Week 9 - Parametric study on Gate valve.
Parametric study on Gate valve.
AIM:To perform a parametric study on gate valve for obtining different mass flow rate at different position.
Given Problem:
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 valves work by inserting a rectangular gate or wedge into the path of a flowing fluid. They are operated by a threaded stem which connects the actuator (generally a hand wheel or motor) to the stem of the gate. If the valve has a rising stem its position can be seen just by looking at the position of the stem. A gate valve is used to control the fluid flow through lifting and descending the gate. A gate distinct feature is to provide an unobstructed passageway, which includes minimal pressure loss over the valve.
When the gate is fully opened there is no restriction to the flow hence the pressure drop is low comparatively. Generally, the gate valve are fully closed or fully open as partially opened valve may experience vibration which may lead to excessive wear. A gate valve's main component is body, seat, gate, stem, bonnet, and actuator. the primary mechanism is straight forward where the handwheel is rotated to move the gate up and down via threads. they require more than a 360-degree turn to fully open the valve.
Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are slower in actuation than quarter-turn valves and are for applications where valve operation is infrequent, such as isolating valves. Gate valves should be used either fully open or fully closed, not to regulate flow. Automated gate valves exist with either an electric or pneumatic actuator, but a manual gate valve is cost-effective since they have infrequent usage. Gate valves are widely used for all types of applications and are suitable for both above-ground and underground installation. They are suitable for most fluids including steam, water, oil, and gas, etc.
Explanation:
At first load the geometry on geometry section.
Geometry:
Then ctrl+3 and in the left portion deselect the Bottom,Bonnet,Hand wheel and then in the Design portion select the Move command and select component and select the Disc portion to give a lift and parametrize the lift by going to Groups and create parameter.Give the lift by selecting the x-y-z and then drag it to upper portion.
Then in the left upper structure portion select the Bottom portion and then go to Design and select the pull tool and then pull the bottom by selecting the portion and entering the value by 800mm as shown in the figure below.
Then go to prepare and select edges and select the portion of the geometry as described below and extrac the fluid volume.
Then deselect the bottom portion of the gate valve and then supress the gate valve for physics and go to design and sketch mode and select the x-axis on the picture and the cut portion on the plain of the fluid body can be seen.
Then desect the Gate Disc and spindle and close the geometry.
Mesh:
Go to mesh-generate mesh and name the inlet and outlet and then by section plane command in the Home cut the geometry by x-y plane to see the inner gate disc lift.
Then update mesh and close it.
Set-Up:
In set up enable the gravity and on z-axis -9.81m/s^2. In the physics portion choose the viscous portion as described below.
In material section choose the water-liquid fluid from the fluent database.
In the cell-zone change the fluid from air to water-liquid.In boundary portion choose inlet as pressure-inlet and choose the inlet gauge pressure as 10 pa and outlet pressure as 0 pa.
Then in solution go to standard solution and initialize it from inlet.
We have to get the mass flow rates at the outlet section for different lifts of gate valve , so go to defination-New-Flux report-mass flow rate. choose mass flow rate at outlet and print to console and create output parameter.
We have to create a contour and animation for demonstrating the velocity of fluid . so first create a plane by result-create-plane
Then create the contour plot at plane3 and then go to solution - create - new animation and create an animation file of contour-1.Then take 200 iteration and calculate. To see mass flow rate at console go to result-report-flux-mass flow rate-compute.
RESULTS:
case-1(40mm lift)
console:
Residual:
Mass flow rate outlet:
Contour:
In parameter we are changing the current position by right clicking on mass flow rate and set as current.
Case-2(30mm lift)
Console:
Residual:
Mass flow rate outlet:
Contour:
Case-3(20mm lift)
Console:
Residual:
Mass flow rate outlet:
Contour:
case-4(10mm lift)
console:
Residual:
Mass flow rate outlet:
Contour:
The negative signs for the mass flow rates imply that the fluid is exiting the domain.The mass flow rate increases with the increase in the lit of the stopper. When the stopper is lifted gradually, the space available for the passage of the fluid increases hence the mass flow increases. When we perform the parametric study, Ansys automatically changes the mesh as per new geometry using the same mesh specifications given earlier, and solves and calculates the output parameters, thereby saving time comparatively if it was done manually.
Calculate the flow coefficient and flow factor for each opening:
The flow coefficient(Cv) 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.
where:
- Q is the rate of flow (expressed in US gallons per minute)
- SG is the specific gravity of the fluid (SG for water= 1)
- ΔP is the pressure drop across the valve (expressed in psi).
The metric equivalent flow factor(Kv) is calculated using metric units
where:
- Q is the rate of flow (expressed in m^3/h)
- SG is the specific gravity of the fluid (SG for water= 1)
- ∆P is the pressure drop across the valve (expressed in bar).
Kv can be calculated from Cv using the equation:
The following table gives the flow factor and flow coefficient of the fluid at different valve displacement magnitudes. Before the parameters are substituted to the formula, the units must be converted to the specific units defined above.
Calculation:
case-4:
For flow factor Kv , Q=(.14841/1000)*3600 = .53427 m^3 / hr
SG=1, ∆P = 10/10^5 bar =10^(-4) bar
so Kv = .44523*√ (1/10^(-4)) = .53427*100 = 53.437
Cv =Kv/0.865 =61.76
Data Table:
| Valve Displacement | Mass Flow rate(kg/s) | Flow Factor( Kv) | Flow Coefficient(Cv) |
| 10 | .14841 | 53.437 | 61.76 |
| 20 | .23818 | 85.744 | 99.12 |
| 30 | .35756 | 128.721 | 148.81 |
| 40 | .46676 | 168.033 | 194.25 |
Now ploting flow factor and flow coefficient vs Displacement in Google sheet(Just copy and paste the above table in google sheet and insert curve and edit and download)
From the above trend plots, we can say that with the increase in the opening of the gate valve the mass flow rate also increases. Along with the mass flow rate, the flow coefficient and flow factor also increase.
Conclusion:
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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. 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. Once you determine that a configuration satisfies your design needs, you are able to promote that configuration back to the model as a CAD edit. You are prompted whether to make changes. Using the parametric study method saves a lot of time in the simulations which require to perform the same operations for different settings multiple times.
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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
- In the parametric study of the gate valve, it was found that as the valve stopping is lifted gradually, the mass flow rate of the fluid, and hence the flow factor and flow coefficient increases.
Video File: