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Aim: To perform a parametric study on the gate valve simulation by setting the opening from 10 % to 80%. Objective: 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. …
Shreyas A M
updated on 22 Mar 2021
To perform a parametric study on the gate valve simulation by setting the opening from 10 % to 80%.
1. Parametric study:
A parametric study in Simulation is done to Map the change in inputs to the corresponding outputs. As long as the input parameter and output parameters are connected, the corresponding output values for change in input values are obtained.
2. 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).
Construction:
Common gate valves are actuated by a threaded stem that connects the actuator (e.g. handwheel or motor) to the gate. They are characterized as having either a rising or a non-rising stem, depending on which end of the stem is threaded. Rising stems are fixed to the gate and rise and lower together as 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.
Use:
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.
3. Mass flow rate:
The mass flow rate is the mass of a liquid substance passing per unit time. In other words, the mass flow rate is defined as the rate of movement of liquid pass through a unit area. The mass flow is directly dependent on the density, velocity of the liquid, and area of cross-section. It is the movement of mass per unit time. The mass flow is denoted by m and the units in kg/s.
The mass flow formula is given by,
m=ρ⋅V⋅Am=ρ⋅V⋅A
ρρ = density of fluid,
V = velocity of the liquid, and
A = area of cross-section
4. Flow co-efficient:
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 :
Cv=Q√SGΔPCv=Q√SGΔP
where:
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.
For gas flow in a pneumatic system, the Cv for the same assembly can be used with a more complex equation. Absolute pressures (psi) must be used for gas rather than simply differential pressure.
For airflow at room temperature, when the outlet pressure is less than 1/2 the absolute inlet pressure, the flow becomes quite simple (although it reaches sonic velocity internally). With Cv = 1.0 and 200 psi inlet pressure, the flow is 100 standard cubic feet per minute (scfm). The flow is proportional to the absolute inlet pressure, so the flow in scfm would equal the Cv flow coefficient if the inlet pressure were reduced to 2 psi and the outlet was connected to a vacuum with less than 1 psi absolute pressure (1.0 scfm when Cv = 1.0, 2 psi input).
Flow factor:
The metric equivalent flow factor (Kv; commonly used everywhere else in the world with the exception of the United States) is calculated using metric units :
Kv=Q√SGΔPKv=Q√SGΔP
where
Kv can be calculated from Cv using the equation:
Kv=0.865⋅Cv⋅KvKv=0.865⋅Cv⋅Kv
1. Procedure of simulation:
For the parametric study,
2. Geometry:
a. Gate valve:
b. Extending the geometry of the pipe by using the pull tool:
c. Moving the gate disc upward accordingly and to perform parametric study based on the movement on the gate disc
d. Performing volume extract to get the fluid volume so that the fluid analysis can be performed.
e. Viewing the change in gate disc by inserting section plane,
Meshing:
Name the inlet and outlet by face selecting command
Elemental size:92.82mm
no. of elements: 137317
3.Fluent set up:
General setup:
Physics set up:
Case 1:10mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:20mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:35mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:45mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:50mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:60mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
Case 1:80mm lift of gate
Residual plot:
velocity contour:
Mass flow rate:
parametric study table:
Calculation of flow coefficient and flow factor :
According to SI units, they can be converted to,
Here, Q=1kg/s i.e. Q=3.6 m^3/hr
ΔP= 10pascal
= 10 * 10^-5 bar (pascal to bar conversion= 1*10^-5 bar)
ΔP= 10^-4 bar.
Also, 1 ÷ √(10-4) = 100
Kv = Q * (( Mass flow rate value in each case) * 1 /√(10-4))
Lift | mass flow rate in kgs-1kgs−1 | Q (m3(hr)-1m3(hr)−1 | flow factor | flow coefficient |
10 | 0.1490 | 0.5364 | 53.64 | 62.01 |
20 | 0.24008 | 0.8642 | 86.42 | 99.9 |
35 | 0.415 | 1.494 | 149.4 | 172.71 |
45 | 0.5131 | 1.847 | 184.7 | 213.52 |
50 | 0.559 | 2.012 | 201.2 | 232.60 |
60 | 0.632 | 2.275 | 227.5 | 263.0 |
80 | 0.7637 | 2.533 | 253.3 | 292.83 |
Lift v/s mass flow rate graph
the flow coefficient and flow factor for each lift plot:
Conclusion:
From the plot, it can be concluded that as the gate disc rises, mass flow rate, flow coefficient and flow factor increases gradually.
The parametric study on the gate valve is performed by varying the lift from 10% to 80%. During the parametric study several parameters and its effects are plotted for representation. It's clear that the fluid flow rate gradually increases with the increase in the lift of the gate disc. Also the flow coefficient and the flow factors are plotted in order to observe the effect during the simulation. Hence in this study the effect of opening the gate valve on the fluid characteristics are established.
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