Week 9 - Parametric study on Gate valve.
Objective:-
For this challenge, you will have 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.
Introduction:-
A gate valve, also known as a sluice valve, is a valve that opens by removing a barrier (gate) from the fluid's course. Gate valves take up very little space along the pipe axis and barely hinder fluid flow when completely opened. The gate faces can be parallel, but they are usually wedge-shaped.
A threaded stem connects the actuator (e.g., handwheel or motor) to the gate in most gate valves. Depending on which end of the stem is threaded, they have either a rising or a non-rising stem. Rising stems are attached to the gate and rise and fall together as the gate opens and closes. The valve is operated, providing a visual indication of valve position. The actuator is attached to a nut that is rotated around the threaded stem to move it. Non-rising stem valves are fixed to, and rotate with, the actuator, and are threaded into the gate. They may have a pointer threaded onto the stem to indicate valve position since the gate's motion is concealed inside the valve. Non-rising stems are used where vertical space is limited.
Uses:-
Gate valves are used to stop the flow of liquids rather than to regulate the flow. The standard gate valve has no blockage in the flow passage when fully open, resulting in very low flow resistance. As the gate is moved, the size of the open flow path varies in a nonlinear fashion. This indicates that the flow rate does not change uniformly when the stem moves. A partially open gate may shake due to fluid flow, depending on its construction.
Gate valves are commonly utilised with bigger pipe diameters (from 2" to the largest pipelines) because they are less complex to build than other types of large-size valves.
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.
Generally in pipelines with high pressure, the gate valve opening can be quite difficult due to the high force exerted on the gate. So they are generally connected with a smaller bypass valve to release the pressure and then they are operated.
Procedure:-
Geometry:
Importing geometry in SpaceClaim The following geometry was imported into SpaceClaim.
It has the following components:
The bonnet is placed below the handwheel and prevents the splashing of fluid from the upper region.
Handwheel and spindle that can be used to lift or lower the gate disc.
The gate disc is attached to the spindle at the bottom.
The bottom is a casing that covers the gate disc and the water flows through it. Two ports serve as an inlet and outlet for the fluid.
To perform the parameterization, Disable all the solid components except the gate dic 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.
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.
Extract the fluid volume.
Prepare > volume extract > select edges > press green tick symbol.
Meshing:-
Open the mesh console.
For the mesh size choose mesh element size = 10mm >> click on generate mesh
Give Name selection.
Setup:-
SOLVER TYPE PRESSURE BASED
SOLVER TIME STEADY STATE
GRAVITY ON( Z AXIS AS -9.81m/s^2)
VISCOUS MODEL K-EPSILON+REALIZABLE+SWIRL FLOW +SCALABLE WALL FUNCTIONS
MATERIAL WATER(LIQUID)
METHOD COUPLED
INLET(PRESSURE INLET) 10 Pa
OUTLET PRESSURE OUTLET( 0 Pa)
Perform general setup such as solver time as steady state, solver time as pressure based and enable gravity.
Use viscous model as k-epsilon realizable swirl scalable.
Create the plot for the mass flow rate at outlet and parametrise it to view the results in the project schematic window.
Create the plot for the pressure at outlet and do parametrise it.
set the boundary conditions. select inlet boundary selection as pressure inlet.
The velocity in y-direction is 0.1415488 m/s.
The Reynolds Number is calculated using the following formula:
Based on these calculations, the Reynolds Number appears to be more than 2000, indicating that the k- model is the best choice.
Use usual initialization to start the problem.
Iterate the simulation 500 times.
Case 1:-
Gate opening is 10mm.
Residual Plot:-
Mass Flow rate:
In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units, and slug per second or pound per second in second in US customary units. Mass flow rate is defined by the limit:
ṁ=dm/dt
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 dop across an orifice valve or other assembly and the corresponding flow rate.
Mathematically the flow coefficient Cv is expressed as:
Cv=Q√(SG/ΔP)
Where
Q is the rate of flow (expressed in US gallons per minute),
SG is the specific gravity of the fluid (for water=1);
∆P is the pressure drop across the valve (expressed in psi)
Flow Factor:
Flow factor (Kv) is the flow coefficient in metric units that is defined as the flow rate in cubic meters per hour(m3/h) of water at a temperature of 16°C with a pressure drop across the valve or any other restricting device of 1 bar. The Kv is related to the head drop (∆h) or pressure drop (∆P) across the valve with the flow rate (Q).
Mathematically, the Flow Factor is given as:
Kv=0.865.Cv
Q = 0.14885 kg/s = 2.35932 gal/min
SG = 1000/998.2≈1
∆P= 0.0014241308
Cv=2.35932√(1/0.0014241308)
=62.519
Kv=0.865⋅Cv
=Kv=0.865x62.519
=54.0789.
Case 2:-
Gate disc lift = 20 mm.
Residual Plot:-
Q = 0.23982 Kg/s = 3.80122 gal/min
SG = 1000/998.2≈1
∆P= 0.0013822448
Cv=3.80122√(1/0.0013822448)
=102.242
Kv=0.865⋅Cv
Kv=0.865x102.242
=88.4393.
Case 3:-
Gate disc lift = 30 mm.
Residual Plot:-
Q = 0.36187 Kg/s = 5.73576 gal/min
SG = 1000/998.2≈1
∆P= 0.001295168
Cv=5.73576√(1/0.001295168)
=159.378
Kv=0.865⋅Cv
Kv=0.865x159.378
=137.862.
Case 4:-
Gate disc lift = 40 mm.
Residual Plot:-
Q = 0.56757 Kg/s = 8.99617 gal/min
SG = 1000/998.2≈1
∆P= 0.00106843
Cv=8.99617√(1/0.00106843)
=275.223
Kv=0.865⋅Cv
Kv=0.865x275.223
=238.068.
Case 5:-
Gate disc lift = 70 mm.
Residual Plot:-
Q = 0.78403 Kg/s = 12.42713 gal/min
SG = 1000/998.2≈1
∆P= 0.0007218264
Cv=12.42713√(1/0.0007218264)
=462.546
Kv=0.865⋅Cv
Kv=0.865x462.546
=400.102.
|
Case |
Mass Flow Rate (kg/S) |
Gate Disc lift (mm) |
Flow Coefficient |
Flow Factor |
|
1 |
2.35932 |
10 |
62.519 |
54.0789 |
|
2 |
3.80122 |
20 |
102.242 |
88.4393 |
|
3 |
5.73576 |
30 |
159.378 |
137.862 |
|
4 |
8.99617 |
50 |
275.223 |
238.068 |
|
5 |
11.55774 |
70 |
403.996 |
349.457 |
From the above results, we clearly see that the mass flow rate increases with the gate disc lift or opening. The same thing happens with the flow coefficient and the flow factor as the mass flow rate increases. Broadly, the mass flow rate, the flow coefficient and the flow factor vary linearly with the gate disc opening.
Conclusion:-
With increasing opening %, the flow-coefficient and flow-factor rise.
With increasing opening percentage, the differential pressure across the gate valve diminishes. This is because the flow is less obstructed.
With rising opening %, mass-flow rate and velocity rise. This is because there are more channels for the water to go through.
The gate valve should be either fully open or entirely closed. A partially open valve causes vibration, which might cause damage to the gate valve.
Also, rather than closing the gate valve abruptly, which generates a water hammer effect that can harm the gate valve.
References:-
Ma, X.H., 2014. The Parametric Design and Finite Element Analysis of Wellhead Gate Valve Based on SolidWorks. AMM. https://doi.org/10.4028/www.scientific.net/amm.614.576.