Parametric Study on Gate valves

PARAMETRIC STUDY OF GATE-VALVE

OBJECTIVE:

1. To perform a parametric study on the gate valve simulation by setting the opening of the valve from 10% to 80%
2. To obtain the mass flow rate at the outlet for each design point.
3. To calculate the flow coefficient and flow factor for each lift of the valve and to plot the graph for each opening of the valve.

DESCRIPTION:

GATE VALVE:

A gate valve, also known as a sluice valve,is a valve that opens by lifiting a barrier out of the path of the fluid.Gate valve requires 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 mostly wedge shaped.Gate valves are designed for fully opened or fully closed service.They installed in pipelines as isolating valves.Operation of the gate valve is performed doing a 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..

Gate valves are often used when minimum pressure loss and a free bore is needed.When fully open,a typical gate valve has no obstruction in the flow path resulting in a very low pressure loss.A gate valve is a multiturn valve, meaning that the operation of the valve is done by means of a threaded stem.As the valve has to turn multiple times to go from open to closed position,the slow operation also prevents wter hammer effects.

Types of Gate valves:

There are different types of gate valves such as ;

• Standard
• Wedge Types
• Solid Tapered Wedge
• Solid Pliable Wedge
• Double Disc Type
• Bellow Design
• Cryogenic Design
• Knife Plate
• Hulk Plate

Application of Gate valve:

• Gate valves without an extra sealing ring on the gate or the seat are used in applications were minor leaking of the valve is not an issue,such as heating circuits or sewer pipes.
• Sockets or butt-welding end-gate valves in air,fuel gas,feedwater,steam,lube oil and other system are typical applications.Threaded gate valves may be used in air ,gaseous or liquid sytems.
• In low pressure and low temperature sytems such as fire protection systems' water piping or water distribution pipeline,flanged gate valves are commonly used.

NUMERICAL SIMULATION:

1.GEOMETRY:

A classical model of the Gate valve has been provided for the numerical simulation

• The assembled geometry of the gate valve model has been shown above , the various components of the gate valve geometry are:

1.Bottom Part

2.Gate Disc

3.Bonnet

4.Hand Wheel

5.Spindle

• The inlet and outlet length of the pipes has been extruded to 800 mm in spaceclaim,so that the fluid can flow through a suffcient length

• A section view of the solid domain has been shown below:

• Our interest for simulation only lies in the region of fluid flow on the pipe and the gate valve as we are required to study the effect of the lift of the gate valve disc on the mass flow rate , therefore the fluid volume has been extracted from the solid domain, which is further used for the study

• A sectional view of the fluid domain with a 40 mm lift of the gate valve disc has been shown below:

Parametric study has been done by making the lift of the valve as the input parameter and its effect on the output parameter such as the mass flow rate has been studied for different cases.

2.MESHING:

A refined mesh profile has been employed during the simulation

• Element Size : 5 mm
• Maximum Element Size: 10 mm
• Type of Element : Tetrahedral
• Number of Nodes : 1,21,930
• Number of Elements :6,11,823

The mesh metric plot has been given below:

1. Element Quality:

Most of the elements are having the quality above 80 % ,which is better.

2. Orthogonal Quality:

The average orthogonal quality of the element is 0.77

3. Skewness:

The skewness of the elements are less that 0.8 which is fairly good.

3.SETUP & SOLUTION:

• Lift of the Gate-valve has been kept as the input parameter and the mass flow rate at the outlet has been parametrised as the ouput parameter.The Boundary condtion and the rest of the setup remains the same for all the cases.

Solver : Type - Pressure-based

Time - Steady State

Velocity Formulation : Absolute

Model : -k-epsilon Realizable with scalable wall functions

- Energy Equation ON

Gravity : -9.81 `m/s^2`along z direction

Material : Fluid - Water-liquid

Cell Zone Condtion : volume_volume : Type - Fluid : water-liquid

Boundary Condition : inlet

-Type : Pressure-inlet ( Gauge Pressure 10 Pa )

- Thermal (300 K)

Oulet

- Type : Pressure-outlet

Solution : Method -Coupler method

Calculation : Number of Iterations : 500

PARAMETRIC STUDY

• The residual plots and the contour for the above cases where obtained and is shown below:

For Lift = 10 mm

1.Residual Plot:

• The Solution has converged at 30 iterations

2. Mass flow rate report plot:

• mass flow rate at outlet = 0.14498 kg/s

3. Velocity Contour Plot:

For Lift = 20 mm

1.Residual Plot:

• Solution converged for about 20 iterations

2.Mass flow rate repot plot:

• mass flow rate at outlet = 0.22834 kg/s

3.Velocity contour Plot:

For Lift = 30 mm

1.Residual Plot:

2.Mass flow rate report plot:

• The flow converged at about 180 iterations
• mass flow rate at the outlet = 0.34361 kg/s

3.Velocity Contour Plot:

For Lift = 40 mm

1.Residual Plot:

2.Mass flow rate report plot:

• The flow converged at about near to 200 iterations as the mass flow rate remains constant
• mass flow rate at outlet = 0.46135

3.Velocity Contour:

For Lift = 50 mm

1.Residual Plot:

2.Mass flow rate Plot:

• mass flow rate at outlet = 0.5676 kg/s

3.Velocity contour:

For Lift = 60 mm

1.Residual Plot:

2.Mass flow rate report plot:

• mass flow rate at outlet = 0.65307 kg/s

3.Velocity Contour:

For Lift = 70 mm

1.Residual Plot:

2.Mass flow rate report plot:

• mass flow rate = 0.72612 kg/s

3.Velocity contour:

For Lift = 80 mm

1.Residual Plot:

2.Mass flow rate report plot:

• mass flow rate = 0.78875 kg/s

3.Velocity contour:

• FLOW COEFFICIENT:

The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow.When the flow goes through a valve or any other device it loses some energy.The flow coefficient is a designing factor which relates the head drop or the pressure drop (`Delta`P) across the valve with a flow rate Q .

Mathematically, the flow coefficient `Cv` (or flow capacity rating of a valve)can be expressed as :

`Cv=Qsqrt((Sg)/(DeltaP)`

where,

Q is the rate of flow

Sg is the specific gravity of the fluid

`DeltaP` is the pressure drop across the valve.

In the more practical terms, the flow coefficient `Cv`is the volume of water at `60^oF` that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

• FLOW FACTOR:

The Flow factor is the flow coefficient expressed in metric units that is defined as the flow rate in cubic meters per hour (`m^3/h`) of water at a temperature of `16^oC` with a pressure across a valve or any other restricting device of 1 bar.

`Kv` can be calculated from `Cv`using the equation :

`Kv=0.865Cv`

The Flow factor and Flow coefficient calculation for each lift of the valve is given below:

The graph showing the variation of the flow factor and flow coeffcient with the opening of the gate valve is given below:

4.RESULTS & CONCLUSION:

1. The mass flow rate of the water at the outlet of the pipe was found to increase with increase in the lift of the gate valve
2. Parametric helps to reduce the calculation as the time for doing the simulation for each case is avoided and the variation of the output parameer with the input parameter can be obtained accurately as per the requirement.
3. The flow coefficient plays a vital role in the selection and sizing of the valves for specific application

-Higher the flow rate means, lower the drop in the pressure across the valve

-With an increase in the lift of the valve , the flow coefficient shows a rising trend, which implies that the drop in pressure is lower at higher lift of the valve

Thank You

Arjun Vs