gate Valve
4. Knife Gate Valve
5. Insider Screw Gate Valve
6. Rising Stem Gate Valve

Functioning principle:

The main components of a gate valve are body, seat, stem, bonnet, and actuator. The main operation mechanism is very simple. When the handwheel is turned, it rotates the fluid, which is translated into the vertical movement of a gate disc via threads. They are considered multi-turn valves as it makes more than one 3600 turns to fully open/close the valve. When the gate is lifted from the path of the flow, the valve opens and when it returns to its closed position, it seals the bore resulting in a full closure of the valve.

Parametric Study:

One of the best ways to get value out of your simulation is to do parametric analysis. With very little marginal work a completed model can be parameterized to simulate scenarios limited only by your computational time and resources.

As you move forward in your design, you can assess the impact that changing certain parameters can have on the design. The parameters can include dimensional parameters. Parametric studies allow you to nominate parameters for evaluation, define the parameter range, specify the design constraints, and analyze the results of each parameter variation.

A parametric study requires the following:

• Design Objective is set to Parametric Dimensions
• Parameters nominated for use in the simulation
• Parameter ranges identified
• Design criteria specified
• Various configurations generated

When you have the configurations generated you can then evaluate your simulation. You can further refine the parameters or design constraints until satisfied with the results.

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Objective:  To perform a parametric study on the gate valve simulation by setting the opening from 10 % to 80%. 

• Obtain the mass flow rates at the outlet for each design point.
• Calculate the flow coefficient and flow factor for each opening and plot the graph.
• Discuss the results of the mass flow rate and flow coefficient.

Modeling Procedure:

After opening SpaceClaim in Fluent, import Geometry named as “Gate Valve. STEP ”.

We can see the simplified geometry of the Gate Valve as given below as well as the Structure of all parts mentioned as given below:

                           

After importing Geometry, hide the "Bottom" Part, so we can clearly see the "Gate Disc".

                               

Then select the “Gate Disc” component and move it an upward direction by “10 mm” lift.
To analyze the flow and its effects, we must allow the flow, and for that, we have given a “10 mm” lift to the “Gate Disc”.
The lift of the "Gate Disc" can be given as shown in the image.

Also, we can see the symbol of “P”.
This symbol “P” is used to parameterize the lift of the “Gate Disc”.
After selecting the symbol “P”, it turns in Grey color, and the message shows that a Group has been created for lift.

            

For fluid simulation, fluid volume needs to be extracted from the model. A s can be seen from creating Fluid Volume, Hide all rest parts of the Gate Valve and suppress it for Physics and save it for further process.

After lifting the “Gate Disc”, move both faces at the inlet and outlet of the “Bottom” part by the amount of 800 mm just to see the fluid flow and its effects as given below:

After the extension, create Fluid volume by selecting the inlet, outlet, and upper edges of the “Bottom” part.
The creation of fluid volume will be as given below:

Mesh:

Mesh for the Fluid Volume of the Gate valve can be seen in images below:

    

Mesh statistics:-

Element Size: 7 mm
Number of Elements: 437178.

Setup and Simulation:

After Meshing, update it for further process and go for the Fluent Setup. In Fluent Setup, necessary details for simulation are as described below:

Analysis type: Steady-state

Solver: Pressure based solver

Gravity: -9.81 m/s2 in Z-Direction

Material Specifications:

Material: water-liquid (h2o)

Density: 998.2 Kg/m3

Viscosity: 0.001003 Kg/ (m-s)

Viscous Model:

Model: K-Epsilon

K-Epsilon Model: Realizable

Near Wall Treatment: Scalable Wall Functions

Boundary Conditions:

• Inlet: >Type: Pressure-Inlet

        Gauge Total Pressure: 10 Pa

• Outlet: >Type: Pressure-outlet

        Gauge Total Pressure: 0 Pa

• Wall: >Type: Wall

        Wall Motion: Stationary Wall

        Shear Condition: No Slip

• Interior: >Type: Interior

NOTE:

Here we have taken Pressure for inlet = 10 Pa.
Typically for Pipe flow, a pressure of 10 Pa is acceptable.

In the Viscous model, we have taken the K-Epsilon model. The reason behind choosing the K-Epsilon Viscous model is characteristic of the flow, which is turbulent.
For Reynolds No. about 2000 and more, flow is turbulent. So we have taken the K-Epsilon Viscous model.
But here, we have given Pressure Inlet, instead of Velocity Inlet. So knowing the velocity of the flow for correct Reynolds No. is required.
So, to know the velocity of the flow, we have to go for initializing the solution.
So, go to Solution, and select Standard Initialization, and Initialize from Inlet.
After initialization, we can get the correct velocity and calculate the Reynolds No. and from that, we can decide for the appropriate viscous model.

Parametric Study:

 

In the above image, we can see the Parameterization of the Lift Parameter. We can see the Parameter Set for the study at different Design Points of Lift of Gate Valve.
On completion of the simulation, select “Parameter Set” and give input for different Design Points.

Then Update all Design points and check all the results of different Design points. In the above image, we can see Mass Flow Rate after Updating all Design Points.

These results are calculated by fluent based on the lift of the “Gate Disc”.
Now we can check all Design Points one by one for detailed results like Pressure and Velocity Contours, Residuals, etc. by selecting each Design Point and making it as “Current”.

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Results and Discussion:

Now we will see all cases of lift of “Gate Disc” from 10mm to 80mm.

