Week 9 - Parametric study on Gate valve.
REPORT ON PARAMETRIC STUDY ON A GATE VALVE
AIM
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.
THEORY
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 (in order to be able to apply pressure on the sealing surface).
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.
Parametric Study :
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Parametric analysis is one of the best ways to get the most out of your simulation. A completed model can be parameterized to simulate scenarios with very little additional work, with the only constraints being your computing power and time.
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We can evaluate the effects of changing particular parameters as you proceed with your design. Dimensional parameters may be among the parameters. You can define the parameter range, specify the design constraints, and evaluate the effects of each parameter variation using parameter studies.
Flow Co-efficient:
Kv can be calculated from Cv using the equation:
- Kv = 0.865*Cv
PROCEDURE
The first step is importing of the geometry and extraction of the volume
Then we provide parameterization
For that we disable all the solid components except the gate disc and spindle.
Go to the design tab and choose the move option and further select move body option and further select the gate disc.Following you will be able to see the coordinate system appear the gate disc,you can then proceed to move the gate disc towards the top of the spindle.
As shown in the image the create parameter option doesnot appear along the dimension of the lift the alternate way to parametrize the same is to go to the groups menu which is adjacent to the structured menu, in the group menu you will able to see the create parameter button,which will be enabled only after you have move the gate disc,click on create parameter following which you will you see a group 1 appear in which you can edit the dimensions of the lift.This will parameterise your gate disc lift,you can confirm the same by checking your workbench.
Then we move the geometry at both sides about 800 mm and update the geometry using the current context which results in the following image
The creation of fluid volue will be as given below
Then we move into the meshing part where we give the names using the name selection as inlet and outlet
Now we generate the mesh with mesh size of 10mm
Now we jump into setting up of the physics part where we give the model types, intial and boundary conditions and run the simulation
Here we use the Steady state solver of pressure based type and we engage the acceleration due to gravity in the negative Y direction
Then we use viscous model as k-epsilon with realizable model and scalable wall function
Then we use the material as water in place of air.
Then we change the cell zone from air to water
Then we create the plot for the mass flow rate at outlet and parametrise it to view the results in the project schematic window.
We also create the plot for the pressure at outlet and do parametrise it.
Then we boundary conditions. select inlet boundary selection as pressure inlet.
Next we select outlet boundary type as pressure outlet.
Then we initialize the problem using standard initialization
Then we create the veloity contour and create the animation of the same by creating a palne along YZ axis.
At last we run the simulation for 250 iterations.
RESULTS
Case 1 : Gate valve simulation at 10% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.1488525*15.85*(1/(0.001423) since, ( 1kg/sec=15.85 gal/min )
Q = 2.359 gallons per minute
Cv = 62.53
Flow factor = 0.865*Cv = 62.53*0.865 = 54.093
Case 2 : Gate valve simulation at 20% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.23824618*15.85 = 3.7762*sqrt(1/0.001381) = 101.61
Flow factor = 87.89
Case 3 : Gate valve simulation at 30% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` =0.36576045*15.85*sqrt(1/0.001285) = 161.69
Flow factor = 139.86
Case 4 : Gate valve simulation at 40% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.49340947*15.85*sqrt(1/0.001161) = 229.520
Flow factor = 198.534
Case 5 : Gate valve simulation at 50% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.58002774*15.85*sqrt(1/0.001041) = 284.93
Flow factor = 246.47
Case 6 : Gate valve simulation at 60% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.65728937*15.85*sqrt(1/0.0009312) = 341.40
Flow factor = 295.41
Case 7 : Gate valve simulation at 70% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.71860725*15.85*sqrt(1/0.0008104) = 400.102
Flow factor = 346.088
Case 8 : Gate valve simulation at 80% opening
RESIDUALS
VELOCITY CONTOUR
MASS FLOW RATE
OUTLET PRESSURE
Flow coefficient , `C_v = Q*((SG)/(DeltaP))^(1/2)` = 0.75477434*15.85*sqrt(1/0.000764) = 432.814
Flow factor = 374.38
So, the Graph of Mass Flow Rate, Flow Coefficient, and Flow Factor goes linearly with Gate Disc Opening.
CONCLUSION
| Disc Lift | Mass Flow Rate | Flow Coefficient | Flow Factor |
| 10 mm | 0.14885256 | 62.53 | 54.093 |
| 20 mm | 0.23824618 | 101.61 | 87.89 |
| 30 mm | 0.36576045 | 161.69 | 139.86 |
| 40 mm | 0.49340947 | 229.520 | 198.534 |
| 50 mm | 0.58002774 | 284.93 | 246.47 |
| 60 mm | 0.65728937 | 341.40 | 295.41 |
| 70 mm | 0.71860725 | 400.102 | 346.088 |
| 80 mm | 0.75477434 | 432.814 | 374.38 |
1. Flow-coefficient and flow-factor increase with increasing opening percentage.
2. Differential pressure across the gate valve decreases with increasing opening percentage. This is because there is less blockage to the flow.
3. Mass-flow rate and velocity increase with increasing opening percentage. This is because there are more pathways for the water to flow.
4. Gate valve should operate in a fully-opened or fully-closed position. A partially-opened valve induces vibration which can damage the gate valve.
5. Also the gate valve should be closed gradually rather than suddenly, as it causes a water hammer effect which can again damage the gate valve.