Gate Valve Parametric Study

AIM

The aim of this challenge is to simulate the flow through a gate valve

OBJECTIVES

• Parametric study for diifferent lifts of the gate valve
• Calculation of flow coefficient and flow factor for all lifts
• Obtaining mass flow rates of all hte cases

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 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. At high pressures, friction can become a problem. As the gate is pushed against its guiding rail by the pressure of the medium, it becomes harder to operate the valve. Large gate valves are sometimes fitted with a bypass controlled by a smaller valve to be able to reduce the pressure before operating the gate valve itself. 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.

GATE VALVE SIMULATION

The gate valve has the following stages for the simulation

• Geometry
• Mesh
• Setup
• Solution
• Results

Geometry

When we import the geometry to the space claim the geometry loads and hide the bottom.

In order to move the disc upwards to provide a lift of 10mm the move tool is used and the gate valve moves up by using move command.

Then we extract the fluid volume where the fluid flows and we extend the flow volume for better flow.

After the solid components are hidden the above figure shows the actual fluid volume. Then we supress the solid components using supress for physics option.

Mesh

In mesh the size of the element is taken as 0.01m and the element count reaches 192957 elements.

Setup

Simulation is setup as follows

1. Solver - pressure based
2. Solver state - steady state
3. gravity - g = -9.81 m/s^2 in Z direction
4. Turbulence Model - K-Epsilon
5. fluid - water
6. Boundary conditions
7. Inlet pressure condition - p = 10 pascals

Residual plot

The simulation was run for 500 iterations and the solution has converged after 350 iteration.

Mass flow rate

The mass flow rate was observed at the outlet of the gate valve.

Results

Velocity Contour

GATE VALVE SIMULATION(PARAMERTIC STUDY)

The gate valve has the following stages for the simulation

• Geometry
• Mesh
• Setup
• Solution
• Results

Geometry

When we import the geometry to the space claim the geometry loads and hide the bottom.

In order to move the disc upwards to provide a lift of 10mm the move tool is used and the gate valve moves up by using move command. For the parametric study we click on the P icon to create the lift as a parameter for different lifts of valve disc.

Then we extract the fluid volume where the fluid flows and we extend the flow volume for better flow.

After the solid components are hidden the above figure shows the actual fluid volume. Then we supress the solid components using supress for physics option.

Section View

We can see that at the last design point the valve disc is raised from 10mm to 80mm. This image is the sectional view for the 80mm lift of the gate disc.

Mesh

In mesh the size of the element is taken as 0.01m and the element count reaches 192957 elements.

Setup

Simulation is setup as follows

1. Solver - pressure based
2. Solver state - steady state
3. gravity - g = -9.81 m/s^2 in Z direction
4. Turbulence Model - K-Epsilon
5. fluid - water
6. Boundary conditions
7. Inlet pressure condition - p = 10 pascals

Residual plot

The simulation was run for 500 iterations and the solution has converged after 350 iteration.

Mass flow rate

The mass flow rate was observed at the outlet of the gate valve.

Results

Velocity Contour

Case 1 lift = 10mm

Velocity Contour

Case 2 lift = 20mm

Velocity Contour

Case 3 lift = 30mm

Velocity Contour

Case 4 lift = 40mm

Velocity Contour

Case 5 lift = 50mm

Velocity Contour

Case 6 lift = 60mm

Velocity Contour

Case 7 lift = 70mm

Velocity Contour

Case 8 lift = 80mm

Parametric table

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 C_v (or flow-capacity rating of valve) can be expressed as :

`C_v=Qsqrtfrac[SG][Delta P]`

Q is the rate of flow,

G is the specific gravity of the fluid (for water = 1),

ΔP is the pressure drop across the valve.

Flow Factor

The metric equivalent flow factor K_v is calculated using metric units

`K_v=Qsqrtfrac[SG][Delta P]`

K_v is the flow factor (expressed in ).

Q is the flowrate (expressed in ]),

SG is the specific gravity of the fluid (for water = 1),

∆P is the differential pressure across the device (expressed in [bar])

K_v can be calculated from C_v using the equation

`K_v=0.865C_v`

Calculations

The calculations for the various cases are

here, Q = 1 kg/s = 3.6 `m^3/[hr]`

`Delta P=10xx10^-5`bar

`DeltaP=10^-4`bar

Flow Factor

1. `K_v=3.6xx0.14165sqrtfrac[1][10^-4]` K_v= 50.994
2. `K_v=3.6xx0.22686sqrtfrac[1][10^-4]` K_v= 81.669
3. `K_v=3.6xx0.34427sqrtfrac[1][10^-4]`K_v= 123.9372
4. `K_v=3.6xx0.4542sqrtfrac[1][10^-4]` K_v= 163.512
5. `K_v=3.6xx0.49661sqrtfrac[1][10^-4]`K_v= 178.7796
6. `K_v=3.6xx0.63118sqrtfrac[1][10^-4]`K_v= 227.2248
7. `K_v=3.6xx0.70784sqrtfrac[1][10^-4]`K_v= 254.8224
8. `K_v=3.6xx0.78243sqrtfrac[1][10^-4]`K_v= 281.6748

Flow Coefficient

1. `C_v=59.952`
2. `C_v= 94.41`
3. `C_v= 143.28`
4. `C_v= 189.03`
5. `C_v= 206.68`
6. `C_v= 262.69`
7. `C_v= 294.59`
8. `C_v= 325.64`

MATLAB CODE FOR PLOT

% Plot for flow factor and flow coefficient
lift = [10,20,30,40,50,60,70,80];

% Flow factor k_v
k_v = [50.994,81.669,123.9372,163.512,178.7796,227.2248,254.8224,281.6748];

% Flow Coefficient c_v
c_v = [59.95,94.41,143.28,189.03,206.68,262.69,294.59,325.64];

figure (1)
plot(lift,k_v,'color','b','marker','*','linewidth',5);
hold on
plot(lift,c_v,'color','r','marker','*','linewidth',5);
xlabel('Lift in mm');
ylabel('c_v & k_v');
title('flow factor and flow Coefficient');
legend('k_v','c_v');

PLOT

CONCLUSION

1. As the lift increases the mass flow rate also increases
2. Parametric study is done to observe the changes of flow parameters
3. Now we see that the velocity profile increases with increase in mass flow rate
4. The flow factor and flow coefficient is calculated and observed.
5. As lift increases the flow factor increases
6. As lift increases the flow coefficient increases
7. Flow coefficient helps in determining the efficiency of the gate valve