Gate Valve Parametric Study
AIM: To perform a parametric study on the gate valve and to calculate flow coefficients and flow factor for each opening.
Software used: Ansys 2020 R1
Objectives:
We 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 :
Gate valves are designed for fully open or fully closed service. They are installed in pipelines as isolating valves, and should not be used as a control or regulating valves. Operation of a gate valve is performed doing an either clockwise to close (CTC) or clockwise to open (CTO) rotating motion of the stem. When operating the valve stem, the gate moves up- or downwards on the threaded part of the stem.
The first design of a product that has been in the head of the engineers is illustrated in computers and then produced by computer-aided machines. The analysis processes of a product of which solid modelling have been accomplished can be carried out by ANSYS and similar analysis programs in the digital environment, before starting manufacturing. These processes give the companies flexibility in the development of a new product by providing design capability with minimum cost and minimum waste of time. ANSYS program, which has been used in this study, can make the analysis of the substances in many subjects including static, dynamic, thermal, harmonic and electromagnetic.
Geometrical Model :
Volume Extracted:
Firstly, we have hidden all the components except the gate disc and with the help of move command, we have moved the gate disc in an upward direction at some distance.
then we carefully select the areas where we have to extract the volume. This can be done by going to prepare tool and selecting volume extract command and we extend the inlet and outlet region by 800 mm.
SET UP:
- When the mesh component is loaded in Ansys fluent steady-state solver is used.
- Gravity on the Z-axis is set at -9.81 m/s. Now we changed the material to water liquid.
- K-Epsilon model is used as the viscous model.
- In boundary conditions, the inlet is changed from velocity inlet to pressure inlet and the pressure is set as 10 Pa.
- One report definition is created as mass flow rate and the output parameter box is clicked so as to get mass flow rate values at each design points.
- Standard Initialization is done.
- Contours like pressure and velocity and their respective animations are created.
Q1. Parametric analysis by setting the opening from 10% to 80%.
Ans: 5 different cases are created to show parametric analysis on the gate valve. Here meshing element size is same but all the cases have different nodes and elements.
CASE 1:
The spindle inside the gate disc: 20 mm
Section Cut geometry:
MESHING:
Element size:10 mm
Nodes: 40076
Elements: 191886
Residual Plot:
Mass Flow Rate:
Pressure Contour:
Velocity Contour:
Computed Mass Flow Rate:
CASE 2:
The spindle inside the gate disc: 35 mm
Section cut Geometry:
Meshing:
Element size:10 mm
Nodes: 40215
Elements: 192575
Residual Plot:
Mass Flow Rate Plot:
Pressure Contour plot:
Velocity Contour Plot:
Computed Mass Flow Rate:
CASE 3:
The spindle inside the gate disc: 50 mm
Section Cut geometry:
Meshing:
Element size:10 mm
Nodes: 39358
Elements: 188648
Mass Flow Rate:
Computed Mass Flow Rate: -0.55005 Kg/s
Pressure Contour:
Velocity Contour:
CASE 4:
The spindle inside the gate disc: 65 mm
Section Cut geometry:
Meshing:
Element size:10 mm
Nodes: 39134
Elements: 186708
Residual Plot:
Mass Flow Rate :
Computed Mass Flow Rate: -0.69679 Kg/s
Pressure Contour:
Velocity Contour:
CASE 5:
The spindle inside the gate disc: 80 mm
Section Cut geometry:
Meshing:
Element size:10 mm
Nodes: 43228
Elements: 206045
Residual Plot:
Mass Flow Rate:
Computed Mass Flow Rate: -0.79214 Kg/s
Pressure Contour:
Velocity Contour:
Q2 Calculate the flow coefficient and flow factor for each opening and plot the graph.
