Week 9 - Parametric study on Gate valve.
OBJECTIVE
In this challenge our objective is to perform parametric study on the gate valve by setting the opening from 10% to 80%.
Thereby we will obtain mass flow rate at the outlet for each opening point.
calculate the flow co-efficient and flow factor for each opening and the plot the graph.
Discuss the result of the massflow rate and flow co-efficient.
Introduction
gate valve
A gate valve ,also known as sluish valve, is a valve that opens by lifting a barrier (gate) out of the path of the fluid gate valve 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)
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 non linear manner asthe gate is moved.This meansthat the flow rate does not change evenly with step 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 larger sizes:
At high pressure,friction can become a problem.As the gate is pushed against its guiding rail by the pressure of the medium.It becomes harder to operate the valve largegate valves aresometimes fitted with a bypass controlled by a smaller valve to be able to reduce the pressure brfore operating the gate valve itself.gate valves without an extra scaling ring on the gate or the seat areused in application where minor leaking of te valve is not an issue such as heating circuitsor sewer pipes.
Gate valves are typically constructed from the cast iron,cast carbon steel, ductile iron, gun metal, stainless steel, alloy steel, and forged steels .The flow co-efficient -Cv, -or the flow factor -Kv are commonly used to specify capacities of control valves.
FLOWCO-EFFICIENT
The flow co-efficient of a device isarelative measure ofitsefficiency at allowing fluid flow. It describe the relationship between the pressure drop across an orifice valve or otherassembly and the corresponding flow rate.
Mathematically, the flow co-efficient Cv (or flow - capacity rating of valve) can be expressed as
Cv = θ.(SG/ΔP)0.333
where
θ is the rate of flow (expressed in usgallons per minute)
SG isthe specific gravity of the flui (for water = 1)
ΔP isthe pressure dropacross valve (ex;press in Ps)
In more practical terms, the flow coefficient Cv isthe volume (in us gallons) of water at 60 f that will flow per
minutre through a valve with a pressure drop of 1 psi across the valve.
FLOW FACTOR
The metric equivalent flowfactor (Kv; commonly used everywhere else in the world with the exception of the united states) is calculatedusing metricunits
Kv = θ.(SG/ΔP)0.333
Where,
Kv is the flow factor expressed in m3.h-1
θ isthe flow rate (expressed in cubic meters per hour m3/h
SG is the specific gravity of the fluid (for water =1)
ΔP isthe differential pressure acrossthedevice (expressed in [bar])
Kv can be calculated from Cv, using the equation
Kv = 0.865.Cv
STEPS FOLLOWED
A) Geometry Preparation
B) Meshing
C) Set up
D) Results
The following steps will be followed in setting upthe simulation in ansys fluent.
2)Geometry Preparation
firstly we will import the geomery in the spaceclaim .
Move the disc by 10mm using the pull tool
we can see small opening in given figure.
In prepare use volume extract option ,to extract fluid volume
Using the pull tool , extend inlet and outlet by 800mm suppress all the solid volume .
suppress the all solid volume
B) Meshing
Create name selection
Basic Mesh
We will refined mesh for the simulation.
C) set up
Following option areselected
Material
Cell zones
Boundary
In solution > intialize the solution
Definition > mass flow rateat outlet
IN POST- PROCESSING
Create planes along the length of the pipe
Create velocity and pressure contour
In solution> Create thevelocity andpressure animation.
D) RESULTS
The following resultswere obtained with 10mm open
Geometry
Mesh
Pressure contour
Velocirty Contour
The following results were obtained with 30mm open
Geometry
Mesh
Pressue contour
Velocity Contour
The following resultswerevobtained with 50mm open
Geometry
Mesh
Pressure Contour
Velocity Contour
The following results were obtained with 70mm open
Geometry
Mesh
Pressure Contour
Velocity Contour
The following results were obtained with 90mm open
Geometry
Mesh
Pressure Contour
Velocity Contour
CONCLUSION
The following table was obtained from the parametric study.
The mass flow rate at each opening of the valve are available in the parametric study table
Graph between opening of the valve in mm and flow co-efficient.
Smaller the valve opening, more the pressure loss and looser the flow rate we need to design the valvesuch that it has large value of the Flow co-efficient at operating condition.