We will discuss each case particularly, for all types of results, and calculate the Flow coefficient and Flow Factor accordingly.
Here we will see Mass Flow Rate at Outlet, Flow Coefficient and Flow Factor, and required Plots for each opening.

Flow Coefficient:

The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice valve or other assembly and the corresponding flow rate.

Mathematically the flow coefficient Cv (or flow-capacity rating of the valve) can be expressed as:

 

Where,

Q is the rate of flow (expressed in US gallons per minute).
SG is the specific gravity of the fluid (for water = 1).
ΔP is the pressure drop across the valve (expressed in psi).

In more practical terms, the flow coefficient Cv is the volume (in US gallons) of water at 60 °F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that are widely accepted by the industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases, and steam using the discharge coefficient.

Flow Factor:

The metric equivalent flow factor (Kv; commonly used in Europe and Asia) is calculated using metric units:

Kv is the flow factor. Q is the flow rate (expressed in cubic meters per hour).
SG is the specific gravity of the fluid (for water = 1).
∆P is the differential pressure across the device (expressed in [bar]).

Kv can be calculated from Cv using the equation as given below:

               Kv = 0.865 (Cv)

The Kv factor of a valve indicates "The water flow in m3/h, at a pressure drop across the valve of 1 kg /cm2 when the valve is completely open.

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Case_1: Gate Disc Lift = 10 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.14955 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.14955 * √(1/10)

        = 0.14955 * 0.316227

   Cv = 0.047291

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.047291

   Kv = 0.0409073

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Case_2: Gate Disc Lift = 20 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.239964 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.239964 * √(1/10)

        = 0.239964 * 0.316227

   Cv = 0.075883

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.075883

   Kv = 0.0656388

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Case_3: Gate Disc Lift = 30 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.36473585 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.36473585 * √(1/10)

        = 0.36473585 * 0.316227

   Cv = 0.1153393

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.1153393

   Kv = 0.0997685

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Case_4: Gate Disc Lift = 40 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.48028597 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.48028597 * √(1/10)

        = 0.48028597 * 0.316227

   Cv = 0.1518793914

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.1518793914

   Kv = 0.13137567

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Case_5: Gate Disc Lift = 50 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.56210791 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.56210791 * √(1/10)

        = 0.56210791 * 0.316227

   Cv = 0.17775369

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.17775369

   Kv = 0.15375694

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Case_6: Gate Disc Lift = 60 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.6292303 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.6292303 * √(1/10)

        = 0.6292303 * 0.316227

   Cv = 0.1989796

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.1989796

   Kv = 0.17211736

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Case_7: Gate Disc Lift = 70 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.73179711 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.73179711 * √(1/10)

        = 0.73179711 * 0.316227

   Cv = 0.231414

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.231414

   Kv = 0.2001731141

__________________________________________________________________________

Case_8: Gate Disc Lift = 80 mm

Residuals

 

Mass Flow Rate

 

Velocity Contour

 

Pressure Contour

 

Flow Coefficient & Flow Factor 

      

Q = 0.7814268 kg/s

SG = 1000/998.2 = 1

ΔP = Pressure difference = 10psi

   Cv = 0.7814268 * √(1/10)

        = 0.7814268 * 0.316227

   Cv = 0.2471082527

   Now, Kv = 0.865 (Cv)

   Kv = 0.865 * 0.2471082527

   Kv = 0.2137486

__________________________________________________________________________

Comparison Table:

   

CASE	MASS FLOW RATE            (in Kg/s)	GATE DISC LIFT           (in mm)	FLOW                COEFFICIENT                (Cv)	FLOW FACTOR              (Kv)
1	0.14955	10	0.047291	0.040907
2	0.23996	20	0.075883	0.065638
3	0.36474	30	0.115339	0.099768
4	0.48029	40	0.151879	0.131375
5	0.56211	50	0.177753	0.153756
6	0.62923	60	0.198979	0.172117
7	0.73179	70	0.231414	0.200173
8	0.78143	80	0.247108	0.213748

Graphs:

Gate Disc Opening Vs Mass Flow Rate, Cv, and Kv:

                   

From the above Tabular Data and Graph, we can observe that

• As the opening of the Gate Valve or Lift of the Gate Disc increases, the Mass Flow Rate increases.
• With Increases in Mass Flow Rate, there is an increment in Flow Coefficient.
• Also, Increases in Flow Factor is observed at each Design Point from 10 to 80 mm Lift.
• The Graph of Mass Flow Rate, Flow Coefficient, and Flow Factor as can be seen goes linearly with the Opening of the Gate disc.

Conclusion:

1. We can conclude from observations that velocity in the first case is very low. As the opening or lift of the Gate Disc increases, the velocity of the flow increases.
2. We can observe that at the front or inlet side of the valve, the pressure is high. As flow passes through the valve opening, it decreases and at the outlet, there are no restrictions to the flow, so pressure becomes 0. It means there is a minimum Pressure Drop.
3. There is a gradual increase in Mass Rate, Flow Coefficient, and Flow Factor as the Lift of the Gate Disc increases, or from 10% to 80%, or 10 mm 80 mm.
4. When the valve is fully open, the Mass Flow rate and Flow Coefficient, and Flow Factor becomes maximum.
5. Thus, a parametric study helps to analyze the different positions of valve opening and gives the benefit to get easy and quick results.