ANS.:- 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 Cv (or flow capacity rating of valve) can be expressed as-
Cv = rate of flow*sqrt(specific gravity/pressure drop)
Flow Factor:- The metric equivalent flow factor (Kv; commonly used in Europe and Asia) is calculated using metric units -
Kv = flow rate*sqrt(specific gravity/pressure drop)
Kv can be calculated from Cv using the equations-
Kv = 0.865*Cv
By using the above formula I calculated the flow coefficient and flow factor as given below-
Given quantities are:
Specific gravity of water = 1
Pressure drop = 10 Pa
Velocity = 0.1415488 m/s
For CASE 1,
Inlet diameter = (100 - 20) = 80 mm = 0.08 m
Area = pi*radius^2 = 3.14*0.04*0.04 = 0.005024 m^2.
Flow rate = Q = Area*velocity = 0.005024*0.1415488 = 0.000711 m^3/sec
Flow Coefficient : Cv = 0.0.000711 * sqrt(1/10) = 0.00022486.
Flow factor : Kv = 0.865 * 0.000224867 = 0.000194509 .
For CASE 2,
Inlet diameter = (100-35) = 65 mm = 0.065 m
Area = pi * radius^2 = 3.14*0.0325*0.0325 = 0.00332 m^2.
Flow rate = Q = Area*velocity = 0.00332*0.1415488 = 0.000469464 m^3/sec
Flow coefficient = Cv = 0.000469464 *sqrt(1/10) = 0.00014857.
Flow factor = Kv = 0.865*Cv = 0.000128415 .
For CASE 3,
Inlet diameter = (100-50) = 50mm = 0.05 m
Area = pi*radius^2 = 3.14*0.025*0.025 = 0.0019625 m^2
Flow rate = Q = Area*velocity = 0.0019625*0.1415488 = 0.000277789 m^3/sec
Flow coefficient = Cv = 0.000277789*sqrt(1/10) = 0.00008784.
Flow factor = Kv = 0.865*Cv = 0.00007599
For CASE 4,
Inlet diameter = (100-65) = 35 mm = 0.035 m
Area = pi*radius^2 = 3.14*0.0175*0.0175 = 0.00096163 m^2
Flow rate =Q = Area*velocity = 0.00096163*0.1415488 = 0.00013612 m^3/sec
Flow coefficient = Cv = 0.00013612*sqrt(1/10) = 0.00004304 .
Flow factor =Kv = 0.865*Cv = 0.00003723 .
For CASE 5,
Inlet diameter = (100-80) = 20mm = 0.02m
Area = pi*radius^2 = 3.14*0.01*0.01 = 0.000314 m^2
Flow rate = Q = Area*velocity = 0.000314*0.1415488 = 0.0000444 m^3/sec
Flow coefficient = Cv = 0.0000444*sqrt(1/10) = 0.000014
Flow factor = Kv = 0865*Cv = 0.000012 .
Plots:
1. Cv vs Lift
2. Kv vs Lift
When the lift increases flow coefficient and flow factor are also increasing.
Q3 .Discuss the results for mass flow rate and flow coefficient.
Mass Flow rate:- The mass flow rate is the mass of a liquid substance passing per unit time. In other words, Mass flow rate is defined as the rate of movement of liquid pass through a unit area. The mass flow is directly depended 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 unit in kg/sec.
The mass flow rate is given by-
m = rho * V * A.
rho -> density of the fluid
V -> velocity of the liquid and
A -> Area of cross-section
Here I calculated mass flow rate at each case of the outlet when the opening is minimum then the mass flow rate is more and when the opening is maximum then the mass flow rate is minimum. Because the mass flow rate depends on the area of opening i.e. cross-section. So, all quantities are the same the only diameter is decreased and that's why mass flow rate decreases.
Plot:
Observations:
(1) The negative sign in the mass flow rate term comes due to mass leaving at the outlet.
(2) During each lift, the volume of fluid volume changes so the number of elements also tend to change.
CONCLUSION:
Calculation of Mass flow rate, flow coefficient and flow factor in the given range from 10% to 80% is done, and I concluded that as the opening range increases we get less mass flow rate because of velocity from inlet to outlet decreases.
In this way, the parametric study helps a designer to analyze and select a valve with the best flow coefficient according to the requirements in very less time.