Week 9 - Parametric study on Gate valve.

A gate valve is the most common valve for water supply systems. It represents a linear-motion isolation valve and has a function to stop or allow the flow. Gate valves got their name from the closure element sliding into the flow stream to provide shutoff and, therefore, acting like a gate. Gate valves can be divided into two main types: Parallel and wedge-shaped. The parallel gate valves use a flat gate between two parallel seats, and a popular type is the knife gate valve designed with a sharp edge on the bottom of the gate. Gate valves are one of the most common valves used as a main shut off valve. They are reliable and long-lasting. Gate valves have a twist-type handle and should only be used to fully open water supply or completely shut off water supply.

gate valve

schematic of gate valve

parametric study:

A parametric study that perturbs design variables in the product design model to explore design alternatives can effectively support product concept designs. A parametric study is simple and easy to perform as long as the mapping between CAD and simulation models has been established.To do a parametric study in just Fluent, what you just need to do is set up all the cases with their own boundary conditions. You can do this manually in the GUI or through text commands. And then individually run all the Fluent cases. Or you can write a journal file that runs all the Fluent cases sequentially.

example of parametric study:

ANSYS FLUENT stages:

1. Model Generation
• SpQcify jobname (this step is optional but recommended).
• Enter Preprocessor,
• Define element types and options.
• Define real constant for the element types (if the element type(s)
require real constants).
• Define material properties.
• Create the model:.
- Build solid model (using either top-down or bottom-up approach).
- Define meshing controls.
• Create the mesh.
• Exit the Preprocessor,
2. Boundary/Initial Conditions and Solution
• E nter Solution Processor,
• Define analysis type and analysis options.
• Specify boundary/initial conditions:
• Degree of freedom constraints.
- Nodal force loads.
• Surface loads.
• Body loads.
• I nertia loads.
• Initial conditions (if the analysis type is transient).
• Save database (this step is not required but is recommended).
• Initiate solution.
• Exit the Solution Processor,
3. Review Results
• Enter the appropriate Postprocessor (General Postprocessor or Time
History Postprocessor),
• Display results.
• List results.

ANSYS:

PRE PROCESSING:

geomentry:

open ansys workbench, create a new system, double click on geomentry to open space claim.

open the gatevalve.step file in geomentry.

then by using the pull tool to pull the inlet and outlet to 80mm.

then hide everything except gate disc and spindle.

then by click on move tool to move the gate disc to 10mm.

now parameter the gate valve by group click on parameter setup.

here the parameter setup is done.

bootom of the gate valve

gate disc

bonnet

spindle

gate valve component

fluid volume

parameter setting.

then close the space claim window.

double click on the mesh to open the ansys mesh window.

firstly create a default mesh.

then modify the element size to get a finer mesh.

name the inlet and outlets properly.

no of nodes and element.

mesh quality.

close the mesh window.

processing:

now open the setip , by double clicking the setup.

Steady-state, pressure-based solver with gravity enabled of value 9.81 m/s^2 in -ve z-direction.

Viscous model: K-epsilon, Realizable with Scalable wall functions.

Material Properties: Water-liquid(H2O), Density:998.2 kg/m^3 , Viscosity:0.001003 kg/(m-s)

Boundary Conditions:

Inlet: Type= Pressure Inlet

Gauge Total Pressure = 10 Pa

Outlet: Type= Pressure Outlet

Gauge Total Pressure = 0 Pa

Wall: No-slip, stationary wall

Interior: Type= Interio

solver.

create material

fluid zone.

viscous model.

inlet.

Residuals:

1. 10 mm opening

Mass flow rate:

1. 10 mm opening

Differential Pressure:

1. 10 mm opening(before valve)

2. 10 mm opening(after valve)

post processing:

now we gor to results and create a velocity stream line for 10mm opening.

parameter:

now click on pparameter.

now create a data point and click on update.

it gives the value of mass flow rate , inlet pressure outlet pressure.

after completeing the update we have to set the dp.

for thet we have to right click on the data point we need and set to current.

go back to the geomentry, mash, setup and results all are updated to the set parameter value.

now calculating the flow coefficient and flow factor.

Valve Flow Coefficient (Cv) is a valve's capacity for a liquid or gas to flow through it. It is technically defined as “the volume of water at 60°F (in US gallons) that will flow through a valve per minute with a pressure drop of 1 psi across the valve.”

The gallons US per minute unit number 15.85 gal/min converts to 1 kg/sec

q=mass flow rate in gpm

p=pressure drop in psi.

for calculating flow factor.

calculation for 10mm opening.

a negative mass flow at a boundary means that mass is leaving your system, and a positive mass flow means that mass is entering your system.

q=0.14848 kg/s

Q=q*15.88

=0.14848*15.88

=2.357 gpm

specific gravity of water sg=1

Pressure drop, or pressure loss, is the difference in pressure as measured between two points in a pipe with flowing fluid. Δp = p1 - p2.

dp=9.8188 pa

DP=dp/6894.745

=9.8188/6894.745

=0.00142 psi

cv=q*sqrt(sg/dp)

=2.357*sqrt(1/0.00142)

=62.548

kv=cv/1.156=>62.548/1.156

=53.761 m^3.h^-1

from the above calculation calculate all the value and plot a graph in excel.

graph of flow coefficient:

flow factor:

the workbench gate valve system is attached.

Conclusion:

1. Flow-coefficient and flow-factor increases with increasing opening percentage and decrease on 60% and again increses.

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 increases with increasing opening percentage. This is because there is more pathway 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.

------------------------thank you--------------------------------------------------------------------------------